Hot deformation characteristics and processing map analysis of a new designed nickel-based alloy for 700 degrees C A-USC power plant

摘要

The deformation behavior of the new designed nickel-based alloy for 700 degrees C advanced ultra-super-critical (A-USC) power plant applications was studied by the isothermal compression tests at temperature range of 1000-1200 degrees C with strain rates of 0.01-10 s(-1) on a Gleeble-1500 thermo-mechanical simulator in order to optimize the hot working parameters and control the microstructure under various deformation conditions. The results show that the flow stress increases with the decreasing temperature and increasing strain rate, and the activation energy of the new alloy is about 474.22 KJ/mol. Then the processing maps were developed on the basis of corrected flow stress data. The flow instability domain lies in the temperature range of 1000-1035 degrees C and strain rate range of 0.03-10 s(-1). The microstructure in the domain is characterized with inhomogeneous microstructure resulting from flow localization which should be avoided in hot working process. The optimum hot working conditions are obtained in the temperature range of 1125-1200 degrees C and strain rate range of 0.01-0.3 s(-1), except the grain growth domain with the strain rate and temperature range of 0.01-0.03 s(-1) and 1175-1200 degrees C. Microstructure observations reveal that full dynamic recrystallization (DRX) occurs in the optimum conditions and the origin microstructure has been substituted by fine and equiaxed DRX grains. The nucleation mechanism of DRX in the new alloy is discontinuous dynamic recrystallization (DDRX) as to the existence of original grain boundaries bulging under the low strain rate. However, the dominant nucleation mechanism of DRX at high strain rate has turned into CDRX. (C) 2015 Elsevier B.V. All rights reserved.