GH625合金长时高温时效的研究

发布时间：2018-05-07 20:17

本文选题：GH625合金 + 析出相　；参考：《兰州理工大学》2017年硕士论文

【摘要】：为加强国产高温合金在民用领域内的高端应用,并从现阶段我国电力系统急需大力发展超超临界火电技术,以满足经济发展对低污染能源需求的实际出发,本文选择700℃超超临界机组耐热部件的候选材料GH625合金为研究对象,采用扫描电子、能谱、X-ray衍射和透射电子等分析手段,并通过常温拉伸和硬度测试试验,考察了某一国产GH625合金在720℃下经长时时效后其组织与力学性能的变化,旨在为国产GH625合金的实际应用提供参考。实验得出的结果如下:(1)通过研究合金在720℃下,经1×103 h、3×103 h和5×103 h时效后,其析出相与组织的演变过程。从中发现,碳化物的分解与转变、γ"相的相接和δ相的析出与长大,是影响晶界形貌变化的主要因素,随时效时间的延长晶界形貌呈现出先粗化后细化再粗化的变化过程;晶内主要沉淀相依照γ'、γ"和δ相的次序先后析出,且随时效时间的延长晶内存在γ"相向δ相的转变,γ"相的过分粗化是该转变发生的主要因素。时效1×103h的晶内沉淀相以均匀分布的γ'、γ"相为主,时效3×103h的晶内沉淀相分布不均匀,γ'、γ"和δ相均出现在基体中,时效5×103h后,晶内沉淀相则以δ相为主。(2)利用X-ray衍射分析,测定试样经不同时效时间后热暴露面氧化层的物相结构。结果表明,NiO、Cr_2O_3和NiCr_2O_4是形成表面氧化层的三种主要物相。(3)基于Ostwald熟化理论,分析γ"相的热稳定性和粗化过程。结果表明,γ"相的粗化符合Ostwald熟化理论,在时效4.541×103h后γ"相在粗化速度较快方向上的尺寸开始趋于一致,其最大平均尺寸为0.24253μm,且在时效过程中γ"相的形貌尺寸分布与该理论中似稳态分布函数的描述高度吻合。同时发现γ"相的相变动力学曲线满足Avrami方程,并求得阿弗拉密指数n约为1符合试验中的实际情况。(4)通过对合金力学性能的测试结合断口形貌观察,分析合金组织与性能的联系,并以修正后的Hollomon模型,求得加工硬化曲线与硬化指数。结果表明,合金中主要强化相的含量与其力学性能相关联;利用加工硬化曲线可求得,硬化在交滑移控制开始时的位错密度值为2.55858×1011cm-2,而该模型下的硬化指数则与应变相关。(5)将国产GH625合金与国际镍公司在相同成型方式和热处理工艺条件下,生产的Inconel 625合金的力学性能进行对比。结果表明,国产GH625合金在主要的室温力学性能指标上差别不明显,但在700℃左右的条件下经长时时效后,在拉伸强度和塑性方面均不及Inconel 625合金。从强化相的析出过程来看主要原因是,国产GH625合金的主要强化γ"相的粗化较快,热稳定性不如Inconel 625合金,导致在本次时效试验的后期大量的δ相过早析出,基体中的固溶元素含量不断减少,弱化了固溶强化的效果所致。(6)对比欧洲700℃超超临界机组(耐热部件)的选材标准。结果表明,该批次合金在720℃下,在105h时效后其氧化失重粗略估算为4.45×10-3g/mm2,满足选材的适用性要求,但在高温环境下合金长期服役过程中组织的稳定性还需提高。
[Abstract]:In order to strengthen the high-end application of domestic high temperature alloy in the civil field, and from the current stage, our power system needs to develop ultra supercritical thermal power technology urgently in order to meet the demand of low pollution energy for economic development. This paper selects GH625 alloy as a candidate material for the heat-resistant components of a super supercritical unit at 700 C as the research object. The changes in the microstructure and mechanical properties of a homemade GH625 alloy at 720 C at 720 C were investigated by drawing electron, energy spectrum, diffraction and transmission electron. The changes of microstructure and mechanical properties of a homemade GH625 alloy at 720 C were investigated in order to provide reference for the practical application of domestic alloy. The results are as follows: (1) through research After aging at 720 C, the evolution process of the precipitated phase and tissue after 1 x 103 h, 3 x 103 h and 5 x 103 h is found. It is found that the decomposition and transformation of carbides, the precipitation and growth of the phase and delta phase are the main factors affecting the change of grain boundary morphology, and the grain boundary morphology shows the first coarse-grained and then coarsening changes with the aging time. The main precipitates in the crystal are precipitated in the order of gamma ", gamma" and delta phase in the crystal, and with the time prolonging of the crystal memory in the gamma "phase to delta phase, the overcoarsening of the phase of gamma" is the main factor of this transformation. The internal precipitation phase of the aged 1 * 103h is dominated by the uniform distribution of gamma and gamma phase, and the distribution of the precipitate phase in the aging 3 * 103h is not distributed. Homogeneous, gamma, gamma and delta phase appear in the matrix. After aging 5 * 103h, the precipitates in the crystal are mainly delta phase. (2) X-ray diffraction analysis is used to determine the phase structure of the surface oxidation layer of the heat storm after different aging time. The results show that NiO, Cr_2O_3 and NiCr_2O_4 are the three main phases of the formation of the surface oxidation layer. (3) based on the Ostwald ripening. The theory is to analyze the thermal stability and coarsening process of the gamma phase. The results show that the roughening of the gamma phase conforms to the Ostwald ripening theory. The size of the phase in the fast direction of the roughening rate begins to conform to the size of 0.24253 m after the aging of 4.541 * 103h, and the size distribution of the gamma phase in the aging process is similar to that in the theory. The description of the distribution function is highly consistent. At the same time, it is found that the phase transformation kinetics curve of the phase satisfies the Avrami equation and the AMF n index is about 1 in accordance with the actual conditions in the experiment. (4) the relationship between the microstructure and properties of the alloy is analyzed by the test of the mechanical properties of the alloy and the fracture morphology, and the modified Hollomon model is obtained. The results show that the main hardening phase content in the alloy is related to the mechanical properties of the alloy, and the dislocation density value at the start of the cross slip control is 2.55858 * 1011cm-2 by the processing hardening curve, and the hardening exponent under this model is related to the strain. (5) the domestic GH625 alloy and the international The mechanical properties of Inconel 625 alloy produced in the same molding and heat treatment conditions were compared. The results showed that the difference in the main mechanical properties of GH625 alloy was not obvious, but under the condition of long time aging at about 700 C, the tensile strength and plasticity of the alloy were less than that of Inconel 625. From the precipitation process of the enhanced phase, the main reason is that the main intensification of the GH625 alloy in China is that the coarsening of the phase is faster and the thermal stability is not as good as the Inconel 625 alloy, which leads to the early precipitation of a large number of delta phase in the later period of this time test, the content of solid solution elements in the matrix is less and less, and the effect of solid solution strengthening is weakened. (6) contrast Europe. The material selection standard of the 700 C super supercritical unit (heat-resistant unit) at 700 C shows that the weight of the batch alloy at 720 C is roughly estimated at 4.45 x 10-3g/mm2 after aging, which meets the application requirements of the material, but the stability of the fabric in the long service process of the alloy needs to be improved in the high temperature environment.

【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG132.3

【参考文献】