A study of the Ni-Pt-Ru and Co-Pt-Ru systems.

Abstract

The solidification projections and 1000°C isothermal sections of the Ni-Pt-Ru and Co-Pt-Ru systems were determined by characterising alloys of different using SEM and XRD on arc-melted as-cast and annealed samples. Hardness measurements were undertaken and the hardness indentations were also used to determine the preliminary toughness of the samples. The solidification projection of the Ni-Pt-Ru system showed that the (Ni,Pt) solvus retreats to the Pt corner in the ternary wherever (Ru) formed where it was not expected and a third phase appeared after heat treatment on a locus from ~Ni20: Pt30: Ru50 to ~Ni10: Pt50: Ru40. A possible miscibility gap in the (Ni,Pt) phase was found in Alloy LG 10. Alloys LG 1 underwent the ordering after heat treatment. The other alloys softened after annealing. Reasonable toughness was exhibited by all the alloys because of the fcc phase that occur in all of them. The Co-Pt-Ru system showed that the α→ε transformation that took place in two of the component binaries was stabilised in the ternary system, in both the as-cast and annealed alloys. The L + (Ru) → fcc (Co,Pt) peritectic reaction was demonstrated by many of the annealed alloys. During heat treatment (Ru) precipitates formed and this indicated that the fcc (Co,Pt) solvus was sloping and retreating towards lower Ru contents at lower temperatures. The hardnesses of the alloys did not change very much after heat treatment, with the exception of Alloys LG 11 and LG 15. Alloy LG 11 showed ordering and Alloy LG 15 showed a significant decrease in hardness due to the coarsening of the microstructure. The toughness remained reasonable for al the alloys as a result of the presence of the fcc phase in all of them.