Materials Technology for Innovative Thermal Power Generation System toward Carbon Neutrality in Japan

In order to achieve carbon neutrality in 2050, a novel thermal power generation plant with higher thermal efficiency (>70%) has to be realized. That is the oxygen/hydrogen combustion turbine generation system combined with an advanced ultra-super critical steam turbine system with steam temperature higher than at least 923 K. This high efficiency large-scale power generation system can endure not only a stable supply of energy with no CO₂ emission but also cover the energy to produce the fuel of hydrogen together with oxygen by water electrolysis by itself. The key issue to realize this plant not a castle in the sky is in the developments of new materials tolerable for the higher temperature operation for both gas turbine components of exhaust gas (steam) duct/exhaust recovery units and steam turbine components of tubes, pipes, casing, valves and so on.

Under the national project of JST-Mirai (Future) program currently going on, we have built up the microstructure design principles to develop these materials, based on metallurgical disciplines of thermodynamics, kinetics, deformation and calculation science. For gas turbine components, novel solid-solution type Ni-Cr-W superalloys was found to exhibit superior creep life longer than 5x10⁴ h under 10 MPa at 1273 K. For steam turbine components, iron-based Laves steels, so called “supersteels” shows the allowable stress higher than 100MPa for10⁵ h at 973 K. In both cases, the superior creep properties can be attributed to the “grain-boundary precipitation strengthening(GBPS)” effect due to bcc α₂-W phase and C14 Fe₂Nb Laves phase, respectively.

In this talk, oxidation and corrosion behavior of the materials under moist/CO₂ environments will also be touched briefly, in addition to the details of alloy design philosophy and strengthening mechanism.

Part of this work was supported by JST-Mirai Program Grant Number JPMJMI21E7, Japan.