热挤压对FGH96镍基粉末高温合金微观组织的影响

研究了热挤压温度、挤压比、挤压速度、挤压前预处理对FGH96镍基粉末高温合金微观组织的影响规律,确定了获得晶粒尺寸小于10 μm的超塑性细晶组织的热挤压方法。研究结果表明,热等静压后FGH96合金发生了再结晶,实现了粉末的完全致密化成形,但晶粒大小极不均匀,且存在明显的原始颗粒边界(PPB)缺陷。采用热挤压前预处理工艺在确保合金晶粒不长大的同时,又可使γ'相粗化,显著降低热挤压变形抗力。随着挤压温度的升高,合金晶粒尺寸呈长大趋势。挤压温度为1 080 ℃时,获得平均晶粒小于10 μm的完全再结晶超塑性组织,挤压温度继续升高,晶粒尺寸将明显长大。随着挤压比的增大,挤压载荷明显增大,采用大于6∶1的挤压比,有利于获得平均晶粒小于10 μm的完全再结晶超塑性组织。载荷随热挤压速度的升高而增大,在保证合金组织为细晶的条件下,应尽量选择较低的挤压速度。由于在热挤压过程中合金已发生了完全的动态再结晶,未观察到明显的取向,力学性能测试结果也表明沿着挤压方向和垂直于挤压方向的性能相当,说明不同挤压方向的微织构对性能没有明显影响。

Effect of hot extrusion on microstructure for nickel-based superalloy FGH96

The influences of hot extrusion temperature, extrusion ratio, extrusion rate and pretreatment before extrusion on microstructure for nickel-based superalloy FGH96 were studied. The hot extrusion method for obtaining superplastic fine grain structure with grain size less than 10 μm was determined. The results showed that the FGH96 superalloy recrystallized after hot isostatic pressing, and the powder was fully densified. However, the grain size was extremely uneven, and there were obvious previous particle boundary (PPB) defects. The pretreatment process before hot extrusion not only ensured that grain size of the alloy did not grow up, but also coarsened the γ' phase, which significantly reduced the deformation resistance of hot extrusion. With the increase of extrusion temperature, the grain size of FGH96 superalloy tended to grow up. The fully recrystallized superplastic structure with average grain size less than 10 μm was obtained when the extrusion temperature was 1 080 ℃. With the increase of extrusion temperature, grain size grew up obviously. With the increase of extrusion ratio, the extrusion loading increased obviously. The fully recrystallized superplastic structure with average grain size less than 10 μm could be obtained when the extrusion ratio was greater than 6∶1. The loading increased with the increase of hot extrusion rate, thus the lower extrusion rate should be selected as far as possible under the condition of fine grain structure. There was no obvious orientation due to the fully dynamic recrystallization of FGH96 superalloy during hot extrusion. The results of mechanical properties test also showed that the properties in both parallel and vertical direction for the extrusion were equivalent and the micro texture in different extrusion directions had no obvious effect on the properties.