Abstract:

B-Al composite coatings were prepared on the surface of TC4 titanium alloy by boronizing at 1050 ℃ for 4-6 h and subsequent aluminizing at 950-1050 ℃ for 4 h through a two-step pack cementation process. The constituent phases, microstructure, composition, hardness, friction coefficient of the composite coatings were analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), wavelength dispersive spectrometer (WDS) and energy dispersive spectrometer (EDS), microhardness tester, and friction and wear tester. The results show that the thickness of the B-Al composite coatings is in the range of 37-115 μm, and the coatings mainly consist of TiB₂ and TiAl₃ phases. The outer layer is TiAl₃ layer with dispersed TiB₂; and TiAl₂, TiAl and Ti₃Al intermetallic compound layers with smaller thickness are formed inward in turn. The surface hardness of the B-Al composite coatings is in the range of 1041.7-1429.4 HV0.1, which is about 3.03-4.16 times of the TC4 alloy. By boronizing at 1050 ℃ for 6 h followed by aluminizing at 1050 ℃ for 4 h, the friction coefficient of the B-Al composite coating is about 0.3, lower than that of TC4 alloy by about 25%.

Key words: TC4 titanium alloy, B-Al composite coatings, friction coefficient, wear resistance