TZM-La2O3 Alloy

With advances in technology and society, performance requirements more stringent to TZM alloy. After the study, adding rare earth can well improve the performance of TZM alloys, including alloy’s recrystallization temperature, ductility and toughness. And adding metal La2O3 in TZM alloy has been widespread concern.
Related scholars using powder metallurgy method with Mo powder, TiH2, ZrH2, of La2O3 and graphite as raw material produce TZM-La2O3 alloy. And then employing pressing process produces TZM-La2O3 0.5mm thick sheet. By studying the recrystallization temperature, strength and toughness of TZM alloy which influence by La2O3 and compare the microstructure and properties effects of TZM-La2O3 by different methods of rolling to better improve the performance of the alloy, to expand its range of applications.
Add La2O3 can refine TZM alloy grain to increase the density and strength. Meanwhile, La2O3 significantly delayed the recrystallization of TZM alloy and with the increase of La2O3 the recrystallization of TZM alloy increase as well. In addition, La2O3 particles for the dislocation has a strong pinning effect making tensile strength and elongation is better than TZM alloy and the overall performance is also good.

Different Compression Rates Influence TZM Alloy Fracture Morphology Ⅱ

When compression rate is 60% TZM alloy has a clear dimple and the fracture mode of grains mainly transgranular fracture mode, a higher proportion of this fracture mode, indicating that the grain boundary of alloy has been some strengthening. But there is still a small part grains are cleavage fracture mode. The whole fracture mode mixed with cleavage fracture, ductile fracture and transgranular fracture mixed.

When the compression rare is 80%, the fracture morphology of TZM alloy shows the river-like pattern cleavage fracture. Although similar fracture pattern with compression rate 60% TZM alloy, but the proportion of grain which occur transgranular fracture and cleavage fracture further improved. And because the cleavage fracture during breaking process will occur plastic deformation so a lot of fibrous tissue will increase in alloy where you can see some small tearing ridge and shallow dimple belt. Usually the ductile fracture of alloy is higher when cleavage fracture happens.

When the compression rate is 90%, fracture morphology of TZM alloy is fiber microstructure and the area of fracture source can see platform, stairs and other morphology. Fracture mode is cleavage fracture and transgranular fracture. At the same time due to the plastic deformation of the grain the gaps and voids are crushed and welded together, so the gaps and voids volume of the alloy significantly smaller and reduced. The alloy has more fibrous tissue and the grains interaction coexist with each other making the alloy bonding force enhancement, material has been significantly strengthened, and tensile strength reached 846Mpa.

Effect of compression ratio of TZM alloy is mainly with the increase of the compression ratio, the alloy becomes denser and fracture mode mainly transition from ductile fracture, transgranular fracture to quasi-cleavage fracture.

Different Compression Rates Influence TZM Alloy Fracture Morphology Ⅰ

At different compression rates TZM alloy fracture morphology is different. TZM alloy which produced by powder metallurgy has four general fracture mode, along strengthen molybdenum particles internal fracture, along strengthen phase particles fracture, along the adhesion and strengthen phase internal fracture, along with enhanced adhesion particles internal fracture.
By analysis TZM alloy fracture surface under different compression ratio found that the un- rolling TZM alloy fracture mode is intergranular brittle fracture, from the SEM image can clearly see each grain exhibit polyhedral shape and full of voids. In the stretching process, these voids as source of crack and they connect with each other resulting in alloy breaks. When TZM alloy compression ratio is 40% the fracture mode is intergranular fracture and cleavage fracture, where individual grains have fracture phenomenon. At the same time, there are some small spherical particles dots and hollow on the grain boundary fracture. These spherical particles dots are TiC which play dispersion strengthen in alloys, but occurs at grain boundaries will reduce the strength of the grain boundaries to a certain extent. And because equiaxed structure and some do not weld holes exist, so the tensile strength is not high.

TZM Alloy Organization Structure

After observing TZM alloy SEM image found there uniformly distributed white spherical particles and the shape of the block material. Analysis element content found that the white spherical particles main element is Ti and matrix elements mainly is Mo, Zr and a small amount of Ti, from this we can see that small amount of Ti and Zr form Mo-Ti and Mo-Zr solid solution in TZM alloy with Mo. Bedsides, the solid solution ability of Zr is better than Ti. And this is because the solid solution of TZM alloy is mainly through Mo matrix to dissolve a small amount of Zr, Ti, C and other element making Mo lattice contorted. The size of the solute and solvent atoms greater the difference, the better the reinforcing effect, on one hand, the size difference factor of Zr and Mo is + 14.3. On the other hand, Ti and Mo size difference factor is + 4.4. So the solid solution ability of Zr is better than Ti. Although C and Mo size difference factor is -34.5 which is very large, but due to the C content is low in TZM alloy and most of C will work with Mo, Ti and Zr react generate carbide, at the same time C will be consumed when occurs reduction reaction. Therefore TZM alloy strengthen mainly Mo-Ti and Mo-Zr solid solution strengthening, as well as TiC and ZrC dispersion strengthened which was generated by Zr, Ti, and C. These organization structures not only improve the mechanical properties of the alloy also increases the alloy recrystallization temperature.