摘要
采用微观测试分析方法对沉淀增强型镍基高温合金Rene 88DT激光快速成形裂纹产生机理进行了研究。发现裂纹为液化裂纹,具有典型的沿晶开裂特征。激光快速成形过程中,沉积当前层时,已经凝固的前一层沉积层经受再热循环,晶界处的γ/γ′低熔共晶发生液化,在随沉积过程进行而逐渐增大的残余拉伸应力的作用下被拉开,形成液化裂纹。激光成形件组织具有典型的外延柱状生长特点,沉积层底部为近似平行于沉积方向的细长枝晶,其顶部由于热流方向改变枝晶发生转向,在沉积下一层时,道与道之间的搭接区容易存在转向枝晶未熔的区域,因此生长方向偏离沉积方向一定角度的枝晶在搭接区交汇形成晶界,使得该区域成为开裂的敏感区域。柱状枝晶的晶界沿层与层之间具有贯通的渠道,液化裂纹一旦形成就会沿晶界迅速扩展,因此裂纹大体沿道与道之间搭接区域发展。
The forming mechanism on the cracks produced in the laser rapid forming （LRF） processing of Rene88DT superalloy has been investigated. The results show that the cracks belong to the liquefying crack with a characteristic of cracking along grains, forming the liquid films along grains due to the liquiefying of γ/γ′ eutectic composition in the pre-layer already solidified by laser scanning. The pre-layer was pulled apart by the increasing residual tensile stress with the laser deposition process. There are columnar dendrites parallel to the laser deposition direction at the bottom of the present laser deposition layer, while at the top, the dendrites haul to the direction perpendicular to it due to the change of heat flux direction. The hauling dendrites exist at the overlapping zone of the subsequent laser deposition layer due to un-melting. As the LRF samples＇ microstructure showing the epitaxial growth, the grain boundary formed in the overlapping zone between laser scanning paths due to the un-melting hauling dendrites. The γ/γ′ eutectic also solidified in the area, making the zone cracking susceptibly. The liquefying cracks will rapidly expand along the penetrating columnar grain boundary between the laser deposition layers. As a result, the cracks enlarged generally along the central line of the overlapping zone.
出处
《稀有金属材料与工程》
SCIE
EI
CAS
CSCD
北大核心
2007年第2期216-220,共5页
Rare Metal Materials and Engineering
基金
国家自然科学基金重点项目(50331010)
国家自然科学基金(50405038和50201012)
作者简介
赵晓明，男，1980年生，博士研究生，西北工业大学凝固技术国家重点实验室，陕西西安710072，电话：029-88493940-8031
