挤压态喷射成形GH738合金热变形行为及组织研究

Deformation mechanism and microstructure evolution of hot extruded GH738 alloy fabricated by spray forming

在温度950~1150℃、应变速率0.001~1 s–1及工程应变50%条件下,利用Gleeble-3500TM热模拟试验机对挤压态喷射成形GH738合金进行热压缩实验,研究合金的流变应力,建立合金热变形本构关系,利用EBSD分析合金组织演变。结果表明:合金流变应力随温度的升高和应变速率的减小而降低,在相同变形条件下,具有细晶组织特征的挤压态喷射成形GH738合金峰值流变应力低于粗晶组织的铸锻GH738合金;挤压态喷射成形GH738合金热变形激活能为651.08 kJ·mol–1,GH738合金的热变形激活能随着初始平均晶粒尺寸的减小而升高;形变温度的升高使挤压态喷射成形GH738合金初始被拉长的晶粒逐渐演变为等轴再结晶晶粒,在1000℃以上获得完全动态再结晶组织,再结晶组织随形变温度的进一步升高发生长大。

The research on hot deformation including flow behavior, microstructure evolution via EBSD method and the constitutive characteristic model of hot extruded GH738 alloy fabricated by spray forming was conducted by using Gleeble-3500 TM simulator at the temperature range of 950~1150 ℃, strain rate range of 0.001~1 s–1 and engineering strain of 50%. The results show that the flow stress decreases with increasing of the deformation temperature and decreasing of the strain rate. The peak flow stress of coarse grain GH738 is higher than that of fine grain within the extruded GH738 alloy. The activation energy Q of extruded GH738 alloy is 651.08 kJ·mol–1. The hot deformation activation energy Q of GH738 alloy is tending to increasing with the decreasing of the original average grain size. The microstructure evolutes from original stretched grain to equiaxed grain with the increasing deformation temperature through the onset of recrystallization. The full dynamic recrystallization microstructure is obtained at the temperature above 1000 ℃ and the microstructure tend to coarsen with the higher deformation temperature.