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TZM Alloy Second Phase Behavior Analysis

The strengthening elements Ti, Zr as carbides and oxides second phase exists in TZM alloy. TZM alloy is an deformation strengthening alloy, but solid solution strengthening and second phase dispersion strengthened alloy will deteriorate its pressure processing performance, so to study and to control the second phase behavior for improving the thermal deformation and properties of the alloy has great significance .

Analyzed alloy tensile fracture and impact fracture SEM showed that there are a lot of second phase at grain boundaries. In alloy carbon and oxygen content is higher (O: 0.08% ~ 0.09%, C: 0.04% ~ 0.05%), so many scholars believe that the second phase on the grain boundaries is Mo2C, (Ti, Zr) O and (Ti, Zr) C. In addition, in the tensile fracture, the researchers found in the grain boundaries and the grain there distributed second phase with different size and some second phases were abnormal thick. The second phase at the grain boundaries shows stretch dimple and between grain boundaries there is good plastic deformation connection. The second phase enriches at the grain boundaries. It is mainly because the sintered alloy in the cooling process the solubility of Ti, Zr and C in Mo was decrease, and therefore the second phase precipitation at grain boundaries. The large size second phase is Zr-containing carbides and oxides, because the sintering furnace cooling rate slowed down, so that the precipitation second phase can fully growth.

A large number of second phases exist in grain boundaries, due to elastic modulus differences, so the deformation can not synchronization, which will make grain boundary to break away form grains, crushing second phase, not only forming crack source, but also reducing the tensile strength and elongation. Further, intergranular second phase broken in the processing will reduce the workability and mechanical properties of the alloy.

Dispersed fine second phase in grain boundaries and in grains will help to improve alloy's recrystallization temperature and tensile strength, which is conductive to improving the properties of alloy. Second phase distribution usually depends on the thermal processing technology, if alloy is capable of rapid cooling and hardening during sintering, so that Ti, Zr and C can solid in Mo lattice, and then through tempered Ti, Zr and C precipitation to form dispersed second phase, witch can improve properties of the alloy.

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