No abstract

A high density plasma nitriding experiment was performed on a circular disk specimen of martensitic stainless steel at the temperature of 673 K for 14.4 ks. The nitrided thickness was 80 μm in depth from the surface with a high surface nitrogen concentration of 31 at%. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDX) and, electron backscattering diffraction (EBSD) were used to analyze the microstructure, the nitrogen content distribution, the phase formation, the grain size, and the straining in the specimen. Phase transformation from martensitic to austenitic phases took place together with high straining as well as grain size re nement.

Fine-grained austenitic stainless steels (FGSS) were plasma nitrided below 700 K to describe their microstructure evolution during the nitrogen supersaturation process and to investigate the post-stressing effect on the microstructure and mechanical properties of nitrided FGSS. Normal- and fine-grained AISI304 plates were nitrided at 623 K and 673 K to investigate the grain size effect on the nitrogen supersaturation process as well as the microstructure evolution during the nitriding process. Fine-grained AISI316 (FGSS316) wires were nitrided at 623 K to demonstrate that their outer surfaces were uniformly nitrided to have the same two-phase, refined microstructure with high nitrogen solute content. This nitrided FGSS316 wire had a core structure where the original FGSS316 core matrix was bound by the nitrided FGSS316 layer. The nitrided wire had higher stiffness, ultimate strength, and elongation in the uniaxial tensile testing than its un-nitrided wires. The core microstructure was refined and homogenized by this applied loading together with an increase of nitrided layer hardness.

Hydrogenated amorphous carbon (a-C:H) films were deposited on the sidewall of 3-mm-wide stainless steel or Si trench, and the adhesion strength of the films was evaluated using a micro-scratch tester. Particularly, the effects of carbon ion implantation and Si-containing interlayer (a-SiCx:H) as the pretreatments on the adhesion strength of the a-C:H films prepared on the trench sidewall were investigated. It was found that both carbon ion implantation and interlayer improved the adhesion strength of the a-C:H films deposited on the trench sidewalls. In addition, the carbon ion implantation dominated the adhesion strength of the a-C:H films for the Si substrates, and the interlayer for the stainless steel substrates. In the case of the stainless steel substrates, the carbon was accumulated on the surface of the trench sidewall instead of implantation, whereas the carbon ions were implanted to the Si substrates on the trench sidewall to form a mixing layer. The a-SiCx:H interlayer forms Fe–Si bonds between the stainless steel substrate and the interlayer, which is thought to improve the adhesion strength. It was also found that there is a negative correlation between the trench depth and the adhesion strength regardless of the pretreatment methods.

This paper concerned with micro-embossing of micro-cavities and micro-grooves into aluminum sheets by CNC-stamping with use of the arrayed DLC multi-punches. Both SKD11 and AISI420 steel die substrates were prepared and DLC-coated with the thickness of 10 to 15 μm. This DLC coating worked as a punch material. The two dimensional micro-patterns were printed onto this DLC film by maskless lithography. The unprinted DLC films were removed by the plasma oxidation to leave the three dimensional DLC-punch array on the steel substrate. This micro-pillared and micro-grooved DLC-punches were placed into the cassette die set for micro-embossing process by using the table-top CNC stamper. The micro-circular patterns transformed to the micro-pillars in the DLC punch by the plasma oxidation. Through the CNC-micro-embossing, this micro-texture further transferred to micro-cavities in the aluminum sheet. The dimensional accuracy of embossed micro-textures by stamping was measured by SEM and three dimensional profilometer with comparison to the tailored micro-pattern and the DLC-punch array configuration.