Hardness behaviour in B2 pseudo-binary systems

Room-temperature hardness data and lattice constants were assembled for a number of Ru and Ir-based ternary systems exhibiting continuous B2 (CsCl) phase fields between the binary compounds. Near-linear relationships were found to exist in the hardness profiles and lattice constants of the RuAlRuTi, RuAlCoAl, RuAlIrAl, IrAlNiAl and RuAlRu2NbAl (L21) pseudo-binary series, suggesting a strong correlation of hardness with just one parameter. Pronounced solution hardening is reported for the RuAlNiAl, RuTiNiTi and RuZrPdZr series. In these cases, no clear correlations with the lattice parameters could be found, indicative of constitutional effects such as defects and ternary ordering. Volume size factors were examined as a basis for predicting lattice constants in these systems. Where such data exist, it was generally found that quantitative size factors yield errors commensurate with the precision of the available data.