Microstructure and mechanical properties of multiphase coating produced by plasma nitriding Ti coated GB-5083 aluminum alloy

In order to improve the surface mechanical properties of GB-5083 aluminum alloy, titanium-aluminum-nitrogen thermo-reactive diffusion coatings were fabricated on the surface of Al substrate through deposition and nitriding process. The substrates were firstly deposited with pure Ti film by magnetron sputtering and then plasma nitrided in an atmosphere of 40% N2-60% H2 at 460 °C. The as-obtained coatings under different nitriding time were characterized by using X-ray diffractometer (XRD), scanning electron microscopy (SEM), microhardness tester, scratch tester and pin-on-disc tribometer. Results showed that the multiphase coating comprising two sub-layers (i.e. the outside TiN0.3 layer, and the inside Al18Ti2Mg3 layer) can be obtained. The coating thickness increased slightly with increasing nitriding time. The hardness of the as-obtained coating has reached about 600 HV, which is much higher than that of the GB-5083 Al substrate. The critical load of adhesive failure for the coating obtained by 16 h nitriding reached 13 N. Compared with the untreated Al alloy, the wear rate of the coated sample decreased 65% after 24 h nitriding treatment. The analysis of worn surfaces indicated that the coated GB-5083 Al alloy exhibited predominant abrasive wear, whereas the uncoated one showed severe adhesive wear.