喷射成形粉末高温合金FGH4095M的制备及组织特征

喷射成形是一种近净成形的在粉末冶金气体雾化制粉技术基础上发展起来的快速凝固技术. 本文采用喷射成形技术制备成分优化后的FGH4095M合金, 研究了喷射成形FGH4095M合金沉积坯的致密度、显微组织特征, 特别是研究了喷射成形高温合金组织中特殊形貌的γ’相. 研究表明, 致密度与沉积坯部位有关, 底部致密度最高, 可达99.63%, 热等静压后的致密度可达100%. 喷射成形合金组织以均匀细小的等轴晶为主, 不存在原始颗粒边界; 一次γ’ 相尺寸约为0.6-0.8 μm, 二次γ’相尺寸约为0.1-0.5 μm, 在二次γ’相的间隙中有少量尺寸约为10-20 nm的三次γ’相. 喷射成形FGH4095M 合金中的二次 γ’相中出现特殊形貌的γ’相, 这是由单个γ’颗粒分裂形成, 与沉积过程的低冷却速度有关. 分裂过程是γ’颗粒总能量降低的过程, γ’颗粒间的弹性交互作用能起到主导作用. 对分裂γ’相的等效直径进行统计, 得到γ’ 相等效直径超过0.40 μm 后, 会出现分裂趋势. 合金具备优异的拉伸性能, 室温塑性得到显著提高, 出现γ’ 相分裂的特殊形貌组织是否对合金性能的提高产生直接影响仍需进行进一步的研究.

Fabrication and microstucture of spray formed powder metallurgy superalloy FGH4095M

Spray forming is a kind of near-net-shaped rapid solidification process based on powder metallurgy gas atomization technology. In this work, the FGH4095M is fabricated by spray forming. The pre-alloy is prepared by vacuum induction melting and vacuum arc remelting techniques. Then the alloy is sprayed by SK2 facility with atomization gas nitrogen at University of Bremen in Germany. In this paper we study the density and microstructure of the spray-formed billet, especially the special morphology of γ’ phase. The results show that density is associated with different parts of the deposited billet. The relative density of the bottom part is higher (99.63%) than those in the other parts. The relative density of top part (98.91%) is lowest. After hot isostatic pressing, the relative density can be up to 100%. Uniform and fine equiaxed grains are the remarkable morphology of spray-formed alloy without prior particle boundary. The sizes of grains are in a range of about l0-40 μm and the grains at bottom part of billet are finest. The grain sizes of primary γ’ phase are in a range of about 0.6-0.8 μm, and the grain sizes of secondary γ’ phase in a range of about 0.1-0.5 μm as well as dispersed spherical tertiary γ’ particles with the sizes of 10-20 nm. The special morphology of secondary γ’ phase occurs with the splitting of γ’ particle, which is related to the low cooling rate of the depositing process. The splitting behavior reduces the total energy of γ’ particle. Total energy of γ’ particle includes elastic interaction energy, elastic strain energy and surface energy, among which the elastic strain energy is invariable. The surface energy increases with the splitting process and the elastic interaction energy reduces. The effect of elastic interaction energy on particles is the major reason why the total energy is reduced. The trend of splitting behavior is analyzed by calculating the equivalent diameter of splitting γ’ particle. It indicates that when the equivalent diameter is over 0.40 μm, there is the possibility to split. Subsequently, spray-formed FGH4095M billet is treated by hot isostatic pressing, isothermal forging and heat treatment process to obtain the FGH4095M alloy turbine disk. The research of tensile property of FGH4095M alloy turbine disk shows an excellent property either at room temperature or at high temperature for the optimized alloy. The relationship between special morphology of γ’ phase and excellent property needs further investigating.