STABILITY OF MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A Ni-BASED SUPERALLOY FOR ADVANCED ULTRA-SUPERCRITICAL FOSSIL POWER

摘要

Optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermodynamic calculations were employed to study the microstructural stability of a new Ni-based alloy (Ni-Cr-Fe-W-Al) designed for advanced ultra-supercritical power plants. Tensile properties and stress-rupture strength were also investigated. The thermodynamic calculation illustrates that the main phases during 700-800°C were γ', M_(23)C_6, M_3B_2 and P phase. The experimental results show that the main precipitates after standard heat treatment were M_(23)C_6 and γ' phase. The average size and the volume fraction of γ' phase were approximately 23nm and 15%, respectively. P-phase predicted by thermodynamic calculation was not identified in specimens isothermally aging at 700-800°C, and the coarsening behavior of γ' followed the Ostwald model. Room temperature micro-hardness (Hv_(0.5)) deceased with the increasing isothermal temperature. The room temperature tensile strength increased obviously with the elongation and reduction of area decreasing after aging at 760°C. The tested samples show high impact properties during prolonged exposure at 700-800°C for 1000h. Stress-rupture tests show that Ni-Cr-Fe-W-Al alloy exhibited high stress-rupture strength at 700-750°C.