The constitution diagram of the tungsten-molybdenum-osmium system

Abstract

Using a combination of thermal, micrographic and X-ray diffraction techniques, tentative constitution diagrams of the ternary system W-Mo-Os have been drawn for the temperatures 1600, 2000, and 2375°C respectively. No ternary intermediate phases of a structure different from those of the constituent binary systems were found. Above 2210°C, the system contains three single phase fields, namely: 1. (a) A body-centered cubic primary solid solution which extends along one edge of the ternary composition triangle from 100 at. % Mo to 100 at. % W and which can take up to 16 at. % Os into solid solution along the Mo-Os edge and 10 at. % Os into solid solution along the W-Os edge at 2210°C. 2. (b) A wide tetragonal σ-phase which forms peritectically at 2430°C and 37 at. % Os in the Mo-Os binary system and which stretches across the composition triangle to the W-Os edge, where the phase forms peritectically at 2945°C and 22 at. % Os. 3. (c) A hexagonal close-packed terminal solid solution based on θ-Os, the phase-field being roughly triangular in shape, the solid-solubility limit stretching from about 52 at. % Os on the Mo-Os edge to about 54 at. % Os on the W-Os edge at 2210°C. At 2210°C, a β-phase having the cubic β-W structure forms in the binary Mo-Os system at the composition Mo 3Os. This increases in size with added tungsten and falling temperature, stretching into the ternary system as a long, narrow phase field as far as 23.0W 54.5Mo 22.5Os at 1600°C.