材料期刊网

利用金属磁记忆技术对裂纹/应力交互影响的Fe314合金激光熔覆层应力状态进行了评价. 基于“当量法”, 通过机加工方法在Fe314合金激光熔覆层中加工宽度恒定, 埋深分别为2.5, 3.0, 3.5和4.0 mm的规则矩形槽模拟不同埋深的裂纹, 研究了裂纹埋深对Fe314合金激光熔覆层磁场强度法向分量H_p(y)的影响规律. 利用SEM对Fe314合金激光熔覆层微观组织进行观察, 结合其微观组织特征分析了对H_p(y)的影响. 结合压磁理论, 澄清了金属磁记忆评价裂纹/应力交互作用下Fe314合金激光熔覆层应力状态的机理, 获得裂纹埋深、载荷及H_p(y)梯度变化值K间关系. 结果表明, 随载荷增大, 磁畴的有序转变导致H_p(y)曲线以过0点为中心呈顺时针转动, H_p(y)曲线斜率与幅值逐渐变大, 裂纹处K逐渐变大; 各向异性组织及层间界面引起应力集中, 从而导致H_p(y)曲线波动明显; 载荷相同时, 裂纹处K随裂纹埋深增大呈二次多项式规律减小; 裂纹埋深相同时, 裂纹处K随载荷增大而增大; 裂纹埋深越小, 载荷对裂纹处K影响越明显. 裂纹埋深大于3.0 mm时, Fe314合金激光熔覆层变形能力弱于45钢变形能力从而导致裂纹处K随载荷增大的速率较慢.

The stress state is important for properties and service life of mechanical parts, so finding an optimal method for evaluation of stress state is urgently needed to be solved. Because of convenience and fast detection speed, metal magnetic memory method has attracted attention of scholars, and some research findings also have been obtained. While current research mainly focuses on evaluation of stress state of single ferromagnetic material, the research on ferromagnetic composite material or ferromagnetic coating material is rare. Because of high energy density, laser cladding technology has been used widely in field of surface engineering. For this reason, the stress state of ferromagnetic laser cladding Fe314 alloy coating is evaluated with metal magnetic memory method. Distribution of stress state is usually affected by flaw including crack and gas hole in laser cladding Fe314 alloy coating, so the interaction influence of crack and load on evaluation of stress state of laser cladding Fe314 alloy coating is discussed in this work. Combing with equivalent method, different cracks, which were substituted with regular rectangular grooves, were machined in laser cladding Fe314 alloy coating. In order to obtain the relationship between burial depth and magnetic field intensity normal component H_p(y), the regular rectangular grooves that had the same width and different buried depths were machined. The microstructure of laser cladding coating was observed by SEM, and the influence of microstructure on magnetic field intensity normal component H_p(y) was also discussed. Based on magnetic-mechanical theory, interaction influence mechanism of crack and load on evaluation stress state of laser cladding coating with metal magnetic memory method was clarified, the relationship between burial depth of crack, load and gradient value K of magnetic field intensity normal component H_p(y) was also obtained. The results show that when zero crossing is seen as center, the magnetic field intensity normal component H_p(y) rotates clockwise as stress increases gradually, the slope and amplitude of H_p(y) curve increases, gradient value K of magnetic field intensity normal component H_p(y) corresponding to crack also increases as stress increases. Stress concentration in different zones is caused by anisotropic microstructure and layer interface of laser cladding Fe314 alloy coating, so the H_p(y) fluctuats obviously. When load is the same, gradient value K of magnetic field intensity normal component H_p(y) corresponding to crack decreases in the regular pattern of quadratic polynomial as burial depth increases. When burial depth is the same, gradient value K of magnetic field intensity normal component H_p(y) corresponding to crack increases as load increases. When burial depth is less, the influence of load on gradient value K is more obvious. When burial depth is bigger than 3.0 mm, advance the speed of gradient value K is relatively slow as load increases, and the difference in deformation capacity between laser cladding Fe314 alloy coating and 45 steel is seen as the main reason for above result.