Mechanical properties of single crystal YAg

Abstract

YAg, a rare earth-precious metal “line compound”, is one member of the family of B2 rare earth intermetallic compounds that exhibit high ductilities. Tensile tests of polycrystalline YAg specimens have produced elongations as high as 27% before failure. In the present work, single crystal specimens of YAg with the B2, CsCl-type crystal structure were tensile tested at room temperature. Specimens with a tensile axis orientation of [0 1 1 ̄ ] displayed slip lines on the specimen faces corresponding to slip on the {1 1 0}〈0 1 0〉 with a critical resolved shear stress of 13 MPa. A specimen with a tensile axis orientation of [1 0 0] showed no slip lines and began to crack at a stress of 300 MPa. The test specimens also displayed some slip lines whose position corresponded to slip on the {1 0 0}〈0 1 0〉 ; these slip lines were found near intersections of {1 1 0}〈0 1 0〉 slip lines, which suggests that the {1 0 0}〈0 1 0〉 may be a secondary slip system in YAg. Transmission electron microscope (TEM) examination of the crystals was performed after tensile testing and the dislocations observed were analyzed by g · b=0 out of contrast analysis. This TEM analysis indicated that the predominant Burgers vector for the dislocations present was 〈1 1 1〉 with some 〈0 1 1〉 dislocations also being observed. This finding is inconsistent with the 〈0 1 0〉 slip direction determined by slip line analysis, and possible explanations for this surprising finding are presented.