On 2018-08-08 14:48:54
Heat treatment of titanium alloy
Precautions for titanium alloy cleaning and heat treatment
When the titanium in the high temperature oxide salt is cleaned, the current will be generated when the workpiece contacts with the iron-based material. Titanium and these iron-based materials form a positive electrode or anode, forming a circuit breaking voltage of about 0.60v. As a result of the release from the rack to the workpiece, the surface will overheat and may catch fire. This effect can be reduced by maintaining a salt bath temperature of no higher than 455 ° C (850 ° f) and using titanium clamps or aluminum insulation between the workpiece and the clamps.
Before salt bath treatment, mechanical grinding can be used to remove the surface pollution of forgings or hot rolled materials with thick scale.
In the process of hot forming or annealing of titanium alloy, silicon-based protective layer can reduce the formation of scale. All coatings shall be removed before acid treatment.
During the production or assembly of vacuum heat treated titanium, a mixed surface pollution is formed, including graphite or molybdenum disulfide with titanium oxide, which shall be cleaned by molten salt bath. According to the industry treatment standard, Changzhou vacuum heat treatment plant recommends that the treatment temperature be maintained at 204 ℃ (400 ℉) to avoid thermal deformation.
When treated in salt bath or alkaline solution, titanium oxide on metal surface will produce chemical reaction to form sodium titanate. Soluble in acids containing sulfur and nitrogen hydrogen fluoride. Sulfuric acid has no corrosive effect on titanium or titanium alloy, and the corrosion is inhibited by increasing 0.25-1.0% copper sulfate or iron sulfate.
Most of the acid pickling after salt dissolving treatment is carried out in the acid solution containing sulfur and nitrogen hydrogen fluoride. The material circulation is carried out by salt dissolving, water rinsing and sulfuric acid until all scales are completely removed. The bright treatment after salt dissolving is completed after short-term cycle soaking in nitric acid and hydrofluoric acid bath solution.