Moの粒界脆化に及ぼす酸素の影響

Abstract

The mechanical properties of polyorystalline molybdenum containing various amounts of oxygen in grain boundaries were studied in order to clarify the effect of oxygen on the brittleness of molybdenum. The mechanical properties were evaluated by tensile and microhardness tests, and the oxygen concentration in grain boundaries was measured by Auger electron spectroscopy. The oxygen concentration in grain boundaries was controlled by changing the heating time of the specimens in an oxidizing atmosphere.The ductile-brittle transition temperature of oxygen contaminated molybdenum was about 100 K higher than that of unoxidized molybdenum. However, it was not changed by increasing the oxygen concentration in grain boundary to more than about 3 at%. The fracture strength at 77 K decreased with increasing oxygen concentration, and it showed a minimum value at 3 at%. Over the oxygen concentration range investigated, the fracture strength showed a tendency to increase and become constant. From the observation by an electron microscope, a step structure of the grain boundary was found for molybdenum of high oxygen concentration. Such change in grain boundary structure was considered to depress the decrease of fracture strength of molybdenum containing oxygen more than 3 at% in grain boundaries.