摘要
采用Gleeble-3500热模拟试验机研究了未均匀化、部分均匀化和完全均匀化处理的高合金化GH742合金铸锭的等温热变形行为.结果表明,随着均匀化程度的提高,合金热变形过程中的流动应力逐渐降低,塑性提高,动态再结晶程度增加;元素偏析和γ'相和δ相等析出相导致变形过程中形成大量的位错和形变带,提高了合金的变形抗力;大块Laves相和Ni_5Ce相等脆性相破碎后容易形成微裂纹;大块、密集分布的一次析出MC型碳化物在变形过程中容易产生条带组织,并形成应力集中区,导致裂纹萌生.采用低温预处理和高温扩散相结合的均匀化制度,能够消除元素偏析和有害脆性相,改善碳化物尺寸和分布,降低热变形抗力,明显提高合金的热塑性,获得均匀的再结晶组织.
As the increases of alloying elements, the highly alloyed Ni-based superalloys are very difficult to deform due to the low deformation plasticity, high flow stress and narrow deformation temperature interval. The hot deformation behavior of highly alloyed as-cast and homogenization treated GH742 alloys was investigated by isothermal compression conducted on a Gleeble-3500 thermosimulation machine. The ingots were homogenization treated at 1140 ℃ for 6 h or at Ii00 ℃ for 30 h and at 1160 ℃ for 40 h, followed by furnace cooling to 800 ℃ and then air cooling to room temperarue. The GH742 alloys possess lower flow stress, higher plasticity and larger recrystallization degree as the homogenization degree increases during the deformation process. High dislocation density and deformation bands are formed due to the elemental segregation and the precipitates of γ＇ and phase in the interdendritic regions, which enhance the flow stress. Mircocracks are initiated when the brittle precipitates such as Laves phase and NisCe phase are crushed by compression. Stress concentration area as well as the banded structure of carbides is formed when the primary MC type carbides are deformed. The two-step homogenization treatment via low temperature pretreatment followed by high temperature diffusion presented by this paper can not only eliminate the elemental segregation and the detrimental precipitates, but also improve the dimension and distribution of MC type carbides, which decreases the flow stress, increases the hot deformation plasticity remarkably, and obtains homogeneously recrystallized microstrueture.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第11期1403-1408,共6页
Acta Metallurgica Sinica
关键词
镍基高温合金
均匀化
热塑性
流动应力
动态再结晶
Ni based superalloy, homogenization, hot plasticity, flow stress, dynamic recrystallization
