Investigations On Micro-arc Oxidation Process And Wear Resistance Of Aluminum Alloy Coating On Titanium Alloy Surface

Titanium alloys are widely used in the aerospace industry,shipbuilding and medical machinery,but its low hardness and poor wear resistance have greatly influenced its use.In order to improve the hardness and wear resistance of titanium alloy,four kinds of target materials,pure aluminium target and Al-Si?at%?target?Al-2.7%Si,Al-5.2%Si,Al-10.3%Si?,were used to prepare coating on TC4 titanium alloy surface.Then ceramic coating was prepared on multi-arc ion coating by micro-arc oxidation technology.By means of SEM,XRD,metallographic microscope,microhardness tester and friction and wear tester,the structure and growth mechanism of micro-arc oxidation ceramic coatings obtained by multi-arc ion plating with different Si content for 4 h and 5 h were analyzed,and the structure,element distribution and wear resistance of micro-arc oxidation ceramic coatings for 5 h were studied.The results show that the multi-arc ion coatings with different Si content are firmly bonded with TC4 titanium alloy matrix without obvious defects.The silicon-rich phase increases with the increase of Si content in the target.The ceramic coating obtained by micro-arc oxidation has crater-like protrusions and micro-cracks on its surface.The ceramic coating is divided into loose layer and dense layer.There is no obvious boundary between the loose layer and the dense layer.The interface between the dense layer and the multi-arc ion coating is dog-tooth interlaced.Under the same micro-arc oxidation time,the thickness and surface roughness of ceramic coatings decrease first and then increase with the increase of Si content,and the thickness and surface roughness of Al-5.2%Si ceramic coatings are the smallest.Compared with the ceramic coating with 4 h micro-arc oxidation time,the ceramic coating with 5 h is thicker and the structure of the ceramic coatings have not changed.The crater-like protrusions on the surface of micro-arc oxidation ceramic coating mainly contain three elements:Al,Si and O.The content of Si element is the most in the loose layer.With the transition of ceramic coating to titanium alloy matrix,the content of Si element decreases gradually,while the distribution of Al element is opposite,and the distribution of O element is uniform.The ceramic coating is mainly composed of?-Al₂O₃ and?-Al₂O₃.It also contains a certain amount of mullite,SiO₂and a small amount of amorphous phase.The hardness of ceramic coating obtained by micro-arc oxidation for 4 h and 5 h was higher than that of TC4 titanium alloy matrix,and the hardness of the compact layer of the same sample was higher than that of the loose layer.The hardness of the compact layer of Al-2.7%Si ceramic coatings oxidized by micro-arc for 4 h is the highest,but the hardness of Al-10.3%Si ceramic coatings decreases.The hardness of pure Al,Al-2.7%Si and Al-5.2%Si ceramic coatings is almost the same when micro-arc oxidation time is 5 h.The ceramic coating of Al-10.3%Si has the lowest hardness.The wear resistance of ceramic coatings prepared by micro-arc oxidation for 5 h was tested.The wear rate and wear amount of Al-2.7%Si ceramic coatings were the smallest and the wear resistance was the best.