Sintering Densification Behavior, Microstructure And Property Of Mo-Zr Alloy

Abstract:Overcoming the low temperature brittleness and improving the elevated temperature property of molybdenum is the key to expand its application in aerospace, national defense, nuke industry and other frontier. This research aims to investigate the effects of Zr additive on the mechanical properties and microstructure at room and high temperature of Mo-Zr alloy which were fabricated via powder metallurgy method, and the strengthening mechanism was discussed. The content of Zr was in the rage of0.1～0.5%. Tensile strength of the alloys at room temperature and800～1100℃were tested and the microstructures of alloys were characterized in terms of fracture morphology, grain size, as well as distribution and composition of the second phase. The main results are as followed.The results indicated that Mo-Zr alloys approached full density after sintering, but with the increasing of Zr content, the relative density of the alloy descending slightly. The alloys could get a high density through solid phase sintering and the solid phase sintering between Mo particles is the main cause leading to the densification of the alloy even at liquid phase sintering temperature.The tensile strength at room temperature of the alloy is effectively enhanced after adding Zr, and is continued rising with the increasing of Zr content. Mo-3.0Zr alloy achieves the highest value603.5MPa which is72.4%higher than pure Mo. The microstructure analysis reveals that a little part of Zr solves into Mo matrix, which enhances the tensile strength of the alloys signally, while the other part of Zr form oxide second phase particles dispersing throughout grain boundary and inner grain and making the grains to be significant refined. Enhancing the pressing pressure leads to a better density but not to the tensile strength, while increasing sintering temperature will do harm to the property of the alloy.Mo-Zr alloy has achieved an excellent high temperature performance, the tensile strength of Mo-3.0Zr at800℃could reach 400MPa, and still show outstanding strength and toughness even if the temperature is as high as1000℃. At elevated temperature, the second phase particle dispersion strengthen turn into the mainly strengthening mechanism of Mo-Zr alloy, and with the increase of Zr content, as well as the second phase particle number, the ability of hindering dislocation slip enhanced, so as to the rising of the800℃tensile strength of the alloy. The high ductility of Mo-Zr alloy is relate to the ductile-brittle transition, while the helical dislocation and edge dislocation take part in slip at the same time also have a hand, the alloys present a dimple fracture mode at high temperature. There are38figures,13tables and101renferences in this paper.