Takehisa Hino

Mechanical Aspects of Structural Optimization in a Bi-Te Thermoelectric Module for Power Generation

The thermal stress and strain occurring on a Bi-Te thermoelectric module subjected to variable thermal conditions were estimated based on three-dimensional elastic-plastic finite element method (FEM) analysis. The analysis showed that mechanical integrity of the interface between a Bi-Te thermoelement and electrodes of Al and Mo coatings formed by atmospheric plasma spraying was significantly reduced and that shear strain rose to 0.6∼1.1% in the vicinity of the interface. Furthermore, to estimate the sensitivity of configurational parameters of the module to the thermal strain, statistical sensitivity analysis based on the design of experiment (DoE) and response surface method (RSM) was conducted. The statistical analysis revealed that the thickness of electrode coatings of Al and Mo affected the thermal strain and that the thinner Al coating and the thicker Mo coating reduced the thermal strain. In this study, a thermal fatigue test machine was newly developed with a view to verifying these analytical studies.

Crystallographic assessment of creep damage in high chromium steel weld joints using EBSD observation

Abstract Microstructural change during creep damage process was investigated on the fine grained heat affected zone (HAZ) and the coarse grained HAZ of 12Cr steel casting base metal welded by 9Cr weld steel, using a scanning electron microscope with electron backscattering diffraction pattern (EBSD) equipment. Creep rupture and interrupted creep test samples were cut at mid-section along longitudinal direction and inverse pole figure, image quality and kernel average misorientation maps were obtained through EBSD observation. The measured quantities were creep void size, grain size, precipitation size, area averaged image quality value IQ ave and area averaged kernel average misorientation KAM ave. Micro Vickers hardness test was also conducted to investigate the hardness distribution across the weld joint. Among various creep damage evaluation parameters, hardness, area fraction of voids, KAM ave and area fraction of precipitates at each HAZ showed apparent changes with creep damage time fraction at HAZ portions of subject material. The hardness was the most useful parameter for both HAZ portions and showed the unique correlation with KAM ave for creep voided portions. It was also demonstrated that EBSD observation was an effective tool for characterising crystallographic change inside grains during creep damage process.

Rafting of Single Crystal Superalloy by High Thermal Stress

Rafting of the nickel-base single crystal superalloy CMSX-2 was investigated under the condition of high thermal stress using a newly constructed experimental equipment. The test piece with the diameter of 25 mm was tested at the maximum material temperature of 1 000 degree Celsius for 80 hours. The results showed that the raft structure occurred only under the influence of thermal stress. The raft structure developed parallel to the direction of the compressive thermal stress because of negative lattice misfit. The thickness of gamma phase and gamma prime phase in rafting increase with the increase in the temperature and the thermal stress.

A New Ni-Base Single Crystal Superalloy TMS-82+

A new single crystal (SC) superalloy TMS-82+ which contains only 2.4% Re has been developed by using a computer aided alloy design program (ADP) developed in the National Institute for Materials Science (NIMS). The compositions were designed as follows; a large negative lattice misfit at operated temperature, 60 vol.% of γ′, solution heat treatment window of >50°C, and creep strength better than 2nd generation superalloys. Corrosion resistance was also considered. A brief explanation of the NIMS-ADP and the whole development works of SC alloy TMS-82+, such as alloy selection, metallurgical and mechanical tests, a full-scale production test and an engine test in the 15MW gas turbine, will be described here.Copyright