在变形温度为1 050~1 140℃、应变速率为0.01~10 s 1和变形率为50%的条件下,采用Gleeble 1500热模拟机研究喷射成形FGH95合金的热压缩变形行为。结果表明：在合金热压缩变形初始阶段,流变应力随应变的增加迅速增大,达到峰值应力后逐渐减小,呈现明显的动态软化特征;合金流变应力随变形温度的升高和应变速率的降低而显著减小;应变速率为0.1~10 s 1时,合金峰值应变随温度升高而减小,并趋于平稳;而应变速率为0.01 s 1时,合金峰值应变在1 100℃出现极大值。考虑变形量对合金热压缩流变行为的影响,引入包含应变量的四次多项式函数对双曲正弦修正的Arrhenius方程进行改进,改进后的本构方程的流变应力预测值与实验值吻合较好,平均相对误差为3.64%。
In order to study the hot workability and to optimize the processing parameters for spray formed FGH4095 superalloy, thermal compression tests for spray formed FGH4095 superalloy have been finished by using a Gleeble 1500 thermal simulated test machine at the strain rates of 0.01-10.0 s-1 and temperatures of 1 050-1 140 ℃. The effects of strain rate and deformation temperature on the true stress-true strain curves and microstructure evolution were investigated. The results show that the generation of dynamic recrystallization (DRX) depends sensitively on deformation temperature. When the temperature was lower than 1 080 ℃, long and narrow necklace grains were shown in the microstructure. When the temperature increased to 1 140 ℃, new recrystallization grains were generated. The size and shape of γ' precipitates in the grains have a very important effect as factors of hindering sufficient migration of dislocations on plastic deformation. The result of thermal processing map is in accord with the microstructure observation, and the best material thermal processing temperature is above 1 128 ℃.
Based on the experimental data from hot compression tests on Gleeble 1500 thermal simulator, the revised constitutive equations of spray-formed FGH95 superalloy considering the effect of strain on the material constants were established. The average absolute relative error(AARE) was employed to verify the validity of the constitutive equation, and the value of AARE is 3.85 %. Subsequently, the revised constitutive equations were successfully used to simulate and analyze the deformation behavior, stress distribution, forming loads and temperature distribution in both dies and billet during the isothermal forging process of turbine disk of large dimension(about 400 mm in diameter) by the means of finite element method(FEM). Moreover, the optimum process parameters are 1,120 °C of forging temperature and 0.01 s-1 of strain rate for the spray-formed FGH95 superalloy turbine disk.
The flow behavior of spray-formed FGH95superalloy(similar to Rene 95)was investigated at temperatures ranging from 1050to 1140℃and strain rate ranging from 0.01to 10s-1.At a given temperature and strain rate,flow stress increases quickly with increasing strain and then reaches a peak,then gradual decreases until high strain,and dynamic softening is observed.Utilizing the hyperbolic sine function and introducing the strain with nonlinear fitting,the revised constitutive equations incorporating the effects of temperature,strain rate and strain for high temperature flow stress prediction of superalloy were established.The revised constitutive equations were implanted into finite element software by second development to simulate the hot compression process successfully,and the effective stress and load stroke curves obtained by numerical simulation are good agreement with the experimental results.
