Titanium alloy has the characteristics of high strength, low density, corrosion resistance, and high-temperature resistance, and is widely used in the manufacture of compressor components in aviation products, such as impellers, forged titanium fans, compressor discs, and blades, cast titanium compressors casings, intermediary machines Cassettes, bearing housings, etc. However, too much hydrogen dissolved in titanium alloys will produce hydrides, making the alloy brittle. Chlorides in cutting fluid may also decompose or volatilize toxic gases during use, resulting in stress corrosion. The contact between tools and fixtures made of lead or zinc-based alloys, copper, tin, and cadmium, and titanium alloys will change the metal properties of the titanium alloy surface. Therefore, titanium alloy parts should avoid contact with pollutants during part processing, or the contaminated surface should be eliminated.
At present, with the mass production of titanium alloy parts, the concept of anti-fatigue manufacturing is gradually being applied to engineering practice in aviation enterprises, and the requirements for the surface state of parts are getting higher and higher. Since 2010, various aviation companies have proposed some manufacturing process requirements for titanium alloy parts according to theoretical analysis, but the effective control measures adopted in the actual process are uneven and not perfect and systematic. The research on anti-pollution methods used in the processing of titanium alloy parts is not systematic and comprehensive enough.
Basic introduction of titanium alloy materials
When the carbon content is greater than 0.2%, hard TiC will be formed in the titanium alloy; when the temperature is high, the TiN hard surface layer will be formed when it interacts with N; when the temperature is above 600 ° C, titanium absorbs oxygen to form a hardened layer with high hardness ; When the hydrogen content rises, an embrittlement layer will also be formed. The depth of the hard and brittle surface layer produced by absorbing gas can reach 0.1-0.15mm, and the hardening degree is 20%-30%. Small thermal conductivity and small modulus of elasticity. The thermal conductivity of titanium λ=15.24W/(m.K) is about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum, while the thermal conductivity of various titanium alloys is about 50% lower than that of titanium.
Anti-stress corrosion and pollution measures of titanium alloy parts in processing
1. Stress corrosion of titanium alloy
Due to the degree of tensile stress induced by machining, assembly or forming operations, the greater the tensile stress, the higher the risk of stress corrosion. Therefore, controlling the method that produces the lowest tensile stress is critical. Conversely, compressive stresses within the material are beneficial to the part.
Stress corrosion occurs only in the presence of contaminants. The risk of stress corrosion increases when contaminants remain on the part, the temperature is high (especially above 250°C) or it is exposed to high temperature for a long time.
2. Pollutants
It is very difficult to distinguish between different alloys and the stress of each part of the part in the manufacture of the product. The following regulations apply to all titanium alloy parts.
Prohibited items: gaseous or liquid organic halogenated agents (chlorinated): chlorine-containing cutting fluids; industrial alcohol or products containing industrial alcohol.
Direct contact between titanium alloys and magnesium, silver, and cadmium metals is not allowed. In particular, tools used in manufacturing cannot be cadmium-plated, but can be nickel-plated, phosphating or alkaline blued.
3) Residual traces of low melting point compounds (paraffin wax, etc.) must be removed before the final surface is formed. The same restrictions also include low melting point metals (lead, tin, zinc and their alloys).
3. Research on cleaning methods
1) Degaussing
The parts are magnetized directly or occasionally during processing, so all parts must be demagnetized before the final cleaning. The demagnetization treatment of all parts should at least achieve a magnetic field strength of no more than 3 gauss (except for parts that are required to be magnetic). When individual parts require magnetization, they should be processed separately to meet the requirements. To maintain the specified magnetic properties during processing, parts should be protected.
2) Ordinary cleaning
Titanium alloy parts should not be in contact with methanol solvents or chloride solvents (such as trichloroethylene, trichloroethane). Use a clean gauze dipped in acetone, methyl ethyl ketone or isopropanone to wipe the surface of the part to remove oil. Non-intermittent water film state: This state refers to the state in which a continuous water film is formed on the surface of a part after being immersed in water, and the water film will not form small water droplets for at least 10s.
3) Pressure washing
Parts with deep grooves should be pressure washed, and the solution should be filtered through a 5μ filter before flushing. Such parts include conduits, fuel manifolds, valve pockets and internal piping in castings.
(1) Before the flushing process, the parts should be degreased first.
(2) Corrosion-prone alloys can't be pressure-washed with water.
(3) Pressurize and cleanse each internal pipe for at least 30 seconds. In actual work, at least reverse flush for 30 seconds.
(4) Mechanical vibration during flushing is very helpful for cleaning parts with internal cavities and pipes.
4) Rinse parts with deionized water
Check whether the acid solution in the wet parts is completely removed, and place blue litmus paper on the parts where acid may remain. If the test paper turns red, residual acid is present and the parts should be rewashed. If the test paper shows no visible discoloration, the acid is considered to have been removed.
Shaanxi Etermetal Co., Ltd. is a titanium products supplier located in "China Titanium Valley". The products we supply include various specifications of titanium rods, titanium plates and titanium pipes. If you are looking for qualified suppliers, welcome to consult and cooperate!
