Mo-ZrO₂系焼結材の機械的性質と破壊靭性

抄録

The improvement of the fracture toughness at room temperature of Mo-sintered material, which is heat-resisting, is strongly required in service. One of improving methods is fabrication of a composite material with dispersion strengthening secondary particles. Therefore, we pointed out previously that ZrO₂, as these secondary particles, was excellent from a standpoint of the utilization as a heat-resisting material and the effect of sintering characteristics and t→m phase transformation on toughness.
The aim of this investigation is to study experimentally the mechanical properties of Mo-ZrO₂ sintered composites, i.e. Young’s modulus, bending strength and fracture toughness, and to understand the effect of ZrO₂ on the mechanical properties of this material.
\ oindentThe results are summarized as follows:
(1) Young’s modulus of Mo-ZrO₂ composite material decreases with increase in the volume fraction of ZrO₂ and agrees well with the results of theoretical prediction based on the self-consistent method, as far as the ZrO₂ content does not exceed 20 vol%.
(2) The size of transformation zone of ZrO₂ in the vicinity of fracture surface is about 3.0-4.0 μm in maximum, and this maximum size depends on the volume fraction of ZrO₂.
(3) The volume fraction of ZrO₂ has a great influence on the bending strength and fracture toughness. That is, the former reaches a maximum value in case of specimens containing 12.5-15.0 vol% ZrO₂ and decreases with increase of ZrO₂ content.
(4) The increment of toughness may be explained by the contribution of the effect of t→m stress induced phase transformation of ZrO₂.