Mechanical Properties of TC11 Titanium Alloy Forgings
Mechanical Properties of TC11 Titanium Alloy Forgings
Effect of Microstructure on Mechanical Properties of TC11 Titanium Alloy Forgings
TC11 titanium alloy belongs to martensitic α+β type heat-strength titanium alloy, and its nominal composition is Ti-6.5Al-3.5Mo-1.5Zr-0.3Si. It has high strength, good medium temperature performance, good corrosion resistance and fatigue resistance. It has the advantages of high strength and can be strengthened by heat treatment. It is the main material for the manufacture of aero-engines, high-pressure compressor discs and blades, and is also used to manufacture important pressure-bearing components on aircraft. The internal structure of the alloy determines its final performance, and a reasonable combination of structure and morphology can greatly improve the mechanical properties of the material. In this paper, different fiber microstructures were obtained by designing different thermal processing and heat treatment processes, and the effect of microstructure on the room temperature tensile properties of TC11 forgings was studied and analyzed.
1. Test materials and methods
The material used in the test is TC11 titanium alloy bar, and the transformation point is 1005℃-1010℃. The raw materials used in the test are prepared by different thermal processing or heat treatment processes to obtain different microstructures. It shows that the corrosive agent used in the metallographic structure is 10%HF + 30% HNO3 + 70% H2O. And use Image-ProPlus software to quantitatively characterize the content of primary α phase: then test the tensile properties at room temperature. The test was carried out on the 1185 type material testing machine.
2. Test results and discussion
2.1 Influence on the mechanical properties of TC11
Figure 1 shows the annealed microstructure of TC11 with different equiaxed contents. The primary phase contents were quantitatively characterized by Image-ProPlus software. The equiaxed phase contents were 44%, 39%, 32%, and 40% in sequence. It can be seen from Figure 1 that the contents of H1, H2 and H3 primary phases show a decreasing trend; the content of H4 equiaxed phase is roughly the same as that of H2, but its size and distribution are different. The grain size inside the H2 sample is uniform, while the H4 sample has an obvious "double-set structure", and there are two size levels of equiaxed α grains.
Figure 2 shows the corresponding relationship between the greenhouse tensile properties and the equiaxed phase content of three TC11 titanium forgings H1, H2, and H3. It can be seen from Figure 2 that with the increase of the equiaxed phase content, the strength of the material decreases and the plasticity increases slightly. This is because with the increase of the equiaxed phase content in the material, the content of β-transformant decreases, resulting in a decrease in the content of the α/β phase interface, which weakens the pinning effect of dislocations, reduces the strength of the material, and improves the plasticity of the material. ; In addition, with the increase of the equiaxed phase content, the distribution effect of alloying elements inside the material intensifies, which means that the Al content of the α sheet in the β-transformer decreases at this time, resulting in a decrease in the strength of the β-transformer, which in turn leads to an increase in the overall strength. decreases, while since the plasticity of the material is not affected by the yielding behavior, it mainly depends on the size of the α-clusters. Therefore, the effect of alloying element distribution on plasticity is very small; finally, with the increase of equiaxed phase content, the deformation compatibility of the material increases, resulting in a slight increase in plasticity. The combined effect of these three results in a decrease in the strength of the material and a slight increase in plasticity with an increase in the equiaxed phase content.
Table 1 shows the comparison of the room temperature tensile properties of H2 and H4. It can be seen from Table 1 that the yield strength and elongation of the H4 sample are significantly better than those of H2, and the tensile strength and area shrinkage are basically the same. It can be seen from the microstructure analysis that the average grain size of the H4 sample is smaller than that of the H2 sample. According to the Hall-Petch formula: it can be seen that the smaller the average grain size, the higher the yield strength of the material. This is because the number of grain boundaries increases at this time, resulting in an increase in the resistance of dislocation movement, which increases the deformation resistance of the metal; on the other hand, the decrease in the average grain size means that the number of grains increases, resulting in plastic deformation of the material It can be dispersed into more grains, so that the deformation coordination of the material increases, resulting in an increase in elongation.
2.2 The effect of secondary lamella α on the mechanical properties of TC11
In Figure 3, H5 and H6 are the microstructures after being cooled by different cooling media at the same annealing temperature. The quantitative characterization of the primary phase content by Image-ProPlus software shows that the phase content is roughly the same, about 30%, and the manager size is about 14.8um. It can be seen from Figure 3 that the H5 and H6 samples have obvious α-phase morphology in the secondary lamellae. The α phase of the secondary lamellae in the H5 sample is short rod-shaped, with a smaller aspect ratio; the secondary lamellae in the H6 sample are fine needle-shaped, and the aspect ratio is higher than that of the H5 sample.
Table 2 shows the comparison of the room temperature tensile properties of H6 and H5. It can be seen from Table 2 that the strength of the H6 sample is significantly better than that of the H5 sample, but its elongation and area shrinkage are slightly decreased.
In the case of a certain content, the proportion of β-transformer is also fixed accordingly. Geometrically speaking, the spherical surface area is the smallest for the same volume. As the α-sheet inside the β-transformer is more detached from the equiaxed shape, that is, the larger the aspect ratio, the higher the surface area ratio, and the larger the phase interface. The pinning effect of the phase interface on dislocations limits the slip of dislocations inside the grains, resulting in an increase in the resistance of dislocations when they move, which increases the deformation resistance of the metal, thereby increasing the strength of the material and decreasing its plasticity.
3. Conclusion
(1) With the increase of phase content, the strength of the material decreases and the plasticity increases slightly; the decrease of the average grain size of the equiaxed phase is beneficial to improve the strong plasticity of the material.
(2) With the increase of the aspect ratio of the α phase of the secondary lamellae, the strength of the material increases and the plasticity decreases.
