摘要
采用ProCAST和CAFE模型模拟了镍基单晶高温合金DD403定向凝固过程中的温度场及晶粒组织.研究了抽拉速率对变截面单晶铸件杂晶形成和铸件板身固液界面形状和位置的影响规律,得到了单晶铸件不出现杂晶的最大抽拉速率——临界抽拉速率（Vc）.结果表明,当采用150 μm/s的抽拉速率时,对于液态金属冷却（LMC）技术,铸件平台的凝固顺序是从中心到两边,杂晶形成倾向较小;而在高速凝固（HRS）条件下,铸件平台的边缘首先冷却,平台边缘容易出现大的过冷而产生杂晶.在本实验条件下,采用HRS技术,临界抽拉速率不得高于125 μm/s;采用LMC技术,最大抽拉速率不宜超过150 μm/s,否则可能会在螺旋段或平台处形成杂晶.当抽拉速率为150 μm/s时,采用LMC法获得的板身部位的轴向温度梯度（Ga）是HRS法的2倍多;一次枝晶臂间距（PDAS）减小了1/3～1/2,且沿铸件轴向的轴向温度梯度和一次枝晶臂间距均较HRS均匀.当抽拉速率在50～200 μm/s范围内增大时,采用LMC技术,铸件板身的固液界面始终保持平直且逐渐下移至隔热挡板中部;而HRS条件下,固液界面逐渐下凹并下移至挡板下方.
The temperature field and grain texture during the directional solidification of Ni-base single crystal superalloy DD403 has been simulated by ProCAST＆CAFE model. The effect of withdrawal rate on stray grains formation and shape as well as location of the solid-liquid interface of the casting between its platform and transition region （airfoil） was analyzed. Critical withdrawal rates （Vc）, which are maximum withdrawal rates of no stray grains formation in the single crystal casting, were obtained with two methods. It is found that the liquid isotherm moves from center to edge at the platform region for liquid metal cooling （LMC） method at a rate of 150 μm/s, inhibiting the formation of stray grains. However, the edge of platform for high rate solidification （HRS） approach with the same withdrawal rate is cooled earlier than the center, and great undercooling of the edge of the platform may occur, which results in stray grains formation there. In this study, Vc cannot be more than 125 μm/s for HRS method; it is recommended the maximum withdrawal rate for LMC approach cannot exceed 150μm/s, otherwise new grains may occur at the pigtail or platform region. When the withdrawal rate is 150 μm/s, the LMC process can create axial thermal gradient （Ga） at airfoil more than double the HRS process with a 1/3-1/2 refinement in primary dendrite arm spacing （PDAS）. In addition, Ga and PDAS are more uniform along the axis of the castings compared with HRS method. As withdrawal rate increases in the range of 50 to 200μm/s, the solid-liquid interface at airfoil remains flat and moves to the middle of the thermal baffle for LMC method; however, it becomes more concave and moves to the underside of the baffle for HRS approach.
出处
《铸造》
CAS
CSCD
北大核心
2014年第2期145-151,共7页
Foundry
基金
国家重点基础研究发展项目(2010CB631202和2011CB610406)
国家自然科学基金(551101120和51171151)
国家高技术研究发展计划项目(2012AA35047)
关键词
温度场
晶粒组织
液态金属冷却
单晶高温合金
临界抽拉速率
数值模拟
temperature field
grain texture
liquid metal cooling
single crystal superalloy
withdrawal rate
numerical simulation
