Rapid solidification of silver-rich Ag–Cu–Zr alloys

Abstract

In this work we explored the possibility of obtaining amorphous/crystalline composites in the Ag-rich\ud side of the Ag–Cu–Zr ternary system exploiting the presence of a miscibility gap in the liquid. Four\ud alloys with nominal composition (at.%) Ag75Cu11Zr14 (alloy A), Ag73Cu17Zr10 (alloy B), Ag47.5Cu22.5Zr30\ud (alloy C), Ag47.5Cu30Zr22.5 (alloy D) were investigated. The effect of the cooling rate and the composition\ud on phase selection and microstructures was evaluated by comparing slowly cooled master ingots and\ud rapidly quenched ribbons. Evidence of the liquid miscibility gap was observed only in alloys B and D,\ud either in the master ingots and the ribbons. After rapid solidification, partial amorphisation was achieved\ud for alloys C and D, where precipitates of the Ag-rich solid solution, showing various sizes, are dispersed in\ud the amorphous matrix. A significant increase in hardness was achieved in the case of partially amorphous\ud ribbons of alloys C and D (442 HV and 533 HV, respectively). Experimental results are discussed on the\ud basis of the recently reassessed ternary Ag–Cu–Zr phase diagram

Liquid separation in Cu–Zr–Ag ternary alloys

“…Kang and Jung found based on their calculations that a stable ternary liquid miscibility gap did exist [10]. A liquid miscibility gap was observed in two master alloy ingots and rapidly quenched ribbons by A. Castellero et al [11]. This research is based on the previous paper of ours [12] that focused on the stable miscibility gap border.…”

Phase Separation in Rapid Solidified Ag-rich Ag-Cu-Zr Alloys

“…Subsequently, the monotectic, peritectic and, finally, peritectiod reactions leaded to the presence of three equilibrium phases. Consequently, the AgCu 4 Zr phase might be formed by the peritectic reaction and then, in this study, completely transformed into Cu 10 Zr 7 phase by the peritectoid reaction above 873 K [5] . However, the same sequence was not applicable with the phase formation in the Ag 60 Cu 20 Zr 20 ribbons.…”

“…Janovszky et al 4 described microstructural evolution of the liquid phase separation in the Ag-Cu-Zr system up to 70 at.% of Ag content. Castellero et al 5 reviewed liquid miscibility gap in the melt-spun Ag-Cu-Zr system at 73 at.% of Ag content.…”

“…Phase transformation of the Ag-rich Ag-Cu-Zr compositions went through many isothermal reactions as follows 5 :…”

“…Lʹ 2 + fcc-Ag → AgZr + AgCu4Zr Peritectic reaction (4) AgZr + AgCu 4 Zr → Cu 10 Zr 7 + fcc-Ag Peritectiod reaction (5) According to the reaction sequences, phase formation of the Ag 70 Cu 15 Zr 15 and Ag 80 Cu 10 Zr 10 alloys started from liquid phase separation with a precipitation of AgZr phase. Subsequently, the monotectic, peritectic and, finally, peritectiod reactions leaded to the presence of three equilibrium phases.…”