Phase Transformations at High Pressures and Temperatures and the Structure of a Hypoeutectic 1Ni—99A1 Alloy

摘要

The phase transformations in a hypoeutectic 1Ni—99A1 alloy are studied by differential barothermal analysis in the temperature range up to 750°C at a compressed argon pressure up to ~100 MPa. The Al matrix of the initial alloy is found to be saturated by micropores at a concentration of 3.7 x 10~(10) cm~(-3). After melting and solidification in a compressed argon atmosphere, the micropore concentration increases to 3.2 x 10~(11) cm~(-3). As a result of melting and solidification at a high pressure, the initial fine-grained structure of the alloy with an average grain size of 16 urn transforms into a coarse-grained structure during dendritic solidification. The processing of electron-microscopic images is used to determine the volume content of intermetallic compound Al_3Ni in the Al matrix. The liquidus temperature of the alloy at 100 MPa increases by 10°C, and the solidus temperature is 5°C higher than the eutectic transformation temperature in aluminum-rich Al—Ni alloys. The solid-phase decomposition of the supersaturated solid solution of nickel in aluminum occurs at 630°C. At 100 MPa, the field of solid solutions of nickel in aluminum extends to 1.2 at % Ni as compared to the Al—Ni system at atmospheric pressure. The lattice parameters of Al and Al_3Ni are found to increase in the alloy solidified at 100 MPa. The microhardness of the Al matrix in the alloy is measured after a barothermography cycle. A portion of the Al—Ni phase diagram is proposed for a pressure of 100 MPa in the nickel content range 0—4.3 at %.