| The aim of this paper is to increase the oxidation properties of the Ti Bw/TC4 titanium matrix composites with network microstructure in high temperature. Ti Al3 coating was successfully made on the Ti Bw/TC4 titanium matrix composites with network microstructure by hot-dipping alumium. The influence of plating auxiliary,surface covering agent, hot-dipping alumium time and heat treating on the coating’s thickness and compactness was studied by scanning electron microscopy(SEM). The hardness of the Ti Al3 coating and matrix material was measured by a Vickers apparatus.High temperature oxidation test was done on the Ti Bw/TC4 titanium matrix composites with network microstructure before and after hot-dipping alumium, and the microstructure and organizational evolution of oxide layer was analyzed by X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectrometer(EDS), finally made a comparative analysis of their oxidation resistance and oxidation mechanism combining the oxidation kinetics curves.The results showed that adding plating auxiliary and surface covering agent improved the effect of hot-dipping alumium and the thickness of Ti Al3 coating was increased. Heat treating after hot-dipping alumium improved the Ti Al3 coating’s thickness and compactness, and as higher of the heat treatment temperature, longer of the heat treatment time, the Ti Al3 coating was thicker. With the same hot-dipping alumium temperature, the loner the hot-dipping alumium time, the thicker the Ti Al3 coating. Hot-dipping alumium(800 ℃,30min), plating auxiliary(6%Na Cl solution and4%KF solution), surface covering agent(50%KCl, 37.5%Na Cl, and 12.5%Na F), heat treatment(650 ℃,5h), is the most suitable hot-dipping alumium process for the Ti Bw/TC4 titanium matrix composites with network microstructure.The results of microhardness showed that the Ti Bw/TC4 titanium matrix composites with network microstructure after hot-dipping alumium was formed by Ti Bw/TC4 layer, Ti Al3 layer and pure Al layer, and their Vickers hardness(HV) are respectively 473/340, 435/142 and 38.The results of high temperature oxidation tests showed that the oxidation product is mainly Ti O2 for the Ti Bw/TC4 titanium matrix composites with network microstructure,while is Ti O2 and Al2O3 after hot-dipping alumium. The Ti Bw/TC4 titanium matrix composites with network microstructure oxided not seriously at the temperature of600℃, with no obvious oxidation layer formed, and the oxidation weight curve was a parabola, however the composites oxided seriously at the temperature of 700℃ and800 ℃, with a mass of oxide skin falling off, and the oxidation weight curve was a straight line. The Ti Bw/TC4 titanium matrix composites with a network microstructure after hot-dipping alumium was almost not oxided at the temperature of 600℃, and was oxided not seriously at the temperature of 700℃ with no obvious oxidation layer, while oxided slightly at the temperature of 800℃ with continuous network oxidation layer units on the surface, which enhanced the adhesion strength of the oxidation layer and the matrix material. Overall hot-dipping alumium to make a Ti Al3 coating greatly enhanced the oxidation resistance of the Ti Bw/TC4 titanium matrix composites at the temperature of 600℃ to 800℃. |
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