Fabrication of Binary Niobium Alloys with Low-Melting Metals by the Deposition of Nanoparticles

Abstract

Binary alloys of niobium with tin, lead, and cadmium are fabricated by the deposition of nanosized metal particles atomized in low-pressure plasma using the thermal-fluctuation melting effect. This effect implies the residence of a small particle in a quasi-liquid state to a certain critical size which, if is exceeded due to vapor condensation or merging (coalescence) with other quasi-liquid particles, leads to the droplet crystallization. Critical sizes are found at which the particles situated in a quasi-liquid state are able to coalescence and formation the alloy–solid solution. They are 2.1–2.2 nm for Nb, 0.4 nm for Sn, 0.6 nm for Pb, and 3.2 nm for Cd. The occurrence boundary of solid solutions of metals in niobium is determined by the following concentrations, at %: Sn 25.5, Pb 23.0, and Cd 64.5. The solid solution is based on the crystal lattice of matrix metal—niobium, in which lead, cadmium, and tin atoms are arranged. In connection with the fact that the sizes of atoms of incorporated metals differ from these for matrix niobium, the lattice parameters of the matrix (Nb) change and additional stresses appear in it up to the lattice destruction. The parameters of the bcc lattice of solid solutions increase with an increase in concentrations of Pb, Cd, and Sn in connection with their atomic sizes more when compared with niobium. The change in the growth rate of the crystal lattice is caused by the change in the schematic of the arrangement of impurity atoms in the matrix niobium lattice for alloys with lead and cadmium. Based on the critical particle sizes of metals, the magnitudes of the surface tension at the crystal–melt boundary are evaluated. They are as follows, J/m²: 1.17–1.22 for Nb, 1.15 × 10^–2 for Sn, 1.48 × 10^–2 for Pb, and 0.142 for Cd. The fabrication of alloys of refractory niobium with tin, lead, and cadmium is an example of using the size effect when fabricating new materials.