激光冲击强化对Ti2AlNb合金微观组织及残余应力的影响

Effect of laser shock peening on microstructure and residual stress of Ti2AlNb alloy

Ti2AlNb(O-Ti2AlNb)具有优异的力学性能,在航空发动机方面有远大应用前景.激光冲击强化(Laser Shock Peening,LSP)是一种先进的表面改性技术,能够在材料表面诱导产生高幅值、大深度的残余压应力,改善材料微观组织,提高材料抗疲劳、高温氧化等性能.本文采用激光冲击强化对Ti2AlNb合金进行表面改性,并研究其组织演变、残余应力以及高温环境对性能的影响.结果表明:激光冲击强化能够显著减小Ti2AlNb合金近表面的晶粒尺寸.显微硬度由冲击前的350 HV提升到395 HV;在冲击区域近表面产生了约-377 MPa的残余压应力;而在高温环境中,由激光冲击强化所诱导的材料近表面残余应力随时间逐渐释放,在600℃条件下,残余应力释放较为缓慢;而在720℃条件下,残余应力迅速释放.

Ti2AlNb-based alloys are developed from conventional titanium aluminides(Ti Al-based alloys and Ti3Al-based alloys).Comparing with Ti Al and Ti3Al-based alloys,Ti2AlNb-based alloys have better mechanical properties of strength density ratio,high temperature fracture toughness and creep resistance.It is expected to replace traditional high temperature materials such as nickel-based alloys for the manufacture of aero-engine components.Laser shock peening(LSP)is an advanced surface modification technology which induces high amplitude,large depth residual compressive stress on the surface of materials.It can effectively enhance mechanical properties of material such as micro-hardness,fatigue resistance,high temperature oxidation performance.Compared to other surface modification technologies such as shot peening and rolling,LSP can not only induce deeper compress residual stress(1-2 mm),which is about five to ten times deeper than that of shot peening,but it can refine the grain or even form nanocrystals which plays a significant role in enhancing properties of material.For these reasons,this surface treatment technology has been widely used in the aircraft and nuclear energy industries.In this paper,the surface modification of Ti2AlNb alloy was carried out by laser shock peening,and the microstructure evolution,residual stress and the performance at high temperature were investigated.The results show that laser shock peening can significantly reduce the grain size of the surface of Ti2AlNb alloy.Dislocation lines,dislocation tangles and dislocation walls were generated after LSP.The micro-hardness is increased from 350 HV to 395 HVand the effect layer is about 1.2 mm.The residual compressive stress of-337 MPa is generated on the surface of the sample.In addition,residual stress is released obviously at high temperature.The residual stress on the surface of sample reduces to-65 MPa after heat treatment at 720℃ for 4 h.The residual stress is almost completely released after heat treatment at 720℃ for 10 h.However,the release rate of residual stress is slowed down at 600℃.The effect of laser shock peening is still presence after heat treatment for 100 h.