Q: We are using ceramic screws in one of vacuum furnaces, they’re breaking due to thermal stresses. There is lots of thermal cycling. Are their any less brittle materials we can use? The environment is low pressure with a max temperature of 1050C. Gases used in the system include: argon, nitrogen, hydrogen and methane.
A: Since you are dealing with a high temperature, oxygen free environment, the best option would be molybdenum screws. Molybdenum fasteners are ideal for oxygen free vacuums up to 1600C. Molybdenum screws will retain their strength at these temperatures without becoming brittle, expanding or softening. However if there is oxygen in your system molybdenum will fail rapidly at temperatures over 500C, where ceramics will not.