Laves phases for high temperatures—Part II: Stability and mechanical properties

The hardness and indentation cracking at room temperature as well as the yield and creep at high temperatures in the range 800 – 1400 °C have been studied for various Laves phases AB2 with the transition metals A=Zr, Nb, Ta and B=Cr, Fe, Co with partial substitution of the B elements Fe and Co by Al, which effects a transition from cubic C15 structure to hexagonal C14 structure in the case of Nb(Co,Al)2. These phases are brittle with a thermally activated brittle-to-ductile transition at about 2/3 of the melting temperature. Above the brittle-to-ductile transition temperature deformability is still restricted with possible deformation twinning and in addition with possible microcracking at higher strains. A close positive correlation of the yield stress, hardness and apparent activation energy of creep with the sublimation enthalpy is observed which is analogous to Grüneisenʹs first rule for the elastic bulk modulus.