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首页> 外文期刊>Journal of Materials Engineering and Performance >Effect of Hot Deformation Parameters on Grain Refinement of an As-Cast Ni-Based Superalloy
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Effect of Hot Deformation Parameters on Grain Refinement of an As-Cast Ni-Based Superalloy

机译：热变形参数对铸造Ni基超合金晶粒细化的影响

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摘要

The grain refinement behavior in superalloys has been identified for a long time, while its exact underlying mechanism remains to be explored. In this study, transmission electron microscope and electron backscatter diffraction technique were employed to investigate the fundamental mechanism governing the process of grain refinement for as-cast superalloys GH4720LI. The results show that grain refinement highly depends on the distributions of gamma ' precipitates. In gamma + gamma ' two-phase region,gamma ' precipitates could promote the dislocation multiplication, hinder the dislocation motion and lead to the formation of high-density dislocation substructure. Hence, the sub-boundaries and high-angle grain boundaries (HABs) are formed resulting from the gradual transformation of the dislocation substructures. In this process, the new grains are developed by quasi-continuous dynamic recrystallization (quasi-CDRX) and discontinuous dynamic recrystallization (DDRX). In addition, strain rate has little influence on grain size and DRX behavior at high strain rate and low temperature. While in gamma single-phase region, the dislocation within grains is partly consumed through continuous original boundary migration (COBM) at 0.01 s(-1). Moreover, in some deformed grains which are expected to possess high dislocation density, new grains can be formed by DDRX. With the strain rate increasing, the process of COBM was suppressed while DDRX was promoted. Therefore, the main dynamic softening mechanism of alloy is DDRX under the high temperature and high strain rate.
机译：高温合金中的晶粒细化行为已经被确定了很长时间，但其确切的潜在机制仍有待探索。本研究采用透射电子显微镜和电子背散射衍射技术研究了GH4720LI铸态高温合金晶粒细化的基本机理。结果表明，晶粒细化在很大程度上取决于γ析出相的分布。在gamma+gamma两相区，gamma沉淀可以促进位错增殖，阻碍位错运动，导致高密度位错亚结构的形成。因此，位错子结构的逐渐转变形成了亚晶界和高角度晶界。在这一过程中，通过准连续动态再结晶（准CDRX）和非连续动态再结晶（DDRX）形成了新的晶粒。此外，在高应变速率和低温下，应变速率对晶粒尺寸和DRX行为的影响很小。而在γ单相区，晶粒内的位错在0.01s（-1）时通过连续原始边界迁移（COBM）被部分消耗。此外，在一些预计具有高位错密度的变形晶粒中，DDRX可以形成新晶粒。随着应变速率的增加，COBM过程被抑制，而DDRX过程被促进。因此，高温高应变速率下合金的主要动态软化机制是DDRX。

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