Effect of forging process on microstructure and mechanical properties of TA11 titanium rod

TA11 titanium alloy (Ti-8Al-1Mo-1V) is a near-A type heat-resistant titanium alloy. It has many advantages such as high room temperature high temperature strength, good thermal stability and high temperature creep performance, and is mainly used for high-speed rotating parts such as aircraft engine compressor disc and 1~3 stage rotor blades. These components, used in harsh working environments for a long time, must have good room temperature and high temperature mechanical properties, especially high thermal stability and high temperature creep properties, because these properties not only determine the service life of the alloy but also determine the safety and reliability of the engine, so it is very necessary to study the microstructure and properties of TA11 titanium rod materials.

Through experimental data analysis, we can see that the difference in tensile properties at room temperature of TA11 titanium alloy rods under the two processes is small, and the difference in strength is not large, and they all meet the standard requirements. Because the equiaxial structure and bimorphic structure of TA11 titanium alloy bar have good thermal stability', the thermal stability performance after heat exposure at 400 °C and 100h is also small, but the creep performance of the A process is greater than 0.2%, which does not meet the requirements of the product standard. The creep performance of process B and C is less than 0.2%, which can meet the requirements of product standards, and process C shows better high-temperature creep performance. Combined with the analysis of Figure 2 and Figure 3, it is concluded that the relative content of primary a and secondary a in the forging tissue of TA11 titanium alloy bar, as well as the morphology of secondary a, have a great influence on its creep properties. The creep performance is better when the primary A content is lower than that when the primary A content is high, and the creep performance is better when the secondary A distributed on the P matrix is a fine needle with consistent local orientation. This is because strip A in microstructure is more resistant to creep than equiax A. In the slow creep process, the slip deformation of the equiaxial structure starts from the individual A grains, and with the increase of strain variables, the A grains occupied by slip occupy more expand to the surrounding P grains, so the creep cavity nucleus is late, but once the cavity is formed, it can expand rapidly and form a quasi-cleavage fracture.

The bar obtained by process C has a clutter level of 0.8-12dB in ultrasonic testing, which is all-inclusive; Product standard requirements for TA11 titanium alloy rods for bipedal blades. This also shows that increasing the forging temperature of TA11 titanium alloy bar, reducing deformation resistance and increasing the forging permeability of the bar can effectively improve its microstructure uniformity and improve its flaw detection level.

Through three forging process tests, comprehensive comparative analysis of the test data of TA11 titanium alloy bar in microstructure, mechanical properties and ultrasonic flaw detection level under different processes, we came to the following conclusions:

1) The influence of forging temperature on the microstructure of TA11 titanium alloy bar is obvious, and when the temperature is low, the primary a content in the bar tissue is higher, and the secondary a phase is less precipitated; After appropriately increasing the forging temperature, the content of primary A decreased significantly, and the precipitated fine needle-like secondary A phase increased.

2) The content of primary A and the morphology of secondary A distributed on the P matrix have a great influence on creep performance, and less primary A plus fine needle-like secondary A tissue can obtain good creep resistance.

3) The forging temperature increases, which increases the forging permeability of TA11 titanium alloy bar, and the structure is more uniform after the long strip or large A is completely broken, thereby improving the ultrasonic flaw detection level.