Yield points in brass crystals

A study has been made of the yielding behaviour of single crystals of brass grown in either argon or nitrogen. Crystals of β-brass showed sharp yield points when grown in nitrogen, but not otherwise. In all β-brass crystals, plastic flow occurred jerkily, each jerk being accompanied by the formation of a group of slip bands, and the yield strength showed a maximum at 200° C. Crystals of α-brass showed yield points at room temperature when they contained 1 % zinc or more, and repeated yielding at 200° C when they contained 10% zinc or more, irrespective of whether they were grown in argon or nitrogen; these yield points are considered to be caused by the segregation of zinc atoms to dislocations and a theoretical estimate is made of the critical amount of zinc needed for the yield phenomenon. Conditions for producing yield points in face-centred cubic metals are briefly discussed.