Shigeyoshi Nakamura

Concentration profiles and the rafting mechanism of Ni base superalloys in the initial stage of high temperature creep tests

The rafting mechanism is one of the most important and interesting phenomena which appears in Ni base superalloys during high temperature creep tests. The precipitated {gamma}{prime} particles, which are arrayed periodically in the {gamma} matrix, coalesce and form rafting structures in the direction perpendicular to tensile stresses. To understand this phenomenon, element profiles and diffusion process have been investigated in the vicinity of the {gamma}/{gamma}{prime} interfaces. In this paper, the authors analyzed accurate element profiles, especially Al and Cr which are main alloying elements, in the most vicinity of {gamma}/{gamma}{prime} interface regions. The rafting mechanism is correlated with the diffusion process on the basis of Al concentration profiles in a few nano meter distance from the {gamma}/{gamma}{prime} interfaces.

Development of 12CR Steel Disc for Heavy Duty Gas Turbines

This paper describes research and development of 12Cr steel for heavy duty gas trubine disc. The 1300°C class gas turbine developed by Hitachi, Ltd. (H25) is commercially operated for land-based power generator (25MVA) which is realized after five years designing.The quantitative study of alloying elements, which increase mechanical properties such as creep rupture strength, tensile strength, and toughness, is discussed. The sixteen pieces of real scale disc for 1300°C class gas turbine are examined to evaluate mechanical properties in terms of real operation. The recent study of 12Cr steel disc for 1500°C class gas turbine is also discussed.© 1994 ASME

Development of Materials and Coating Processes for High Temperature Heavy Duty Gas Turbines

This paper describes materials developed for the first stage nozzle and all stages turbine disc, and the new coating processes of the first stage bucket for high temperature, heavy duty gas turbines.A cobalt base casting superalloy (30Cr-10Ni-7W-0.2Nb-0.15Zr-0.2Ti-bal.Co), having high creep rupture strength and ductility, was used for the first stage nozzle and 12Cr forging material, having high creep rupture strength, was used for all stages turbine disc of the high temperature, heavy duty gas turbine, the H25. To increase hot corrosion properties of the first stage bucket, MCrAlY was applied on the bucket external surfaces by a low-pressure plasma-spray coating technique. A procedure of chemical vapor deposition for Al coating on the bucket internal cooling paths was also established for future high temperature gas turbines.Copyright