喷射成形镍基高温合金热变形特性及微观组织变化

CHARACTERISTICS OF HOT COMPRESSION DEFORMATION AND MICROSTRUCTURE EVOLUTION OF SPRAY FORMED NICKEL BASE SUPERALLOY

采用Gleeble-1500D热力模拟试验机对喷射成形+热等静压制备的镍基高温合金,在变形温度1050—1140℃,应变速率0.01—10.0s^(-1),工程应变量50%的条件下进行了热压缩实验.利用实验数据建立了合金的热加工图和热激活能图,对变形过程中组织演化进行了研究.结果表明,热等静压并没有使喷射成形高温合金晶粒尺寸明显长大.真应力-应变曲线出现了屈服降落现象;合金热加工图失稳区出现在温度区间1050—1110℃,应变速率0.01s^(-1)处;在1110—1140℃,应变速率1.0—10.0s^(-1)区间功率耗散值(η)出现最大值;在1140℃,应变速率1.0—10.0 s^(-1)区间激活能出现一个小平台区.在变形温度1110—1140℃、应变速率1.0—10.0 s^(-1)、变形量50%的条件下,可得到完全再结晶组织,该变形条件与热加工图中功率耗散最大值所在区间和激活能图中小平台区所在区间相对应.

The hot compression test of the spray formed plus hot isostatic pressed （HIP） nickel- based superalloy was conducted on Gleeble-1500D thermal mechanical simulator at a temperature range of 1050--1140 ℃, and strain rate range of 0.01-10.0 s^-1 with engineering strain 50%. The processing map and activation energy map of the alloy were established by using tested data, and microstructure evolution of deformed samples was also examined. The results show that the grain size of spray formed alloy does not significantly increase after HIP. Due to the variations of dislocation movement and density in deformation, the yield drop was observed only at higher temperature. Processing map and activation energy map indicate that the instability domain of the alloy is at the temperature range of 1050--1110 ℃ and strain rate of 0.01 s^-1, and the highest efficiency of power dissipation （η） appeared at 1110--1140 ℃ and 1.0--10.0 s^-1, and a platform region was also observed at 1140 and 1.0--10.0 s^-1. So, the optimum conditions for thermomechanical processing correspond to the η maximum region and activation energy platform region, at which the full dynamic recrystallization （DRX） occurred.