TC4 titanium alloy has a wide range of applications, and the fields of application are aviation, aerospace industry, which has higher requirements for the process. In the titanium alloy process transformation process needs its heat treatment, which needs to analyze the phase transition temperature range of titanium alloy, the text for a titanium alloy specimen using three methods of testing, to obtain the phase transition temperature value.
1. Properties and phase transition temperature of TC4 titanium alloy
The composition of TC4 titanium alloy (Ti-6Al-4V) is composed of α and β two-phase titanium alloys, the advantages of which are: (1) strong workmanship; (2) plasticity; (3) weldable and corrosion-resistant.TC4 titanium alloys have a wide range of applications, which are mainly embodied in the aviation and aerospace industries in China.
The processing of titanium and titanium alloys requires heat treatment, so the determination of the phase transition temperature of TC4 titanium alloy is very important, but also the application parameters of the TC4 titanium alloy treatment process, the treatment is done when the thermal processing treatment, processing titanium alloy, so that the formation of the shape of the purpose of the titanium alloy, you need to control the applicable temperature of the titanium alloy, which is also in the titanium alloy heat treatment process of the oxygen and nitrogen pollution indicators of the important reference basis. In the use of titanium alloy materials in the process, the phase transition temperature or phase transition temperature range needs to have an accurate value, and the value of the phase transition temperature of titanium alloys is different with the different compositions of titanium alloys and different processing histories, and the phase transition temperature of each batch of raw materials is also different.
2.Measurement and analysis of phase transition temperature of TC4 titanium alloy
2.1 Determination of phase change temperature by different methods
2.1.1 Calculation method for the determination of phase transition temperature
The change in phase transition temperature of titanium alloy is the change of each element in it after thermal processing, and the temperature change is deduced by the calculation method, which can provide the selection range of quenching temperature in the continuous temperature rise metallographic method [1].
The formula for the determination of the phase change temperature of titanium alloys using the computational method is:
In the formula 885°C is the phase transition temperature of simple 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 transformation temperature, the formula is calculated as:
The effect of the content of components in titanium alloys on the phase transition temperature is shown in Table 1.
Table 1 The effect of the content of components in titanium alloys on the phase transition temperature
Phase type Element Mass content (ppm) Influence value (℃)
α 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
β H 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 deduced to be 885°C + (Al) 126.75°C - (V) 56.7°C - (Fe) 2.01°C - (Si) 0.1°C + (C) 4.4°C + (O) 34.0°C + (N) 5.5°C - (H) 1.1°C = 995.7°C.
2.1.2 Determination of the phase transition temperature by differential thermal analysis
Differential thermal analysis method is to analyze the specimen with the help of a differential thermal analyzer, compare it with the specimen under the same conditions, and establish a curve comparison graph according to the relationship between the two temperature difference changes, and make a determination of the state of matter [2]. The specimen is cooled by air cooling, which is more difficult to control the elimination of deformation stress, so there is residual stress in the DSC specimen, and after the test starts, the temperature will gradually increase, during which is the release of residual stress, and the release of residual stress belongs to the exothermic behavior, so the DSC curve of the specimen in the first stage will deviate from the baseline, and upward exothermic.
2.1.3 Determination of phase change temperature by continuous heating metallographic method
In the thermal process operation, the quenching temperature range is determined according to the phase change temperature value derived from the calculation method and the differential thermal analysis method, and the temperature is controlled in 980, 985, 990, 995, 1000, 1005℃ respectively, and the quenching temperature interval is determined to be 5℃. The average temperature between the quenching temperature of the α-phase and the temperature near the disappearance of the α-phase is the phase transition temperature.
3.Conclusion
In summary, TC4 titanium alloy has a wide range of applications, and its fabrication process requires heat treatment process of titanium alloy, so it is necessary to know the value of phase transition temperature of titanium alloy. In this paper, the phase transition temperature range of the specimen titanium alloy is tested by three testing methods, and the difference of its measurement value is not big, and each method can provide accurate data, but the operation methods are different. The final result is that the average value of phase change temperature of TC4 titanium alloy is 998°C.
