Behavior of W-based materials in hot helium gas

A number of W-based materials (pure tungsten and some of its alloys) prepared by powder metallurgy techniques was exposed to He atmosphere at 720 ºC and 500 kPa for 500 h. Morphological surface changes were observed by SEM, chemical and phase composition was analyzed by EDS and XRD, respectively. The internal microstructure was observed by a combination of SEM, FIB and TEM techniques. Mechanical properties were determined by instrumented indentation. Some alloys developed a thin oxide layer, in some cases new morphological features were observed, while some samples remained mostly intact. The observed changes are correlated with specific compositions and microstructures.