Gas Nitriding Mechanism in Titanium Powder Injection Molded Products

Gas surface treatment is considered to be especially effective for Titanium because of its high reactivity. In this study, we investigated the gas nitriding mechanism in titanium sintered parts produced by metal powder injection molding (MIM) process. In MIM process, gas nitriding can be surface-treated subsequently after debinding and sintering process. Then, the microstructure and nitrogen content of sintered MIM parts are considered to be greatly influenced by not only nitriding conditions but also sintered conditions. In this study, the effects of sintering time on microstructure such as nitrided layer thickness and hardness was investigated. Focus was given to the effects of specimen size on nitriding process, because the size of micro metal injection molding (μ-MIM) product is so small and the specific surface of that product is so large that the mechanical and functional properties can be subject to change by nitriding.

Study on Nitriding Mechanism for Aluminum Using Barrel Nitriding

In a previous study, an aluminum nitride (AlN) layer was formed below the melting point of aluminum (Al) on the surface of an Al substrate (JIS-A1050) in a barrel with alumina/aluminum-magnesium alloy powder which activates the substrate in the nitrogen atmosphere. In this study, the mechanism of formation of AlN in the barrel was examined. AlN formation requires an incubation period. During the incubation period, a white region on the surface is observed by the optical microscopy. The Electron Probe Micro Analyzer (EPMA) show that this region contains magnesium (Mg). It seems that Mg penetrates and diffuses from the filled Al-Mg powder in the barrel. After that, the nitride is partially generated at the surface of the Al substrate, and it grows with the substrate surface. The AlN layer thickness increases proportionally with the square root of time, and it has good adhesion.