Influences of hydrostatic pressure during casting and Pd contenton as-cast phase in Zr-Al-Ni-Cu-Pd bulk alloys

Abstract

The influences of sample diameter (D), Pd content (x), and hydrostatic pressure (P) in a chamber during casting on the structure of as cast Zr65Al7.5Ni10Cu17.5−xPdx(x=10,17.5at.%) bulk alloys were investigated. Zr65Al7.5Ni10Cu7.5Pd10 and Zr65Al7.5Ni10Pd17.5 alloys (D=3mm) cast in a vacuum chamber (P∼4.0×10−3Pa) were mainly of the tetragonal-Zr2Ni equilibrium phase and nanosize icosahedral primary phase, respectively, while the same alloys cast in inert argon gas at atmospheric pressure (P∼0.1MPa) were of the single glassy phase. Due to the higher cooling rate obtained by decreasing the sample diameter (D=2mm) even in the vacuum chamber, the Zr65Al7.5Ni10Pd17.5 alloy was still of the icosahedral phase, while the Zr65Al7.5Ni10Cu7.5Pd10 alloy froze into a single glassy phase. These results indicate that the temperature- and time- transformation curves for the icosahedral and subsequent equilibrium phase formations in the alloy system shifts to a shorter time side with decreasing P, and the pressure sensitivity of the icosahedral phase formation increases with x.