電子ビーム溶解Mo板材の焼鈍脆性改善に及ぼす微量添加元素(B, Re)の影響

概要

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It is well known that molybdenum (Mo) shows recrystallization embrittlement around room temperature after it is exposed for a long period at elevated temperature. This phenomenon is considered to be caused by the weak grain boundary compared with the strong matrix. We tried to use the both elements, B (∼0.44at%) or/and Re (∼1.0at%), in order to strengthen the grain boundary and to decrease the flow stress of the matrix, respectively. The remarkable results are as follows. 1) The most ductile state is attained by heating Mo just above the recrystallization temperature (1173K), not heating to the recovery one. 2) The recrystallized Mo alloys with fine grain size and strong grain boundary are obtained by the addition of B, but the ones recrystallized above 1623K give rise to an abrupt decrease in ductility. It shows that the structure, not size, of grain boundary determines the ductility of Mo alloys. 3) Rhenium brings about a so-called solute softening, and a little addition of Re with B will be able to realize high ductility of the Mo alloy recrystallized at the elevated temperature over 1773K.
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