To Study the Role of WC Reinforcement and Deep Cryogenic Treatment on AZ91 MMNC Wear Behavior Using Multilevel Factorial Design

The present investigation explores the collective outcome of hard particle reinforcement with deep cryogenic treatment (DCT) on wear responses of magnesium metal matrix nanocomposites (MMNC). A multilevel factorial design of experiments with control factors of applied load (20 and 40 N), sliding speed (1.3, 1.7, 2.2, and 3.3 m/s), reinforcement % (0% and 1.5%), and cryogenic treatment (cryogenic-treated and nontreated) was deployed. Around 1.5 wt % WC-reinforced MMNC were fabricated using stir-casting process. DCT was performed at −190 °C with soaking time of 24 h. The dry sliding wear trials were done on pin-on-disk tribometer with MMNC pin and EN8 steel disk for a constant sliding distance of 2 km. The WC reinforcement contributed toward the improvement in wear rate of MMNC appreciably by absorbing the load and frictional heat at all loads and speeds. During DCT of AZ91, the secondary ß-phase (Mg17Al12) was precipitated that enriched the wear resistance, only for the higher load of 40 N. Scanning electron microscope analyses of the cryogenic-treated MMNC ensured the existence of both ß-phase precipitates and WC in the contact area. As a result, the adhesiveness of this pin was lesser, which attributed to the improved wear resistance (approximately 33%) as compared to base alloy. The coefficient of friction was also less for cryogenic-treated MMNC. A regression analysis was made to correlate the control elements and the responses.