Plasma Nitriding of 2024 Al Alloy Deposited with Ti Film: Effects of N_2-H_2 Ratio on Microstructure Evolution and Mechanical Properties

摘要

2024 Al alloys were firstly deposited with pure Ti film (～5.0 μm in thickness) using magnetron sputtering, then plasma nitrided for 8 h at 490°C under N_2-H_2 gas mixtures with different N_2 content (15, 40 and 50%). The Ti-N and Ti-Al diffusion reactions were activated simultaneously on the surface of Al alloy to obtain duplex coatings. The results showed that the duplex coatings were composed of nitride/aluminide layers (TiN_(0.3)/Al_3Ti/Al_(18)Ti_2Mg_3 layers). With increasing the N_2 content in the gas mixture, the peak ratio I_(002)/I_(100) of the outer TiN_(0.3) phase increased and the nitride particles grew larger. The surface hardness of coatings increased with the increasing N_2-H_2 ratio, reaching the maximum value of 630 HV under 50%N_2 + 50%H_2. The coatings obtained under gas mixture with high N content showed larger fluctuation at the initial stage during friction tests. All the obtained coatings showed the similar friction coefficient (～0.30) at the stable stage, much lower than the untreated Al alloy (～0.45). The sample nitrided under 50%N_2 + 50%H_2 exhibited the lowest wear rate, 60% lower than that of the uncoated one. The nitrided samples exhibited predominant abrasive wear and adhesive wear.