Study On The Hot Deformation Behavior And Recrystallization Evolution Of Nimonic 80A Superalloy

Nimonic 80A is a nickel-based superalloy which is widely used in aerospace, nuclear power, chemical industry, shipbuilding industry and automobile industry due to its excellent corrosion, oxidation and creep resistance. Nimonic 80A superalloy belongs to deformation superalloy which is usually deformed by hot rolling or hot forging. Microstructure evolution such as dynamic recrystallization(DRX), metadynamic recrystallization(MDRX), static recrystallization(SRX) and grain growth will occur during hot working process, which has a great influence on the microstructure and property of the material. In addition, the hot working parameters such as deformation temperature, strain, strain rate and initial grain size have a great influence on the microsturcture evolution process. Therefore, study on the hot deformation behavior and microstructure evolution of Nimonic 80A superalloy is of great significance for the establishing and optimizing of hot working process as well as improving the quality of products. In this paper, DRX, MDRX, SRX and grain growth experiments were carried out. The austenite grain evolution behaviors of Nimonic 80A superalloy were studied. Then, a whole set of mathematical models which are used for investigating the microstructural evolutions of hot working process were obtained. The main research contents and conclusions of the thesis are as follows:1. In order to investigate the DRX behaviors of Nimonic 80A superalloy, a series of Gleeble-1500 isothermal single hot compression tests were performed under different deformation temperature and strain rate. The true strain-stress curves and microstructure were obtained and the effects of deformation temperature and strain rate on the DRX behaviors were discussed. The results reveal that the effects of deformation temperature, strain rate on the DRX behaviors are significant. The DRX grain size increases with the increase of deformation temperature or the decrease of the strain rate. According to the experimental results, the constitutive modle and the DRX kinetic model of Nimonic 80A superalloy were proposed. Based on the dynamic materials model(DMM), the processing maps under different strain were build. The results show that the high workability region locates at 1150?1180?, 0.1?1s-1.2. In order to investigate the MDRX behaviors of deformed Nimonic 80A superalloy, a series of Gleeble-1500 isothermal interrupted hot compression tests were performed under different inter-pass time, deformation temperature, strain rate, pre-strain and intial grain size. The true strain-stress curves and microstructure were obtained and the effect of deformation temperature, strain rate, pre-strain and intial grain size on the MDRX behaviors were discussed. The results reveal that the effects of deformation temperature, strain rate on the MDRX behaviors are significant while the effect of pre-strain and initial grian size are not obvious. The softening fraction increases with the increase of deformation temperature, strain rate and the MDRX grain size increases with the increase of deformation temperature or the decrease of the strain rate. Based on the experimental results, the MDRX kinetic model of Nimonic 80A superalloy was proposed.3. In order to investigate the MDRX behaviors of deformed Nimonic 80A superalloy, a series of Gleeble-1500 isothermal interrupted hot compression tests were performed under different inter-pass time, deformation temperature, strain rate, pre-strain and initial grain size. The true strain-stress curves and microstructure were obtained and the effect of deformation temperature, strain rate, pre-strain and intial grain size on the SRX behaviors were discussed. The results reveal that the effect of pre-strain on the SRX behaviors is significant while the initial grain size is not. The static softening fraction increases with the increase of deformation temperature, strain rate and pre-strain and the SRX grain size increases with the increase of deformation temperature or the decrease of the strain rate. Based on the experimental results, the SRX kinetic model of Nimonic 80A superalloy was proposed.4. In order to investigate the grain growth behaviors of Nimonic 80A superalloy, a series of Gleeble-1500 isothermal heating tests were performed under different heating temperature and holding time. The effect of heating temperature and holding time on grain growth were discussed. The Beck and Sellars grain growth model were obtained. The results show that the effect of heating temperature is larger than holding time, and Sellars model is more accuracy to describe the grain growth behavior of Nimonic 80A superalloy.