Title: Two-Layer Nanostructuring of AISI316/316L Stainless Steels for Medical and Special Tooling via Low temperature Plasma Nitriding

 

Director, professor at the Surface Engineering Design Laboratory, SIT (Shibaura Institute of Technology), Japan. He received PhD from The University of Tokyo in 1980. He became a research associate, Institute of Aerospace and Aeronautics in 1980, a lecturer in 1985, an associate professor in 1986 and a professor in 1996 till 2004 at the University of Tokyo. After the research professor in the University of Toronto from 2005 to 2008, he has been working as a professor in SIT from 2009 till now. His research interests include the micro-manufacturing, the innovations in manufacturing and materials processing, and, the materials science and engineering. He has published over 800 papers in Japanese and International Journals and over 90 patents. He has received lots of awards from academic societies including the Distinguished Achievement Award, Japan Institute of Metals, 2011, the Gold Medal, 2017, the Achievement Award, 2019, Japan Society of Technology of Plasticity (JSTP), respectively, the best presentation award at the Conference, AWMFT-2021, and the best paper award in 1st place and best presentation award, ICTMP2024.　He was elected as an emeritus member on JSTP in 2023.

 

High density plasma immersion nitriding was developed for low temperature surface treatment of metals and alloys. The austenitic stainless steels in series of AISI316 and AISI316L were plasma nitrided at 673 K and 623 K to have a nano-grained, two-phase surface layer. In these low temperatures, no chromium and ion nitrides were synthesized as a precipitate in the surface layer. It was massively nitrogen supersaturated (MNSed) to induce the expansion of g-phase supercells via nearly full occupation of vacancy sites by nitrogen solutes. This expansion in the MNSed layer also induces the plastic straining just below the MNS front in the matrix to preserve the strain compatibility through the MNS front. After precise EBSD analyses, this plastic straining was represented as dense slip-line field with high KAM profile. Two-phase structure analyzed by EBSD was in correspondence to two cluster system, where nitrogen rich phase with high chromium content is neighboring within 5 nm range to nitrogen poor phase with high iron and nickel contents. Two applications were explained using this two-layer nanostructured AISI316 and AISI316L by MNS. The MNSed AISI316L substrate was machined and finished by using the PCD-chipped cutting tool to yield a mold for hot-stamping the oxide glass preform to optical lenses and elements. The MNSed AISI316 rod had a two-layered microstructure in similar manner to the Japan sward where the nanostructured surface layer via MNS is continuously connected to the ductile matrix of AISI316. A proto type of micro-surgery knife was produced by this treatment.