Trends of High Temperature Materials Development in Japan

The thermal efficiency improvement in fire power stations is becoming increasingly important especially for cutting CO2 emission to prevent the global warming. Among the fire power, the advanced combined-cycle plants exhibit the highest efficiency, which is over 50% with inlet gas temperature as high as 1450C. Even 60-65% efficiency would be achieved provided that the inlet gas temperature is increased up to 1700C. To achieve this, however, materials with higher temperature capabilities are needed for turbine blades and vanes. Advanced jet engines also need such materials with even higher performance to increase the inlet gas temperature and the thrust.

Ni-base superalloys have been used as the blade and vane materials. By applying new processes such as directional solidification (DS) and single crystal (SC) solidification techniques, and also materials design techniques to design chemical compositions and microstructures, the temperature capability of superalloys has been improved by 350(C in these 50 years. So-called third generation SC superalloys with 5-6 wt% Re were developed in USA, UK and Japan and practically used in USA and UK as their jet engine turbine blade materials. An extensive effort is now made to develop the fourth generation superalloys; even platinum group metals additions have been tried.

So-called new materials, including refractory metals and alloys, ceramics, etc. have extensively been investigated as alternative materials, though actual practical application has been limited except for some ceramics used as turbo charger rotors in automobile engines. In the last few years, however, some attractive materials were proposed in Japan. They are a new eutectic ceramic, namely, melt growth ceramics (MGC), refractory superalloys based on platinum group metals, and so on.

In the first part of my talk, the possibility with superalloys is discussed after introducing past and present national projects in Japan. In the second part, the efforts being made in Japan towards new materials beyond superalloys are introduced. In the last part, an outline of the "High Temperature Materials 21 (HTM-21)" Project launched at NRIM in June 1999 is introduced. The targets for superalloy, ceramic and refractory superalloy developments, the total research plan, and some typical result being obtained so far are introduced, leaving the details to be presented later in this Symposium as HTM 21 Project reports.