Geodynamics Research Center Professor |
超高圧力下での直接相転換法により新しい超微細ナノ多結晶cBNを合成した.本報では,その結晶構造および機械的性質を明らかにするとともに,超精密鏡面切削加工用工具への応用について検討した.その結果,高速度鋼やインコネルなどの難削材の超精密鏡面の創成が可能であることなどを明らかにした.
超高圧力下で合成したナノ多結晶cBNを用いて開発したcBN砥粒の圧壊試験を試み,その破壊強度や破壊モードなどの破壊のメカニズムを検討した。その結果,ナノ多結晶cBN砥粒が従来の単結晶cBN砥粒よりも数倍高い破壊強度を持つことなど,新しい知見を得たので報告する.
This work investigated the microstructural evolution occurring during high-temperature tensile tests (743 K, strain rate 1×10−3 s−1) of a friction stir processed polycrystalline solid solution 5083 aluminum alloy, along with the effect of the microstructure change on the room-temperature mechanical properties. Grain refinement was effectively achieved in the stir zone, with the mean observed grain size less than 10 µm. The nominal stress–nominal strain curve indicated that the flow stress drastically increased until a maximum stress value at which point fracture occurred. The value of elongation to failure exceeded 300%; this high ductility can be referred to as superplastic-like elongation. The area fraction of cavity increased with increasing strain. Room-temperature tensile tests at a strain rate of 1×10−3 s−1 revealed that the strength and ductility decreased with an increasing area fraction of cavity, and that the extent to which the strength and ductility are affected depends on the cavity.