喷丸对TNM-TiAl合金组织以及450℃下高周疲劳性能的影响

Effect of Shot Peening on Microstructure and High-cycle Fatigue Properties of TNM-TiAl Alloy at 450℃

目的针对TNM-TiAl合金(Ti-43.5Al-4Nb-1Mo-0.1B)服役时受高周疲劳影响的问题,揭示喷丸处理技术对TNM-TiAl合金疲劳性能的影响规律。方法通过扫描电镜和透射电镜分析喷丸前后的组织演变,测量喷丸前后合金表面残余应力、表面粗糙度和显微硬度分布规律,采用梯度法测量喷丸前后的高周疲劳极限,并分析断口形貌和断口附近组织。结果喷丸后合金表面粗糙并且存在烧蚀坑,表面附近的片层团发生弯曲,在组织内部引入大量位错、位错缠结以及位错胞等缺陷。喷丸后表面粗糙度明显提高,显微硬度提高了209HV0.05,从表面到内部形成深度为260μm的硬度梯度。喷丸后试样表面的残余压应力为446 MPa,深度约为85μm。喷丸后在450℃下保温30 h后合金表面最大硬度仍比喷丸前的硬度高166HV0.05,硬化深度约为150μm。未喷丸光滑试样、喷丸光滑试样、未喷丸缺口试样和喷丸缺口试样的疲劳极限分别为615、637、385、455 MPa,光滑试样断裂类型为穿晶解理型脆性断裂,而缺口试样为穿晶脆性断裂。结论喷丸能够显著提高最大残余压应力和引入应力的深度,且喷丸引入的组织具有一定的热稳定性,喷丸明显提高了TNM-TiAl合金的疲劳极限。

The work aims to investigate the effect of shot peening on the fatigue properties of TNM-TiAl alloy,in order to solve the problem of high-cycle fatigue affecting TNM-TiAl alloy(Ti-43.5Al-4Nb-1Mo-0.1B)in service.Scanning electron microscopy and transmission electron microscopy were employed to characterize the microstructure of TNM-TiAl alloy before and after shot peening.The distribution laws of surface residual stress,roughness and microhardness of the alloy before and after shot peening were analyzed.The high-cycle fatigue limit was examined with gradient method,and the fracture morphology and microstructure surrounding the fracture were analyzed.After shot peening,the surface of TNM-TiAl alloy was rough with some ablation pits and the lamellar colonies near the surface bent.Large amounts of defects were generated,such as dislocation,dislocation tangle and dislocation cell.After shot peening,the roughness was improved significantly,the microhardness increased by 209HV0.05,and a hardness gradient of 260μm was formed from the surface to the interior.The residual compressive stress on the surface after shot peening was 446 MPa,with a depth of approximately 85μm.After holding for 30 h at 450℃,the maximum surface hardness of the alloy after shot peening was still 166HV0.05 higher than that before shot peening,and the hardening depth was about 150μm.The fatigue limits of non-shot peened smooth specimens,shot peened smooth specimens,non-shot peened notched specimens,and shot peened notched specimens were 615,637,385 and 455 MPa,respectively.The fracture type of smooth specimens was brittle transgranular cleavage,while that of notched specimens was brittle transgranular.Shot peening can significantly increase the maximum residual compressive stress and the depth of the introduced stress.The microstructure introduced by shot peening has a certain thermal stability,and shot peening significantly improves the fatigue limit of TNM-TiAl alloy.