| High parameters of Ultra-supercritical Steam Power Plant (USC) technology is the preferential choice for China to develop clean coal power generation technology at present. The requirements of heat-resistant materials are increasingly harsh with the improvement of steam parameters. As a key material in the USC, turbine blade needs to adopt nickel-based alloys when the steam temperature reaches 700℃. Waspaloy alloy is one of the main candidate materials of turbine blade in 700℃ ultra-supercritical power plant. The hot deformation behavior of Waspaloy alloy, the effect of heat treatment process, the microstructure and mechanical properties changed after long exposure at 700℃, and the creep fracture life were studied systematically in this paper with the aid of optical microscope, SEM, TEM and X-ray diffraction and other test methods. Meanwhile the chemical composition optimization and improvement of Waspaloy alloy had been studied. The main results obtained were as follows:The hot deformation characteristics of Waspaloy over a temperature range of 1000℃ to 1200℃ and strain range of 0.01 s-1 to 10.0 s-1 were investigate. The average apparent activation energy (Q) of Waspaloy was calculated to be 430.9 kJ/mol, and the hot deformation equation and quantitative relationship between Z value and the peak strain were obtained. The processing map was established on basis of dynamic materials model with flow stress data. The processing map showed a dynamic recrystallization (DRX) domain in the 1050℃ to 1150℃ temperature range and 0.01s-1 to 1.0 s-1 strain rate range with a peak efficiency of 45%, which was considered to be the optimum region for hot working. Moreover, the materials undergo flow instability in a temperature range of 1000℃ to 1050℃ and strain range of 1.0 s-1 to 10.0 s-1, and adiabatic shear bands was observed in this domain.Effect on microstructure and properties of Waspaloy alloy with different treatment process were investigate. With the raised of solution temperature, alloy strength was declining and grain size continue to grow. When the solution temperature was less than, the grain size met the ASTM standards. Only a few undissolved primary MC carbides when the solution holding time reached 4h at 1080℃. The strength was highest and plenty of M23C6 were precipitated with chain-like distribution on grain boundary when the temperature of high-temperature-aging was 845℃. Alloy had good strength when aged at 700℃ for 16h.As a 700℃-Class steam turbine blade material, the suitable heat treatment of Waspaloy alloy were 1080℃ x4h followed by oil cooling, then 845℃×4h followed by air-cooled, at last 760℃ 16h followed by air cooled.Effect on microstructure and properties of Waspaloy alloy after 10000h exposure at 700℃ were investigate The major precipitation phases were MC carbides with Ti-rich, M23C6 carbides with Cr-rich and γ’phase, and few M6C carbides, the other phases were not founded. The alloy exhibited good organizational stability. Gamma prime phase, which appears pherical shape, were dispersely precipitated insid e grains, and the particle size followed normal distribution. The discipline of y’phase met the curing mechanism, and the growth of γ’phase was not obvious after aging for 10000h. M23C6 carbides were mainly precipitated on the grain boundary, and its morphology were gradually growing from scattered tiny granulation to long continuous distribution, and gradually grow. The reaction between MC phase and matrix were followed MC+y→M23C6+γ’, but the decomposition reaction rate was very slow. In the initial aging, the continuous precipitation of y’phase cause to strength of alloy improved significantly. When the aging time after more than 2000h, the growth up of y’phase particles leaded to a slow decline of strength.Content of element C and element Ti in Waspaloy alloy were optimized. Improved C content could effectively increase the quality of carbides in alloy, reinforce the pinning effect to the grain boundary, refine the grain size, but don’t change the kinds of precipitations in alloy, and had no significant effect on the carbide distribution and the morphology of γ’phase. When the C content was 0.016%, the strength and short-term rupture property was poor; when C content was 0.056%-0.096%, the short-term and extrapolated long-term rupture property increased. The increased of Ti content did not change the kinds of precipitations, can significant increase the quality of y’phase and improve the of alloy, but not good for the extrapolated long-term rupture property. When the Ti content was 3.18%, the alloy had good strength and extrapolated long-term rupture property.The role of W element in Waspaloy alloy were investigate, the results showed that:adding 2%(mass fraction) W in the alloy did not change the kinds of precipitations, and showed good microstructure stability after long exposure, refined y’phase size and significant reduced the coarsening rate of y’phase. W mainly distributed in the matrix and the y’phase, both solid solution strengthening and precipitation strengthening. Adding W could increase number of coincidence site lattice grain boundaries (∑=3) and reduce interface energy of grain boundary, increase the grain boundaries strength, improve the short-term and extrapolated long-term rupture property of alloy. The extrapolated valuation of endurance strength is 271MPa on 100000h at 700℃, which was about 14.0% higher than before components improved.
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