材料期刊网

目的 研究在低应力多碰条件下,在零件表面激光熔覆制备指数分布梯度涂层的效应.方法 采用网格坐标划分法,在低应力条件下通过对Ni基指数分布梯度熔覆层的0Cr18Ni9试件进行多碰试验,获取变形数据,计算获得变形率,绘制规律曲线.借助工具显微镜,获得碰撞前后组织金相图.结果 采用的碰撞应力仅有115 MPa,远低于涂层材料与基体的静压缩屈服强度,但指数分布的梯度涂层发生了可测的塑性变形,第一网格层变形率最为明显,达到了18.97%,第二网格层变形率为15.03%,靠近基体的最后一个网格层的变形率为0.29%,可以表明指数分布梯度涂层在低应力多碰后的形变具有"趋表效应".基体的形变情况与梯度涂层的形变基本一致,从距表面6 mm处开始,涂层与基体结合处由于有瞬间激光高温熔覆,出现了应变的突变现象,宏观塑性变形增大,变形率突增到3.92%,但基体的形变总的来说也符合"趋表效应".同时借助金相图看到的晶体滑移现象也证实了这一点.结论 在低应力多碰作用后,试件表层的累积变形量最大,随着涂层深度的增加梯度减小,表明具有"趋表效应",同时抗多冲形变的能力显著增强.

The work aims to study effects of exponential gradient coating prepared on surface of parts by laser cladding un-der low stress repeated impact. Multipacting experiment was performed to 0Cr18Ni9 specimen on Ni-based exponential gradient cladding layer under low stress in grid coordinate division method, so as to acquire deformation data, calculate deformation rate and draw law curve. Phase diagram of the microstructure before and after collision was obtained by means of microscope. The impact stress applied was only 115 MPa, far below static compressive yield strength of the coating material and substrate, but the exponential gradient coating was subject to measurable plastic deformation. Deformation rate of the first grid layer was up to 18.97%, the most significant of all, and that of the second grid layer was up to 15.03%, that of the last grid layer close to the substrate was 0.29%, indicating that deformation of the exponential gradient coating had the "skin effect" after low stress and multipacting. The deformation of the substrate was basically consistent with that of the gradient coating. As juncture between coating and substrate was subject to instant high temperature laser cladding, the strain changed suddenly at the distance of at least 6 mm from the surface macroscopic plastic deformation increased, deformation rate increased to 3.92% sharply, but de-formation of the substrate was generally consistent with the "skin effect". Meanwhile, translation gliding observed with the phase diagram confirmed the fact as well. Under the low stress and repeated impact, the accumulated deformation of the speci-men surface is the maximum, and the gradient decreases with the increase of the coating depth, which has confirmed the "skin effect". At the same time, the resistance to repeated impact deformation is remarkably enhanced.