Effect of Ni on Microstructure and Mechanical Property of a Co-Ti-V-Based Superalloy

The effect of Ni on microstructure, elemental partition behavior, γ ′ phase solvus temperature, lattice misfit between γ and γ ′ phases, and mechanical properties of the Co-8Ti-11V-xNi alloys was investigated. The result shows that the lattice misfit in the alloys decreases from 0.74% to 0.61% as the Ni content increases from 0 to 10%, and the average sizes of the cuboidal γ ′ phase were measured to be 312.10 nm, 112.86 nm, and 141.84 nm for the Co-8Ti-11V, Co-8Ti-11V-5Ni, and Co-8Ti-11V-10Ni, respectively. Ti, V, and Ni exhibit a slight tendency to partition into the γ ′ phase, while Co shows a slight tendency to partition into the γ phase. The solvus temperatures of the γ ′ phase were measured to be 1167°C, 1114°C, and 1108°C for the Co-8Ti-11V, Co-8Ti-11V-5Ni, and Co-8Ti-11V-10Ni alloys, respectively, by using differential scanning calorimetry (DSC). Moreover, the yield strength and ultimate strength of the Co-8Ti-11V, Co-8Ti-11V-5Ni, and Co-8Ti-11V-10Ni alloys were investigated, and the yield strength and ultimate strength of the 10Ni alloy were highest, at 219 MPa and 240 MPa. After compression at 1000°C, the dislocations cannot effectively shear the γ ′ phase in the 0Ni and 10Ni alloys, resulting in a relatively high compressive strength of the 0Ni and 10Ni alloys. However, the γ ′ phase of the 5Ni alloy is no longer visible, and its strength is the lowest.

Partition behavior of platinum-group elements during the segregation of arsenide melts from sulfide magma

Evidence of immiscibility between arsenide and sulfide melts has been observed both in experimental studies and natural samples from several localities worldwide (e.g., Ronda, Spain; Beni Bousera, Morocco; Dundonald Beach South, Canada). Platinum-group elements (PGE) have shown to have a strong affinity for arsenide melts, but little is known about their partitioning behavior between arsenide and sulfide melts. In this study, we experimentally determine the partition coefficients of PGE (Pt, Pd, Ir, Ru, and Os) between both types of melt in As-saturated sulfide systems doped with trace amounts of PGE. Results show that all PGE display a strong preference to the arsenide melt with DPGEAs/sulf melts ranging from 20 to 2700, with Ir and Pt showing a marked preference for arsenide melts. These partition coefficients values are similar to estimates made from natural samples and demonstrate that the separation of arsenide melts from sulfide magmas can be an efficient mechanism to scavenge PGE from magmas and to fractionate Os, Ru, and Pd from Pt and Ir.