摘要高温氧化、晶间腐蚀(IGC)以及晶间应力腐蚀开裂(IGSCC)是镍基合金材料在长期高温服役环境下失效的主要原因，采用形变热处理的晶界工程方法可以有效地提高材料的高温抗氧化和抗腐蚀性能。本文采用典型的面心立方金属的镍基合金—Hastelloy X（HX合金）合金，通过形变热处理工艺，提高合金的高温抗氧化和抗腐蚀性能。利用EBSD和电化学方法对比研究了冷轧量、退火温度及退火时间对HX合金组织和性能的影响，得到了以下结论：67154

（1）Hastelloy X合金经过适当的形变热处理后，产生大量的不同形态的退火孪晶，打断了连通的自由晶界，有效地阻断了腐蚀的继续扩展，大大提高了合金耐腐蚀性能。

（2）在1050℃退火60分钟的退火工艺下，不同冷轧量的电化学对比结果显示：5％冷轧变形量的试样的腐蚀敏感性最低。经EBSD分析得知，5%变形量的试样的特殊晶界比例比母材高5.46%。大变形量对试样退火后晶间腐蚀性能的提高没有促进作用，这是因为较大变形量的试样在退火过程中主要发生的是以一般大角度自由晶界形成为特征的再结晶行为，导致其特殊晶界含量的降低，最终使得其晶间腐蚀抗力减弱。

（3）试样经过5%冷轧变形在1030℃退火处理30min后，试样的耐腐蚀性能最好。EBSD显示其特殊晶界的比例比母材高出10.82%。较低的温度很有可能使得组织不能发生晶界的迁移以及反应，从而导致特殊CSL晶界比例的降低。退火温度过高，时间过长，容易导致再结晶晶核的长大，导致随机大角度晶界比例的增加。退火时间过短，部分亚晶没有足够的时间吞并更加细小的亚晶而形成再结晶晶粒，因而晶粒内部不利于退火孪晶的形成。

毕业论文关键词  晶界工程 热机械处理 电化学分析 EBSD

毕业设计说明书（论文）外文摘要

Title  The research of the impact of grain boundary optimization on Hastelloy X alloy’s resistant to corrosion performance

Abstract

The high-temperature oxidation, intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) of nickel-based alloy material are the main reasons for failure in the long-term high temperature service environment. The use of thermomechanical treatment of grain boundary engineering can effectively improve the  high temperature oxidation resistance and corrosion resistance of the alloy . In this paper, grain boundary engineering(GBE) was performed on a typical face-centered cubic metal Hastelloy X by means of thermomechanical processing (TMP) to optimize grain boundary character distribution and improve the oxidation resistance and corrosion resistance in high temperature. EBSD and electrochemical methods were used to investigated the effect of thermomechanical processing on microstructure and properties of Hastelloy X. The main results are as follows:

 (1) Through an appropriate thermomechanical processing, Hastelloy X will form a large number of annealing twins in different morphologies, which interrupted the connectivity of the free grain boundaries, effectively blocked the corrosion to expand, and greatly improved the corrosion resistance of the alloy.

(2) Before annealing at 1030℃ for 60min, the contrast of electrochemical results of different cold rolling reductions show that: the sample which was reduced 5% by cold rolling has lowest corrosion sensitivity.Through EBSD we can know that,the percentage of special CSL of 5% of the deformation of specimen is higher 5.46% than the parent metal.Increasing the cold rolling reduction has no effect on improving the corrosion resistance, because the large deformation of the specimen during annealing occurs mainly on the general freedom of wide-angle grain boundaries, which are characterized by the formation of recrystallization behavior, and leads to a lower proportion of special grain boundaries. Eventually it weakens intergranular corrosion resistance.