液氮冷却条件下激光快速熔凝Ni-28 wt%Sn合金组织演变

发布时间：2019-08-09 12:17

【摘要】：研究了在液氮冷却条件下激光快速熔凝Ni-28 wt%Sn亚共晶合金的组织演化过程.结果显示,熔池从上至下可以分为三个区域:表层为平行激光扫描方向的α-Ni转向枝晶区;中部为近乎垂直于熔池底部外延生长的α-Ni柱状晶区;底部为少量的残留α-Ni初生相和大量的枝晶间(α-Ni+Ni3Sn)共晶组织.激光熔凝区组织受原始基材组织的影响很大,熔池中的α-Ni枝晶生长方向受到了热流方向和枝晶择优取向的双重影响.与基材中存在的层片状、棒状和少量离异(α-Ni+Ni3Sn)共晶的混合组织相比,熔池内的共晶组织皆为细小的规则(α-Ni+Ni3Sn)层片状共晶,皆垂直于熔池底部外延生长,并且从熔池顶部至底部,共晶层片间距逐渐增大.分别应用描述快速枝晶生长的Kurz-Giovanola-Trivedi模型和描述快速共晶生长的Trivedi-Magnin-Kurz模型对熔池表层凝固界面前沿的过冷度进行估算,发现熔池表层α-Ni枝晶和(α-Ni+Ni3Sn)层片共晶的生长过冷度在50.4—112.5 K之间,远大于相应深过冷凝固(α-Ni+Ni3Sn)反常共晶生长的临界过冷度20 K,这说明文献报道的临界过冷度并不是反常共晶出现的充分条件.
[Abstract]:The microstructure evolution of Ni-28 wt%Sn hypoeutectic alloy by laser rapid melting under liquid nitrogen cooling was studied. The results show that the molten pool can be divided into three regions from top to bottom: the surface layer is a 伪-Ni steering dendritic region parallel to the laser scanning direction; the middle part is a 伪-Ni columnar region grown almost perpendicular to the bottom of the molten pool; and the bottom is a small amount of residual 伪-Ni primary phase and a large number of interdendritic (伪-Ni Ni3Sn) eutectic structure. The microstructure of laser melting zone is greatly affected by the microstructure of the original substrate, and the growth direction of 伪-Ni dendrite in the molten pool is affected by both the heat flow direction and the preferred orientation of dendrite. Compared with the lamellar, rod-like and a small amount of divorced (伪-Ni Ni3Sn) eutectic mixed microstructure in the substrate, the eutectic structure in the molten pool is fine regular (伪-Ni Ni3Sn) lamellar eutectic, all of which grow perpendicular to the bottom of the molten pool, and the eutectic lamellar spacing increases gradually from the top to the bottom of the molten pool. The Kurz-Giovanola-Trivedi model describing rapid dendritic growth and Trivedi-Magnin-Kurz model describing rapid eutectic growth were used to estimate the undercooling along the surface solidification boundary of molten pool. It was found that the growth undercooling of 伪-Ni dendrite and (伪-Ni Ni3Sn) eutectic on the surface of molten pool was between 50.4 and 112.5 K, which was much higher than the critical undercooling of 伪-Ni Ni3Sn abnormal eutectic growth. This shows that the critical undercooling reported in the literature is not a sufficient condition for the occurrence of abnormal eutectic.
【作者单位】：西北工业大学凝固技术国家重点实验室;
【基金】：国家自然科学基金(批准号:51323008,51105311,51271213) 国家重点基础研究发展计划(批准号:2011CB610402) 国家高技术研究发展计划(批准号:2013AA031103) 高等学校博士学科点专项科研基金(批准号:20116102110016) 中国高等学校学科创新引智计划(批准号:08040)资助的课题~~
【分类号】：TG665

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