Iranian Journal of Materials Science and Engineering

In this study an effort has been made for the plasma ion nitriding (PIN) of Inconel 600 and 601 alloys at low temperatures. After plasma ion nitriding, microstructure study, growth kinetics of nitrided layer formation and wear properties were investigated by various characterization techniques such as; scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, micro-hardness measurement and wear test by pin on disk technique. It was found that, surface micro-hardness increases after PIN process. A mix peak of epsilon (ε) phase with fcc (γ) phase was detected for all temperature range (350 ⁰C to 450 ⁰C), while the chromium nitride (CrN) phase was detected at elevated temperature range ~450 ⁰C in inconel 601 alloy. The calculated values of diffusion coefficient and activation energy for diffusion of nitrogen are in accordance with the literature. Volume loss and wear rate of the plasma nitrided samples decreases, but it increases as PIN process temperature increases.

Aluminum matrix composites are candidate materials for aerospace and automotive industries owing to their specific properties such as high elastic modulus (E), improved strength and low wear rate. The effect of thixoforming process on the wear behavior of an Al-Mg₂Si composite was studied in this paper. During applying thixoforming process, casting defects  such as macrosegration, shrinkage and porosity are being effectively reduced. These advantages are sufficient to attract more exploration works of thixoforming operation. Thermal analysis of the composite, as-cast microstructure, wear surface and subsurface area of the thixoformed alloy were  investigated. Wear behavior of  the specimens were examined using a pin-on-disk machine  based on ASTM-G99, at the applied loads of 25, 50 and 75 N and the constant sliding velocity of 0.25m/s. The worn surfaces and subsurfaces were examined by scanning electron microscopy (SEM). The experimental results indicated that the thixoformed specimens exhibited superior wear resistance than the as-cast alloy. Moreover, the dominant wear mechanism is an adhesive wear followed by the formation of a mechanical mixed layer (MML). However, a severer wear regime occurs in the as cast specimens compared with the thixoformed ones