Titanium Alloy
Titanium is an important structural metal developed in the 1950s. Titanium alloys have high strength, good corrosion resistance, and high heat resistance. From the 1950s to the 1960s, it was mainly to develop high-temperature titanium alloys for aircraft engines and structural titanium alloys for airframes.

From the 1950s to the 1960s, it was mainly to develop high-temperature titanium alloys for aircraft engines and structural titanium alloys for airframes. In the 1970s, a number of corrosion-resistant titanium alloys were developed. Since the 1980s, corrosion-resistant titanium alloys and high-strength titanium alloys have been further developed. development of. The service temperature of heat-resistant titanium alloy has increased from 400℃ in the 1950s to 600～650℃ in the 90s. The emergence of A2 (Ti3Al) and r (TiAl) based alloys makes titanium in the engine's use part is advancing from the cold end (fan and compressor) of the engine to the hot end (turbine) of the engine. Structural titanium alloys are developing toward high strength, high plasticity, high strength, high toughness, high modulus, and high damage tolerance.

In addition, since the 1970s, shape memory alloys such as Ti-Ni, Ti-Ni-Fe, and Ti-Ni-Nb have appeared, and are increasingly used in engineering.

There are hundreds of titanium alloys developed in the world, and the most well-known alloys are 20 to 30, such as Ti-6Al-4V, Ti-5Al-2.5Sn, Ti-2Al-2.5Zr, Ti-32Mo, Ti- Mo-Ni, Ti-Pd, SP-700, Ti-6242, Ti-10-5-3, Ti-1023, BT9, BT20, IMI829, IMI834, etc. [2,4].

According to relevant statistical data, the amount of titanium used in my country's chemical industry reached 25,000 tons in 2012, a decrease from 2011. This is the first time that my country's chemical titanium market has experienced negative growth since 2009. In recent years, the chemical industry has been the largest user of titanium processing materials, and its proportion in the total amount of titanium materials has been maintained at more than 50%. In 2011, it accounted for 55%. However, as the economy is in a downturn, the chemical industry has not only significantly reduced new construction projects, but also faced industrial restructuring, some products have new production capacity under control, and backward production capacity will also be phased out. Affected by this, its shrinkage of the amount of titanium processing materials has become logical. Prior to this, some insiders predicted that the amount of titanium used in the chemical industry will peak between 2013 and 2015. Judging from the current market performance, the weakening of the overall economy in 2012 may make the recession period of titanium for chemical industry advance.

Performance

Titanium is a new type of metal. The performance of titanium is related to the content of impurities such as carbon, nitrogen, hydrogen, and oxygen. The purity of titanium iodide does not exceed 0.1%, but its strength is low and its plasticity is high. The properties of 99.5% industrial pure titanium are: density ρ=4.5g/cubic centimeter, melting point 1725℃, thermal conductivity λ=15.24W/(mK), tensile strength σb=539MPa, elongation δ=25%, cross section Shrinkage ψ=25%, elastic modulus E=1.078×105MPa, hardness HB195.

High strength
The density of titanium alloy is generally about 4.51g/cubic centimeter, which is only 60% of steel. The density of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloy is much greater than other metal structural materials. See Table 7-1, which can produce parts with high unit strength, good rigidity and light weight. Titanium alloys are used for aircraft engine components, skeletons, skins, fasteners, and landing gear.

High thermal strength
The use temperature is several hundred degrees higher than that of aluminum alloy. It can still maintain the required strength at medium temperature. It can work for a long time at a temperature of 450 to 500 ℃. These two types of titanium alloys are still very high in the range of 150 ℃ to 500 ℃. Specific strength, while the specific strength of aluminum alloy at 150 ℃ significantly decreased. The working temperature of titanium alloy can reach 500 ℃, aluminum alloy is below 200 ℃.

Good corrosion resistance
Titanium alloys work in humid atmosphere and seawater media, and their corrosion resistance is far superior to stainless steel; they are particularly resistant to pitting, acid corrosion, and stress corrosion; organic substances such as alkali, chloride, chlorine, nitric acid, and sulfuric acid Etc. have excellent corrosion resistance. But titanium has poor corrosion resistance to media with reducing oxygen and chromium salts.

Good low temperature performance
Titanium alloy can still maintain its mechanical properties under low temperature and ultra-low temperature. Titanium alloys with good low temperature performance and extremely low interstitial elements, such as TA7, can maintain a certain plasticity at -253℃. Therefore, titanium alloy is also an important low-temperature structural material.

Great chemical activity
Titanium has a high chemical activity and is compatible with O, N, H in the atmosphere

Titanium alloy products

, CO, CO2, steam, ammonia, etc. produce strong chemical reactions. 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; above 600 ℃, titanium absorbs oxygen to form a hardened layer with high hardness ; Increased hydrogen content will also form a brittle layer. The depth of the hard and brittle surface produced by absorbing gas can reach 0.1～0.15 mm, and the degree of hardening is 20%～30%. Titanium also has a large chemical affinity, and is prone to adhere to friction surfaces.

Low thermal conductivity
The thermal conductivity of titanium λ = 15.24W/ (m.K) is about 1/4 of nickel, 1/5 of iron, 1/14 of aluminum, and the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The elastic modulus of titanium alloy is about 1/2 of that of steel, so its rigidity is poor and it is easy to deform. It is not suitable to make slender rods and thin-walled parts. The springback of the processed surface during cutting is very large, which is about 2 to 3 of stainless steel Times, causing violent friction, adhesion, adhesive wear on the flank of the tool.