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采用激光原位合成技术在BT3-1钛合金表面制备了高铌Ti-Al金属间化合物复合涂层。根据XRD谱分析涂层的物相结构,通过GSL-1600X型管式炉测试950 ℃循环氧化条件下热处理前后基材和涂层单位面积的氧化增重,绘制氧化动力学曲线,并据此比较涂层和基材的抗氧化性能。借助OM和SEM观察了氧化前后涂层的微观形貌,探讨了其高温抗氧化机理。结果表明,热处理前的涂层主要由单质Nb、金属间化合物γ-TiAl、α₂-Ti₃Al和Ti₃Al₂等物相组成,热处理后的涂层,单质Nb固溶到γ-TiAl和α₂-Ti₃Al中,同时形成了新相Ti₃AlNb_0.3,涂层近似为γ-TiAl+α₂-Ti₃Al双相组织。热处理前涂层的氧化动力学曲线介于线性规律和抛物线规律之间,其高温抗氧化性能比钛合金基材提高了2倍。热处理后涂层的氧化动力学曲线近似呈抛物线规律,且氧化速率小,其高温抗氧化性能比钛合金基材提高了20倍以上。950 ℃循环氧化条件下,涂层氧化层表面形成了连续致密的胶囊状氧化物,氧化层紧密粘附在未氧化涂层部分,氧化层对涂层起到了良好保护作用,而钛合金基材表面则形成疏松多孔的絮状氧化物,氧化层从基材处碎裂、剥落。Nb的合金化显著改善了Ti-Al金属间化合物的高温抗氧化性能。

Titanium alloys are widely used as structural material in aerospace, automobile, biomedical and other fields because of its low density, high specific strength, good corrosion resistance and good biocompatibility. But high coefficient of friction, poor wear resistance and high-temperature oxidation resistance are the main reasons for limiting the use of titanium alloy in complex working conditions. In order to improve the high-temperature oxidation resistance and optimize the microstructure of titanium alloy, high Nb content Ti-Al intermetallic composite coating was fabricated by laser in situ synthesis technique on BT3-1 titanium alloy surface. Phase structure of the composite coating was analyzed according to XRD spectra. Unit area oxidation weight gain of the titanium alloy substrate and coating before and after heat treatment were tested by GSL-1600X tube furnace under 950 ℃. The oxidation kinetics curves were drawn and the high temperature oxidation resistance was compared. The microstructures of coating before and after oxidation were observed by OM and SEM, and the high-temperature oxidation resistance mechanism was analyzed. The results show that the coating mainly consists of Nb, intermetallic γ-TiAl, α₂-Ti₃Al and Ti₃Al₂ phases before heat treatment. But after heat treatment, Nb is dissolved in γ-TiAl and α₂-Ti₃Al, and a new phase Ti₃AlNb_0.3 is generated in the coating. The coating is approximately γ-TiAl+α₂-Ti₃Al duplex structure. The oxidation kinetics curves of coating is between linear and parabolic rule before heat treatment, its high temperature oxidation resistance increased by 2 times of titanium alloy substrate. The oxidation kinetics curves of coating is approximately parabolic law after heat treatment, and the rate of oxidation is small, its high temperature oxidation resistance increased more than 20 times of titanium alloy substrate. Under 950 ℃ cyclic oxidation conditions, the oxide layer surface of coating forms a continuous dense capsule oxide, and oxide layer closely connect the unoxidized coating portion, the oxide layer plays a good protective role of the composite coating. But for titanium alloy substrate, the oxide layer surface is loose and porous oxide, the oxide layer is fractured and removed from the substrate surface. Nb alloying significantly improves the high temperature oxidation resistance of Ti-Al intermetallic coating.