ABSTRACT Hot extrusion (HEX) and isothermal forging (ITF) are two critical processing methods in manufacturing of Ni-based powder metallurgy (P/M) superalloys. Hot compressions with different parameters were performed on a novel Ni-based P/M superalloy in as-extruded condition to simulate ITF and the related microstructure evolution. The results revealed that the as-extruded alloy was fully recrystallised with no preferred orientation, while hot deformation at relatively high strain rate could induce the formation of <101> texture. Low-angle grain boundaries were formed due to the rearrangement of deformation-induced dislocations. The existence of high-angle grain boundaries led to dislocation pile-ups and resultant local stress concentration. The grains were remarkably refined after hot deformation due to dynamic recrystallisation and corresponding reduction of average grain size varied from 20 to 67%. The average particle size of γ′ phases enlarged after hot deformation through an Ostwald ripening process and varied from ∼142.5 to ∼235.0 nm in different conditions while their initial sizes were ∼137.2 nm. The effect of strain rate on the particle size of γ′ phases was much greater than the deformation temperature that exhibited a stronger influence on their area fraction.

中文翻译：

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一种新型挤压态镍基粉末冶金高温合金的热变形诱导微观结构演化

摘要 热挤压 (HEX) 和等温锻造 (ITF) 是制造镍基粉末冶金 (P/M) 高温合金的两种关键加工方法。在挤压状态下对新型镍基粉末冶金高温合金进行不同参数的热压缩，以模拟 ITF 和相关的微观结构演变。结果表明，挤压态合金完全再结晶，没有择优取向，而在相对高应变速率下的热变形会导致<101>织构的形成。由于变形诱导位错的重排，形成了小角度晶界。大角度晶界的存在导致位错堆积和由此产生的局部应力集中。由于动态再结晶和相应的平均晶粒尺寸减少 20% 至 67%，热变形后晶粒显着细化。通过奥斯特瓦尔德熟化过程热变形后，γ'相的平均粒径在不同条件下从~142.5 到~235.0 nm 不等，而它们的初始尺寸为~137.2 nm。应变速率对γ'相粒径的影响远大于变形温度，后者对其面积分数的影响更大。