Environmental embrittlement and grain boundary segregation of boron and carbon in Ni3(Si, Ti) alloys

The effect of the addition of small amounts of boron and carbon on the environmental embrittlement of Ni3(Si, Ti) alloys was investigated by the room temperature tensile test. It is shown that the addition of boron to Ni3(Si, Ti) alloys completely suppresses the embrittlement in air and distilled water over the whole range of strain rates, and slightly suppresses the embrittlement in H2 gas. The addition of carbon to Ni3(Si, Ti) alloys completely suppresses the embrittlement in air and distilled water at high strain rates, moderately suppresses the embrittlement at low strain rates and slightly suppresses the embrittlement in H2 gas over the whole range of strain rates. The distinction between the embrittlement in air (or distilled water) and H2 gas is due to the different decomposition kinetics into hydrogen atoms for H2O and H2 molecules. The beneficial action of dopant atoms on the environmental embrittlement is attributed to boron (and carbon) segregation to grain boundaries, where they compete for site occupation and/or diffusion with hydrogen atoms, resulting in the alteration of the grain boundary to transgranular fracture mode.