This material is based upon work supported by the National Science Foundation under Grant No. 1751699. In-kind support of AM material specimens provided by the National Institute of Standards and Technology (NIST) is also acknowledged and appreciated.

1. Sample preparation for photolithography
<ol>
	<li>Cut a sample from the area of interest and polish it using a semi-automatic polishing machine.
	<ol>
		<li>Use a slow dicing saw or a band saw to cut a section of ~6 mm from the area of interest to be studied. For this study, the material was cut from the gage section of an AM 17-4 PH fatigue specimen, as shown in Figure 1.</li>
		<li>Prepare the cut sample in a metallographic mount for polishing.</li>
		<li>Use a semi-automatic polisher to polish the sample to mirror-like surface (having a surface roughness on the order of 1 &#181;m) starting from 400 grit abrasive paper and moving to 1 &#181;m diamond particles. To ensure sufficient polish at each abrasion level and uniform surface abrasions, alternate the polishing direction by 90&#176; following each grit level. Maintain a flat surface during polishing to avoid issues during a later spin coating process.</li>
	</ol>
	</li>
	<li>Section the material into a thin disk.
	<ol>
		<li>Protect the polished surface using an adhesive tape.</li>
		<li>Use a slow speed saw to align and cut a thin section (0.5-1 mm). 
		&#8203;NOTE: An even section will be important for the spin coating process.</li>
	</ol>
	</li>
</ol>
2. Photolithography
<ol>
	<li>Clean the sample.
	<ol>
		<li>Remove the protective adhesive tape from the polished surface and place the sample with the polished surface facing up in a beaker with acetone. Use an ultrasonic cleaner to clean the sample for 5 min. Use enough acetone to cover the sample.</li>
		<li>Remove the sample from the acetone and dry it using compressed air.</li>
		<li>Submerge the sample in isopropanol and use an ultrasonic cleaner to clean the sample for 5 min. Use enough isopropanol to cover the sample.</li>
		<li>Remove the sample from the container with isopropanol and dry the sample with compressed air.</li>
		<li>Place the sample in a holding container and perform an oxygen plasma cleaning for 1 min.</li>
	</ol>
	</li>
	<li>Prepare the photoresist solution in advance.
	<ol>
		<li>Using a mixer, mix 27.2 g (50 wt%) of liquid PGMEA and 25.1 g (50 wt%) of SU-8 3025 for 2 min.</li>
		<li>De-foam the mixture for 1 min.</li>
	</ol>
	</li>
	<li>Perform the photo-resist patterning.
	<ol>
		<li>Place the sample (polished side up) on the spin-coater.</li>
		<li>Use compressed air to remove any dust or particle on the surface of the sample.</li>
		<li>Apply photoresist on the sample and run the spin-coater using the parameters shown in Table 1. 
		NOTE: The thickness of the resulting SU-8 photoresist used in this study was measured to be near 1.5 &#181;m on average.</li>
		<li>Place the sample on a hot plate and heat at 65 &#176;C for 5 min.</li>
		<li>Heat the sample at 95 &#176;C for 10 min.</li>
		<li>Remove the sample from the hot plate and allow the sample to cool to room temperature.</li>
		<li>Using a photomask with an array of squares measuring 70 &#181;m on each side, expose the sample for 10-15 s at a power density of ~75 mJ/cm2.</li>
		<li>Heat the sample to 65 &#176;C for 5 min on a hotplate.</li>
		<li>Heat the sample to 95 &#176;C for 10 min on a hotplate and then let the sample to cool to room temperature before continuing to the next step.</li>
		<li>Submerge the sample (with the pattern facing up) in a clean container with propylene glycol monomethyl ether acetate (PGMEA) and agitate it for 10 min. Use enough PGMEA to cover the sample.</li>
		<li>Remove the sample and splash with isopropanol before carefully drying with compressed air. 
		&#8203;NOTE: Figure 2 shows the final result of a patterned SU-8 on the sample. In Figure 2, there are locations on the steel surface having no photoresist (note the bottom-left specimen surface) likely due to uneven surface affecting the spin coat. For the purpose of this study (creating local micro-tensile specimens), it is considered a satisfactory pattern.</li>
	</ol>
	</li>
</ol>
3. Wet-etching
<ol>
	<li>Prepare the AM 17-4PH stainless steel aqueous etchant9 shown in Table 2.</li>
	<li>Inside of a fume hood, place the sample in a beaker and place it on top of a hotplate at ~65-70 &#176;C.</li>
	<li>Leave the sample on the hot plate for 5 min.</li>
	<li>With the sample on the hot plate, place a few drops of the prepared etchant so that the patterned surface is completely covered. Leave the etchant for 5 min.</li>
	<li>Remove the sample from the beaker and neutralize the etchant with water. 
	&#8203;NOTE: Figure 3 shows the resulting sample after etching. Note in Figure 3 that the remaining photoresist prevents the etchant from reacting the steel surface, creating localized platform areas of unremoved material.</li>
</ol>
4. Focused Ion Beam milling of specimen geometry
<ol>
	<li>Prepare the sample for the FIB-milling process.
	<ol>
		<li>Place the sample in a container with isopropanol. Use an ultrasonic cleaner to clean the sample for 5 min. Use enough isopropanol to cover the sample.</li>
		<li>Remove and dry the sample with compressed air.</li>
		<li>Using a conductive adhesive, mount the sample on a stub compatible with the nanoindentation device to be used during later testing.</li>
		<li>Drill a hole in a 45&#176; SEM mounting stub and use a carbon tape to place the indenter stub and specimen on a 45&#176; SEM stub, as shown in Figure 4. 
		NOTE: This step is intended to reduce direct contact with the sample once the micro tensile specimen is fabricated, decreasing the chance of damaging the sample.</li>
		<li>Place the sample in an SEM and identify an etched square to perform the FIB milling. 
		NOTE: For this study, remaining material squares ~9 &#181;m in height or larger were desired due to the chosen specimen geometry.</li>
		<li>Orient the chosen FIB location at the top of the SEM stub to avoid contact issues during alignment in the SEM.</li>
	</ol>
	</li>
	<li>Perform FIB milling. 
	NOTE: A SEM operated at 30 kV was used in this study. Although a specific procedure cannot be outlined, as it requires adjustment based on specific equipment, milling from outside to inside is a good practice to avoid material re-deposition within the specimen location. Additionally, it is good practice to use maximum energy to remove bulk material, but reduce the FIB energy while approaching the final specimen dimensions.
	<ol>
		<li>Use the maximum power (20 mA, 30 kV) to remove any undesired bulk material from the remaining etched platform as shown in Figure 5.</li>
		<li>Use lower power (7 mA, 30 kV) or (5 mA, 30 kV) to make a rectangle with slightly larger dimensions than needed for the final specimen geometry (see Figure 6).</li>
		<li>With even lower power (1 mA, 30 kV) or (0.5 mA, 30 kV), perform cross section cuts near to the final micro-tensile specimen dimensions. 
		NOTE: Following this FIB step (shown in Figure 7), the sample should have the required outer dimensions but should be missing the dog-bone shape profile.</li>
		<li>Rotate the sample at 180&#176;.</li>
		<li>Using low power (0.5 mA, 30 kV) or (0.3 mA, 30 kV), perform the final FIB milling step to create the specimen geometry desired. Create and use bitmap to control the FIB intensity and location for the repeatability in the creation of final geometry for multiple specimens. 
		&#8203;NOTE: Figure 8 shows an SEM image of the resulting micro-tensile specimen fabricated from the steps described in sections 4.2.1 through 4.2.5. Dimensions of the tensile specimen are shown in Figure 9.</li>
	</ol>
	</li>
</ol>
5. Grip fabrication
<ol>
	<li>Make alignment marks on the nanoindentation tip to be used for tensile testing.
	<ol>
		<li>Mount the tip on the desired nanoindentation transducer.</li>
		<li>Using a laser scribe, make two alignment marks near the tip, as shown in Figure 10, to allow for proper tip orientation prior to fabrication of the tensile grip through FIB milling. Use a circular notch and linescribe as two alignment sources as the tip rotates during fabrication of the tensile grip geometry.</li>
	</ol>
	</li>
	<li>FIB-mill the nanoindentation tip to make the tension grip.
	<ol>
		<li>Place the marked tip on a SEM stub and align the markings as shown in Figure 10.</li>
		<li>Using the FIB, reduce the width of the indenter tip as shown in Figure 11A. 
		NOTE: Reducing the indenter tip width is helpful in the maneuverability and clearance of the final tensile grip during tension testing.</li>
		<li>Remove the indenter tip from the SEM, use the alignment marks to rotate the tip at 90&#176;. Use the FIB as shown in Figure 11B to reduce the thickness of the indenter tip.</li>
		<li>Remove the indenter tip from the SEM. Use the alignment marks back to 0&#176; (front view) and create the final tensile grip geometry with the FIB as shown in Figure 11C. To reduce re-deposition of the removed material during the FIB process, remove the narrow tensile grip area before removing the wider grip area.</li>
	</ol>
	</li>
</ol>
6. Micro-tensile test
<ol>
	<li>Mount the specimen and indenter tip on the nanoindenter device.</li>
	<li>Install the nanoindentation machine in the SEM following the manufacturer&#39;s recommendations. To ensure adequate imaging during in situ testing, avoid significant machine tilt. 
	NOTE: For this test, a tilt of 5&#176; was used. Excessive tilting will result in a perspective view and make it difficult to align the tensile grip with the test sample.</li>
	<li>To prevent an unexpected event during the tensile testing, perform the desired displacement-based tensile loading protocol in air, away from the sample. 
	NOTE: This air displacement test will preserve the fabricated tensile grip in the event of unexpected displacements during the protocol.</li>
	<li>With caution, slowly approach the tip to the sample&#39;s surface.</li>
	<li>Move and align the tensile grip with the test sample, as shown in Figure 12.</li>
	<li>Perform the tensile test. 
	NOTE: The test performed in this study considered a displacement-controlled protocol at a rate of 0.004 &#181;m/s (resulting in an applied strain rate of 0.001 &#181;m/ &#181;m/s for the 4 &#181;m tall specimen), a maximum displacement of 2.5 &#181;m, and a returning rate of 0.050 &#181;m/s. To perform the tensile test in the transducer used for this test, a negative displacement indentation (-2.5 &#181;m) and negative rate (-0.004 &#181;m/s) was used.</li>
</ol>

<ol>
	<li>Ju-Young, K., Jang, D., Greer, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tensile+and+compressive+behavior+of+tungsten,+molybdenum,+tantalum+and+niobium+at+the+nanoscale.">Tensile and compressive behavior of tungsten, molybdenum, tantalum and niobium at the nanoscale.</a> Acta Materialia. 58 (7), 2355-2363 (2010).</li><li>Kihara, Y., 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=Tensile+behavior+of+micro-sized+specimen+made+of+single+crystalline+nickel.">Tensile behavior of micro-sized specimen made of single crystalline nickel.</a> Materials Letters. 153, 36-39 (2015).</li><li>Julia, R. G., Kim, J. Y., Burek, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+in-situ+mechanical+testing+of+nanoscale+single-crystalline+nanopillars.">The in-situ mechanical testing of nanoscale single-crystalline nanopillars.</a> JOM: The Journal of Minerals, Metals &amp; Materials Society. 61 (12), 19 (2009).</li><li>Kiener, D., 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=A+further+step+towards+an+understanding+of+size-dependent+crystal+plasticity:+In+situ+tension+experiments+of+miniaturized+single-crystal+copper+samples.">A further step towards an understanding of size-dependent crystal plasticity: In situ tension experiments of miniaturized single-crystal copper samples.</a> Acta Materialia. 56 (3), 580-592 (2008).</li><li>Sumigawa, T., 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=In+situ+observation+on+formation+process+of+nanoscale+cracking+during+tension-compression+fatigue+of+single+crystal+copper+micron-scale+specimen.">In situ observation on formation process of nanoscale cracking during tension-compression fatigue of single crystal copper micron-scale specimen.</a> Acta Materialia. 153, 270-278 (2018).</li><li>Kim, J. -. Y., Julia, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tensile+and+compressive+behavior+of+gold+and+molybdenum+single+crystals+at+the+nano-scale.">Tensile and compressive behavior of gold and molybdenum single crystals at the nano-scale.</a> Acta Materialia. 57 (17), 5245-5253 (2009).</li><li>Kiener, D., Minor, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Source+truncation+and+exhaustion:+insights+from+quantitative+in+situ+TEM+tensile+testing.">Source truncation and exhaustion: insights from quantitative in situ TEM tensile testing.</a> Nano Letters. 11 (9), 3816-3820 (2011).</li><li>Reichardt, 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=In+situ+micro+tensile+testing+of+He++2+ion+irradiated+and+implanted+single+crystal+nickel+film.">In situ micro tensile testing of He+ 2 ion irradiated and implanted single crystal nickel film.</a> Acta Materialia. 100, 147-154 (2015).</li><li>Nageswara Rao, P., Kunzru, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+microchannels+on+stainless+steel+by+wet+chemical+etching.">Fabrication of microchannels on stainless steel by wet chemical etching.</a> Journal of Micromechanics and Microengineering. 17 (12), 99-106 (2007).</li><li>Okayasu, M., Fukui, H., Ohfuji, H., Shiraishi, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strain-induced+martensite+formation+in+austenitic+stainless+steel.">Strain-induced martensite formation in austenitic stainless steel.</a> Journal of Material Science. 48, 6157-6166 (2013).</li></ol>

The authors declare that they have no competing financial interests.

A verified methodology for AM 17-4PH stainless steel micro-specimen fabrication and tension testing were presented, including a detailed protocol for fabrication of a micro-tensile grip. Specimen fabrication protocols described result in improved fabrication efficiency by combining photolithography, wet-etching, and FIB milling procedures. Material etching prior to FIB milling helped to remove bulk material and reduce material re-deposition that often occurs during FIB use. The described photolithography and etching procedures allowed for fabrication of the micro-tensile specimens above the surrounding material surface, providing clear access for the tensile grip prior to testing. While this protocol was described and performed for micro-tensile testing, the same procedures would be helpful for micro-compression testing.
During the development of this process, variation within the photo-resist mask patterning was noticed, as shown in Figure 2. This is likely caused by surface inconsistencies created during dicing or poor adhesion of the photoresist to the sample surface. It was noticed that when wet etching was performed at room temperature, much of the photoresist was removed, due to under etching or poor adhesion; therefore, it is recommended to warm the sample before and during the etching process, as mentioned in the protocol. If significant under-etching (etching below the photoresist) is noticed, increasing the sample temperature may help. The provided protocol uses an SU-8 photoresist due to availability; however, other photoresist and etchant combinations may also be effective.
Tensile-grip-to-specimen alignment and sample engagement were the main challenges of micro-tensile testing. By reducing the indenter tip dimensions as described in the protocol, alignment and engagement between the tensile grip and specimen was improved. Due to SEM view perspective limitations, it was often difficult to tell whether the sample was within the tensile grip. Reducing the grip thickness will likely provide better perspective control.
Micro-specimen preparation and micro-tensile material testing is often a lengthy process, requiring several hours of FIB fabrication time and indenter alignment. The methods and protocols prepared herein serve as a verified guide for efficient micro-tensile fabrication and testing. Note that the micro specimen protocol allows for high throughput (rapid) specimen fabrication from bulk AM 17-4PH stainless steel volumes by combining photolithography, chemical etching, and focused ion beam milling.

Mechanical material testing at the micro- and nano-scales can provide important information on fundamental material behavior through identifying length-scale dependencies caused by void or inclusion effects in bulk material volumes. Additionally, micro- and nano-mechanical testing allows for structural component measurements in small-scale structures (such as those in micro electromechanical systems (MEMS))1,2,3,4,5. Nanoindentation and micro compression are currently the most common micro- and nano-mechanical material testing approaches; however, the resulting compression and modulus measurements are often insufficient to characterize material failure mechanisms present in larger bulk material volumes. To identify differences between bulk and micro-mechanical material behavior, particularly for materials having many inclusions and void defects such as those created during additive manufacturing (AM) processes, efficient methods for micro-tension testing are needed.
Although several micromechanical tension testing studies exist for electronic and single-crystalline materials3,6, specimen fabrication and tension testing procedures for additively manufactured (AM) steel materials are lacking. Material length-scale dependencies documented in2,3,4,5,6 suggest material hardening effects in single-crystalline materials at sub-micron length-scales. As an example, observations from micro-mechanical tension testing of single-crystal copper highlight material hardening due to dislocation starvation and truncation of spiral dislocation sources4,5,7. Reichardt et al.8 identifies irradiation hardening effects at the micro scale, observable through micro-mechanical tension testing.
Micro-tensile material measurements requiring attachment of the indenter probe to the specimen are more complex than corresponding micro-compression tests but provide material fracture behavior applicable for bulk material volume predictions under more complex loading (axial tension, bending, etc.). Fabrication of micro-tensile specimens often relies heavily on Focused Ion Beam (FIB) milling from the bulk material volumes. Because FIB milling processes involve highly localized material removal (at the micro and nano-scales), large area removal through FIB milling often results in lengthy micro-specimen fabrication times. The work presented here explores a methodology to improve efficiency in micro-tensile specimen fabrication for AM 17-4PH stainless steels by combining photolithographic processes, chemical etching, and FIB milling. Additionally, procedures for the micro-mechanical tension testing of fabricated AM steel specimens are presented and testing results are discussed.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>45 &#176; SEM stub</td>
			<td>TED Pella</td>
			<td>16104</td>
			<td>https://www.tedpella.com/SEM_html/SEMpinmount.htm</td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>VWR</td>
			<td>CAS: 67-64-1</td>
			<td>https://us.vwr.com/store/product/4533063/acetone-99-5-acs-vwr-chemicals-bdh</td>
		</tr>
		<tr>
			<td>Branson 1510 Ultrasonic Cleaner</td>
			<td>Branson Ultrasonic</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Carbon conductive tabs</td>
			<td>PELCO image tabs</td>
			<td>16084-20</td>
			<td>https://www.tedpella.com/SEMmisc_html/semadhes.htm.aspx#16084-4</td>
		</tr>
		<tr>
			<td>CrystalBond</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FEI Nova Nanolab 200 Dual-Beam Workstation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ferric Chloride</td>
			<td>VWR</td>
			<td>CAS: 7705-08-0</td>
			<td>https://us.vwr.com/store/product/7516265/iron-iii-chloride-anhydrous-98-pure</td>
		</tr>
		<tr>
			<td>Hydrochloric Acid (12.1M)</td>
			<td>EMD</td>
			<td>CAS: 7647-01-0, HX0603</td>
			<td>https://www.emdmillipore.com/US/en/product/Hydrochloric-Acid,EMD_CHEM-HX0603</td>
		</tr>
		<tr>
			<td>Hysitron PI-88</td>
			<td>Bruker</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ISOMET Low Speed Saw</td>
			<td>Buehler</td>
			<td>11-1180-160</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>VWR</td>
			<td>CAS: 67-63-0</td>
			<td>https://us.vwr.com/store/product/4549282/2-propanol-99-5-acs-vwr-chemicals-bdh</td>
		</tr>
		<tr>
			<td>ISOTEMP Hot Plate</td>
			<td>Fisher Scientific</td>
			<td></td>
			<td>https://www.fishersci.com/shop/products/fisherbrand-isotemp-hot-plate-stirrer-ambient-540-c-ceramic/p-9078002</td>
		</tr>
		<tr>
			<td>Kapton Tape</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Metaserv 2000 Grinder/Polisher</td>
			<td>Buehler</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nitric Acid (68-70%)</td>
			<td>VWR</td>
			<td>CAS:7697-37-2MW, BDH3130</td>
			<td>https://us.vwr.com/store/catalog/product.jsp?catalog_number=BDH3130-2.5LP</td>
		</tr>
		<tr>
			<td>PE-25 Serie Plasma System</td>
			<td>Plasma Etch</td>
			<td>PE-25</td>
			<td>https://www.plasmaetch.com/pe-25-plasma-cleaner.php</td>
		</tr>
		<tr>
			<td>PGMEA</td>
			<td>J.T. Baker</td>
			<td>CAS: 108-65-6</td>
			<td>https://us.vwr.com/store/product/4539301/2-methoxy-1-methylethyl-acetate-pgmea-99-0-by-gc-stabilized-bts-220-j-t-baker</td>
		</tr>
		<tr>
			<td>PhenoCure Compression Mounting Compound</td>
			<td>Buehler</td>
			<td>20-3100-080</td>
			<td>https://shop.buehler.com/phenocure-blk-powder-5lbs</td>
		</tr>
		<tr>
			<td>PI-88 Sample mount</td>
			<td>Bruker</td>
			<td>5-2238-10</td>
			<td></td>
		</tr>
		<tr>
			<td>PI-FIB STOCK</td>
			<td>Bruker</td>
			<td>TI-0280</td>
			<td></td>
		</tr>
		<tr>
			<td>SimpliMet 4000 Mounting Press</td>
			<td>Buehler</td>
			<td></td>
			<td>https://www.buehler.com/simpliMet-4000-mounting-press.php</td>
		</tr>
		<tr>
			<td>Spin Coater</td>
			<td>Laurell Technologies Copr.</td>
			<td>WS-650MZ-23NPPB</td>
			<td></td>
		</tr>
		<tr>
			<td>SU-8 3025</td>
			<td>Kayaku Advanced Materials (MicroChem)</td>
			<td>Y311072 0500L1GL</td>
			<td>https://www.fishersci.com/shop/products/su-8-3025-500ml/nc0057282</td>
		</tr>
		<tr>
			<td>Tescan VEGA 3 SEM</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Thinky AR-1000 Conditioning Mixer</td>
			<td>Thinky</td>
			<td>AR-100</td>
			<td>https://www.thinkymixer.com/en-us/product/ar-100/</td>
		</tr>
	</tbody>
</table>

micromechanical tension testing of additively manufactured 17-4 ph stainless steel specimens

This study presents a methodology for the rapid fabrication and micro-tensile testing of additively manufactured (AM) 17-4PH stainless steels by combining photolithography, wet-etching, focused ion beam (FIB) milling, and modified nanoindentation. Detailed procedures for proper sample surface preparation, photo-resist placement, etchant preparation, and FIB sequencing are described herein to allow for high throughput (rapid) specimen fabrication from bulk AM 17-4PH stainless steel volumes. Additionally, procedures for the nano-indenter tip modification to allow tensile testing are presented and a representative micro specimen is fabricated and tested to failure in tension. Tensile-grip-to-specimen alignment and sample engagement were the main challenges of the micro-tensile testing; however, by reducing the indenter tip dimensions, alignment and engagement between the tensile grip and specimen were improved. Results from the representative micro-scale in situ SEM tensile test indicate a single slip plane specimen fracture (typical of a ductile single crystal failure), differing from macro-scale AM 17-4PH post-yield tensile behavior.

A material sample from an AM 17-4 PH stainless steel specimen (previously tested in low-cycle fatigue) was prepared and tested using the protocol described, to understand the fundamental material behavior of AM metals (independent of structural defect influence). Typical sample volumes used for material characterization can contain distributed fabrication/structural defects that make discerning between actual material behavior and structural fabrication effects difficult. Following the protocol described in sections 2 through 6 a micro specimen was fabricated and tested to failure in tension, successfully demonstrating the described techniques and producing material test data at scales free from volumetric defect influences. Prior to micro-mechanical testing, X-ray diffraction (XRD) spectra from the prepared steel surface (see Figure 13), show a mostly martensitic grain structure as would be expected from a previously strained material10.
Figure 14&#160;shows the resulting load-displacement behavior of the micro-tensile AM 17-4PH steel sample, having a maximum tensile strength of 3,145 &#181;N at a displacement of 418 nm. From in situ SEM observations during loading, fracture of the micro-specimen occurred along a single slip plane (typical of a ductile single crystal failure) and different from typical post-yield strain hardening behavior observed during macro-scale material tension testing of AM 17-4PH stainless steels. Frames 4-6 of Figure 14 show the single failure slip plane during tension testing of the fabricated micro specimen.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62433/62433fig1v3.jpg" /> 
Figure 1: Bulk material where the sample was taken from. The material sample for micro-mechanical testing (~6 mm in thickness) was cut from the gage section of an AM 17-4 PH fatigue specimen. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62433/62433fig2v4.jpg" /> 
Figure 2: Material section having an array of squares (70 &#181;m x 70 &#181;m) patterned using photolithography. The 70 &#181;m x 70 &#181;m photoresist array allows for selective etching of the steel surface for bulk surface material removal. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62433/62433fig03.jpg" /> 
Figure 3: SEM images of the AM 17-4PH steel surface following etching. Surface high-relief locations created by the protective photoresist pattern following etching allow micro-specimen fabrication above the specimen surface elevation. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62433/62433fig4v3.jpg" /> 
Figure 4: Sample holder set-up that helps the direct contact of the sample once the micro-tensile specimen is fabricated. The etched AM 17-4 PH sample is placed on the nanoindentation device stub before being mounted to a 45-degree SEM stub (using carbon tape) to reducing handling of the specimen after micro-specimen fabrication. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/62433/62433fig05.jpg" /> 
Figure 5: Illustration of first FIB milling step with area to be removed by FIB (left), and remaining material (right). The surface high-relief material remaining after etching is removed using FIB milling, leaving a rectangular volume of material. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/62433/62433fig06.jpg" /> 
Figure 6: Illustration of second FIB milling step. The rectangular volume of material is further reduced using FIB milling, approaching the desired specimen outer dimension tolerances. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/62433/62433fig07.jpg" /> 
Figure 7: Illustration of third FIB milling step. The remaining material volume is refined using FIB milling to the desired specimen outer dimension tolerances. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/62433/62433fig08.jpg" /> 
Figure 8: SEM image of a micro-tensile sample. Using FIB milling, the profile of the remaining material volume is reduced to create the final micro-tensile specimen geometry. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/62433/62433fig9v3.jpg" /> 
Figure 9: Micro-tensile specimen dimensions. Between the specimen grip areas, a reduced cross-sectional dimension measuring 1 &#956;m by 1 &#956;m is located within a 4&#956;m gauge length. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig09large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/62433/62433fig10.jpg" /> 
Figure 10: Alignment marks performed in the tip for reference. A semi-circular edge hole and circumferential scribe mark provide two sources of indenter tip alignment prior to fabrication of the tensile grip. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/62433/62433fig11.jpg" /> 
Figure 11: Sequential tensile grip fabrication steps. (A) Formation of tensile grip outer profile using FIB milling. (B) Reduction in tensile grip thickness following 90&#176; rotation. (C) Formation of tensile grip inner profile from original orientation. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/62433/62433fig12v4.jpg" /> 
Figure 12: Grip and sample aligned to perform the tensile test. The fabricated tensile grip is positioned around the micro-tensile specimen such that an upward movement of the tensile grip will engage with the specimen. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 13" class="xfigimg" src="/files/ftp_upload/62433/62433fig13.jpg" /> 
Figure 13: XRD spectra of tested sample. Shown is the relationship between X-ray scatter intensity and sample angle. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig13large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 14" class="xfigimg" src="/files/ftp_upload/62433/62433fig14.jpg" /> 
Figure 14: Tensile load-displacement curve of AM 17-4 PH Steel. (Top) Frame-by-frame progression of applied specimen displacement. (Bottom) Resulting sample behavior comparing measured load (in &#956;N of force) and applied displacement (in nm), indicating a material ultimate strength of 3,145 &#956;N at an applied displacement of 418 nm. <a href="https://www.jove.com/files/ftp_upload/62433/62433fig14large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Process</td>
			<td>Details</td>
			<td>Time (s)</td>
		</tr>
		<tr>
			<td>Acceleration</td>
			<td>From 0 to 500 rpm at 100 rpm/s</td>
			<td>5</td>
		</tr>
		<tr>
			<td>Spin</td>
			<td>500 rpms</td>
			<td>5</td>
		</tr>
		<tr>
			<td>Acceleration</td>
			<td>From 500 rpm to 3,000 rpm at 500 rpm/s</td>
			<td>5</td>
		</tr>
		<tr>
			<td>Spin</td>
			<td>3,000 rpm</td>
			<td>25</td>
		</tr>
	</tbody>
</table>
Table 1: Parameters used for the spin-coating. Process steps are to be performed consecutively.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>FeCl3 (wt%)</td>
			<td>HCl (wt%)</td>
			<td>HNO3 (wt%)</td>
		</tr>
		<tr>
			<td>10</td>
			<td>10</td>
			<td>5</td>
		</tr>
	</tbody>
</table>
Table 2: Chemical composition of the etchant used for AM 17-4PH Stainless Steel9. All solution chemical quantities are listed as percentage by weight.

Watch this Scientific Journal Video about Micromechanical Tension Testing of Additively Manufactured 17-4 PH Stainless Steel Specimens at JoVE.com

Micromechanical Tension Testing of Additively Manufactured 17-4 PH Stainless Steel Specimens

Presented here is a procedure for measuring fundamental material properties through micromechanical tension testing. Described are the methods for micro-tensile specimen fabrication (allowing rapid micro-specimen fabrication from bulk material volumes by combining photolithography, chemical etching, and focused ion beam milling), indenter tip modification, and micromechanical tension testing (including an example).

This study presents a methodology for the rapid fabrication and micro-tensile testing of additively manufactured (AM) 17-4PH stainless steels by combining ...

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3.2K Views.  University of Arkansas. Presented here is a procedure for measuring fundamental material properties through micromechanical tension testing. Described are the methods for micro-tensile specimen fabrication (allowing rapid micro-specimen fabrication from bulk material volumes by combining photolithography, chemical etching, and focused ion beam milling), indenter tip modification, and micromechanical tension testing (including an example).

Video: Micromechanical Tension Testing of Additively Manufactured 17-4 PH Stainless Steel Specimens

Fabrication of VB2/Air Cells for Electrochemical Testing

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for synthesizing nanoscopic VB2 is presented as well as step-by-step procedure for applying a zirconium oxide coating to the VB2 particles for stabilization upon discharge. The process for disassembling existing zinc/air cells is shown, in addition construction of the new working electrode to replace the conventional zinc/air cell anode with a the nanoscopic VB2 anode. Finally, discharge of the completed VB2/air battery is reported. We show that using the zinc/air cell as a test bed is useful to provide a consistent configuration to study the performance of the high-energy high capacity nanoscopic VB2 anode.

Fabrication of VB2/Air Cells for Electrochemical Testing

A protocol is presented to study multi-electron metal/air battery systems by using previous technology developed for the zinc/air cell. Electrochemical testing is then performed on fabricated batteries to evaluate performance.

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for ...

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Mechanical Expansion of Steel Tubing as a Solution to Leaky Wellbores

Wellbore cement, a procedural component of wellbore completion operations, primarily provides zonal isolation and mechanical support of the metal pipe (casing), and protects metal components from corrosive fluids. These are essential for uncompromised wellbore integrity. Cements can undergo multiple forms of failure, such as debonding at the cement/rock and cement/metal interfaces, fracturing, and defects within the cement matrix. Failures and defects within the cement will ultimately lead to fluid migration, resulting in inter-zonal fluid migration and premature well abandonment. Currently, there are over 1.8 million operating wells worldwide and over one third of these wells have leak related problems defined as Sustained Casing Pressure (SCP)1. 
The focus of this research was to develop an experimental setup at bench-scale to explore the effect of mechanical manipulation of wellbore casing-cement composite samples as a potential technology for the remediation of gas leaks. 
The experimental methodology utilized in this study enabled formation of an impermeable seal at the pipe/cement interface in a simulated wellbore system. Successful nitrogen gas flow-through measurements demonstrated that an existing microannulus was sealed at laboratory experimental conditions and fluid flow prevented by mechanical manipulation of the metal/cement composite sample. Furthermore, this methodology can be applied not only for the remediation of leaky wellbores, but also in plugging and abandonment procedures as well as wellbore completions technology, and potentially preventing negative impacts of wellbores on subsurface and surface environments.

This article reports on a laboratory scale investigation of an existing field procedure and its adaptation for sealing of leaky wellbores. It consists of mechanical expansion of metal pipe, which results in an improved metal/cement bond, ultimate sealing of hydraulic pathways and prevention of gas leaks caused by the presence of a microannular channel.

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The Evolution of Silica Nanoparticle-polyester Coatings on Surfaces Exposed to Sunlight

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, building and food industries, amongst others. Polyester and coatings containing both polyester and silica nanoparticles (SiO2NPs) have been widely used to protect steel substrata from corrosion. In this study, we utilized X-ray photoelectron spectroscopy, attenuated total reflection infrared micro-spectroscopy, water contact angle measurements, optical profiling and atomic force microscopy to provide an insight into how exposure to sunlight can cause changes in the micro- and nanoscale integrity of the coatings. No significant change in surface micro-topography was detected using optical profilometry, however, statistically significant nanoscale changes to the surface were detected using atomic force microscopy. Analysis of the X-ray photoelectron spectroscopy and attenuated total reflection infrared micro-spectroscopy data revealed that degradation of the ester groups had occurred through exposure to ultraviolet light to form COO&#903;, -H2C&#903;, -O&#903;, -CO&#903; radicals. During the degradation process, CO and CO2 were also produced.

Two types of surfaces, polyester-coated steel and polyester coated with a layer of silica nanoparticles, were studied. Both surfaces were exposed to sunlight, which was found to cause substantial changes in the chemistry and nanoscale topography of the surface.

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, ...

Subsurface Defect Localization by Structured Heating Using Laser Projected Photothermal Thermography

The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering thermal wave fields that are disturbed by the defect. This effect is measured and used to locate the defect. We form the destructively interfering wave fields by using a modified projector. The original light engine of the projector is replaced with a fiber-coupled high-power diode laser. Its beam is shaped and aligned to the projector&#39;s spatial light modulator and optimized for optimal optical throughput and homogeneous projection by first characterizing the beam profile, and, second, correcting it mechanically and numerically. A high-performance infrared (IR) camera is set up according to the tight geometrical situation (including corrections of the geometrical image distortions) and the requirement to detect weak temperature oscillations at the sample surface. Data acquisition can be performed once a synchronization between the individual thermal wave field sources, the scanning stage, and the IR camera is established by using a dedicated experimental setup which needs to be tuned to the specific material being investigated. During data post-processing, the relevant information on the presence of a defect below the surface of the sample is extracted. It is retrieved from the oscillating part of the acquired thermal radiation coming from the so-called depletion line of the sample surface. The exact location of the defect is deduced from the analysis of the spatial-temporal shape of these oscillations in a final step. The method is reference-free and very sensitive to changes within the thermal wave field. So far, the method has been tested with steel samples but is applicable to different materials as well, in particular to temperature sensitive materials.

This method aims at locating vertical subsurface defects. Here, we couple a laser with a spatial light modulator and trigger its video input to heat a sample surface deterministically with two anti-phased modulated lines while acquiring highly resolved thermal images. The defect position is retrieved from evaluating thermal wave interference minima.

The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering ...

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.

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Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A typical anti-wetting superhydrophobic surface easily fails when exposed to a high-temperature liquid. Recently, Nepenthes-inspired slippery surfaces demonstrated a new way to solve the adhesion problem. A lubricant layer on the slippery surface can act as a barrier between the repelled materials and the surface structure. However, the slippery surfaces in previous studies rarely showed high-temperature resistance. Here, we describe a protocol for the preparation of slippery surfaces with high-temperature resistance. A photolithography-assisted method was used to fabricate pillar structures on stainless steel. By functionalizing the surface with saline, a slippery surface was prepared by adding silicone oil. The prepared slippery surface maintained the anti-wetting property for water, even when the surface was heated to 300 &#176;C. Also, the slippery surface exhibited great anti-adhesion effects on soft tissues at high temperatures. This type of slippery surface on stainless steel has applications in medical devices, mechanical equipment, etc.

Slippery surfaces provide a new way to solve the adhesion problem. This protocol describes how to fabricate slippery surfaces at high temperatures. The results demonstrate that the slippery surfaces showed anti-wetting for liquids and a remarkable anti-adhesion effect on soft tissues at high temperatures.

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Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the Earth&#39;s magnetic field, for manufacturing a cementitious composite reinforced with aligned steel fibers. Aligned steel fiber reinforced cementitious composites (ASFRC) were prepared by applying a uniform electromagnetic field to fresh mortar containing short steel fibers, whereby the short steel fibers were driven to rotate in alignment with the magnetic field. The degree of alignment of steel fibers in hardened ASFRC was assessed both by counting steel fibers in fractured cross-sections and by X-ray computed tomography analysis. The results from the two methods show that the steel fibers in ASFRC were highly aligned while the steel fibers in non-magnetically treated composites were randomly distributed. The aligned steel fibers had a much higher reinforcing efficiency, and the composites, therefore, exhibited significantly enhanced flexural strength and toughness. The ASFRC is thus superior to SFRC in that it can withstand greater tensile stress and more effectively resist cracking.

This protocol describes an approach for manufacturing aligned steel fiber reinforced cementitious composite by applying a uniform electromagnetic field. Aligned steel fiber reinforced cementitious composite exhibits superior mechanical properties to ordinary fiber reinforced concrete.

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Ultrasonic Fatigue Testing in the Tension-Compression Mode

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on exposing the specimen to longitudinal vibrations on its resonance frequency close to 20 kHz. With use of this method, it is possible to significantly decrease the time required for the test, when compared to conventional testing devices usually working at frequencies under 200 Hz. It is also used to simulate loading of material during operation in high speed conditions, such as those experienced by components of jet engines or car turbo pumps. It is necessary to operate only in the high and ultra-high cycle region, due to the possibility of extremely high deformation rates, which can have a significant influence on the test results. Specimen shape and dimensions have to be carefully selected and calculated to fulfill the resonance condition of the ultrasonic system; thus, it is not possible to test the full components or specimens of arbitrary shape. Before each test, it is necessary to harmonize the specimen with the frequency of the ultrasonic system to compensate for deviations of the real shape from the ideal one. It is not possible to run a test until a total fracture of the specimen, since the test is automatically terminated after initiation and propagation of the crack to a certain length, when the stiffness of the system changes enough to shift the system out of the resonance frequency. This manuscript describes the process of evaluation of materials' fatigue properties at high-frequency ultrasonic fatigue loading with use of mechanical resonance at a frequency close to 20 kHz. The protocol includes a detailed description of all steps required for a correct test, including specimen design, stress calculation, harmonizing with the resonance frequency, performing the test, and final static fracture.

A protocol for ultrasonic fatigue testing in the high and ultra-high cycle region in axial tension-compression loading mode.

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Applicability Analysis of Assessment Methods for Morphological Parameters of Corroded Steel Bars

The irregular and uneven residual sections along the length of a corroded steel bar substantially change its mechanical properties and significantly dominate the safety and performance of an existing concrete structure. As a result, it is important to measure the geometry and amount of corrosion of a steel bar in a structure properly to assess the residual bearing capacity and service life of the structure. This paper introduces and compares five different methods for measuring the geometry and amount of corrosion of a steel bar. A single 500 mm long and 14 mm diameter steel bar is the specimen that is subjected to accelerated corrosion in this protocol. Its morphology and the amount of corrosion were carefully measured before and after using mass loss measurements, a Vernier caliper, drainage measurements, 3D scanning, and X-ray micro-computed tomography (XCT). The applicability and suitability of these different methods were then evaluated. The results show that the Vernier caliper is the best choice for measuring the morphology of a non-corroded bar, while 3D scanning is the most suitable for quantifying the morphology of a corroded bar.

This paper measures the geometry and the amount of corrosion of a steel bar using different methods: mass loss, calipers, drainage measurements, 3D scanning, and X-ray micro-computed tomography (XCT).

The irregular and uneven residual sections along the length of a corroded steel bar substantially change its mechanical properties and significantly ...