对304不锈钢板进行了激光填粉焊接试验, 研究了不同焊接工艺参数对焊缝横截面形貌、抗拉强度、断口形貌的影响规律, 并获得了最优工艺参数组合。结果表明, 在试验范围内, 焊缝宽度与激光能量密度正相关。从零离焦量向正、负离焦量变化时, 上焊缝宽度增加, 下焊缝宽度减小; 低功率和零离焦量会降低试样的抗拉强度。焊接件抗拉强度随着焊接速度的增加呈先增大后减小的趋势; 断口形貌随抗拉强度的增大依次表现为解理断裂台阶状, 准解理断裂河流状, 塑性断裂韧窝状。由正交试验得到的焊接最优工艺参数为：激光功率2.7 kW, 焊接速度160 mm·min-1, 离焦量+5 mm。

为制备低残余应力涂层, 在304不锈钢表面激光熔覆Fe-Mn-Si形状记忆合金涂层。采用ANSYSTM有限元分析软件分析其应力场, 利用机械钻孔法测量相同工艺条件下的激光熔覆试样的残余应力分布特性对模拟结果进行验证, 并采用XRD分析Fe-Mn-Si记忆合金涂层低残余应力机理。结果表明, 激光熔覆产生的应力诱发Fe-Mn-Si记忆合金各涂层γ→ε马氏体转变, 将残余应力释放, 得到低残余应力涂层。在受到各道激光照射(光斑接近至远离)过程中产生的热应力交替呈现为“拉-压-拉”应力状态, 越远离激光热源中心, 热应力越小; 冷却完成后, 激光涂层上残余应力表现为拉应力, 最大应力位于基体与涂层交界处; 在垂直与平行于激光熔覆两个方向上, 涂层中的残余应力均呈现两侧大中间小的分布规律, 在厚度方向上, 熔覆涂层表面至涂层中心残余拉应力逐渐增加到最大值后, 过涂层中心至熔化边界残余拉应力的数值开始逐渐降低, 过涂层边界后, 基体承受压应力并逐渐趋于零应力应力状态。

The stainless Fe-Mn-Si shape memory alloy (SMA) coating was prepared on the surface of AISI 304 stainless steel. The principal residual stress measured by the mechanical hole-drilling method indicates that the Fe-Mn-Si SMA cladding specimen possesses a lower residual stress compared with the 304 stainless steel cladding specimen. The mean stress values of the former and the latter on 10-mm-thick substrate are 4.751 MPa and 7.399 MPa, respectively. What’s more, their deformation values on 2-mm-thick substrate are about 0° and 15°, respectively. Meanwhile, the variation trend and the value of the residual stress simulated by the ANSYS finite element software consist with experimental results. The X-ray diffraction (XRD) pattern shows ε-martensite exists in Fe-Mn-Si SMA coating, which verifies the mechanism of low residual stress. That’s the γ→ε martensite phase transformation, which relaxes the residual stress of the specimen and reduces its deformation in the laser cladding processing.

Fe-Mn-Si-Cr-Ni composite powders are utilized to form a functional shape memory alloy cladding layer (SMACL) using a laser cladding method. The microstructure, microhardness, and phase composition of the SMACL are measured, and the extent of deformation of the laser cladding samples is determined. The SMACL is composed of planar, cellular, and dendritic crystals, equiaxed grains, and oxides with increasing distance from the substrate surface. The SMACL is further composed of \varepsilon -martensite and \gamma -austenite phases, while the tempered SMACL consists mainly of \gamma -austenite. Extensive deformation occurs in AISI 304 stainless steel laser cladding samples. By contrast, limited deformation is observed in the SMACL samples.