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TZM Alloy Second Phase Strengthening Mechanism

Comparing composite phase alloy with single phase alloy, composite phase alloy not only has matrix phase, but has the second phase. The second phase uniformly distributed in the matrix phase and will produce a significant strengthening effect, namely, the second phase strengthening. TZM alloy belonging composite phase alloy. In the second phase strengthening of TZM alloy can be divided into carbide strengthening and dispersion strengthening. In alloy Ti, Zr will react with C to form insoluble fine carbide particles and to produce a second phase strengthening. The second phase dispersed distributed at the grain boundaries can stabilize forging structure and effectively block dislocation movement, thus preventing recrystallization or elongated recrystallized grains structure to prevent the conversion of equiaxed grains, which makes alloy be strengthened.

In TZM alloy, second phase strengthening effect connects with Ti, Zr and C mass ratio and C content. In general, when (Ti + Zr) and C mass ratio between 4 and 10 the strengthening effect is the best, but over this range are not conducive to improve the alloy strength. In addition, during the manufacturing process should to strictly control the C content. Because if the C content is too high, the excess C will react with Mo to generate Mo₂C, resulting in hard brittle second phase ion exceed which dispersed in the grain boundary, reducing strength and toughness of the alloy, and is not conducive to improving the mechanical properties.

Near Mo grain boundaries have some black material gathered, the black substance is mainly Ti, Zr or carbide. With trace elements and carbide increase, this gathering is becoming more apparent. These substances not only can effectively improve the performance of molybdenum alloy, but also to prevent the grain boundaries campaigns and dislocations movement, raising the recrystallization temperature, can strengthen the role.

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