激光钎焊多层金刚石磨粒与镍铬合金的微观结合形态

Microscopic bonding morphology of laser brazing multilayer diamond grains with Ni-Cr alloy

在45钢基体上进行了镍铬合金钎料与金刚石磨粒的多层钎焊加工,借助光学显微镜、扫描电镜、能谱分析等研究了钎料与金刚石磨粒的结合形态、钎料层组织结构及其变化规律、金刚石表面损伤形态、金刚石与钎料结合处以及钎焊层的元素分布规律。结果表明:从与基体结合处到钎焊层表面分别形成了平面晶、胞状晶、树枝晶、柱状晶以及等轴晶的显微组织形态。输入的线能量影响钎料与金刚石的浸润结合、及钎焊层晶粒大小。逐道搭接钎焊时的热积累改变了搭接线附近的晶粒生长方向和大小,在逐层堆叠时的层与层结合线附近存在粗化晶粒区。金刚石磨粒的存在促使其周边形成等轴晶和垂直其界面生长的柱状晶和树枝晶。钎焊层内C元素含量在靠近上表面附近较高。钎焊层内部金刚石与钎料之间存在一元素过渡区域,Cr和Si元素在过渡区存在聚集现象,有利于形成Cr和Si的碳化物,促进金刚石与钎料间的冶金结合。钎焊层内的金刚石磨粒出现不同程度损伤及石墨化形态。

Multilayer brazing of nickel chromium alloy filler metal and diamond abrasive particles was carried out on 45 steel substrate, and the bonding morphology of Ni-Cr brazing alloy and diamond abrasive particles, the microstructure and variation of brazing layer, the damage morphology of diamond surface, the bonding area between diamond and Ni-Cr brazing alloy and the element distribution of brazing layer were studied by means of optical microscope, scanning electron microscopy and energy dispersive spectrometry. The results show that the microstructure of planar crystal, cellular crystal, dendritic, columnar crystal and equiaxed crystal are formed from the interface with the matrix to the surface of the brazing layer. The input wire energy affects the infiltration and bonding between solder and diamond and the grain size of the brazing layer. The growth direction and size of grain near the bonding line are changed by the heat accumulation during lap-by-lap brazing, and there is a coarsening grain zone near the layer to layer bonding line. The existence of diamond abrasive particles leads to the formation of equiaxed crystals and columnar and dendritic crystals growing perpendicular to their interfaces. The content of C element in the brazing layer is higher near the upper surface. There is an element transition zone between diamond and solder in the brazing layer, and Cr and Si elements accumulate in the transition zone, which is conducive to the formation of Cr and Si carbides and promotes the metallurgical bonding between diamond and solder. The diamond abrasive particles in the brazing layer show different degrees of damage and graphitization.