The main measures to prevent the pollution of titanium tube and titanium alloy

Titanium is a highly reactive metal whose activity increases with increasing temperature. Titanium and its alloys can react with oxygen in the presence of air or oxygen. A layer of protective film is formed when the heating temperature is less than 428 degrees, the oxidation film thickness increased when the temperature increases. When the temperature is above 538 degrees, the oxidation film began to lose the protective effect, the oxygen started to diffuse through the membrane to the metal, forming obvious infiltration. If the temperature rises above 815 degrees, the titanium surface will form a layer of loose oxide.
The effect of hydrogen and titanium alloy is related to the heating temperature and time. When the temperature is below 427 degrees, if there is a layer of oxide film on the surface of the alloy, the hydrogen can be prevented from being sucked in, and when the temperature is higher than the temperature of 427 degrees, the hydrogen begins to enter the alloy structure through the oxide layer.
In order to prevent the oxidation of titanium alloy during superplastic forming, as well as the absorption of hydrogen and other trace elements, it is necessary to take technical measures to improve the performance of titanium alloy parts.
At present, the main measures are: coating protection, vacuum heating and inert gas (argon) protection.
1. Coating protection method:
It is coated with a certain thickness of the protective coating after cleaning on the surface of the formed blank, and the part is removed by alkali washing, acid washing or sand blowing.
The coating should have the following main properties:
a. High temperature resistance, can be used at 750 - 1050 degrees Celsius.
b. Should have a certain degree of lubrication, to prevent the billet in the formation of abrasions.
c. The coating can be firmly attached to the surface of the workpiece at the operating temperature.
d. Easy to remove after heating.
e. No harmful substances, no environmental pollution and affect human health.
After the identification, the coating material suitable for titanium tube and titanium alloy superplastic forming: Ti - 2 alcohol soluble preparation can be used in combination with Ti - 3 graphite lubricant, which is suitable for hot forming at 750 - 1050 degrees. KBC - 12 water-soluble preparation, can be used in conjunction with graphite water.
2. Vacuum forming:
The vacuum forming is the most ideal for the titanium alloy which has a thin wall thickness, high brightness and high sensitivity to hydrogen embrittlement.



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