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The Vickers hardnesses of 21 as-cast Ni-Ru-Zr alloys of different compositions were studied, and nanohardness indentations were done on the individual phases. The results were used to explain the brittleness by assessing the proportions of the phases, and their morphologies. The compound hardnesses varied between 704 - 1289 HV, with ~ZrRu2 being the hardest phase, and ~Zr2Ni7 being the least hard phase. The sample hardnesses were 300 - 1015 HV. Most of the samples were brittle, although there were regions of toughness around Ni36:Ru13:Zr51 and Ni20:Ru5:Zr75 (at.%). No alloy was identified to have potential good mechanical properties.

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Microhardness values of alloys in the Pt-Cr-V and Pt-Al-V systems were determined using an indenter which incorporated an optical microscope. The values were analysed with respect to the phases identified in each of the alloys. Identification of the phases had been done earlier using scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. The hardness values were determined for samples in the as-cast and annealed conditions and superposed on the solidification projection and isothermal section at 1000°C. The results showed that the hardness depended largely on the phases present in the alloys and generally increased after annealing. However, in a few cases, grain growth and the resulting microstructural coarseness resulted in lower hardness values after annealing. The hardness of the alloys of the Pt-Cr-V and PtAl-V systems was also compared with those of Pt-Al-Cr and other Pt-Al based alloys. Comparison was also made with some Pt-Al based alloys of the higher order systems such as Pt-Al-Cr-Ru-V and Pt-Al-Cr-Ru-V-Nb. In general, higher hardness was exhibited by alloys containing ternary phases.Pt-based ternary alloys, Pr-Cr-V, Pt-Al-V, hardness, microstructure.

The microstructures of as-cast and annealed platinum alloys of different compositions were revealed after electrolytic etching in hydrochloric acid/sodium chloride solution using direct current. It was shown that the etching process enhances good microstructural images of platinum-aluminium based alloys.

Platinum-based alloys are being developed with microstructures similar to nickel-based superalloys for potential high-temperature applications in aggressive environments. Since the chemistries of nickel and platinum are similar, Pt-based alloys can be made with gamma prime ~Pt 3 Al precipitates in a gamma (Pt) matrix. Currently, the Pt-Al-Cr-Ru system is one of the bases for developing Pt-based alloys, where Al allows the formation of the Pt 3 Al precipitate and also gives protection from the alumina scale formed, Cr provides oxidation resistance and stabilization for the L1 2 ~Pt 3 Al phase, and Ru provides solid solution strengthening in the (Pt) matrix.Four Pt-Al-Cr-Ru-V and two Pt-Al-Cr-Ru-V-Nb alloys were made, with compositions based on a quaternary alloy, ~Pt 82 :Al 12 :Cr 4 :Ru 2 , which had previously been identified as having optimum properties. Four of the ascast alloys had the targeted two-phase structure of ~Pt 3 Al and (Pt), and two were single-phase ~Pt 3 Al. Vanadium partitioned more to (Pt) than to ~Pt 3 Al. There was an improvement in hardness compared to the quaternary alloys. The best addition of V was ~15 at.%; higher additions resulted in brittle intermetallic phases of the Pt-V system. The effect of Nb could not be ascertained because of its high losses.