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In this study, the thermomechanical stress and fatigue analysis of a high voltage and high current (3,300 V/ 1200 A) insulated gate bipolar transistor (IGBT) module used for electric locomotive applications were performed under thermal cycling condition. Especially, the reliability of the copper wire and the ribbon wire were compared with that of the conventional aluminum wire. The copper wire showed three times higher stress than the aluminum wire. The ribbon type wire showed a higher stress than the circular type wire, and the copper ribbon wire showed the highest stress. The fatigue analysis results of the chip solder connecting the chip and the direct bond copper (DBC) indicated that the crack of the solder mainly occurred at the outer edge of the solder. In case of the circular wire, cracking of the solder occurred at 35,000 thermal cycles, and the crack area in the copper wire was larger than that of the aluminum wire. On the other hand, when the ribbon wire was used, the crack area was smaller than that of the circular wire. In case of the solder existing between DBC and base plate, the crack growth rate was similar regardless of the material and shape of the wire. However, cracking occurred earlier than chip solder, and more than half of the solder was failed at 40,000 cycles. Therefore, it is expected that the reliability of the solder between DBC and base plate would be worse than the chip solder.

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Three 9Cr Fe-base ODS alloys were prepared by MA (mechanical alloying) and HIP (hot isostatic processing) processes. The addition of Ti was confirmed to have a significant effect on the tensile properties at high temperature as well as at room temperature, while the V addition did not clearly show its effect on the microstructure or on the mechanical porperties at both temperatures. Fine and evenly distributed Y and Ti containing complex oxide was detected in the Ti added ODS alloy. They were attributed to the good high temperature strengths. Different cooling rates from the normalizing temperature did not result in a significant change in the grain boundary characters, but rather significant differences were observed in the mechanical properties. This is mainly attributed to the difference of the matrix phase rather than to the grain size distribution or the grain boundary characters.