Characterization of the Nano-Scale Surface Layer of a Tempered Martensitic Steel Synthesized by Ultrasonic Nanocrystalline Surface Modification Treatment

Study of the Microstructural Evolution of Tempered Martensite Ferritic Steel T91 upon Ultrasonic Nanocrystalline Surface Modification

“…TEM examination of the microstructure was carried out on the plan-view specimens at different depth (based on the OM, SEM, and EBSD analyses), whose specimens were prepared by twin jet-polishing using a solution of 95% acetic acid and 5% perchloric acid at room temperature. To prepare TEM plan-view specimens at specific depths, the punched 3 mm disks were thinned from bottom by mechanical polishing to the thickness of 60 mm, and then back-forward jet-polished, of which the details are explained elsewhere (He et al, 2014). TEM investigation was then conducted using a JEM-2100F (JEOL) and a Philips CM200FEG (Philips, Netherlands) operated at 200 keV.…”

“…The results of microstructural analyses of the treated specimens indicated that the grain refinement in the surface is responsible for the improvement of corrosion resistance (Ren et al, 2010). Ultrasonic nanocrystalline surface modification (UNSM) has been developed recently and applied successfully to various single phase steels (Yu et al, 2009) and alloys (Ahn et al, 2012;He et al, 2014). In this study, TMF T91 steel, which has a ferritic matrix with various numbers of second phase precipitates dispersed in various boundaries, was subjected to UNSM treatment and analyzed.…”

Microstructural Characterization of SS304 upon Various Shot Peening Treatments

“…Generally, the deformation depth was measured from the cross-sectional SEM. This indicates that the combination of the microhardness and EBDS analyses is an effective way to study the overall deformation depth and micro structural evolution (He et al, 2014).…”

“…XRD analyses of the surface layer were performed on a Philips X'pert MPD X-ray (Philips, Netherlands) diffractometer with the CuK α1 radiation. The top-most specimens for TEM study were prepared by a modified jet-polishing method as detailed in He et al (2014). In brief, after careful polishing of the 3 mm disk down to 60 μm from the untreated side, the treated surface was then covered by a protective light-transparent plastic film, which was then electropolished and stopped just before the perforation.…”

“…The tip, with the energy of the ultrasonic generator and static load strikes the surface of work piece more than 20,000 times/s with 1,000 to 100,000 shots/mm 2 . The respective strain rates of the ABSP, USP, and UNSM are estimated to be ~10 6 (Umemote et al, 2003), 10 2 to 10 3 (Lu & Hansen, 2009) and 10 3 to 10 5 s -1 (He et al, 2014), depending on the process parameters. However, the ABSP and USP are more flexible than the UNSM, which is mostly used to modify the work pieces with more complicated shape such as gears, various bearings, tools, etc.…”