20th World Congress on Materials Science and Engineering
Brandenburg University of Technology, Germany
Title: Investigation of high temperature cyclic loading behavior of molybdenum-hafniumcarbide
Biography: Athar Safari
The isothermal forging of titanium aluminides takes place between 1100°C and 1250°C with very low strain rates. This requires materials for the forming tools which have high stability at elevated forming temperatures as well as high resistance against wear, good oxidation resistance and heat resistance. At present, forging dies made of molybdenum alloys, which enable the shaping of titanium aluminide materials in an isothermal forging process, are used. Particle-reinforced molybdenum-hafnium-carbon alloys (MHC) exhibit a sufficiently high yield strength at 1200°C and a much better heat resistance than nickel-base alloys, iron aluminides or high-strength steels. Further progress in the development of new titanium aluminide alloys requires advanced forging tools and thus more knowledge about the tool material. Despite the great potential and application technological acceptance of MHC in high temperature applications, the thermo-mechanical behavior of this alloy with special focus on alternating load is not completely understood. Considering the forging process as a high temperature long-term low cycle fatigue process, in this study the mechanical behavior of MHC was investigated after several cyclic loading patterns. The tests were performed under different stress levels and different speed conditions. Microstructural observations, using optical microscopy and secondary electron microscopy were carried out. Hardness measurements were performed before and after cyclic loading in different conditions. The results show a decrease in the number of cycles until sample failure with increasing level of applied stress and an increase in the number of cycles until failure with increasing velocity.