Name: determining the mechanical strength of ultra-fine-grained metals
Uploaded: 2021-11-22T13:00:00
Description: Watch this Scientific Journal Video about Determining the Mechanical Strength of Ultra-Fine-Grained Metals at JoVE.com

We acknowledge support from the National Natural Science Foundation of China (NSFC) under grant numbers 11621062, 11772294, U1530402, and 11811530001. This research was also partially supported by the China Postdoctoral Science Foundation (2021M690044). This research used the resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract number DE-AC02-05CH11231 and the Shanghai Synchrotron Radiation Facility. This research was partially supported by COMPRES, the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR 1606856.

1. Sample preparation
<ol>
	<li>Obtain 3 nm, 20 nm, 40 nm, 70 nm, 100 nm, 200 nm, and 500 nm nickel powder from commercial sources (see Table of Materials). The morphology characterization is shown in Figure 1.</li>
	<li>Prepare 8 nm nickel particles by heating 3 nm nickel particles using a reaction kettle (see Table of Materials).
	<ol>
		<li>Put ~20 mL of absolute ethanol and ~50 mg of 3 nm nickel powder into the reaction kettle. NOTE: T...

Computational simulations have been widely employed to study the grain size effect on the strength of nanometals5,6,16,17,27,42. Perfect dislocations, partial dislocations, and GB deformation have been proposed to play decisive roles in the deformation mechanisms of the nanomaterials. In a molecular dynamics simulation, Yamak...

The resistance to plastic deformation determines the materials&#39; strength. The strength of the metals usually increases with the decreasing grain sizes. This size strengthening phenomenon can be well illustrated by the traditional Hall-Petch relationship theory from the millimeter down to submicron regime1,2, which is based on the dislocation-mediated deformation mechanism of bulk-sized metals, i.e., dislocations pile up at grain boundaries (GBs) and hinder their motions, leading to the mechanical strengthening in metals3,4.
In contrast, mechanical softening, often referred to as the inverse Hall-Petch relationship, has been reported for fine nanometals in the last two decades5,6,7,8,9,10. Therefore, the strength of the nanometals is still puzzling as continuous hardening was detected for grain sizes down to ~10 nm11,12, while the cases of size softening below 10 nm regime were also reported7,8,9,10. The main difficulty or challenge for this debated topic is to make statistically reproducible measurements on the mechanical properties of ultrafine nanometals and establish a reliable correlation between the strength and grain size of the nanometals. Another part of the difficulty comes from the ambiguity in the plastic deformation mechanisms of the nanometals. Various defects or processes at nanoscale have been reported, including dislocations13,14, deformation twinning15,16,17, stacking faults15,18, GB migration19, GB sliding5,6,20,21, grain rotation22,23,24, atomic bond parameters25,26,27,28, etc. However, which one dominates the plastic deformation and thus determines the strength of nanometals is still unclear.
For these above issues, traditional approaches of mechanical strength examining, such as tensile test29, Vickers hardness test30,31, nano-indentation test32, micropillar compression33,34,35, etc. are less effective because the high quality of large pieces of nanostructured materials is so difficult to fabricate and conventional indenter is much larger than single nanoparticle of materials (for the single-particle mechanics). In this study, we introduce radial DAC XRD techniques36,37,38 to material science to in situ track the yield stress and deformation texturing of nano nickel of various grain sizes, which are used in the geoscience field in previous studies. It has been found that the mechanical strengthening can be extended down to 3 nm, much smaller than the previously reported most substantial sizes of nanometals, which enlarges the regime of conventional Hall-Petch relationship, implying the significance of rDAC XRD techniques to material science.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>20 nm Ni</td>
			<td>Nanomaterialstore</td>
			<td>SN1601</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>3 nm Ni</td>
			<td>nanoComposix</td>
			<td></td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>40, 70, 100, 200, 500 nm Ni</td>
			<td>US nano</td>
			<td>US1120</td>
			<td>Flammable</td>
		</tr>
		<tr>
			<td>Absolute ethanol</td>
			<td></td>
			<td></td>
			<td>as the solution to make 8 nm Ni</td>
		</tr>
		<tr>
			<td>Absolute isopropanol</td>
			<td></td>
			<td></td>
			<td>as the solution to make 12 nm Ni</td>
		</tr>
		<tr>
			<td>Amorphous boron powder</td>
			<td>alfa asear</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Copper mesh</td>
			<td>Beijing Zhongjingkeyi Technology Co., Ltd.</td>
			<td></td>
			<td>TEM grid</td>
		</tr>
		<tr>
			<td>Epoxy glue</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td></td>
			<td></td>
			<td>clean experimental setup</td>
		</tr>
		<tr>
			<td>Focused ion beam</td>
			<td>FEI</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glass slide</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glue tape</td>
			<td>Scotch</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Kapton</td>
			<td>DuPont</td>
			<td></td>
			<td>Polyimide film material</td>
		</tr>
		<tr>
			<td>Laser drilling machine</td>
			<td></td>
			<td></td>
			<td>located in high pressure lab of ALS</td>
		</tr>
		<tr>
			<td>Monochromatic synchrotron X-ray</td>
			<td>Beamline 12.2.2, Advanced Light Source (ALS), Lawrence Berkeley National Laboratory</td>
			<td></td>
			<td>X-ray energy: 25-30 keV</td>
		</tr>
		<tr>
			<td>Optical microscope</td>
			<td>Leica</td>
			<td></td>
			<td>to mount the gasket and load samples</td>
		</tr>
		<tr>
			<td>Pt powder</td>
			<td>thermofisher</td>
			<td>38374</td>
			<td></td>
		</tr>
		<tr>
			<td>Reaction kettle</td>
			<td>Xian Yichuang Co.,Ltd.</td>
			<td></td>
			<td>50 mL</td>
		</tr>
		<tr>
			<td>Sand paper</td>
			<td></td>
			<td></td>
			<td>from 400 mesh to 1000 mesh</td>
		</tr>
		<tr>
			<td>Transmission Electron Microscopy</td>
			<td>FEI</td>
			<td></td>
			<td>Titan G2 60-300</td>
		</tr>
		<tr>
			<td>Two-dimension image plate</td>
			<td>ALS, BL 12.2.2</td>
			<td></td>
			<td>mar 345</td>
		</tr>
	</tbody>
</table>

determining the mechanical strength of ultra-fine-grained metals

The mechanical strengthening of metals is the long-standing challenge and popular topic of materials science in industries and academia. The size dependence of the strength of the nanometals has been attracting a lot of interest. However, characterizing the strength of materials at the lower nanometer scale has been a big challenge because the traditional techniques become no longer effective and reliable, such as nano-indentation, micropillar compression, tensile, etc. The current protocol employs radial diamond-anvil cell (rDAC) X-ray diffraction (XRD) techniques to track differential stress changes and determine the strength of ultrafine metals. It is found that ultrafine nickel particles have more significant yield strength than coarser particles, and the size strengthening of nickel continues down to 3 nm. This vital finding immensely depends on effective and reliable characterizing techniques. The rDAC XRD method is expected to play a significant role in studying and exploring nanomaterial mechanics.

Under hydrostatic compression, unrolled X-ray diffraction lines should be straight, not curved. However, under non-hydrostatic pressure, the curvature (ellipticity of the XRD rings, which translates into the non-linearity of the lines plotted along the azimuth angle) significantly increases ultrafine-grained-nickel at similar pressures (Figure 4). At a similar pressure, the differential strain of the 3 nm sized nickel is the highest. The mechanical strength results (stress-strain curves) are...

Watch this Scientific Journal Video about Determining the Mechanical Strength of Ultra-Fine-Grained Metals at JoVE.com

Determining the Mechanical Strength of Ultra-Fine-Grained Metals

The protocol presented here describes the high-pressure radial diamond-anvil-cell experiments and analyzing the related data, which are essential for obtaining the mechanical strength of the nanomaterials with a significant breakthrough to the traditional approach.

The mechanical strengthening of metals is the long-standing challenge and popular topic of materials science in industries and academia. The size ...

The grained particle allow us to track the change of different stress and determine the strength of ASFA metal, which overcome the deficiency of traditional techniques. This technique can be used to statistically examine the mechanical property of even sub 10 nanometer grain size metal with a reproducible and reliable results To prepare captain supporting gaskets, use laser drilling machine to cut the inner circle, followed by the outer rectangular part. The rectangular dimension is eight by 1.4 millimeters.Next, prepare boron epoxy gaskets from a 10 millimeter diameter boron disc by manually polishing the raw discs with sandpaper to a thickness of 60 to 100 micrometers. Then cut the inner circles and outer circle with a laser drilling machine. Repeat and stop the procedure immediately when the right sized and center drilled gasket comes off.Next, to assemble the gaskets, place a captain supporting gasket on a glass slide and place a drilled boron gasket on the inner hole of the captain gasket, ensuring that the larger end of the boron gasket is at the top. Then put another clean glass slide on the top, hold it firmly and press until the boron gasket is firmly inserted in the hole of the captain gasket. Store the fabricated gasket assemblies between two clean glass slides and wrap them with glue tape for future use.To mount the gasket assembly, mark a dot locating the center of the diamond on the computer monitor connected to the optical microscope, then mount the boron epoxy gasket and mark the center of the gasket hole. Next, use a glass slide to press down the gasket assembly such that the gasket firmly sets on the diamond of the piston. For cleaning and compacting the gasket setup, load samples with a chunk size smaller than the gasket hole, such that there is no overflow of materials on the gasket surface.After loading a new piece of sample, close the cell to achieve compactness. Use a monochromatic synchrotron x-ray to conduct diffraction experiments. Focus the x-ray beam to approximately a 30 by 30 square micrometer surface area on the sample.Collect the x-ray diffraction patterns at pressure intervals of one to two gigapascals by a two dimension image plate with a resolution of 100 micrometers per pixel. Under hydrostatic compression, unrolled x-ray dIffraction lines should be straight not curved. Under non hydrostatic pressure, the curvature significantly increases with the decreasing grain size at similar pressures, suggesting continuous mechanical strengthening.At similar pressures, the differential stress of the three nanometer sized nickel is the highest. In transmission electron microscopy images of representative nickel, quenched from around 40 gigapascals, a high content of dislocations is seen in the course grained sample as expected. In contrast, nano twins are well captured in the high pressure recovered nano crystalline nickel accompanied by some stacking faults.In short, twining induced by stacking faults observed in these measurements originates from the nucleation and motion of partial dislocations. We need to load the sample properly to ensure the chamber is full of powder and the gasket would not crack at high pressure. We can perform TM limit under recovery sample and then examine the microstructure and the deformation defect for determining the deformation mechanism.We have also used this technique to explore as a research topic such as probing green rotation at a nano scale energy reading, the ductility of the nano ceramics.

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