Thermal shock tests for refractory metals

The major aim of the present investigation was to establish a standard test procedure applicable to refractory metals for the evaluation of thermal shock behaviour. Powder metallurgy processed flat specimens of W, Mo and Ta were subjected to the beam of a 10 kW carbon dioxide laser. Both pulsed and continuous modes of the laser were applied to create single spots as well as straight line traces. The heat treated specimens were then characterized in terms of their microstructural changes and mechanical strength. Thermal shock induced cracks were investigated by conventional metallography and scanning electron microscopy. In W and Mo, grain size growth has been observed even at moderate thermal loads, whereas the microstructure of Ta remained unaffected up to the highest levels. In bending tests, W exhibits a dramatic thermal shock failure, whereas Mo partially, and Ta completely, retain their mechanical strength.