In order to investigate the effect of dispersion of fine nitride particles on the low-temperature toughness of molybdenum, bend tests were performed for TZM alloy which had been internally nitrided by N₂ gas and demonstrated surface hardness of 250Hv and 300Hv. In this study the low-temperature fracture strength and ductility were represented by critical stress and critical temperature, respectively.
The results are summarized as follows. (1) Yield strength of the nitrided specimens was generally much higher than that of the recrystallized ones. (2) Critical stress of the nitrided specimens was approximately as high as that of the recrystallized ones. (3) Fracture mode of the nitrided specimens was almost similar to that of the recrystallized ones. Transgranular fracture was predominant. (4) Ductility of the nitrided specimens was much lower than that of the recrystallized ones. These results are attributed to the distribution of nitride particles. Very fine nitride particles were observed predominantly in the matrix, but not at and near the grain boundaries.