【作者】 辛艳辉；

【导师】 林建国；

【作者基本信息】 湘潭大学 ， 材料物理与化学， 2003， 硕士

【摘要】 γ-TiAl合金具有低密度、较高的比强度和比刚度，以及优良的高温性能，被认为是一种极具应用潜力的新型高温结构材料。如何改善TiAl合金的高温抗氧化问题，是提高TiAl合金使用温度的关键问题之一，同时，当TiAl合金用作高温运动部件时，还必须提高其高温耐磨损性能。本文利用激光表面合金化技术，用高纯C和C+Nb粉作为合金元素，在Ti-46Al-2Cr-1.5Nb-1V铸态合金表面“原位”生长出TiC颗粒，使其表面形成了以TiC颗粒为增强相的复合材料表面改性层，并利用光学金相(OM)，X射线衍射(XRD)，扫描电镜(SEM)等实验手段，对激光表面改性层的显微组织、相组成进行了观察，并分析了显微组织与激光工艺参数的影响。对经激光表面改性后的试样在高温(870℃)抗氧化性能进行研究，同时还对激光表面改性层的室温耐磨损性能进行了研究，得出了以下主要结论：(1)C+Nb表面合金化后，在TiAl合金表面“原位”生长出TiC颗粒，TiC颗粒在合金表面是梯度分布，其体积分数由外向里逐渐减少，表面改性层与基体呈完全的冶金结合。(2)激光表面改性层的显微组织受到激光工艺参数的影响，如在功率和束斑直径相同的条件下，随着扫描速率的增加，生成的TiC颗粒形态由颗粒状逐渐向针片状过渡。(3)在870℃条件下，经激光表面处理后的试样抗氧化性能明显提高，经C+Nb合金化的试样表现出较高的抗氧化性能。(4)在870℃条件下，经100小时氧化后，TiC颗粒会发生分解。(5)激光表面改性层的显微硬度由外向里连续降低，其最大硬度值与变化梯度受激光工艺参数的影响，扫描速率越慢，功率越大，其改性层的平均硬度值越高，硬度变化梯度越平缓。(6)经C+Nb表面合金化试样室温滑动耐磨性明显提高，其耐辛艳辉湘潭大学硕士论文磨机理表现为显微切削，轻微的粘附转移和碳化汤雨丽面氰更多还原

【Abstract】 γ-TiAl alloy is considered as one of the promising light-weight structural materials at elevated-temperature due to its excellent combination of low density, high specific strength and stiffness, and superior high elevated-temperature properties. How to improve high temperature oxidation resistance of TiAl alloy is one of keys to enhance the temperature for its application. At the same time, and the wear resistance of this alloy also must be improved when it is used as moving tribological components.In the paper, laser surface alloying with C and C+Nb powders with high purity was used to modify the surface properties of Ti-46Al-2Cr-1.5Nb-lV alloy, and a composite surface layer reinforced by "in-situ" titanium carbide was formed in the alloy. The microstructures of modified layer were observed, and the compositions were determined by using X-ray , SEM,Optical Microscope (OM) etc. The effects of laser process parameters on the microstructure of the modified surface were analyzed. The Oxidation behavior of the alloy with the modified surface was studied at 870癈 high temperature, and the wear properties of the modified layer at room temperature was investigated. The primary results are as follows:1. By laser surface alloying with C and C+Nb powders, a composite layer reinforced by "in-situ" TiC particles was produced at the surface of the alloy. TiC particles distribute at the surface in the gradient. The volume fraction of the particles decreased with the increase of the depth. No interface between modified layer and substrate was observed, indicating that they are in metallurgical bond.2. The microstructure of the modified layer was strongly dependent on the laser process parameters. At the conditions of the same powerand beam diameter, TiC changed in shape from the particle to the needle with the increase of the scanning rate.3. By laser surface alloying with C and C+Nb powders, the oxidation resistance at 870℃ of alloy improved obviously after, and the sample alloying with C+Nb exhibits the best oxidation resistance.4. At 870℃, TiC can decompose after oxidation for l00h.5. Micro-hardness of laser modified layer decreased continuously with the increase of the depth. Its highest hardness value and gradient were associated with laser process parameters, namely, slower scan rate and greater laser power result in a higher average hardness value and a smoother gradient.6. By laser surface alloying with C+Nb, the gliding wear resistance of the alloy at room temperature was improved greatly. The wear resistant mechanisms are mainly micro-cutting, slight adhesive transfer and fragmentation and spalling of the reinforcing phases resulting from partial cracking.更多还原