激光熔覆原位自生Ti-Al-Si复合涂层的微观组织和高温抗氧化性能

Microstructure and high-temperature oxidation resistance of laser cladding in-situ synthesis Ti-Al-Si composite coatings

为提高钛合金的高温抗氧化性能,采用激光熔覆原位自生技术,在TC4钛合金表面自行设计并制备了原子百分比为Ti∶Al∶Si=41∶41∶18和Ti∶Al∶Si=35∶35∶30的两种涂层。通过XRD、OM、SEM表征了涂层的微观组织和物相组成;借助管式电阻炉测试了涂层和基体试样在800℃×24h×5次循环氧化条件下的高温抗氧化性能;结合氧化增重和氧化动力学曲线分析了涂层的高温抗氧化机理。结果表明,涂层主要由Ti5Si3、Ti7Al5Si12、Ti3Al、TiAl和TiAl3等物相组成。涂层中没有出现一般激光熔覆所产生的外延生长柱状晶组织,全部为细小等轴晶。在800℃×24h×5次循环氧化条件下,TC4基材单位面积的氧化增重约为35.1mg·cm-2,涂层的约为2.8mg·cm-2和3.3mg·cm-2。两种涂层的高温抗氧化性能较钛合金基材分别提高了12.5倍和10.6倍。激光熔覆原位自生Ti-Al-Si复合涂层能明显改善TC4钛合金的高温抗氧化性能。涂层抗氧化性改善的机理,一方面是表面生成了连续致密的TiO2、Al2O3、SiO2氧化层,阻碍了氧扩散;另一方面是提高了氧化层的黏附性,使氧化层不易从涂层表面剥落,对涂层未氧化部分起到了很好的保护作用。

To improve the high-temperature oxidation resistance of titanium alloys.Two kinds of Ti∶Al∶Si=41∶41∶18(at.%)and Ti∶Al∶Si=35∶35∶30(at.%)composite coatings were fabricated by laser cladding in-situ synthesis on TC4 titanium alloy.The microstructure and phase composition of the composite coatings were characterized by X-ray Diffraction(XRD),Optical Microscopy(OM)and Scanning Electron Microscope(SEM).The oxidation resistance of the coatings and the substrate sample under 800 ℃×24 h×5 times cycle oxidation condition was tested by tube resistance furnace.The mechanism of high-temperature oxidation resistance was analyzed by oxidation kinetics curves and oxidation mass gain.The results show that the cladding coatings are mainly composed of Ti5 Si3,Ti7 Al5 Si12,Ti3 Al,TiAl and TiAl3 phases,and there are no epitaxial columnar crystal structures as considered by ageneral laser cladding coating,all of which are fine equiaxed crystals.Under the condition of 800℃×24 h×5 times cycle oxidation,the weight gain per unit area of TC4 substrate is about 35.1 mg·cm-2,and the laser cladding composite coatings are about2.8 mg·cm-2 and 3.3 mg·cm-2.The high-temperature oxidation resistance of the two kinds of coatings is 12.5 and 10.6 times higher than that of the titanium alloy substrate.The oxidation resistance of laser cladding in-situ synthesis Ti-Al-Si composite coatings has been significantly improved.On the one hand,the continuous dense TiO2,Al2 O3 and SiO2 oxide layers have been obtained on the surface,which hinders the diffusion of oxygen and improves the oxidation behaviors.On the other hand,the adhesion of the oxide layer is improved so that the oxide layer is not easily peeled off from the coating surface and the non-oxidized portion of the coating is well protected.