激光增材制造金刚石/Ni-Cr合金的裂纹特征

Crack characteristics of diamond/Ni-Cr alloy prepared by laser additive manufacturing

采用激光增材制造制备了多层金刚石/Ni-Cr合金试样,研究了裂纹随堆叠层数增加的变化规律、试样表面与内部的微观组织形态特征、表面与内部的微观裂纹萌生位置及宏观裂纹的形态特征以及裂纹的延伸扩展规律。结果表明:表面裂纹数量随堆叠层数增加先增加后减小。试样表面粗大晶粒组织与细晶粒组织交替排列,后成形熔覆道对已成形熔覆道微观组织具有明显热影响作用。试样内部组织从靠近基板到表面呈现细小→粗大→细小的形态,内部磨粒周边的组织比远离磨粒的组织粗大。表面微观裂纹主要萌生于粗大组织区和磨粒周边,粗大组织和磨粒有利于裂纹的扩张与延伸。在平行于激光扫描方向的熔覆层表面拉应力作用下,表面宏观裂纹主要呈现出垂直熔覆道的形态。内部微观裂纹萌生于磨粒周边、粗大组织区以及碳化物夹杂处。内部宏观裂纹可由内部裂纹向外延伸形成或由表面裂纹向内延伸形成。内部裂纹的桥接、磨粒周围缝隙、破碎的磨粒、碳化物夹杂及粗大组织均会助长内部裂纹的扩张和延伸。

Multilayer diamond/Ni-Cr alloy specimens were prepared by laser additive manufacturing.The variation of cracks with the increase of stacking layers,the microstructure characteristics on the surface and inside of the specimens,the micro crack initiation positions on the surface and inside,the morphology characteristics of macro cracks and the extension and propagation rule of cracks were studied.The results show that the number of surface cracks first increases and then decreases with the increase of stacking layers.The coarse grain structure and fine grain structure on the surface of the specimens are arranged alternately.The post forming cladding channel has an obvious thermal effect on the microstructure of the formed cladding channel.The internal microstructure of the specimens presents in the form of fine→coarse→fine from close to the substrate to the surface,and the microstructure around the internal abrasive particles is coarser than that away from the abrasive particles.The surface micro cracks mainly initiate in the coarse structure area and around the abrasive particles,and the coarse structure and abrasive particles are conducive to the propagation and extension of the cracks.Under the action of the surface tensile stress of the cladding layer parallel to the laser scanning direction,the surface macro crack mainly presents the shape of vertical cladding channel.The internal micro cracks initiate around the abrasive particles,in the coarse structure area and in the carbide inclusions.The internal macro cracks can be formed by the outward extension of internal cracks or by the inward extension of surface cracks.The bridging of internal cracks,gaps around abrasive particles,broken abrasive particles,carbide inclusions and coarse structure will promote the propagation and extension of internal cracks.