GH99高温合金高温变形行为及组织演化规律研究

发布时间：2018-05-29 19:08

本文选题：GH99高温合金 + 高温变形　；参考：《哈尔滨工业大学》2015年博士论文

【摘要】：GH99是一种典型的γ′相强化型镍基高温合金,合金中的W、Mo、Co等元素可以起到固溶强化作用,B、Ce、Mg等元素可以起到晶界强化作用。该合金具有优良的高温力学性能,抗蠕变性能和耐腐蚀性能,目前主要用于航空航天的发动机中。该合金的最高使用温度可以达到1000℃,是使用温度较高的一种高温合金。该合金的热变形行为对温度和应变速率等工艺参数非常敏感,其变形抗力很大,成形非常困难。GH99合金的合金化程度很高,其在高温条件下的组织演变非常复杂,而且高温变形时的工艺参数也会对该合金的微观组织造成很大影响,其组织控制难度很大。此外,该合金中存在大量的退火孪晶,探索退火孪晶在热处理过程及高温变形过程中的演化规律也十分必要。本文研究了GH99合金热处理过程中的组织演化特点,采用高温压缩实验研究该合金的高温变形力学行为,同时探索了该合金高温变形过程中动态再结晶组织以及退火孪晶的演化规律。通过对该合金进行热处理实验,得到了合金中Σ3晶界和γ′相在不同热处理条件下的演化规律。固溶处理过程中,随着固溶温度的升高和保温时间的延长,Σ3晶界体积分数会呈现出先增大后减小的趋势。时效处理过程中,Σ3晶界结构非常稳定,且其体积分数变化不大,一直维持在0.553~0.633范围内。此外,随着时效温度的升高和保温时间的延长,合金中γ′相的粗化现象明显,其长大激活能约为248.8kJ/mol。随着γ′相的逐渐长大,部分γ′相形状会由球形变成方形。通过研究该合金的高温变形力学行为,建立了该合金在加工硬化-动态回复阶段和动态再结晶阶段的本构方程,并验证了该本构方程的准确性。同时,利用Arrhenius方程计算出了该合金的热变形激活能,Q=427.626kJ/mol。基于DMM模型,建立了GH99合金不同应变下的功率耗散图,结合微观组织观察得到了该合金成形的最佳工艺参数为:温度区间1090-1160℃,应变速率区间0.01-0.3s-1。利用四种失稳判据(Prasad、Murty、Gegel和Malas)绘制GH99合金在真应变为0.65时的热加工图,结合微观组织观察发现了该合金的两个失稳区:第一个位于温度区间1010~1080℃,应变速率区间0.16~1s-1范围内;第二个位于温度区间1080~1160℃,应变速率区间0.32~1s-1范围内。通过微观组织观察发现GH99合金热成形过程中失稳变形的主要机制是局部流动和绝热剪切带。利用EBSD技术,对GH99合金高温压缩过程中动态再结晶组织的演化规律进行了深入研究。结果表明:随着变形温度的升高和应变速率的减小,动态再结晶晶粒尺寸与其体积分数会不断增大。依据动态再结晶组织随着工艺参数的演化规律,建立了该合金的动态再结晶动力学模型和动态再结晶晶粒尺寸预测模型。此外,GH99合金的动态再结晶形核机制主要包括两种:不连续动态再结晶与连续动态再结晶。虽然这两种机制在该合金的高温变形过程中同时进行,但连续动态再结晶只是一种辅助形核机制。不连续动态再结晶包括晶粒形核与长大两个过程,其中长大过程在高温低应变速率条件下占主导地位,而形核在低温高应变速率条件下占据主导地位。连续动态再结晶虽然只是一种辅助机制,但是它在高温变形的初始阶段得到一定强化,随着应变的增大,它的作用再次削弱。此外,连续动态再结晶的作用还会随着变形温度的升高而削弱,随着应变速率的增大而增强。利用EBSD技术,对GH99合金高温压缩过程中退火孪晶的演化规律进行了深入研究。结果表明:高温压缩初始阶段,原始晶粒内部的Σ3n(n=1,2,3)晶界大量消失,导致Σ3n(n=1,2,3)晶界的体积分数和Σ3晶界密度降低。随着应变的逐渐增大,大量的Σ3晶界在动态再结晶组织中以共格Σ3晶界的形式出现,从而导致Σ3n(n=1,2,3)晶界的体积分数和Σ3晶界密度逐渐增大。此外,在GH99合金高温变形过程中,新的Σ3晶界主要通过偶然生长机制形成,而Σ9和Σ27晶界则主要通过晶界再生机制形成。此外,随着变形温度的升高和应变速率的减小,该合金中的Σ3n(n=1,2,3)晶界体积分数和Σ3晶界密度都会呈现出先增大而后减小的趋势,而Σ3晶界中共格Σ3晶界的比例则会不断增大。
[Abstract]:GH99 is a typical type of Ni based superalloy of gamma phase intensification. The elements such as W, Mo, and Co in the alloy can play a solid solution strengthening effect. B, Ce, Mg and other elements can enhance the grain boundary. The alloy has excellent high temperature mechanical properties, vermicular resistance and corrosion resistance. The alloy is mainly used in aero and aerospace engines. The maximum use temperature can reach 1000 C, a high temperature alloy. The thermal deformation behavior of the alloy is very sensitive to the temperature and strain rate, its deformation resistance is great, the forming is very difficult and the alloying degree of.GH99 alloy is very high. The microstructure evolution of the alloy at high temperature is very complex, and the high temperature is very high. The process parameters of the deformation will also have a great influence on the microstructure of the alloy, and its microstructure is difficult to control. In addition, there are a large number of annealing twins in the alloy. It is necessary to explore the evolution law of annealing twins during heat treatment and high temperature deformation. In this paper, the structure of the heat treatment of GH99 alloy was studied. The mechanical behavior of high temperature deformation of the alloy was studied by high temperature compression test. At the same time, the evolution law of dynamic recrystallization and annealing twins in the process of high temperature deformation was explored. Through the heat treatment experiment on the alloy, the evolution law of the grain boundary and gamma phase in the alloy under different heat treatment conditions was obtained. In the process of solid solution treatment, with the increase of the solid solution temperature and the prolongation of the holding time, the volume fraction of the grain boundary of the sigma 3 will increase first and then decrease. During the aging treatment, the structure of the sigma 3 grain boundary is very stable, and its volume fraction is not changed much, and it is kept in the range of 0.553~0.633. In addition, with the increase of aging temperature and heat preservation The growth activation energy of the alloy is about 248.8kJ/mol. with the gradual growth of the gamma phase, and the shape of partial gamma phase will turn from spherical to square. By studying the mechanical behavior of the alloy at high temperature, the constitutive model of the alloy in the stage of working hardening dynamic recovery and dynamic recrystallization is established. The accuracy of the constitutive equation is verified. At the same time, the thermal deformation activation energy of the alloy is calculated by Arrhenius equation. Based on the DMM model, the power dissipation diagram of the GH99 alloy under different strain is established. The optimum process parameters of the alloy forming are obtained by observing the microstructure of the GH99 alloy. The temperature range is 1090-1160. The strain rate interval 0.01-0.3s-1. uses four Instability Criteria (Prasad, Murty, Gegel and Malas) to draw the thermal processing diagram of GH99 alloy at the true strain of 0.65. In combination with the microstructure observation, two instability regions of the alloy are found: the first is in the temperature range 1010~1080, the strain rate interval 0.16~1s-1 range, and the second at the temperature. It is found that the main mechanism of the instability deformation in the hot forming process of GH99 alloy is the local flow and the adiabatic shear band. The evolution law of the dynamic recrystallized microstructure of the GH99 alloy during the high temperature compression process is studied by the EBSD technology. The results show that the evolution of the dynamic recrystallized microstructure of the GH99 alloy during the high temperature compression process is deeply studied. The dynamic recrystallization grain size and its volume fraction will increase with the increase of the deformation temperature and the decrease of the strain rate. The dynamic recrystallization dynamic model and the dynamic recrystallization grain size prediction model of the alloy are established according to the evolution of the dynamic recrystallization structure. In addition, the dynamic remould of the GH99 alloy is reformed. The crystalline nucleation mechanism mainly includes two kinds: discontinuous dynamic recrystallization and continuous dynamic recrystallization. Although these two mechanisms are carried out at the same time during the high temperature deformation of the alloy, continuous dynamic recrystallization is only a auxiliary nucleation mechanism. The discontinuous dynamic recrystallization includes two processes of grain nucleation and growth, in which the growth process is high Under the condition of low temperature and low strain rate, the core is dominant at low temperature and high strain rate. Continuous dynamic recrystallization is only a auxiliary mechanism, but it is strengthened at the initial stage of high temperature deformation. With the increase of strain, its use is weakened again. In addition, the effect of continuous dynamic recrystallization is made. With the increase of deformation temperature and the increase of strain rate, the evolution of annealing twins in the process of high temperature compression of GH99 alloy was studied by EBSD technology. The results showed that the grain boundary of the sigma 3N (n=1,2,3) inside the original grain was disappearing in the initial stage of high temperature compression, leading to the grain boundary of the sigma 3N (n=1,2,3). The density of volume fraction and sigma 3 grain boundary decreases. As the strain increases, a large number of sigma 3 grain boundaries appear in the form of a common sigma 3 grain boundary in the dynamic recrystallized tissue, which leads to the increase of the volume fraction of the grain boundary and the density of the sigma 3 grain boundary in the sigma 3N (n=1,2,3). In addition, the new sigma 3 grain boundary is mainly produced by accidental birth during the high temperature deformation process of GH99 gold. The long mechanism is formed, while the grain boundary regeneration mechanism is mainly formed in the grain boundary of the sigma 9 and the sigma 27. In addition, the grain boundary volume fraction and the sigma 3 grain boundary density in the alloy will increase first and then decrease with the increase of the deformation temperature and the decrease of the strain rate, while the proportion of the grain boundary of the sigma 3N in the sigma 3 grain boundary will increase continuously. Big.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG132.3

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