Name: processing of bulk nanocrystalline metals at the us army research laboratory
Uploaded: 2018-03-07T14:00:00
Description: Watch this Scientific Journal Video about Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory at JoVE.com

1. Small Scale Synthesis of Nanocrystalline Powders under Ambient Conditions
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	<li>In a controlled argon atmosphere glove box, place 10 g of the primary element (e.g., Fe in FeNiZr alloy) and 100 g of&#160;stainless steel/tool steel milling balls in the desired milling jar. 
	NOTE: Loading of powder into milling jar inside a glove box is required to ensure minimal uptake in oxygen and/or moisture content 18,19.</li>
	<li>After loading, seal th...

<ol>
	<li>Perez, R. J., Jiang, H. G., Lavernia, E. J., Dogan, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Grain+Growth+of+Nanocrystalline+Cryomilled+Fe-Al+Powders.">Grain Growth of Nanocrystalline Cryomilled Fe-Al Powders.</a> Metall Mater Trans A. 29 (10), 2469-2475 (1998).</li><li>Shaw, L., Luo, H., Villegas, J., Miracle, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+Stability+of+Nanostructured+Al93Fe3Cr2Ti2+Alloys+Prepared+by+Mechanical+Alloying.">Thermal Stability of Nanostructured Al93Fe3Cr2Ti2 Alloys Prepared by Mechanical Alloying.</a> Acta Mater. 51 (9), 2647-2663 (2003).</li><li>Boylan, K., Ostrander, D., Erb, U., Palumbo, G., Aust, K. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solute+Distribution+in+Nanocrystalline+Ni-W+Alloys+Examined+Through+Atom+Probe+Tomography.">Solute Distribution in Nanocrystalline Ni-W Alloys Examined Through Atom Probe Tomography.</a> Philos Mag. 86 (28), 4459-4475 (2006).</li><li>Darling, K. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Grain-size+Stabilization+in+Nanocrystalline+FeZr+Alloys.">Grain-size Stabilization in Nanocrystalline FeZr Alloys.</a> Scripta Mater. 59 (5), 530-533 (2008).</li><li>Lavernia, E. J., Han, B. Q., Schoenung, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cryomilled+Nanostructured+Materials:+Processing+and+Properties.">Cryomilled Nanostructured Materials: Processing and Properties.</a> Mat Sci Eng A-Struct. 493, 207-214 (2008).</li><li>Darling, K. A., VanLeeuwen, B. K., Koch, C. C., Scattergood, R. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+Stability+of+Nanocrystalline+Fe-Zr+Alloys.">Thermal Stability of Nanocrystalline Fe-Zr Alloys.</a> Mat Sci Eng A-Struct. 527 (15), 3572-3580 (2010).</li><li>Darling, K. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stabilized+Nanocrystalline+Iron-based+Alloys:+Guiding+Efforts+in+Alloy+Selection.">Stabilized Nanocrystalline Iron-based Alloys: Guiding Efforts in Alloy Selection.</a> Mat Sci Eng A-Struct. 528 (13-14), 4365-4371 (2011).</li><li>Dake, J. M., Krill, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sudden+Loss+of+Thermal+Stability+in+Fe-based+Nanocrystalline+Alloys.">Sudden Loss of Thermal Stability in Fe-based Nanocrystalline Alloys.</a> Scripta Mater. 66 (6), 390-393 (2012).</li><li>Ma, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+Behavior+and+Strengthening+Mechanisms+in+Ultrafine+Grain+Precipitation-Strengthened+Aluminum+Alloy.">Mechanical Behavior and Strengthening Mechanisms in Ultrafine Grain Precipitation-Strengthened Aluminum Alloy.</a> Acta Mater. 62, 141-155 (2014).</li><li>Chookajorn, T., Schuh, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoscale+Segregation+Behavior+and+High-temperature+Stability+of+Nanocrystalline+W-20+at%+Ti.">Nanoscale Segregation Behavior and High-temperature Stability of Nanocrystalline W-20 at% Ti.</a> Act Mater. 73, 128-138 (2014).</li><li>Kalidindi, A. R., Schuh, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stability+Criteria+for+Nanocrystalline+Alloys.">Stability Criteria for Nanocrystalline Alloys.</a> Acta Mater. 132, 128-137 (2017).</li><li>Suryanarayana, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+Alloying+and+Milling.">Mechanical Alloying and Milling.</a> Prog Mater Sci. 46 (1-2), 1-184 (2001).</li><li>Darling, K. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+and+Mechanical+Properties+of+Fe-Ni-Zr+Oxide-Dispersion-Strengthened+(ODS)+Alloys.">Structure and Mechanical Properties of Fe-Ni-Zr Oxide-Dispersion-Strengthened (ODS) Alloys.</a> J Nucl Mater. 467 (1), 205-213 (2015).</li><li>Darling, K. A., Roberts, A. J., Mishin, Y., Mathaudhu, S. N., Kecskes, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Grain+Size+Stabilization+of+Nanocrystalline+Copper+at+High+Temperatures+by+Alloying+with+Tantalum.">Grain Size Stabilization of Nanocrystalline Copper at High Temperatures by Alloying with Tantalum.</a> J Alloy Compd. 573 (5), 142-150 (2013).</li><li>Boschetto, A., Bellusci, M., La Barbera, A., Padella, A., Veniali, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinematic+Observations+and+Energy+Modeling+of+a+Zoz+Simoloyer+High-Energy+Ball+Milling+Device.">Kinematic Observations and Energy Modeling of a Zoz Simoloyer High-Energy Ball Milling Device.</a> Int J Adv Manuf Tech. 69 (9-12), 2423-2435 (2013).</li><li>Karthik, B., Gautam, G. S., Karthikeyan, N. R., Murty, B. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+Mechanical+Milling+in+Simoloyer:+An+Energy+Modeling+Approach.">Analysis of Mechanical Milling in Simoloyer: An Energy Modeling Approach.</a> Metall Mater Trans A. 43 (4), 1323-1327 (2012).</li><li>Giannuzzi, L. A., Stevie, F. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Review+of+Focused+Ion+Beam+Milling+Techniques+for+TEM+Specimen+Preparation.">A Review of Focused Ion Beam Milling Techniques for TEM Specimen Preparation.</a> Micron. 30 (3), 197-204 (1999).</li><li>Hornbuckle, B. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Ta+Solute+Concentration+on+the+Microstructural+Evolution+in+Immiscible+Cu-Ta+Alloys.">Effect of Ta Solute Concentration on the Microstructural Evolution in Immiscible Cu-Ta Alloys.</a> JOM. 67 (12), 2802-2809 (2015).</li><li>Darling, K. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extreme+Creep+Resistance+in+a+Microstructurally+Stable+Nanocrystalline+Alloy.">Extreme Creep Resistance in a Microstructurally Stable Nanocrystalline Alloy.</a> Nature. 537, 378-381 (2016).</li><li>Segal, V. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Materials+Processing+by+Simple+Shear.">Materials Processing by Simple Shear.</a> Mat Sci Eng A-Struct. 197 (2), 157-164 (1995).</li><li>Segal, V. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Equal+channel+angular+extrusion:+From+Macromechanics+to+Structure+Formation.">Equal channel angular extrusion: From Macromechanics to Structure Formation.</a> Mat Sci Eng A-Struct. 271 (1-2), 322-333 (1999).</li><li>Valiev, R. Z., Langdon, T. 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B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compaction+of+Amorphous+Aluminum+Alloy+Powder+by+Direct+Extrusion+and+Equal+Channel+Angular+Extrusion.">Compaction of Amorphous Aluminum Alloy Powder by Direct Extrusion and Equal Channel Angular Extrusion.</a> Mat Sci Eng A-Struct. 393 (1-2), 12-21 (2005).</li><li>Frolov, T., Darling, K. A., Kecskes, L. J., Mishin, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stabilization+and+Strengthening+of+Nanocrystalline+Copper+by+Alloying+with+Tantalum.">Stabilization and Strengthening of Nanocrystalline Copper by Alloying with Tantalum.</a> Acta Mater. 60 (5), 2158-2168 (2012).</li><li>Darling, K. 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Compared to other synthesis techniques, mechanical alloying is an extremely versatile method for producing metal and alloyed powders with grain sizes &lt;&lt;100 nm. Indeed, mechanical alloying is one of the few ways in which large volumes of nanostructured materials can be produced in a cost effective and easily scalable manner. Furthermore, high-energy ball milling has been shown to vastly increase the limit of solid solubility in many metallic systems in which equilibrium room temperature solubility does not otherwis...

Nanocrystalline metals prepared by high energy mechanical alloying have been shown to exhibit superior mechanical strength as compared to their coarse-grained counterparts. However, as dictated by thermodynamic principles, nanocrystalline microstructures are subject to grain coarsening at elevated temperatures. As such, processing and applications of these materials is currently limited by the ability to create stabilized microstructures in bulk form. Given the potential of these materials, two primary methods are being pursued in an effort to develop such systems. The first, based on a kinetic approach, utilizes several mechanisms to apply a pinning force on the grain boundaries (GBs) in order to prevent grain growth. Typical mechanisms employed to pin the GBs are secondary phases (Zener pinning)1,2,3 and/or solute drag effects4,5. The second method, based on a thermodynamics approach, suppresses grain growth by reducing the GB free energy through solute atoms partitioning to the GBs6,7,8,9,10,11,12,13,14,15,16.
As the first step to developing alloys with a nanograined microstructure, the fundamental understanding into thermodynamic and kinetic principles that govern grain growth and microstructural stability at elevated temperatures was established. Computational materials science was also used to guide alloy development. Using these insights, small scale lots of various alloy powders were produced using high energy milling and evaluated for a broad range of physical and mechanical properties. For the more promising systems, advanced characterization techniques were developed in order to fully link the microstructure of the powder to the observed properties and performance.
Simultaneously, the infrastructure and equipment needed to produce bulk components from the nanocrystalline powders was acquired. Once this equipment was in place, the processing science required to fully consolidate bulk materials from the alloy powders was developed through a series of small scale experiments. Once bulk specimens were available, a series of experiments were performed to understand the mechanical response of these materials under a broad range of conditions (such as fatigue, creep, high strain rate, etc.). The knowledge gained from these experiments has been used to develop possible application spaces that will enable the commercialization of the stabilized bulk nanocrystalline alloys.
Collectively, meeting these tasks has led to the development within the U.S. Army Research Laboratory (ARL) of a nanocrystalline metals research center consisting of 4 main labs. This laboratory complex represents a total investment of 20 million USD and is unique in that it spans aspects of fundamental, applied, and manufacturing science. The primary purpose of these labs is to transition proof-of-concept ideas to the pilot-scale and pre-manufacturing levels. In doing so, it is anticipated that the labs will enable the production of prototype parts, develop the necessary know-how and manufacturing science for scaled-up processing, and allow for linkages internally as well as to external research institutes or industrial partners via the commercialization and transition of this advanced powder technology.
As indicated earlier, the first step is to identify, produce, and rapidly assess new alloy prototypes for both feasibility of synthesis and fabrication into prototype parts. To accomplish this, several unique, custom-designed high energy shaker mills have been constructed with the capability to process powders over a wide range of temperatures from -196 &#176;C to 200 &#176;C. As the name implies, these mills produce approximately 10-20 g of fine powders through the violent shaking action that causes repetitive impacts between powder and grinding media to produce powders in which each particle has a composition in proportion to the starting elemental powder mix. While suitable for the rapid screening of powders, mills of this type are clearly not suitable for powder production on the (near) industrial scale (e.g., kilograms).
Given the need to produce powder in large quantities and in as continuous a process as possible, a search was undertaken to identify potentially viable methods and equipment. Planetary ball mills use a support disk which rotates in the opposite direction from the vertically oriented vials, resulting in particle size reduction due to both grinding and collisions caused by centrifugal forces. Lot sizes for most planetary mills range up to approximately 2 kg. Unlike conventional mills, attritor mills consists of a series of impellers inside a vertical drum. The rotation of the impellers cause the motion of the grinding media, resulting in particle size reduction through collisions between powder, balls, and the impellers. Larger attritor mills are capable of producing over 200 kg per run. Although both of these mills offer significant increases in lot sizes relative to shaker mills, they are not capable of running in a continuous fashion but must rather be loaded and unloaded manually for each run.
Due to these shortcomings, attention shifted to a series of high energy, horizontal rotary ball mills. Capable of processing as much as 200 kg per batch, these mills are also capable of operating under inert atmospheres as well as vacuum. Finally, the milling chamber has been designed with an airlock that allows for the rapid and automated removal of powder once the milling process has been completed. Combined with an automatic powder injection system, this means that the ball mill is capable of running in a fairly continuous manner, thereby making it a highly viable system for industrial settings. Due to these combination of features, ARL has recently purchased and installed two mills and is now engaged in upscaling internal powder processing efforts.
While the powder processing efforts represent a central aspect of on-going efforts, the characterization and consolidation of the most promising alloy powders are also areas of focused research. Indeed, as detailed below, ARL has made notable investments in the requisite analytical and test equipment needed to fully evaluate key features of the new powders. Moreover, successful consolidation of samples now allows for conventional full scale mechanical testing and characterization (e.g., tension, fatigue, creep, shock and ballistic evaluation) of these materials which has typically not been feasible for this class of material. This article reports the protocols utilized at ARL for initial synthesis, scale-up, consolidation and characterization of bulk nanocrystalline metals and alloys.
The two main labs for powder synthesis can be seen in Figure 1. Figure 1A shows the small-scale powder processing lab which enables the rapid development of concepts and alloy design. This lab contains several custom-designed high energy mills with the capability to process powders over a range of temperatures (room temperature to 400 &#176;C and 10 to -196 &#176;C). The lab also contains a custom horizontal tube furnace designed for the rapid assessment of the thermal and microstructural stability (e.g., grain growth studies) of new metal alloys. Finally, the lab also houses several unique small-scale mechanical test setups including tension, shear punch, and impression creep testing devices, as well as a state-of-the-art instrumented nano-indenter. Once thoroughly tested and of shown promise, selected alloys are moved to the large scale processing lab (Figure 1B), where the engineering and manufacturing protocols are developed to allow large scale (e.g., kilogram) production of the specific powder. In total, the labs represent a total investment on the order of 2 million USD and covers the transition of novel metal powders from the lab bench to the pilot-scale manufacturing levels, thereby enabling the production of prototype parts.
High energy ball milling/mechanical alloying is a versatile process for producing nanocrystalline metals and alloys in powder form17. Starting with coarse grained powders (typically mean grain size ~5-10 &#181;m), it is possible to obtain nanocrystalline powders with mean grain size &#60; 100 nm after milling. This milling is routinely performed in a vibratory/shaker mill. The milling vial is filled with the desired amount of powder as well as milling balls, typically stainless steel. This mill shakes the vials in a motion that involves back and forth oscillations with short lateral movements at a rate of approximately 1080 cycles min-1. With each complex motion the balls collide with one another, impact against the inside of the vial and the lid, and simultaneously reduce the powder to finer size. The kinetic energy imparted into the powder is equal to half the mass times the square of the average velocity (19 m s-1) of the bearings. The mill power, e.g. the energy delivered per unit time, increases with the frequency of the mill (15-26 Hz). Taking the typical number of balls and the lowest frequency for a given 20 h period, the total number of impacts exceeds 1.5 billon. During these impacts the powder undergoes repeated fracturing and cold-welding until the point where the constituents are mixed at the atomic level. Microscopically this mixing and refinement of the microstructure is facilitated by localized deformation in the form of shear bands as well as a high density of dislocations and point defects which breaks down the microstructure. Eventually, as the heat of collision raises the local temperature, recombination and annihilation of these defects occurs at a steady state with their generation. The defect structures eventually, though reorganization, result in the formation of smaller and smaller high angle equiaxed grains. Thus, ball milling is a process that induces severe plastic deformation manifested by the presence of a high density of defects. This process allows for increased diffusivity of solute elements and the refinement and dispersion of secondary phases and the overall nanostructuring of the microstructure.
High energy cryomilling is a milling process similar to high energy ball milling except for the fact that the milling vial is maintained at cryogenic temperature during the milling process. In order to achieve a uniform temperature in the vial, the mill has been modified as follows. The milling vial is first placed inside a Teflon sleeve which is then sealed with a Teflon cap. The sleeve is connected to a dewar containing the appropriate cryogen (liquid nitrogen (LN2) or liquid argon (LAr)) through stainless steel and plastic tubing. The cryogen flows through the sleeve throughout the milling process to cool the milling vial and maintain the milling vial at the boiling temperature of the cryogen, such as -196 &#176;C for LN2 and -186 &#176;C for LAr. The low temperatures of cryogenic processing lead to the increased fragmentation of more ductile metals which otherwise cannot be milled at room temperature. Additionally, the cryogenic temperatures reduce thermally activated diffusional processes such as grain growth and phase separation thereby allowing increased refinement of the microstructure and solubility of insoluble elemental species.
The high energy horizontal rotary ball mill is a high energy milling system that consists of a horizontal stainless-steel milling jar with a high-speed rotor with several blades fixed on a drive shaft. The powder to be milled is transferred inside the jar along with the milling balls. Movement of the balls and powder is achieved through the rotation of the shaft inside the jar. The shaft rotates at high speed and the milling steel balls collide, accelerate, and transfer their kinetic energy to the powders. The range of rpm is 100 - 1000 and the average velocity of the balls is 14 m s-1. In particular, mills are equipped to operate over a range of milling temperature (-30 &#176;C to 200 &#176;C high) and can be run under vacuum (mTorr) or in over pressure mode (1500 Torr) (utilizing various types of cover gas). In addition to the base unit, the mill is equipped with a carrier gas discharge unit as well as connection assemblies which allows the loading and unloading of powder under inert gas cover. This apparatus can be seen in Figure 2A along with a typical 8 L steel milling jar (Figure 2B). In addition to the larger mill, ARL has purchased a smaller mill which has been converted to run under liquid nitrogen (Figure 2C). This mill can produce between 100-400 g of processed powder per running cycle.

<table border="0" cellpadding="0" cellspacing="0" width="1063">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Copper powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">42623</td>
			<td style="width:331px;">Spherical, -100+325 mesh, 99.9%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Tantalum powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">10345</td>
			<td>99.97%, -325 mesh</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Iron powder</td>
			<td style="width:243px;">Alfa Aesar&#160;</td>
			<td style="width:141px;">00170</td>
			<td>Spherical, &#60;10 micron, 99.9+%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Nickel powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">43214</td>
			<td>-325 mesh, 99.8%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Zirconium powder</td>
			<td style="width:243px;">American Elements</td>
			<td style="width:141px;">ZR-M-03-P</td>
			<td>99.90%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">SPEX mills (high energy shaker mills)</td>
			<td style="width:243px;">SPEX SamplePrep</td>
			<td style="width:141px;">8000M&#160;</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Zoz mills (high energy horizontal rotary ball mill)</td>
			<td style="width:243px;">Zoz GmbH</td>
			<td style="width:141px;">CM01 (small mill) CM08 (large mill)</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Focused Ion Beam</td>
			<td style="width:243px;">FEI&#160;</td>
			<td style="width:141px;">Nova600i Nanolab dual beam FIB/SEM</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Scanning Electron Microscope</td>
			<td style="width:243px;">FEI&#160;</td>
			<td style="width:141px;">Nova600i Nanolab dual beam FIB/SEM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Precision Ion Polishing System</td>
			<td style="width:243px;">Gatan&#160;</td>
			<td style="width:141px;">Model 695</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Transmission Electron Microscope</td>
			<td style="width:243px;">JEOL&#160;</td>
			<td style="width:141px;">2100F&#160;</td>
			<td>multipurpose field emission TEM</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Atom Probe Tomography</td>
			<td style="width:243px;">CAMECA</td>
			<td style="width:141px;">&#160;LEAP 5000XR</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Equal Channel Angular Extrusion</td>
			<td style="width:243px;">ShearForm</td>
			<td style="width:141px;">custom built</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Hot Isostatic Press</td>
			<td style="width:243px;">Matsys</td>
			<td style="width:141px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

processing of bulk nanocrystalline metals at the us army research laboratory

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued development of nanocrystalline metals. Despite these efforts, the transition of these materials from the lab bench to actual applications has been blocked by the inability to produce large scale parts that retain the desired nanocrystalline microstructures. Following the development of a method proven to stabilize the nanosized grain structure to temperatures approaching that of the melting point for the given metal, the US Army Research Laboratory (ARL) has progressed to the next stage in the development of these materials - namely the production of large scale parts suitable for testing and evaluation in a range of relevant test environments. This report provides a broad overview of the ongoing efforts in the processing, characterization, and consolidation of these materials at ARL. In particular, focus is placed on the methodology used for producing the nanocrystalline metal powders, in both small and large-scale amounts, that are at the center of ongoing research efforts.

Approximately 10 g of powder are produced per each run in the high energy shaker mill. After successful synthesis of novel nanocrystalline metals and alloys in high energy shaker mill, scale-up is conducted in a high energy horizontal rotary ball mill.
Typically, nanostructured powders are generated using high energy milling processes, wherein the grain size of a small amount of powder is refined, approximately 10 g per batch. T...

Watch this Scientific Journal Video about Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory at JoVE.com

Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory

This paper provides a brief overview of the ongoing efforts at the Army Research Laboratory on the processing of bulk nanocrystalline metals with an emphasis on the methodologies used for the production of the novel metal powders.

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued ...

The overall goal of this procedure is to produce mechanically alloyed nanocrystalline powders that can be processed into bulk stabilized nanocrystalline metals and alloys. To meet ever increasing material performance demands, the U.S.Army has undertaken the development of stabilized bulk nanocrystalline alloys for use across a wide range of operating conditions. Ball milling is one of the few synthesis techniques conducive to producing large volumes of nanocrystalline powders, thereby facilitating industrial scale production of this universal structural applications.Advanced characterization techniques such as transmission electron microscopy and atom protomography coupled with sight specific materials extraction we have focused on the milling, enable the determination of structure, property, processing relationships, and the bulk alloys. In addition to additive manufacturing, ARL has a variety of consolidation techniques including equal channel angular excrusion, or ECAE, field assisted sintering technology, or FAST, and hot isostatic pressing, or HIP. To begin the small scale synthesis, in an argon filled glove box, place 10 grams of the primary element for the alloy and 100 grams of stainless steel or tool steel milling balls in a stainless steel milling jar.Close the milling jar and remove it from the glove box. Clamp the jar in a vice and tighten the lid with a wrench. Then secure the fully sealed jar in the clamp of a high energy shaker mill.Perform a one hour milling cycle to coat both the interior of the jar and the milling balls with the primary element. Then remove the jar from the mill and return it to the argon filled glove box. Open the jar and remove loose powder from the milling balls and the jar.Add to the coated jar a total of 10 grams of elemental powders in the required ratios for the alloy. Add the coated milling balls to obtain a 10 to 1 mass ratio of milling balls to powder. Close the jar and remove it from the glove box.Tighten the lid of the milling jar with the vice and wrench before loading the jar into the high energy shaker mill. Once the milling jar has been secured in the mill, initiate a milling cycle of a duration appropriate for the alloy being produced. When the milling cycle is finished, return the jar to the argon filled glove box.Carefully remove the lid and transfer the nanocrystalline powder to a sample vial for storage. To begin the cryogenic small scale synthesis, coat the inside of a milling jar in the appropriate milling media with the primary element of the desired alloy as previously described. Then in an argon filled glove box, place the required amounts of elemental alloying powders in the coated jar with the milling media.Tightly close the jar and remove the jar from the glove box. Use a vice and wrench to tighten the jar lid completely. Fit the jar into a PTFE sleeve connected to a dewar of liquid nitrogen or liquid argon.Place a PTFE cap on the jar and sleeve then place the enclosed jar in the clamp of the high energy shaker mill. Ensure that the milling jar is secure and properly sealed. Then open the flow of the cryogen to the milling jar.Allow the cryogen to flow for about 30 minutes or until the cryogen has been visibly flowing from the outlet for two minutes to ensure that the jar reaches the desired temperature. Initiate a milling cycle of the desired duration. Upon completion, stop the flow of the cryogen and carefully remove the milling jar from the PTFE sleeve.Place the jar in front of a hot air drier and allow the jar to warm to room temperature. Then transfer the jar into the argon filled glove box. Carefully open the jar and transfer the nanocrystalline powder to a storage vial.To begin the large scale synthesis, in an argon filled glove box load the primary elemental powder for the alloy into a glass jar. Load up to one kilogram of the elemental alloying powders into a second glass jar. Seal both jars with caps designed to transfer powder to the milling vessel without exposure to air.Remove the sealed jars from the glove box. Next, connect a stainless steel eight liter milling vessel with a cooling jacket to a high energy horizontal rotary ball mill, then load approximately one kilogram of 440C stainless steel ball bearings into the vessel. Connect an argon gas line and ethylene glycol cooling lines to the vessel.Backfill and purge the vessel with argon gas to remove air then connect the glass jar to the primary elemental powder to the powder loading assembly of the ball mill. Use a double ball valve to transfer the primary elemental powder from the glass jar to the milling vessel under an argon atmosphere. Close the valve to seal the chamber then connect the powder extraction system to the milling vessel.Backfill and purge the extraction system with argon gas to remove air. Perform a short coding run with the primary elemental powder. Remove loose powder under an argon atmosphere when finished, then transfer the elemental alloying powders from the glass jar to the milling vessel under an argon atmosphere as previously described.Start flowing ethylene glycol at minus 25 degrees celsius through the outer jacket of the vessel. Once the vessel is cooled, run the ball mill for 12 to 30 hours at a rotational speed of 400 to 800 rpm. Finally, transfer the alloy powders to the storage jar under an argon atmosphere using the powder extractor.Store the jar in an argon filled glove box. Small scale powder synthesis generally resulted in nanocrystalline microstructures with an average powder particle size between 10 and 500 micrometers. Powders were processed with ECAE which allowed significant refinement of the microstructure and texture.Bright-field STEM of an ECAE processed copper 10 atomic percent tantalum sample allowed grain sizes to be measured from the clearly resolved grains. High-angle Annular Dark Field STEM showed the high number density of tantalum particles and the wide range of particle sizes. For example, this 40 nanometer wide tantalum particle was surrounded by tantalum particles with diameters of 5 to 20 nanometers.The large tantalum particle featured a partial shell around it's lower half. The high number density of tantalum particles was quantified with atom probe tomography. APT was also used to locate and quantify tungsten dioxide and sodium particles in an electroplated nickel tungsten alloy.Along with STEM, the 3D atom maps and mass spectra from APT were essential for a full understanding of the microstructure and mechanisms of mechanically alloyed nanocrystalline powders. Bulk sample consolidation of iron nickel zirconium powder by hot isostatic pressing resulted in a maximum density of about 96%Conventional excrusion at 1000 degrees celsius successfully consolidated bulk iron nickel zirconium samples from powders. The powder processing methods developed at the Army Research Lab have resulted in a variety of nanocrystalline stabilized metal alloy powders.The excellent thermal stability of these powders enables the consolidation and evaluation of bulk components in ways that were previously not possible.

processing-bulk-nanocrystalline-metals-at-us-army-research

Research

JoVE Journal

Engineering

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

The high-pressure and high-temperature experiments described here mimic planet interior differentiation processes. The processes are visualized and better understood by high-resolution 3D imaging and quantitative chemical analysis.

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to ...

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

Research and Development of High-performance Explosives

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance tests to verify theoretical calculations. For newly developed formulations, the process begins with small-scale mixes, thermal testing, and impact and friction sensitivity. Only then do subsequent larger scale formulations proceed to detonation testing, which will be covered in this paper. Recent advances in characterization techniques have led to unparalleled precision in the characterization of early-time evolution of detonations. The new technique of Photonic Doppler Velocimetry (PDV) for the measurement of detonation pressure will be shared and compared with traditional fiber-optic detonation velocity and plate-dent calculation of detonation pressure. In particular, the role of aluminum in explosive formulations will be discussed. Recent developments led to the development of explosive formulations that result in reaction of aluminum very early in the detonation product expansion. This enhanced reaction leads to changes in the detonation velocity and pressure due to reaction of the aluminum with oxygen in the expanding gas products.

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance tests to verify theoretical calculations. This paper will share typical development tests associated with the measurement of detonation velocity and detonation pressure.

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance ...

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

Light Enhanced Hydrofluoric Acid Passivation: A Sensitive Technique for Detecting Bulk Silicon Defects

A procedure to measure the bulk lifetime (&#62;100 &#181;sec) of silicon wafers by temporarily attaining a very high level of surface passivation when immersing the wafers in hydrofluoric acid (HF) is presented. By this procedure three critical steps are required to attain the bulk lifetime. Firstly, prior to immersing silicon wafers into HF, they are chemically cleaned and subsequently etched in 25% tetramethylammonium hydroxide. Secondly, the chemically treated wafers are then placed into a large plastic container filled with a mixture of HF and hydrochloric acid, and then centered over an inductive coil for photoconductance (PC) measurements. Thirdly, to inhibit surface recombination and measure the bulk lifetime, the wafers are illuminated at 0.2 suns for 1 min&#160;using a halogen lamp, the illumination is switched off, and a PC measurement is immediately taken. By this procedure, the characteristics of bulk silicon defects can be accurately determined. Furthermore, it is anticipated that a sensitive RT surface passivation technique will be imperative for examining bulk silicon defects when their concentration is low (&#60;1012 cm-3).

A RT liquid surface passivation technique to investigate the recombination activity of bulk silicon defects is described. For the technique to be successful, three critical steps are required: (i) chemical cleaning and etching of silicon, (ii) immersion of silicon in 15% hydrofluoric acid and (iii) illumination for 1 min.

A procedure to measure the bulk lifetime (&#62;100 &#181;sec) of silicon wafers by temporarily attaining a very high level of surface passivation when ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify their influence on void formation in composite parts. Wicking in a fibrous medium described by the Washburn equation was considered equivalent to a flow under the effect of capillary pressure according to the Darcy law. Experimental tests for the characterization of wicking were conducted with both carbon and flax fiber reinforcement. Quasi-unidirectional fabrics were then tested by means of a tensiometer to determine the morphological and wetting parameters along the fiber direction. The procedure was shown to be promising when the morphology of the fabric is unchanged during capillary wicking. In the case of carbon fabrics, the capillary pressure can be calculated. Flax fibers are sensitive to moisture sorption and swell in water. This phenomenon has to be taken into account to assess the wetting parameters. In order to make fibers less sensitive to water sorption, a thermal treatment was carried out on flax reinforcements. This treatment enhances fiber morphological stability and prevents swelling in water. It was shown that treated fabrics have a linear wicking trend similar to those found in carbon fabrics, allowing for the determination of capillary pressure.

An experimental method to measure geometrical parameters and the apparent advancing contact angles describing capillary wicking in unidirectional synthetic and natural fabrics is proposed. These parameters are mandatory for the determination of the capillary pressures that must be taken into account for liquid composite molding (LCM) applications.

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify ...

Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and nanocrystalline materials. The traditional techniques associated with scanning electron microscopy (SEM), such as electron backscatter diffraction (EBSD), do not possess the required spatial resolution due to the large interaction volume between the electrons from the beam and the atoms of the material. Transmission electron microscopy (TEM) has the required spatial resolution. However, due to a lack of automation in the analysis system, the rate of data acquisition is slow which limits the area of the specimen that can be characterized. This paper presents a new characterization technique, Transmission Kikuchi Diffraction (TKD), which enables the analysis of the microstructure of UFG and nanocrystalline materials using an SEM equipped with a standard EBSD system. The spatial resolution of this technique can reach 2 nm. This technique can be applied to a large range of materials that would be difficult to analyze using traditional EBSD. After presenting the experimental set up and describing the different steps necessary to realize a TKD analysis, examples of its use on metal alloys and minerals are shown to illustrate the resolution of the technique and its flexibility in term of material to be characterized.

This paper provides a detailed method to characterize the microstructure of ultra-fine grained and nanocrystalline materials using a scanning electron microscope equipped with a standard electron backscatter diffraction system. Metal alloys and minerals presenting refined microstructures are analyzed using this technique, showing the diversity of its possible applications.

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...