Microstructure and properties of a refractory NbCrMo0.5Ta0.5TiZr alloy

A new refractory alloy, Nb20Cr20Mo10Ta10Ti20Zr20, was produced by vacuum arc melting. To close shrinkage porosity, it was hot isostatically pressed (HIPd) at T = 1723 K and P = 207 MPa for 3 h. In both as-solidified and HIPd conditions, the alloy contained three phases: two body centered cubic (BCC1 and BCC2) and one face centered cubic (FCC). The BCC1 phase was enriched with Nb, Mo and Ta and depleted with Zr and Cr, and its lattice parameter after HIP was a = 324.76 ± 0.16 pm. The BCC2 phase was enriched with Zr and Ti and considerably depleted with Mo, Cr and Ta, and its lattice parameter after HIP was estimated to be a = 341.0 ± 1.0 pm. The FCC phase was highly enriched with Cr and it was identified as a Laves C15 phase, (Zr,Ta)(Cr,Mo,Nb)2, with the lattice parameter a = 733.38 ± 0.18 pm. The volume fractions of the BCC1, BCC2 and FCC phases were 67%, 16% and 17%, respectively. The alloy density and Vickers microhardness were ρ = 8.23 ± 0.01 g/cm3 and Hv = 5288 ± 71 MPa. The alloy had compression yield strength of 1595 MPa at 296 K, 983 MPa at 1073 K, 546 MPa at 1273 K and 171 MPa at 1473 K. During deformation at 296 K and 1073 K, the alloy showed a mixture of ductile and brittle fracture after plastic compression strain of ∼5–6%. No macroscopic fracture was observed after 50% compression strain at 1273 K and 1473 K. Phase transformations and particle coarsening considerably accelerated by the plastic deformation occurred in the temperature range of 1073–1473 K.

► A new refractory alloy, Nb20Cr20Mo10Ta10Ti20Zr20, consists of two disordered BCC phases and one ordered Laves phase.
► The alloy density is 8.23 g/cm3 and Vickers microhardness is 5288 MPa.
► The alloy yield strength values are 1595 MPa, 983 MPa, 546 MPa and 171 MPa at 296 K, 1073 K, 1273 K and 1473 K, respectively.
► Phase transformations and particle coarsening accelerated by the plastic deformation occur at 1073–1473 K.