本文選題：GH99高溫合金 + 高溫變形��； 參考：《哈爾濱工業(yè)大學》2015年博士論文

【摘要】：GH99是一種典型的γ′相強化型鎳基高溫合金,合金中的W、Mo、Co等元素可以起到固溶強化作用,B、Ce、Mg等元素可以起到晶界強化作用。該合金具有優(yōu)良的高溫力學性能,抗蠕變性能和耐腐蝕性能,目前主要用于航空航天的發(fā)動機中。該合金的最高使用溫度可以達到1000℃,是使用溫度較高的一種高溫合金。該合金的熱變形行為對溫度和應變速率等工藝參數(shù)非常敏感,其變形抗力很大,成形非常困難。GH99合金的合金化程度很高,其在高溫條件下的組織演變非常復雜,而且高溫變形時的工藝參數(shù)也會對該合金的微觀組織造成很大影響,其組織控制難度很大。此外,該合金中存在大量的退火孿晶,探索退火孿晶在熱處理過程及高溫變形過程中的演化規(guī)律也十分必要。本文研究了GH99合金熱處理過程中的組織演化特點,采用高溫壓縮實驗研究該合金的高溫變形力學行為,同時探索了該合金高溫變形過程中動態(tài)再結晶組織以及退火孿晶的演化規(guī)律。通過對該合金進行熱處理實驗,得到了合金中Σ3晶界和γ′相在不同熱處理條件下的演化規(guī)律。固溶處理過程中,隨著固溶溫度的升高和保溫時間的延長,Σ3晶界體積分數(shù)會呈現(xiàn)出先增大后減小的趨勢。時效處理過程中,Σ3晶界結構非常穩(wěn)定,且其體積分數(shù)變化不大,一直維持在0.553~0.633范圍內(nèi)。此外,隨著時效溫度的升高和保溫時間的延長,合金中γ′相的粗化現(xiàn)象明顯,其長大激活能約為248.8kJ/mol。隨著γ′相的逐漸長大,部分γ′相形狀會由球形變成方形。通過研究該合金的高溫變形力學行為,建立了該合金在加工硬化-動態(tài)回復階段和動態(tài)再結晶階段的本構方程,并驗證了該本構方程的準確性。同時,利用Arrhenius方程計算出了該合金的熱變形激活能,Q=427.626kJ/mol�；贒MM模型,建立了GH99合金不同應變下的功率耗散圖,結合微觀組織觀察得到了該合金成形的最佳工藝參數(shù)為:溫度區(qū)間1090-1160℃,應變速率區(qū)間0.01-0.3s-1。利用四種失穩(wěn)判據(jù)(Prasad、Murty、Gegel和Malas)繪制GH99合金在真應變?yōu)?.65時的熱加工圖,結合微觀組織觀察發(fā)現(xiàn)了該合金的兩個失穩(wěn)區(qū):第一個位于溫度區(qū)間1010~1080℃,應變速率區(qū)間0.16~1s-1范圍內(nèi);第二個位于溫度區(qū)間1080~1160℃,應變速率區(qū)間0.32~1s-1范圍內(nèi)。通過微觀組織觀察發(fā)現(xiàn)GH99合金熱成形過程中失穩(wěn)變形的主要機制是局部流動和絕熱剪切帶。利用EBSD技術,對GH99合金高溫壓縮過程中動態(tài)再結晶組織的演化規(guī)律進行了深入研究。結果表明:隨著變形溫度的升高和應變速率的減小,動態(tài)再結晶晶粒尺寸與其體積分數(shù)會不斷增大。依據(jù)動態(tài)再結晶組織隨著工藝參數(shù)的演化規(guī)律,建立了該合金的動態(tài)再結晶動力學模型和動態(tài)再結晶晶粒尺寸預測模型。此外,GH99合金的動態(tài)再結晶形核機制主要包括兩種:不連續(xù)動態(tài)再結晶與連續(xù)動態(tài)再結晶。雖然這兩種機制在該合金的高溫變形過程中同時進行,但連續(xù)動態(tài)再結晶只是一種輔助形核機制。不連續(xù)動態(tài)再結晶包括晶粒形核與長大兩個過程,其中長大過程在高溫低應變速率條件下占主導地位,而形核在低溫高應變速率條件下占據(jù)主導地位。連續(xù)動態(tài)再結晶雖然只是一種輔助機制,但是它在高溫變形的初始階段得到一定強化,隨著應變的增大,它的作用再次削弱。此外,連續(xù)動態(tài)再結晶的作用還會隨著變形溫度的升高而削弱,隨著應變速率的增大而增強。利用EBSD技術,對GH99合金高溫壓縮過程中退火孿晶的演化規(guī)律進行了深入研究。結果表明:高溫壓縮初始階段,原始晶粒內(nèi)部的Σ3n(n=1,2,3)晶界大量消失,導致Σ3n(n=1,2,3)晶界的體積分數(shù)和Σ3晶界密度降低。隨著應變的逐漸增大,大量的Σ3晶界在動態(tài)再結晶組織中以共格Σ3晶界的形式出現(xiàn),從而導致Σ3n(n=1,2,3)晶界的體積分數(shù)和Σ3晶界密度逐漸增大。此外,在GH99合金高溫變形過程中,新的Σ3晶界主要通過偶然生長機制形成,而Σ9和Σ27晶界則主要通過晶界再生機制形成。此外,隨著變形溫度的升高和應變速率的減小,該合金中的Σ3n(n=1,2,3)晶界體積分數(shù)和Σ3晶界密度都會呈現(xiàn)出先增大而后減小的趨勢,而Σ3晶界中共格Σ3晶界的比例則會不斷增大。
[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.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG132.3

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