【作者】 丁丽锋；

【导师】 孙锋； 沈红卫；

【作者基本信息】 上海交通大学 ， 材料科学与工程， 2011， 硕士

【摘要】 GH80A合金是以Ni-Cr为基体的高温合金,通过添加一定量的Al、Ti,并进行时效处理,形成??强化相获得强化,同时由于加入了微量B元素使晶界也得到了极大的强化。为了加快该合金在超超临界发电机组的使用,迫切要求自行掌握该钢种的性能数据和组织演化,以便更安全的使用。本文采用热力学计算、高分辨扫描电镜、综合相分析、力学性能测试等多种手段的综合分析方法,研究了GH80A合金的基本组织,不同热处理制度下强化相的析出规律以及高温长期时效后组织的稳定性;此外还利用热模拟机(Gleeble-3500)对GH80A合金锻造工艺进行模拟,分析GH80A合金动态再结晶机制及晶粒长大动力学,双重晶粒度的组织特性分析及对材料性能的影响。结果发现:热处理制度的研究得出GH80A合金较佳固溶温度为1080℃,845℃/24h/AC+700℃/16h/AC的两段时效处理使合金中析出大小两种尺寸?′相,两种尺寸?′相的配合有利于获得良好的综合性能。微观组织观察和化学相分析表明,标准热处理态的GH80A合金中,细小的?′相粒子均匀分布在γ基体中,?′相的平均尺寸约为50nm。颗粒状M7C3和M23C6碳化物粒子在晶界以不连续状态析出。其中?′相含量为17.713%,M7C3和M23C6的总量为0.636%,此外还有少量MC碳化物。热力学相计算表明GH80A合金中的主要平衡析出相为?′相和MC,M7C3,M23C6三种碳化物,没有TCP有害相的存在。随着Al、Ti含量的增加,?′相的析出量和析出温度均有显著增加;C含量的增加会显著提高MC, M7C3, M23C6三种碳化物的析出量,但对M7C3和M23C6析出温度的影响不大,而C含量的增加会显著提高MC的开始析出温度,增加MC的液析能力。合金在不同温度(550～750℃)下长期时效处理(200～5000h)后的组织稳定性研究得出,GH80A合金在550℃长期时效过程中,晶内γ’相大小基本不变,组织非常稳定。从600℃,650℃和700℃时效1000h的组织来看,合金的组织亦比较稳定。750℃高温时效时,随着时效时间的延长,γ’相数量逐步减少,尺寸增加,γ’相的形貌由球形向方形转变。锻造工艺加工的GH80A中存有复杂晶粒度结构。大的变形量与高的变形温度有利于形成均匀的晶粒结构。相同变形量时,高的变形温度,也更有利于形成均匀的晶粒结构,变形温度越高,得到的DRX晶粒度越大。相同变形温度时,大的变形量更有利于形成均匀的晶粒结构,变形量越大,得到的DRX晶粒度越细小。变形速率越大,再结晶晶粒也越细小。通过对动态再结晶机制的研究得出,在1000℃以上的变形温度下,动态再结晶是以原始晶界弓出形核,表现为非连续动态再结晶;而在950℃时,动态再结晶是以亚晶旋转形核,表现为连续动态再结晶。由此得到的均匀组织的最小晶粒尺寸为4μm (1000℃,变形速率为1s-1);而950℃下可得到2.3μm的再结晶晶粒尺寸,但是为不均匀的组织。不同原始组织750℃,310MPa条件下的持久蠕变显示,平均晶粒度越大,蠕变及持久性能越好;而组织越均匀,持久时间越长,实验结果波动也较小。更多还原

【Abstract】 GH80A is a high temperature alloy as Ni-Cr matrix,by adding a certain amount of Al,Ti and conducting aging process,it would form the strengthening phase ??. Besides,the grain boundary have been strengthened by adding the element B.In order to speed up the use of GH80A,we need to master the property data and structure evolution of this alloy for safer use.This paper utilized thermodynamic calculation,SEM,analysis of comprehensive phase and mechanical properties test to investigate the basic structure of GH80A,the precipitation law of strengthen phase under different heat treatment,the stability of structure after long-term aging under high temperature.In addition,this paper simulated the forging process of GH80A by thermal simulationmachine(Gleeble-3500) to analyze dynamic recrystallization mechanism,grain growth dynamics,the structure characteristic and effect on material properties of double-level grain size.The results are as follows:The research of heat treatment showed the proper solution temperature of GH80A is 1080℃.Two aging process of 845℃/24h/AC+700℃/16h/AC made the precipitation of two different size ??.Two size ?? phase is conducive to gain great comprehensive properties.Microstructural observation and analysis of chemical phase showed that in the GH80A which is under standard heat treatment statement,the ?? phase particles uniformly distribute in theγmatrix,the average size of ?? phase is about 50nm.M7C3 and M23C6 carbide particles are precipitating as non-continuous state on grain boundary.The content of ?? phase is 17.713%,the total content of M7C3 and M23C6 is 0.636% and a small amount of MC carbides.The thermodynamic calculation showed that the main balance precipitation phases of GH80A are ??,MC,M7C3 and M23C6.There is no harmful phase TCP.With the increasing of Al,Ti,the precipitation amount of ?? phase and precipitation temperature significantly increased;The increasing content of C significantly increase the precipitation amount of MC,M7C3 and M23C6 but have little effect on the precipitation temperature of the M7C3 and M23C6.The increasing content of C would significantly enhance the start precipitation temperature of MC,raise the liquid precipitation capacity of MC.The structure stability investigation of alloy under different temperature (550~ 750℃) and long-term aging treatment (200~ 5000h) showed,during long-term aging treatment at 550℃,the size of ?? phase is essentially constant,the structure is stable.The structure of alloy under 600℃,650℃and 700℃,1000h aging treatment is also stable.During the high temperature aging under 750℃,with the extension of aging time,the amount of ?? phase gradually reduce and the size get larger.The morphology of ?? phase change from ball to square.GH80A under forging process have complex grain size structure.Large deformation and high deformation temperature is conducive to the formation of uniform grain structure.The higher deformation temperature is more conducive to the formation of uniform grain structure when the deformation is the same,the higher deformation temperature make the grain size of DRX larger.Larger deformation is more conducive to form uniform grain structure under same deformation temperature.The larger deformation make the grain size of DRX smaller.The higher deformation rate make the recrystallization grain more fine.The investigation of dynamic recrystallization mechanism obtained,when the deformation temperature is above 1000℃,dynamic recrystallization take the nucleation from original grain boundary as non-continuous dynamic recrystallization.The dynamic recrystallization take nucleation from the subgrain rotation as continuous dynamic recrystallization when the temperature is 950℃.The smallest grain size of uniform structure is 4μm (1000℃,the deformation rate of 1s-1);and it could also get recrystallized grain size of 2.3μm under 950℃but for non uniform structure.The sustained creep of different original structure under 750℃,310Mpa indicated that larger average grain size make the better creep and rupture properties;the much more uniform structure and longer time make less volatile research results.更多还原