摘要
采用液态金属冷却高温度梯度定向凝固设备.研究了抽拉速率跃迁对单晶高温合金DD3一次枝晶间距和微观偏析的影响.结果表明,单晶高温合金枝晶一次间距表现出明显的历史相关性.当抽拉速率(或生长速率)分别从600和300μm/s跃迁到100μm/s和直接以100μm/s速率生长时,一次间距分别为56.5,86和111.5μm.而生长速率分别从50和100μm/s跃迁到300μm/s和直接以300μm/s速率生长获得的一次间距分别为109,93和70μm.一次间距值与Hunt-Lu模型预测的基本吻合,但实验结果证明其上限与下限的比值λ_1^(max)/λ_1^(min)>2,与Ma Sahm的预测结果一致.成分分析表明,相同稳态条件下枝晶的一次间距变小.偏析也有所降低.
The microstructure of single crystal Ni-based superalloys is virtually determined by both processing parameters of growth rate v and thermal gradient G ahead of the solidification front. Previous researches have established the relationship between dendrite spacings and G or v under supposing those parameters to be constant from beginning to end of solidification,resulting in the disaccord between the predicted and experimental results for actual blade productions.Furthermore, previous experimental and theoretical works seldom involve the influence of processing parameter change on dendrite growth for multi-component industrial alloys.Therefore,investigation of directional solidified microstructure varying with processing parameter is the focus of present study.The influence of the withdrawing rate transition during directional solidification on the primary dendrite arm spacing （PDAS） and microsegregation for single crystal superalloy DD3 has been studied by liquid metal cooled（LMC） directional solidification method.A wide range of withdrawing rate variations from 50 to 600μm/s is allowable under G high to 250 K/cm.The results indicate that the average PDAS is remarkably dependent on the history of growth rate variation.The smaller PDASs of 56.5 and 86μm can be obtained under withdrawing rate transition from higher values of 600 and 300μm/s into 100μm/s,while they are kept being 111.5μm if withdrawing rate is 100μm/s all the time.In contrast,PDASs increase to 109 and 93μm under withdrawing rate transition from lower values of 50 and 100μm/s into 300μm/s,while they are kept being a small value of 70μm if growth rate is 300μm/s at beginning.These experimental results agree approximately with those from Hunt-Lu model,but the maximum to minimum ratio of PDASs at a given solidification parameter,i.e.,λ_1^（max）/λ_1^（min）,is proved to be more than 2.It is also shown that the dendrite microsegregation will be lessened with the decrease of PDASs at the same current solidification parameters.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2009年第10期1225-1231,共7页
Acta Metallurgica Sinica
基金
国家重点基础研究发展计划项目2006CB605202
国家自然科学基金项目50771081和50827102资助~~
关键词
单晶高温合金
生长速率
跃迁
一次间距
微观偏析
single crystal superalloy
growth rate
transition
primary dendrite arm spacing
microsegregation
