Mirrored symbols, opposite effects: Impact of Ga and Ag additions on the martensite decomposition of the Cu81Al19 alloy

Although the presence of martensite is desirable in several applications of increasingly complex Cu-rich Cu-Al alloys, there is a lack of understanding about the effects of alloying in its stability. Martensite decomposition was investigated in as-quenched Cu81Al19, Cu79Al19Ga2, and Cu79Al19Ag2 alloys (compositions in atomic percentage) by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry, and Vickers microhardness measurements. It was found that the similarity of crystalline structure between alloying element and host phase, as well as the interactions between ternary addition atoms and Al interfere with the stages of the martensite decomposition during heating. The Ga addition refined the microstructure, resulted in the precipitation of other phases, and favored the eutectoid reaction in the Cu81Al19 alloy. The Ag addition increased the tendency for martensite ordering, stabilized the beta 1 phase, and induced the precipitation of Ag particles from martensite on heating. Possible technological consequences arising from these results were also discussed.