Research Of Composite Coating On TC4 Titanium Alloy Surface

Because of its high specific strength,stable property in middle temperature and good resistance to corruption,Titanium alloy has become an important structural material in aeronautics and astronautics.But its low intensity,large friction coefficient,likelihood to serious adhesive and oxidative wear have greatly influenced its security and reliability.The task use the hot-dip aluminizing and micro-arc oxidation technology to form a compact and gradient layer,and study the differences of hardness,abrasive resistance and corruption resistance before and after the modification.The study contains two parts: one part is to get a hot dip aluminum coating on the Titanium alloy that is suitable for the micro-arc oxidation experiment;the other part is to use the micro-arc experiment on the coating and detect the properties.To respectively study the influence of the hot dip temperature,time and thermal diffusion on thickness and quality of the coating,single variable control method is adopted during the hot dip aluminum experiment on TC4 alloy.And the experiment shows that when the hot dip temperature is 730?,hot dip time is 3min,keep a 3h diffusion at a thermal diffusion temperature of 800?,the layer is about 120?m in height and is of perfect quality,with main composition the TiAl₃ alloy.Observed from the SEM,the hot dip layer's height and the pure aluminum layer's height will decrease while alloy layer's height keeps increase with the hot dip temperature rising.When the hot dip time reaches 90s³00s,with the time growing,the total thickness and thickness of the pure aluminum will decrease,the alloy's thickness of the layer will crease.After under 730? dipped for 180 s and under 800? diffused for 180 min,the pure aluminum layer almost disappear,transferred into TiAl₃ diffusion layer.The layer's surface morphology is similar with TiAl alloy after the micro-arc oxidation treatment,when the diffusion layer after micro-arc process for 30 min,there are TiAl_O5 in the layer,the ceramic coating will become thicker with the oxidation time growth,the maximum hardness can reach to 870 HV,apparently higher than that of the diffusion coating.The abrasive resistance will increase and then decrease with the oxidation time growth,the minimum friction coefficient is 0.25;The corruption resistance will increase and then decrease with the oxidation time,the minimum corrosion potential is-0.51 v,when the time of micro-oxidation is 30 min,the wear resistance and corrosion resistance of the coating is the best.