WC/钢复合材料渗硼中WC颗粒对硼化物生长的影响

采用粉末渗硼法,对三种WC含量不同的WC/钢复合材料进行渗硼处理.利用SEM、XRD及自制的黑白图片伪彩色处理仪等方法对渗硼层的组织结构、硬度分布、渗硼层厚度及渗硼层内裂纹萌生进行研究,重点分析了WC含量及分布状况对硼化物生长的影响.结果表明：进行渗硼后,材料表面可获得高硬度FeB＋Fe2B的渗硼层,且随WC含量的增加,Fe2B含量相对增加.在渗硼过程中,WC颗粒对硼化物的生长起阻碍作用,而且含量愈多,阻碍作用愈大,渗硼层愈浅.当WC颗粒的分布方向与渗硼方向平行时,对硼化物生长的阻碍作用最小,渗硼层厚且致密,且在冷却时不易产生裂纹;当WC颗粒的分布方向与渗硼方向垂直时,对硼化物的生长阻碍作用最大,获得的渗硼层较浅,并且在渗层中出现明显的疏松区;当WC粒子呈无序分布,对硼化物的生长阻碍作用介于上面两者之间.硼化物生长时,遇到大颗粒WC其尖端变钝并停止生长;遇到小颗粒WC可以＂吞食＂.

Effect of WC particles to the grouth of borides during boronizing of WC/steel composites

WC/steel composites with different WC contents were boronized by powder boronizing.The microstructure,hardness,depth of the boronized layer and formation of microcrack in the boronized layer were investigated by SEM,XRD and self-made Black-and-White Photo Fake Colouring Processor.Furthermore,the influence of the distribution and contents of WC particles in the composite on growth of borides are emphatically analyzed.The results show that the boronized layer consists of FeB and Fe_2B,which has high hardness,and the relative contents of Fe_2B increases with increasing content of WC particles in the composites.During the boronizing process,the WC particles play a role of hindering the growth of boride.The more the contents of WC particles are,the greater the hindering effect is,simultaneously,the thinner the layer of boride is.When the distribution orientation of WC particle is parallel with the direction of boronizing direction,the less hindering effect to the growth of boride is observed and deeper layer of boride,in which no crack is observed,is obtained.When the distribution direction of WC particle is perpendicular to the direction of boronizing,the hindering effect to the growth of boride is greatest,and the layer of boride is thinner,additionally,the loosen region is obviously detected in the boronized layer.The hindering effect to the growth of boride in as-sintered composite with a homogeneous distribution of WC particles is between the both as mentioned above.The peak of boride blunts after meeting a coarse WC particle and stops growing during the growth of boride.However,for fine WC particles,borides engulf them and continue to grow along primary direction.