A Family of V-Based Null Matrix Alloys with Atomic and Mesoscopic Homogeneity

Abstract

Since the development of Ti_2.08Zr null matrix alloy by Sidhu et al. in 1956, only a handful of new null matrix alloys have been reported over the past 70 years. Most of them are not suitable to be utilized in applications due to the poor chemical/physical stabilities and the presence of strong short-range ordering in the structures. For the first time, a new family of V-based null matrix alloys V_1–xM_x (M = Al, Nb, Ta, Ni, Fe, Sn, and Mo; x < 0.1 in molar ratio) were synthesized by an arc melting method. The structural and physical properties were systematically evaluated. All of the alloys crystallize into a cubic body center structure with a space group of Im3̅m. Based on the neutron diffraction (ND), X-ray diffraction, and X-ray pair distribution function, the dopants (except Mo) and V atoms were atomically homogeneous and distributed into the 2a sites of Im3̅m. Small angle neutron scattering was used to probe the bulk neutron transparent properties and the possibilities of dopant clustering at the mesoscopic level. These conditions yield a specific feature in which the ND patterns of the alloys have no diffraction peaks. Hard X-ray absorption spectroscopy revealed that the valence states of V remained 0 in all investigated alloys. Nonetheless, a small degree of charge redistribution were observed. The Coulombic energies of configurations of supercells with different degrees of dopants clustering were also computed for comparison. Tensile tests were also conducted to evaluate the mechanical stress and strain properties. The high-temperature oxidation properties were examined by thermogravimetric analysis differential scanning calorimetry. Among the investigated samples, Nb-doped and Ni-doped V-based alloys show superior chemical and mechanical properties, which could be promising to be utilized to develop advanced in situ devices and high-temperature/pressure neutron scattering sample holders for ND and total scattering measurements.