Fracture toughness of polycrystalline YCu, DyCu, and YAg

Room temperature fracture toughness was measured for YCu, DyCu, and YAg. Standard tensile tests indicated that YCu was the least ductile of these three intermetallics (11% elongation at failure); DyCu had an intermediate ductility (16% elongation at failure); while YAg was the most ductile (20% elongation at failure). The KIC value was determined directly for YCu using ASTM test method E 399-90; JIC values were measured using ASTM test method E 813-89 for DyCu and YAg, and these JIC values were converted to KIC values. The KIC values were found to be 12.0 MPa m for YCu, 25.5 MPa m for DyCu, and 19.1 MPa m for YAg. These values are relatively high for polycrystalline, fully ordered, stoichiometric intermetallic compounds tested in room air of normal humidity. Factors that may contribute to the high fracture toughness of these materials are discussed.