【作者】 胡超；

【导师】 张鹏；

【作者基本信息】 哈尔滨工业大学 ， 材料工程， 2015， 硕士

【摘要】 GH4698镍基高温合金是一种广泛应用于航空航天领域的合金,在高温下机械性能良好,抗氧化性能和抗疲劳特性优良,制成的涡轮盘等部件使用可靠性较高。此种合金由于含有大量强化机体的添加元素因此强度硬度非常高,在室温下其强度可达到钢材的数倍以上,该合金的塑性成形需要在高温下进行,因此掌握高温下GH4698合金的塑性流动行为以及最佳锻造工艺就显得尤为重要。研究表明金属的本构方程可描述其塑性流动行为,而金属热加工图可以确定最佳锻造工艺,故在本文中对它们展开了研究。本文中利用MTS810.13试验机获得了GH4698高温合金在1223K~1423K温度范围内的热压缩真应力-应变曲线,通过分析所得到的不同应变速率下的应力数据研究了该合金的流动应力与变形温度及应变速率等参数之间的关系,发现同一温度下材料的流动应力值随着应变速率的增大而增大,同一应变速率下材料的流动应力值随着温度的升高而减小,且所有应力-应变曲线的形状都是相似的。为了描述GH4698高温合金的塑性流动行为,本文中基于两种不同的数学模型分别建立了材料在高温下的本构方程。通过综合分析所建立的本构方程的精确度、误差分布情况以及计算量最终得出文中选用的基于考虑应变影响的Arrhenius模型和学者修正后的Zerilli-Armstrong模型所建立的本构关系精度都比较好,但学者修正后的Zerilli-Armstrong模型计算量较大且误差分布区间较广,因此考虑应变影响的Arrhenius本构模型计算更方便,且在预测单个应力时误差更小。为了确定GH4698高温合金的最佳锻造工艺,本文中基于相关准则建立了此合金在特定温度范围内的热加工图。通过分析加工效率图的高效区间得知该金属在高温、中等应变速率变形条件下加工效率值较高,通过分析失稳图上的失稳区间可知该金属主要在低温、低应变速率和高温、高应变速率变形条件下容易发生流变失稳。最终通过分析及实验验证得出该金属在温度为1300K~1423K、应变速率在0.01s-1~1s-1时加工性能最好,此时即可保证加工效率较高又不会出现流变失稳现象。为了研究GH4698高温合金在热变形过程中的回复再结晶现象,本文中通过相关理论研究发现材料在临界应变位置其加工硬化率曲线会出现拐点特征,基于此建立起了该金属的临界应变方程以及回复再结晶体积分数方程,通过分析晶粒尺寸与不同参数之间的关系并基于相关模型建立起了该金属的再结晶晶粒长大模型,通过对比分析试验所测得的实际晶粒尺寸与模型预测尺寸发现此模型误差较小,可用来描述该金属在热变形或热处理过程中的晶粒长大现象。更多还原

【Abstract】 GH4698 superalloy is a kind of alloy which is widely used in aviation and space industry. This alloy shows outstanding mechanical properties, anti-oxidant and anti-fatigue performance under high temperature. Components like turbine disks which are made of this superalloy have high application reliability. The strength and hardness of this alloy are very strong because it contains abundant adding elements which intensify matrix body, so the strength of this superalloy at room temperature can be several times over steel. The plastic forming process of the alloy needs to be done under high temperature. Therefore, it is of great importance to understand the plastic deformation behavior and find out the best forging parameter of GH4698 superalloy.Researches have indicated the constitutive modeling of metal can describe the plastic deformation behavior while hot process map of metal is defined as a powerful tool to determine the best forging parameters. Thus, study on them is carried out in this dissertation.The true strain-stress curves of GH4698 superalloy between temperatures range of1223K~1423K were obtained by making use of MTS810.13 test machine in this dissertation. The stress data under different strain rates were analyzed and the relations among flow stress, deformation temperature, strain rate and other parameters of this alloy were also discussed. It turns out that the flow stress of material increases with the increase of strain rate under the same temperature; the flow stress of material decreases with the rise of temperature under the same strain rate. Additionally, the shapes of all true strain-stress curves are similar with each other.In order to describe the plastic deformation behavior of GH4698 superalloy, this dissertation builds up the constitutive modeling of the metal under high temperature by using two different mathematical models. A comprehensive analysis was also made on precision, error distribution and amount of calculation of the established constitutive modeling. The result shows that the constitutive relations, built from the Arrhenius model and modified Zerilli-Armstrong model, are all quite precise in this dissertation.However, the modified Zerilli-Armstrong model has a huge amount of calculation and wide distribution interval of error. Considering the influence of strain, Arrhenius constitutive model is more convenient to calculate and has less error in predicting every single stress.In order to determine the best forging parameters of GH4698 superalloy, based on correlation criterion, this dissertation establishes the hot processing map of this alloy under particular temperature range. Through the full analyze of the domains on theestablished hot process efficiency map, the high process efficiency domain of this metal were finally found under high temperature, moderate strain rate deformation situation.Meanwhile, the instability domains on the instability map shows that flow instability will occur when this metal is under the condition of low temperature with low strain rate or high temperature with high strain rate. Eventually, through the analysis and tests, it is confirmed this metal shows best processing property under temperature range of1300K~1423K with strain rate range of 0.01s-1~1s-1. At this time, a higher process efficiency can be guaranteed without instability flow phenomenon.So as to research the dynamic recrystallization phenomenon of GH4698 superalloy in hot deformation process, and according to some relevant theories, this dissertation founds out that the process hardening rate curve of material will show a inflection point feature at the critical strain location. Based on this feature, the equations of critical strain and recrystallization volume fraction were both established. By analyzing the relationship between grain size and different parameters, the grain growth model of this superalloy was also established. Experiments were carried out to make a comparative analysis of the actual grain size and the predicted grain size. The result shows that this established grain growth model has little error and can be used to describe the grain growth phenomenon of this metal in the process of hot deformation or heat treatment.更多还原