Microstructure and Properties of Nickel-Based Superalloy Prepared by Two-Phase Zone Directional Solidification

Abstract

The principle of two-phase zone directional solidification technique is presented in this paper, taking the GH4738 nickel-based superalloy as the object, under the conditions of the mold temperature at 1350 °C and withdrawing speed from 3 to 6 mm/min. GH4738 nickel-based superalloy billets were prepared by two-phase zone directional solidification equipment developed all by the authors. The microstructure and mechanical properties of two-phase zone directionally solidified GH4738 nickel-based superalloy were investigated by metallographic microscope and mechanical testing machine. The effect of withdrawing speed on the microstructure and mechanical properties of the alloy were studied. The results show that, the microstructure of two-phase zone directionally solidified GH4738 nickel-based superalloy was composed of irregular columnar crystals with the branches. As the withdrawing speed increased from 3 to 6 mm/min, the grain size of the columnar crystal decreased, the branches’ number of the columnar crystals increased, the tensile strength of the alloy increased from 823 to 844 MPa, the elongation decreased from 43.3 to 36%. When the mold temperature was 1350 °C, the withdrawing speed was 6 mm/min, the tensile strength was 844 MPa and the elongation was 36%. Compared with the traditional vacuum induction melting of cast, the tensile strength of nickel-based superalloy GH4738 increased 20 MPa and the elongation increased by 9.2%. The nickel-based superalloy billets prepared by two-phase zone directional solidification had higher comprehensive mechanical properties.