Microstructure evolution and mechanical behaviors of alumina-based ceramic shell for directional solidification of turbine blades

Abstract

The high temperature mechanical behaviors of Al2O3-based ceramic shell for the directional solidification of turbine blades were investigated. Isothermal uniaxial compression tests of ceramic shell samples were conducted on a Gleeble-1500D mechanical simulator with an innovative auxiliary thermal system. The microstructures of sintered, heat-treated, and tested samples were characterized using scanning electron microscope and X-ray powder diffraction. The experimental stress–strain results of heat-treated samples were obtained. The eutectic mixture region composed of ZrO2 and SiO2 that regenerated by the decomposition reaction of excess zirconium silicate appears in the samples after heat treatment at 1500. The fracture type of CST25 and CST700 is brittle fracture, but CST1100 and CST1400 have thermo-viscoelastic and viscoplastic properties under stress conditions at high temperatures (>1100). The evolution of zirconium silicate decomposition reaction during the directional solidification process is analyzed. The SiO2 particles provide the major viscosity source of the ceramic shell at high temperatures. The thermo-viscodamage constitutive model of Al2O3-based ceramic shell for the directional solidification of single crystal superalloy is established. Keywords: Single crystal superalloy, Alumina-based shell, High temperature, Mechanical behavior, Constitutive model