Abstract: Phase transition temperature is very important for titanium alloy processing technology. Titanium alloy processing requires heat treatment. Specific values of phase transition temperature range of titanium alloy need to be calculated. In this paper, the calculation method, differential thermal analysis method and continuous heating metallographic method were used to measure the titanium alloy samples, and the phase transition temperature range was obtained. In this paper, three test methods are analyzed, and the phase transition temperature of TC4 titanium alloy is 998 ℃.

Foreword

TC4 titanium alloy has a wide range of applications, and its application fields are in the aerospace and aerospace industries, which require higher technology. The titanium alloy needs to be heat-treated during the technological transformation process. This requires analysis of the phase transition temperature range of the titanium alloy. In this paper, three methods are used to test a titanium alloy sample to obtain the phase transition temperature value.

1.TC4 titanium alloy properties and phase transition temperature

The composition of TC4 titanium alloy (Ti-6Al-4V) is composed of α and β two-phase titanium alloy. Its advantages are: (1) strong processability; (2) strong plasticity; (3) weldable and corrosion resistant. TC4 titanium alloy is widely used, which is mainly reflected in the aviation and aerospace industries in China.

The processing of titanium and titanium alloys requires heat treatment, so the measurement of the phase transition temperature of TC4 titanium alloy is very important. It is also the application parameter of the TC4 titanium alloy treatment process. During the processing, heat treatment is performed to process the titanium alloy to form the target shape It is necessary to control the applicable temperature of titanium alloy, which is also an important reference for oxygen and nitrogen pollution indicators in the titanium alloy heat treatment process. In the use of titanium alloy materials, the phase transition temperature or phase transition temperature range needs to have accurate values. The phase transition temperature of titanium alloys varies with the composition of the titanium alloy and the processing history. The phase transition temperature of each batch of raw materials Also different.

2.Measurement and Analysis of TC4 Titanium Alloy Phase Transition Temperature

2.1 Determination of phase transition temperature by different methods

2.1.1 Calculation of phase transition temperature

The change of the transformation temperature of titanium alloy is the change of each element after hot working, and the temperature change is calculated by calculation method. The calculation method can provide the selection range of quenching temperature in continuous heating metallography method [1].

The calculation formula for the phase transition temperature of titanium alloy using calculation method is:

In the formula, 885 ° C is the phase transition temperature of pure titanium; W is the mass value of each element; q is the effect of each element on the phase transition temperature.

According to the influence of the chemical composition and impurity content of TC4 titanium alloy on the phase transition temperature, the calculation formula is:

The effect of the content of the components in the titanium alloy on the phase transition temperature is shown in Table 1.

Table 1 Effect of the content of the components in the titanium alloy on the phase transition temperature

Phase type element mass content (ppm) influence value (℃)

Alpha phase Al 6.12 ± 0.21 + 14.5 ± 0.2

N 0.01 ± 0.02 + 23.2 ± 0.1

O 0.16 ± 0.01 + 5.5 ± 0.5

C 0.012 ± 0.11 + 2.5 ± 0.2

βH 0.005 ± 0.110-5.1 ± 0.1

V 4.02 ± 0.05-15.0 ± 0.2

Fe 122.0 ± 1.21-15.3 ± 1.2

Si 0.01 ± 0.12-1.0 ± 0.2

According to the calculation method, the phase transition temperature of TC4 titanium alloy is calculated to be 885 ℃ + (aluminum) 126.75 ℃-(vanadium) 56.7 ℃-(iron) 2.01 ℃-(silicon) 0.1 ℃ + (carbon) 4.4 ℃ + (oxygen) 34.0 ℃ + (nitrogen) 5.5 ℃-(hydrogen) 1.1 ℃ = 995.7 ℃.

2.1.2 Determination of phase transition temperature by differential thermal analysis

The differential thermal analysis method is to analyze the sample with the help of a differential thermal analyzer, and compare it with the sample under the same conditions, and establish a curve comparison chart based on the temperature difference between the two to determine the state of the substance [2]. The sample is cooled by air cooling, which is difficult to control the deformation stress. Therefore, residual stress is stored in the DSC sample. After the test starts, the temperature will gradually increase. During this period, the residual stress is released. Thermal behavior, so the DSC curve of the sample before the sample will deviate from the baseline and release heat upward.

2.1.3 Determination of phase transition temperature by continuous heating metallographic method

In the thermal process operation, the quenching temperature range is determined according to the phase transition temperature values obtained by the calculation method and the differential thermal analysis method. The temperatures are controlled at 980, 985, 990, 995, 1000, and 1005 ° C, respectively, and the quenching temperature interval is determined as 5 ° C. The average temperature between the quenching temperature of the α phase and the temperature at which the α phase disappears is the phase transition temperature.

3. Conclusion

In summary, TC4 titanium alloy has a wide range of applications, and its manufacturing process requires heat treatment of the titanium alloy. Therefore, it is necessary to understand the phase transition temperature of the titanium alloy. In this paper, the phase transition temperature range of the sample titanium alloy is tested by three test methods. The measured values are not much different. Each method can provide accurate data, but the operation methods are different. It was finally concluded that the average phase transition temperature of the TC4 titanium alloy was 998 ° C.