Microstructure evolution and wear resistance of nitride/aluminide coatings on the surface of Ti-coated 2024 Al alloy during plasma nitriding

摘要

A duplex surface treatment consisting in depositing a Ti film followed by plasma nitriding was adopted to improve the wear resistance of 2024 Al alloys. Nano-grained Ti films were firstly deposited on the substrate surface by using magnetron sputtering, then plasma nitrided for 8 hat 400 degrees C, 430 degrees C, 460 degrees C and 490 degrees C, in a gas mixture of 40% N-2+60% H-2. Duplex coatings composed of three sublayers (i.e.the outmost TiN0.3 layer, the intermediate Al3Ti layer and the inside Al18Ti2Mg3 layer) were obtained at nitriding temperature higher than 460 degrees C. The coatings obtained at 400 degrees C and 430 degrees C consisted of mainly alpha-TiN0.3 with (002) preferred orientation. The surface hardness of the coatings increased at higher nitriding temperature, reaching the maximum of 500 HV at 490 degrees C, which was about 8 times higher than that of the uncoated alloy. The friction coefficients of 2024 Al alloy decreased in the coatings prepared at higher nitriding temperature, reaching the lowest values of 0.31 at 490 degrees C. The wear rate of the coated samples decreased by 56% compared with the uncoated ones. The analysis of worn surface indicated that the nitrided samples exhibited severe adhesive wear at 400 degrees C that changed to predominant abrasive wear at increased nitriding temperature.