Drawability and frictional behavior of pure molybdenum sheet in deep-drawing process at elevated temperature

摘要

Forming of pure molybdenum crucible is greatly demanded for its broad application in production of single crystal sapphire. To fabricate molybdenum crucible and other sheet metal products of molybdenum, it is necessary to determine the limiting draw ratio and frictional data with the aid of finite element analysis to reduce the massive experiments. To ensure the accuracy of finite element analysis, it is crucial to determine the reproducible frictional data. In this study, an evaluation methodology combined hot deep-drawing test with numerical simulation used to investigate the formability and tribological behavior of pure molybdenum at elevated temperature. For calculation of friction coefficient, the isothermal deep-drawing tests were carried out at the temperature ranging from 993 to 1143 K under lubricated and dry conditions. According to the predicted relation between frictional coefficient and forming temperature, the influences of forming temperature, lubrication, and blank diameter on friction are discussed, and the limiting draw ratios of molybdenum sheet at various temperatures are obtained. It is found that there is a significant improvement in drawability of pure molybdenum from 1.2 at room temperature to 1.98 at 1143 K by using boron nitride lubricant. However, the effect of forming temperature on the formability of molybdenum sheet is not significant under dry friction condition. Compared with the experimental results, the method used for evaluation of the formability and friction characteristic in hot deep drawing of molybdenum sheet is verified efficiently.