Views:1 Author:Site Editor Publish Time: 2016-04-28 Origin:Site
Titanium is a highly active metal, almost reactive with all elements. At high temperature,it also react organic reactions with CO, CO2, water vapor, NH4, and many volatile. In the process of heating,surface contamination and chemical composition change are the results of the metal elements reaction with titanium surface. Some gases will not only form titanium compounds on the surface, but also can enter the metal lattice to react the gap formation of solid solution. In an industrial pressure, the curve of oxygen, nitrogen absorption of pure titanium has a variety of changes at kinds of atmosphere environments.
Titanium and its alloys interacts with oxygen in air or oxygen atmosphere when heating..It forms a protective layer of oxide film when heated in less than 428 ℃, oxidation film thickness increases together with temperature, but oxide film starts to lose protection when temperature higher than 538 ℃. The oxygen passes through the film to the metal internal
diffusion to create an apparent permeability formation of gas reservoirs. If up to 815 ℃ above, a layer of loose scale on the surface of titanium alloy formed.
The reaction of titanium alloy and hydrogen is related with the heating temperature and time. In less than 427 ℃, if the titanium alloy surface with a layer of oxide film it can be resistance on inhalation of hydrogen. Above 427 ℃, the hydrogen began to pass through the oxide into the organization of alloy. The inhalation of hydrogen effected on the
properties of titanium alloy and alloy organization status.they have a direct relationship. Because the solubility of hydrogen atoms in the beta phase is much bigger than in the alpha phase, so the beta phase proportion and morphology of alloy is one of the main factors in determining how much hydrogen pollution.
In addition, the oil, the smudges is the cause of the increased carbon. Sweating smudges on surface when heating will cause the chloride adhesive. It caused hot salt stress corrosion in the course of subsequent use. The increase of gap elements not only directly affect the mechanical properties of titanium and titanium alloy, but also will affect α+ beta/beta
phase transformation point of titanium alloy and some of the phase change process. Therefore, it’s a very important to prevent pollution when heating titanium and titanium alloy.
For beta type of titanium alloy,vacuum forming is the most ideal. Especially when thin thickness and high surface brightness,embrittlement sensitivity.Vacuum forming is not necessarily requires expensive vacuum heating equipment.As long as it creates a sealed space between billet and mold on inferior vena, on the heating process with vacuum unit will
gradually take off the air in the inferior vena. Especially when forming temperature above 400 ℃ to make the vacuum of mold of the inferior vena up to 10 ^ (3) torr,turning the forming conversion line valves, filling the argon gas, then it can be accomplished. Using this method, satisfactory will be found when titanium foil corrugated plate forming. The
hydrogen content is lower than the standard requirements when vacuum control in 10 ^ (3) torr, when the vacuum degree reaches 10 ^ (5) torr you will see the bright surface of the parts.
So in order to reduce all kinds of influence of atmosphere environment, the vacuum quenching furnace and vacuum annealing furnace heating is generally used. the inert gas in the vacuum furnace can protect the titanium and titanium alloy materials in the process of heating without being contaminated.