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针对激光熔覆层残余应力过大导致变形、开裂的问题,采用激光冲击技术对Fe314合金熔覆层进行了表面冲击处理,分析了熔覆层残余拉应力分布形式及消除机理。结果显示,激光熔覆时采用相对较大的激光比能量,即慢扫描速度、小光斑直径和低送粉速率工艺可有效降低熔覆层残余拉应力。而激光冲击大幅降低了熔覆层残余拉应力,随着冲击次数提高,熔覆层拉应力减小,但拉应力降低幅度呈逐渐减弱趋势。冲击波力学效应引发的极大应变率使熔覆层表层发生微塑性变形,形成压应力场,大幅抵消熔覆层初始态残余拉应力。材料压缩变形时在γ-Fe晶粒内萌发大量位错线,位错发生多系滑移并相互缠结形成位错墙,引发细晶强化作用。
Aiming at the problem of deformation and cracking caused by excessive residual stress of laser cladding layer, the surface impact treatment of Fe314 alloy cladding layer was carried out by laser shock technique. The distribution of residual tensile stress and its elimination mechanism were analyzed. The results show that the relatively large laser specific energy, ie slow scan speed, small spot diameter and low powder feeding rate, can effectively reduce the residual tensile stress of cladding layer during laser cladding. The laser shock greatly reduces the residual tensile stress of the cladding layer. With the increase of the impact times, the tensile stress of the cladding layer decreases, but the decreasing extent of tensile stress decreases gradually. The maximum strain rate induced by the shock wave mechanics effect makes the surface of cladding layer undergo micro-plastic deformation to form compressive stress field, which largely counteracts residual tensile stress in the initial state of cladding layer. When compressive deformation, a large number of dislocation lines were germinated in the γ-Fe grains. The dislocations were multi-system slippery and entangled with each other to form dislocation walls, resulting in fine grain strengthening.