Influence of impurities and addition elements on the intergranular corrosion and embrittlement of nickel base alloys

The specific influence of some addition elements on the intergranular corrosion and hydrogen embrittlement of very high purity nickel base alloys was studied. Tests showed that titanium reduce intergranular corrosion susceptibility. However in these alloys titanium is not an effective stabilizer but acts on the chromium depletion mechanism. High purity alloys are very susceptible to hydrogen embrittlement and the fracture is of intergranular mode. In contrast with carbon doped alloys in solution annealed conditions, the fracture path observed is transgranular. Additionaly in carbide sensitized materials brittle fracture is intergranular. From these results it was concluded that brittle fracture of sensitized boundaries seems to be a consequence of the lower carbon content in the vicinity of the carbide particles. This conclusion is in marked contrast with the more usual assumption that brittle fracture of sensitized industrial alloys is related to the stresses developed in carbide precipitation process