摘要
裂纹是激光选区熔化(SLM,selective laser melting)镍基高温合金最严重的缺陷之一,严重削弱了材料的力学性能。采用逐行扫描策略制备了Inconel 625合金试样,利用扫描电子显微镜(SEM)、电子背散射衍射(EBSD)等检测方法研究了裂纹微观形貌、周边元素和晶粒分布等。SEM结果显示在常温下成形件内部形成大量细小裂纹,裂纹长度约100μm。裂纹形成的内因是在快速凝固的过程中,由于Nb,Mo元素的局部偏析,形成(γ+Laves)共晶凝固。同时在脆性相Laves周围形成应力集中,导致沿着晶界开裂,SLM高凝固速率产生的残余应力是微裂纹产生的直接原因。通过基板加热工艺减小热残余应力,利用X射线测定了不同预热温度(150和300℃)下的残余应力值。结果显示基板预热降低了热残余应力,并最终抑制了裂纹的产生,随着温度的升高,裂纹数量逐渐减少,在预热温度300℃时裂纹数量最少。
Micro crack was one of the most serious defects in selective laser melting （ SLM）, weakening the mechanical properties of materials. In this paper, test specimens of Inconel 625 alloy were fabricated by progressive alternative scan strategy in SLM process. The microstructure of the crack, elements around the crack and the distribution of the grain were detected by scanning electron micro- scope（SEM） and electron backscattered diffraction（EBSD）. The SEM results showed that a large numbers of tiny craeks occurred at room temperature, with the average length of approximately 100 μm. Internal cause of crack formation was due to the local segregation of Nb and Mo elements in the process of rapid solidification. It generated eutectie solidification （γ＋ Laves）. At the same time, stress concentration formed around the brittle phase Laves, leading to cracking along the grain boundary. Residual thermal stress caused by high solidification rate was the direct reason. Residual stresses were reduced by substrate heating process and residual stresses were measured by X-ray stress analyzer at different substrate preheating temperatures （ 150 and 300 ℃ ）. Residual stresses were reduced in the process and cracks were greatly eliminated by preheating at different temperatures. With the increase of temperature, the number of cracks gradually reduced. When preheated at 300 ℃ , the number of cracks was the smallest.
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2015年第11期961-966,共6页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(551375188
551375189)
国家科技部科技支撑计划项目(2012BAF08B03)
上海市科技创新行动计划项目(13111104900)
黑龙江省自然科学基金重点项目(ZD201104)资助
