Molybdenum News Center

Ti and Zr Affected TZM Alloy Sintered Blank

Ti and Zr elements will reduce the density of TZM sintered blank. This is because Ti and Zr add into TZM in the form of ZrH2 TiH2 and in the 400 ~ 800 ℃ sintering process the ZrH2 and TiH2 will decompose into hydrogen, resulting in alloys’ porosity slightly increased.

Ti and Zr alloy elements in the sintering process will reduce the density of the alloy, but they also can refine the grain size of the sintered blank. Observed SEM pictures of molybdenum and TZM alloy’s grain found that the grain size of molybdenum is about 10 ~ 20um and there isn’t second phase particles between grains, fewer voids. On the other hand, TZM alloy grain size is generally between 5 ~ 15um, and there are a lot of second-phase particles and voids alloy between Mo grains. Besides, there is evenly distributed a large number of spherical particles and spherical dimples among Mo grains and Mo grain boundaries. These spherical particles are kind of compound which are composed of Mo, Ti, Zr and O, namely, (Mo, Ti, Zr) xOy compound. (Mo, Ti, Zr) xOy compound is conductive to absorb O existed in the alloy and has dislocation pinning effect. In addition, in the sintering process it also can prevent grain growth, and refine grains to improve the strength of alloy.

Ti and Zr will react with C and Mo to form a second phase and voids which can inhibit grain growth. The average grain size of pure molybdenum is 22.3um and average crystal size of TZM alloy is about 15.9um. The grain boundary can provide resistance for material deformation. With grain refining, polycrystal strength is higher, therefore the strength of alloy increase.

But the voids and second-phase particles in Mo grain section is prone to form micro-cracks and microscopic voids, thereby reducing the fracture toughness of the alloy. And there will have intergranular brittle fracture during using. If second phase size and void is smaller and the distribution is more dispersed, the strengthening effect is more obvious. However, when the second phase particle size is large, it will reduce the properties of the alloy.

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