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摘要本文研究了纯镍(99.99%)分别经过Bc路径等通道径角挤压(Equal channel angular pressing, ECAP)达1，2，8道次和液氮冷轧(87%LNR)以及8道次ECAP+LNR87%的组织以及随后热处理过程中样品的硬度变化和微观组织演变。通过TEM表征了大变形后样品的组织，通过拉伸实验测对变形样品的强度及断口进行了分析。通过等温退火，以及等时退火对8p、LNR87%和8P+LNR87%的样品进行了热处理。利用EBSD和显微硬度测试对退火过程中材料的组织和硬度变化进行了表征，分析了各样品的软化行为。结果显示通过对ECAP8道次的样品进行液氮轧制，可以显著提高细化极限，在一文方向上细化至纳米水平（70-100nm），但是该样品的热稳定最低。将经过8道次ECAP的样品进行液氮冷轧能突破ECAP的晶粒细化极限，但热稳定性更差。退火过程中超细晶纯镍组织的改变与不连续再结晶有关，相比界面张力高位错密度是不连续再结晶的主要驱动力。30093
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关键词 等通道径角挤压 液氮冷轧 超细晶镍 热稳定性
毕业论文设计说明书外文摘要
Title Thermal stability of ultrafine-grained pure Nickel
Abstract
Pure nickel (99.99%) was processed by Equal channel angular pressing with route Bc up to 1,2 and 8 passes. Liquid nitrogen rolling (LNR) was also used to process coarse grained (CG) nickel and ultra-fine grained nickel (8p). The microstructure of deformed samples were characterized by TEM and EBSD. Mechanical properties (strength and fracture) of deformed samples were tested and analyzed. Thermal stability of nickel with eight passes (8p), liquid nitrogen rolling (LNR 87%) and 8p+LNR87% were investigated through isothermal annealing and isochronal annealing. The EBSD results and microhardness evolution of samples after heat treatment were recorded and used to evaluate the softening behavior. Results showed that liquid nitrogen rolling can improve the grain refinement of ECAPed sample from ~500nm to ~100nm, however the thermal stability of 8p+LNR87% is lower than other samples. The microstructure evolution of nickel during annealing is related to discontinuous recrystallization, and the high dislocation density provides the driving force compared with the grain boundary curvature.
Keywords Equal Channel Angular Pressing Liquid Nitrogen Rolling Ultrafine-grained pure Nickel Thermal stability
目 次
1 引言 1
1.1研究背景 1
1.2 等通道转角挤压法(Equal channel angular pressing, ECAP) 2
1.3 液氮冷轧（Liquid Nitrogen Rolling,LNR） 4
1.4 常见超细晶金属材料热稳定性的研究现状 5
1.5 本次毕业设计探索的内容、目标及创新性 5
2 实验材料及方法 7
2.1 实验材料 7
2.2 实验路线及方案 7
2.3 实验设备 8
2.4 实验方法 9
3 变形组织和性能 13
3.1 8p、LNR87%和8p+LNR87%变形组织观察 13
3.2 8p、LNR87%和8p+LNR87%力学性能 13
3.3 8p、LNR87%和8p+LNR87%拉伸试验断口分析 14
4 超细晶纯镍热稳定性分析 15
4.1 8p、LNR87%和8p+LNR87%退火组织观察 15
4.2 超细晶纯镍退火显微硬度变化 17
4.3 超细晶镍再结晶机理分析 20