phase change temperature is very important for the processing of titanium alloy, titanium alloy processing needs heat treatment, the phase change temperature range of titanium alloy needs to calculate the specific value.In this paper, calculation method, differential thermal analysis method and continuous temperature rise metallography method were used to determine the phase transition temperature range of titanium alloy samples.Three test methods were analyzed and the phase transition temperature of TC4 titanium alloy was 998℃.
TC4 titanium alloy has a wide range of applications in the aviation and aerospace industries, which have high requirements on the process.In the process of technological transformation of titanium alloy, it is necessary to conduct heat treatment, which requires the analysis of the phase transition temperature range of titanium alloy.
1. Properties and phase transition temperature of TC4 titanium alloy
TC4 titanium alloy (ti-6al-4v) is composed of two phase titanium alloy, the advantages are :(1) strong processing;(2) strong plasticity;(3) welding and corrosion resistance.TC4 titanium alloy is widely used in aviation and aerospace industry in China.
For titanium and titanium alloy processing and heat treatment is required, so the determination of the phase transition temperature of TC4 titanium alloy is very important, also is the application of the parameters of TC4 titanium alloy processing technology, processing to do thermal processing, processing of titanium alloy, to form the objective shape, need to control the temperature in the application of titanium alloy, which is in the titanium alloy heat treatment process of oxygen and nitrogen pollution index of the important reference basis.In the process of using titanium alloy materials, phase change temperature or phase change temperature range need to have accurate value, and the phase change temperature of titanium alloy with different composition and different processing history, the phase change temperature of each batch of raw materials is different.
2. Determination and analysis of phase transition temperature of TC4 titanium alloy
2.1 determination of phase transition temperature by different methods
2.1.1 determination of phase transition temperature by calculation method
The change of phase transition temperature of titanium alloy is the change of each element after thermal processing, and the calculation method can be used to calculate the change of temperature.
The calculation method was used to determine the phase transition temperature of titanium alloy as follows:
In the formula, 885℃ is the phase transition temperature of pure titanium.W is the mass value of each element;Q is the influence of each element on the phase transition temperature.
According to the influence of chemical composition and impurity content of TC4 titanium alloy on phase transition temperature, the calculation formula is as follows:
Effect of composition content in titanium alloy on phase transition temperature.
According to the calculation method, the phase transition temperature of TC4 titanium alloy is 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 samples are cooled by air cooling, which is difficult to control to eliminate the deformation stress, so there is residual stress in the DSC samples. After the test begins, the temperature will gradually increase, during which the residual stress will be released. The release of residual stress is an exothermic behavior, so the DSC curve in the previous stage of the samples will deviate from the baseline and release heat upward.
2.1.3 determination of phase transition temperature by continuous heating metallography
In the thermal process operation, the quenching temperature range is determined according to the phase change temperature value obtained by the calculation method and differential thermal analysis method, and the temperature is controlled at 980, 985, 990, 995, 1000 and 1005℃, respectively. The quenching temperature interval is determined to be 5℃.The average temperature between the quenching temperature of the phase and the vanishing temperature of the adjacent phase is the phase transition temperature.
In summary, TC4 titanium alloy has a wide range of applications, and its manufacturing process requires the heat treatment of titanium alloy. Therefore, it is necessary to know the phase change temperature value of titanium alloy.In this paper, the phase transition temperature range of the sample titanium alloy was measured by three test methods, and the difference of the measured values was not significant.Finally, the average phase transition temperature of TC4 titanium alloy was 998℃.