Study On Hot Deformation Behavior And Processing Map Of MoLa Alloy

MoLa alloy,a kind of extremely important strategic resources,is a refractory metal,having low coefficient of linear expansion,excellent thermal conductivity,satisfactory electrical conductivity and high elastic modulus,and is thus very popular in metallurgy,oil,electronic product and nuclear industry.Hot processing is one of the most important way of plastic processing for this alloy and appropriate control of processing parameters is essential to obtain favorable microstructure and mechanical properties.Hot processing is one of the most important way of plastic processing for this alloy and appropriate control of processing parameters is essential to obtain favorable microstructure and mechanical properties.This work studied the hot deformation behavior and processing map for MoLa alloy in the temperature range of800 ?-1150 ? and strain rate range of 0.001s-1-10s-1.The result has a guiding significance to MoLa alloy structural design,the selection of process parameters and the improvement of the alloy performance,etc.The isothermal compression tests with constant strain rate for MoLa alloy were conducted by Geeble1500 hot simulator.It was found that the flow stress of the MoLa are greatly influenced by the deformation temperature and strain rate,by analyzing the flow stress curve of MoLa alloy under different deformation parameters.The flow stress is reduced,and show different degree of softening phenomenon,with the the temperature and the reduction of strain rate.The deformation mechanism mainly is dynamic recovery.Test results show that the flow stress decreases with either the increase of temperature or the decrease of strain rate.The deformation mechanism mainly is dynamic recovery.At the temperature 800-1150 ?,and the strain rate0.001s-1,softening phenomenon is the most significant,with the flow stress,decreasing with the increase of strain.There is no obvious wave change on the declining curve which showed continuous dynamic softening.A Arrhenius model with Zener-Hollomon parameter modification and a PSO-BP neural network have been established to describe the changing rule of flow stress with the strain rate and deformation temperature.The result showed that the PSO-BP neural network was more accurate than the Arrhenius model.The correlation coefficient and the average relative error of PSO-BP neural network respectively was 0.995 and1.48%.And the data points with less than 10% of the predicted value accounted for98.95% of all test data.So it is clear that the PSO-BP model has good accuracy.The processing maps of MoLa alloy have been plotted by using polar reciprocity model and Prasad criterion,Murty criterion respectively at strains of 0.3,0.5,0.6,0.8and 0.92.The Prasad criterion,and the Murty criterion were based on material dynamic model.Found the PRM is more accurate than Prasad criterion and Murty criterion by observation of microstructure.the prediction of Prasad criterion and Murty criterion were about the same.But the Prasad criterion is more accurate than Murty criterion,given the observation of microstructure.The intrinsic hot workability maps have been constructed based on the polar reciprocity model.Combing microstructure observation,it has been found that the buckling form in instability area mainly was local plastic deformation,and deformation mechanism in stability region mainly was dynamic recovery.The optimal processing parameters ranges of MoLa alloy could be inferred to be the deformation temperature range of 1100-1150 ? and the strain rates range of 0.001-0.05 s-1.