激光选区熔化钨基复合材料形貌演变及缺陷形成机制研究

Study on the evolution of morphology and the formation mechanism of defects in tungsten matrix composites manufactured by selective laser melting

钨基复合材料具有优异的综合性能,如高熔点、优异力学性能、低热膨胀系数、高硬度、良好热导率及优异耐腐蚀性能等,因此被广泛应用于航空航天、核工业、医疗装备及电子器件等领域。针对传统粉末冶金工艺制备钨基复合材料存在的结构设计受限及性能提升困难等瓶颈问题,采用激光选区熔化(SLM)技术制备钨基复合材料。首先,研究了激光体积能量密度对W-Y_(2)O_(3)钨基复合材料物相结构的影响;其次,研究了激光体积能量密度对W-Y_(2)O_(3)钨基复合材料表面形貌及内部组织演变行为的影响;最后,阐明了SLM成形W-Y_(2)O_(3)钨基复合材料缺陷形成机制。结果表明:通过优化SLM成形工艺参数可以抑制未熔化球形粉、孔洞及表面凹凸不平等缺陷的形成,但依旧无法抑制钨基复合材料中裂纹成形缺陷的萌生。SLM工艺特性引入的高温度梯度和高热应力与钨的高韧脆转变温度二者协同作用能够诱导裂纹萌生,并沿着低结合强度钨晶界进行扩展形成网状裂纹。本研究的开展不仅能为SLM成形钨基复合材料缺陷形成机制提供理论基础,还为增材制造制备无成形缺陷钨基复合材料提供技术支撑。

Tungsten(W)matrix composites are widely used in aerospace,nuclear industry,medical equipment,electronic devices and other fields because of their excellent comprehensive properties,such as high melting point,excellent mechanical properties,low coefficient of thermal expansion,high hardness,good thermal conductivity and excellent corrosion resistance.Aiming at the bottlenecks of the traditional powder metallurgy process for the preparation of tungsten matrix composites,such as limited structural design and difficulties in performance enhancement,the present study utilizes the advantages of the high degree of freedom in structural design of selective laser melting(SLM)technology for the preparation of tungsten matrix composites.In this work,the effect of laser bulk energy density on the phase of W-Y_(2)O_(3)tungsten matrix composites was first investigated.The effects of surface morphology and internal microstructure evolution behavior of W-Y_(2)O_(3)tungsten matrix composites were also investigated.The defect formation mechanism of SLM-formed W-Y_(2)O_(3)tungsten matrix composites was elucidated.The results showed that the optimization of SLM process parameters can inhibit the formation of defects such as unmelted spherical powder,pores and surface unevenness,but still cannot inhibit the emergence of cracks in tungsten matrix composites.The high-temperature gradient and thermal stress introduced by the SLM process and the high ductile-to-brittle transition temperature of tungsten can induce crack initiation and expand along the grain boundaries of tungsten with low bonding strength to form network cracks.This study not only provides a theoretical basis for the formation mechanism of defects in SLM-formed tungsten matrix composites,but also provides technical support for the preparation of tungsten matrix composites without defects by additive manufacturing.