Low-density, refractory multi-principal element alloys of the Cr–Nb–Ti–V–Zr system: Microstructure and phase analysis

The crystal structure, microstructure, density and Vickers hardness of four multi-principal element alloys, NbTiVZr, NbTiV2Zr, CrNbTiZr, and CrNbTiVZr, are reported. The characteristics of these potential new high-temperature structural alloys are explored. The alloys were prepared by vacuum arc melting followed by hot isostatic pressing (at 1200 °C, 207 MPa for 1 h) and homogenization annealing (at 1200 °C for 24 h). The alloys have densities of 6.52, 6.34, 6.67 and 6.57 g cm−3, and Vickers microhardness values of 3.29, 2.99, 4.10 and 4.72 GPa, respectively. The NbTiVZr alloy is essentially a single-phase alloy consisting of a coarse-grained disordered body-centered cubic (bcc) phase with fine, submicron-size precipitates inside the grains. The NbTiV2Zr alloy contains three disordered bcc phases. The CrNbTiZr and CrNbTiVZr alloys contain a disordered bcc phase and an ordered Laves phase. The lattice parameters and compositions of the identified phases are reported. The experimental data are compared with the results of the thermodynamic modeling of non-equilibrium and equilibrium phases in these alloys.