The constitution diagram of the system molybdenum-osmium

Abstract

The constitution diagram of the molybdenum-osmium binary system has been elucidated using a combination of micrographiec and X-ray diffraction techniques. The system contains four single phase fields, namely: 1. (a) The body-centered cubic α-Mo primary solid solution which retains approximately 19.5 at.% Os at the eutectic temperature of 2,380°C, dropping to approximately 7.0 at.% Os at 1,000°C. 2. (b) a narrow intermediate phase field ranging from about 24 to 25.5 at.% Os and having a cubic phase structure similar to that of β-W (A15 type), the phase being formed via a peritectoid reaction at 2,210°C between α-Mo and σ-phase. 3. (c) a tetragonal σ-phase which forms peritectically at 2,430°C between liquid containing approximately 22 at. % Os and θ-Os primary solid solution containing 48 at.% Os, the σ-phase field broadening out and extending at 1,000°C from 30 to 39 at.% Os. 4. (d) a terminal solid solution, θ, which is based on the hexagonal close packed structure of osmium, the phase extending from 48 at.% Os at 2,430°C, the temperature of the σ-phase peritectic horizontal, to a solid solubility limit at 61 at. % Os at 1,000°C. Lattice parameters have been evaluated for α, β, σ, and θ-phase alloys along with their Vickers hardness values. Analogies are drawn between the Mo-Os and W-Os systems and with other Mo and W alloy systems containing the platinum metals.