难熔金属元素对模型Ni-Al-Cr基高温合金相析出行为影响研究
发布时间：2019-05-09 05:28
【摘要】：镍基高温合金由于其独特的双相组织而具备优异的高温机械性能和抗氧化等综合性能,已成为制造先进航空航天发动机和燃气轮机叶片的主要材料。现代商用镍基合金大多在Ni-Al-Cr三元系基础上添加多种合金元素(尤其是难熔金属元素)制备而成。这些难熔金属元素同时分布于γ(FCC)和γ'(L12)两相,主导合金的相析出行为,对合金显微组织和高温力学性能有决定性的影响。因此,开展难熔金属元素对镍基合金相析出行为影响的研究,为高性能合金优化设计提供理论指导,具有一定的科学意义及实践价值。本课题在美国西北大学原子探针技术中心开展的镍基高温合金及难熔金属元素添加对合金性能影响研究体系基础上,采用原子探针层析技术(Atom probe tomography,APT)和第一性原理等实验和理论方法,针对不同固溶时效参数下的多种模型Ni-Al-Cr基合金,研究分析难熔金属元素R(W、Re、Ru、Ta)对模型合金纳米结构、化学成分及界面特征的影响,主要研究内容及结论如下:(1)探索难熔金属元素W、Re交互作用对模型Ni-Al-Cr基合金析出相纳米结构演化的影响。利用APT实现元素原子的三维重构,实验结果显示,在淬火状态下的合金中,已有球形γ'相颗粒析出。淬火状态和时效0.25 h时,部分γ'相颗粒由脖颈连通,说明在早期粗化阶段,经典Ostwald熟化机制和析出相颗粒合并机制共存。随着时效时间延长,析出相平均半径不断增大,数量密度则不断降低。在析出相体积分数稳定时效期间,平均半径和数量密度粗化时间指数和UO模型预测值接近,说明合金至少处于准稳态粗化状态。(2)分析W、Re对模型Ni-Al-Cr基合金化学演化的影响,测试分析相析出过程中合金元素在两相和界面区域的分布规律。结果显示,在整个时效过程中,Ni的两相浓度无明显变化,Al、W元素不断扩散进入γ'相,Cr、Re元素则倾向流入基体相。W、Re元素扩散性能较差,在两相中的分配演化速率缓慢,因此,添加W、Re可减缓合金成分平衡进程。合金界面宽度值随时效时间延长而变小,时效256 h后,标准化界面宽度趋于零,说明长期时效后合金的界面区域非常狭窄。(3)结合APT和显微硬度测试结果,针对系统添加难熔金属元素的多种模型Ni-Al-Cr基合金,开展长期时效后合金元素分布规律研究。研究结果表明,难熔金属元素Re、Ru优先分配至γ相,W、Ta原子则更多分布在γ'相中,4种元素均优先占据γ'(L12)相的Al位。添加难熔金属元素后,更多Ni原子停留于γ相中。难熔金属元素可强化Al、Cr两相分配行为,提高析出相体积分数,对两者的强化效果遵循同样规律。得益于难熔金属元素的固溶强化作用与γ'相体积分数的增长,合金硬度提高。(4)分析模型Ni-Al-Cr基合金长期时效后仍然存在的Ni界面过剩现象,探索添加难熔金属元素对界面偏聚行为的影响机制。结合实验APT径向分布函数以及第一性原理计算结果,对R(W、Re、Ru、Ta)和S(S=Al、Cr)原子结合能进行计算,并分析R和S原子之间的空间相关性和结合能状态。分析结果显示,难熔金属元素和溶质元素原子之间存在化学结合能,R-S结合能会改变进出γ'相元素的扩散流矢量,增大界面区域宽度,导致界面处Ni原子局部富集和贫化行为更为显著。由于难熔金属元素在基体中扩散速率相对较慢,R-Cr吸引结合能将减缓溶质扩散流,导致Ni扩散性能下降,阻滞Ni原子在界面附近的迁移。
[Abstract]:The nickel-based high-temperature alloy has excellent high-temperature mechanical property and oxidation resistance due to its unique dual-phase structure, and has become the main material for manufacturing advanced aerospace engine and gas turbine blade. Modern commercial nickel-based alloys are mostly prepared by adding various alloying elements (especially refractory metal elements) on the basis of the Ni-Al-Cr ternary system. These refractory metal elements are also distributed in the two phases of the two phases of the metal (FCC) and the sulfur (L12), and the phase precipitation behavior of the main alloy has a decisive influence on the microstructure and the high-temperature mechanical properties of the alloy. Therefore, the research on the influence of the refractory metal elements on the precipitation behavior of the nickel-based alloy is carried out, In order to provide theoretical guidance for high-performance alloy optimization design, it is of scientific significance and practical value. The nickel-based high-temperature alloy and refractory metal element in the technology center of the atomic probe of Northwestern University of the United States have been added to the research system of the effect of the alloy on the properties of the alloy. Based on the experimental and theoretical methods of atomic probe tomography (APT) and the first principle, a variety of Ni-Al-Cr based alloys with different solution aging parameters were studied, and the nano-structure of the model was studied by the study of the refractory metal elements R (W, Re, Ru, Ta). The main research contents and conclusions are as follows: (1) The influence of the interaction of refractory metal elements W and Re on the evolution of the precipitation phase of the model Ni-Al-Cr based alloy is studied. The three-dimensional reconstruction of the element atoms is realized by APT, and the results show that, In the alloy in the quenching state, the spherical graphite 'phase particles are precipitated. In that quench state and the age of 0.25 h, some of the phase-phase particles are in communication with the neck, which indicate that the classical Ostwald ripening mechanism and the precipitation-phase particle combine mechanism coexist in the early coarsening stage, and the average radius of the precipitated phase increases as the aging time is prolonged. (2) analyzing the effect of W and Re on the chemical evolution of the model Ni-Al-Cr based alloy, The distribution of the alloying elements in the two phases and the interface region during the precipitation process of the test and analysis phase is studied. The results show that, during the whole aging process, the two-phase concentration of Ni is not obviously changed, and the Al and W elements continue to diffuse into the matrix phase, and the elements of Cr and Re tend to flow into the matrix phase. W, Re element diffusion performance is poor, the distribution and evolution rate of the two phases is slow, and therefore, adding W and Re can slow down the balance process of the alloy composition. The interface width of the alloy becomes smaller at any time, and after the aging is 256 h, the width of the standardized interface tends to be zero, which indicates that the interface region of the alloy after the long-term aging is very narrow. And (3) combining the results of APT and microhardness test, and carrying out the study on the distribution of the alloy elements after long-term aging for various models of Ni-Al-Cr based alloy with refractory metal elements added to the system. The results show that the refractory metal elements Re and Ru are preferentially distributed to the Al phase, W and Ta atoms are more distributed in the 1 'phase, and the four elements preferentially occupy the Al position of the 1' (L12) phase. After the addition of the refractory metal elements, the more Ni atoms stay in the conductive phase. The refractory metal element can strengthen the two-phase distribution of Al and Cr, improve the volume fraction of the precipitated phase, and observe the same law for the strengthening effect of the two phases. due to the increase of the solid solution strengthening effect of the refractory metal element and the volume fraction of the graphite ', the hardness of the alloy is improved. (4) the Ni-Al-Cr based alloy still has an excess of the Ni interface after the long-term aging of the Ni-Al-Cr based alloy, The binding energy of R (W, Re, Ru, Ta) and S (S = Al, Cr) is calculated by combining the radial distribution function of APT and the calculation result of the first principle. and the spatial correlation and the binding energy state between the R and S atoms are analyzed. The analysis results show that the chemical binding energy exists between the refractory metal element and the solute element atom, the binding energy of the R-S changes the diffusion flow vector of the element of the inlet and outlet ', and the width of the interface area is increased, Resulting in a more significant local enrichment and depletion behavior of the ni atoms at the interface. Because the diffusion rate of the refractory metal elements in the matrix is relatively slow, the binding energy of the R-Cr will slow the diffusion of the solute, resulting in a decrease in the diffusion of the Ni and the blocking of the migration of the Ni atoms in the vicinity of the interface.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG132.3
本文编号：2472512
[Abstract]:The nickel-based high-temperature alloy has excellent high-temperature mechanical property and oxidation resistance due to its unique dual-phase structure, and has become the main material for manufacturing advanced aerospace engine and gas turbine blade. Modern commercial nickel-based alloys are mostly prepared by adding various alloying elements (especially refractory metal elements) on the basis of the Ni-Al-Cr ternary system. These refractory metal elements are also distributed in the two phases of the two phases of the metal (FCC) and the sulfur (L12), and the phase precipitation behavior of the main alloy has a decisive influence on the microstructure and the high-temperature mechanical properties of the alloy. Therefore, the research on the influence of the refractory metal elements on the precipitation behavior of the nickel-based alloy is carried out, In order to provide theoretical guidance for high-performance alloy optimization design, it is of scientific significance and practical value. The nickel-based high-temperature alloy and refractory metal element in the technology center of the atomic probe of Northwestern University of the United States have been added to the research system of the effect of the alloy on the properties of the alloy. Based on the experimental and theoretical methods of atomic probe tomography (APT) and the first principle, a variety of Ni-Al-Cr based alloys with different solution aging parameters were studied, and the nano-structure of the model was studied by the study of the refractory metal elements R (W, Re, Ru, Ta). The main research contents and conclusions are as follows: (1) The influence of the interaction of refractory metal elements W and Re on the evolution of the precipitation phase of the model Ni-Al-Cr based alloy is studied. The three-dimensional reconstruction of the element atoms is realized by APT, and the results show that, In the alloy in the quenching state, the spherical graphite 'phase particles are precipitated. In that quench state and the age of 0.25 h, some of the phase-phase particles are in communication with the neck, which indicate that the classical Ostwald ripening mechanism and the precipitation-phase particle combine mechanism coexist in the early coarsening stage, and the average radius of the precipitated phase increases as the aging time is prolonged. (2) analyzing the effect of W and Re on the chemical evolution of the model Ni-Al-Cr based alloy, The distribution of the alloying elements in the two phases and the interface region during the precipitation process of the test and analysis phase is studied. The results show that, during the whole aging process, the two-phase concentration of Ni is not obviously changed, and the Al and W elements continue to diffuse into the matrix phase, and the elements of Cr and Re tend to flow into the matrix phase. W, Re element diffusion performance is poor, the distribution and evolution rate of the two phases is slow, and therefore, adding W and Re can slow down the balance process of the alloy composition. The interface width of the alloy becomes smaller at any time, and after the aging is 256 h, the width of the standardized interface tends to be zero, which indicates that the interface region of the alloy after the long-term aging is very narrow. And (3) combining the results of APT and microhardness test, and carrying out the study on the distribution of the alloy elements after long-term aging for various models of Ni-Al-Cr based alloy with refractory metal elements added to the system. The results show that the refractory metal elements Re and Ru are preferentially distributed to the Al phase, W and Ta atoms are more distributed in the 1 'phase, and the four elements preferentially occupy the Al position of the 1' (L12) phase. After the addition of the refractory metal elements, the more Ni atoms stay in the conductive phase. The refractory metal element can strengthen the two-phase distribution of Al and Cr, improve the volume fraction of the precipitated phase, and observe the same law for the strengthening effect of the two phases. due to the increase of the solid solution strengthening effect of the refractory metal element and the volume fraction of the graphite ', the hardness of the alloy is improved. (4) the Ni-Al-Cr based alloy still has an excess of the Ni interface after the long-term aging of the Ni-Al-Cr based alloy, The binding energy of R (W, Re, Ru, Ta) and S (S = Al, Cr) is calculated by combining the radial distribution function of APT and the calculation result of the first principle. and the spatial correlation and the binding energy state between the R and S atoms are analyzed. The analysis results show that the chemical binding energy exists between the refractory metal element and the solute element atom, the binding energy of the R-S changes the diffusion flow vector of the element of the inlet and outlet ', and the width of the interface area is increased, Resulting in a more significant local enrichment and depletion behavior of the ni atoms at the interface. Because the diffusion rate of the refractory metal elements in the matrix is relatively slow, the binding energy of the R-Cr will slow the diffusion of the solute, resulting in a decrease in the diffusion of the Ni and the blocking of the migration of the Ni atoms in the vicinity of the interface.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG132.3
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