High-Entropy V-Based Null Matrix Alloys─Short/Long-Range Structural Features, Chemical Stabilities, and Mechanical Properties.

Null matrix alloys are special types of alloys with no peaks in the neutron diffraction patterns. These types of materials have tremendous applications in the neutron scattering community as main components for manufacturing advanced reaction vessels for measurements. In the literature, null matrix alloys are often reported to be composed of two different elements/isotopes. In other words, null matrix alloys with more than two elements/isotopes have never been reported. One main reason was the limited solubility of dopants in the parent phases. As such, their physical/chemical properties could not be easily modified through the conventional doping strategies. For the first time, a new family of high-entropy V-based (HEV) alloys, composed of more than five elements, were developed using a two-step arc-melting method. The six investigated samples included VNbTaAlFeSn (HEV1), VNbTaAlFeMo (HEV2), VNbTaAlSnMo (HEV3), VNbTaFeSnMo (HEV4), VNbAlFeSnMo (HEV5), and VTaAlFeSnMo (HEV6). All six HEV alloys did not show any diffraction peaks in the neutron diffraction patterns. The dopants were found to be homogeneously distributed over the 2a sites of the 3̅ structure of V by the Rietveld refinement on high-resolution X-ray diffraction data. X-ray pair distribution function (PDF) analysis and small-angle neutron scattering (SANS) ruled out the possibility of chemical ordering or clustering in the investigated samples. Based on the chemical oxidation analysis of O at high temperatures, the HEV alloys are found to be more resistant than that the binary V-based alloys. Among the investigated HEV alloys, HEV4 was found to have the highest engineering yield strength. This work provides an important guideline of designing complex null matrix alloys/materials with novel properties.