Introduction of Titanium Alloy (2)

Aug. 17, 2011 - PRLog -- Property
Titanium is a new type of metal, its performance related to the carbon, nitrogen, hydrogen, oxygen and other impurities, the most pure iodide titanium impurities does not exceed 0.1%, but its intensity is low, plasticity is high.

99.5% of industrial pure titanium properties: density ρ = 4.5g/cm3, melting point 1725 ℃, thermal conductivity λ = 15.24W / (mK), tensile strength σb = 539MPa, elongation δ = 25%, reduction of area rate ψ = 25%, elastic modulus E = 1.078 × 105MPa, hardness HB195.
High strength
The density of titanium is generally about 4.5g/cm3, only 60% of steel, pure titanium's strength was nearly normal strength of steel, lots of high-strength titanium alloy more than structural steel. Therefore, the ratio of titanium strength (strength / density) is much larger than other metal structural materials, it can be a unit of high strength, rigid, lightweight parts and components. Currently titanium alloy are used in engine components, skeleton, skin, and landing gear fasteners and so on.

High heat intensity
Using temperature is several hundred degrees higher than aluminum, at moderate temperatures can still maintain the required strength in the 450 ~ 500 ℃ temperature long-term work.

These two types of titanium alloy have still a very high specific strength in the range of 150℃ ~ 500℃, while rate intensity of aluminum alloy decreased significantly at 150 ℃. The operating temperature of titanium alloy can up to 500 ℃, aluminum alloy is below 200℃.

Good corrosion resistance
Titanium alloy can work in humid atmosphere and seawater, its corrosion resistance far superior than stainless steel; have particularly strong resistance of pitting, etching and stress corrosion; and so have excellent corrosion resistance to alkali, chloride, chlorine, organic materials, nitric acid, sulfuric acid. But its corrosion resistance is poor with the reduction of titanium oxide and chromium salts medium.

Good low temperature performance

Titanium alloys can maintain its mechanical properties at low temperatures and extremely low temperatures. The titanium elements of good low temperature performance, low gap elements, such as TA7, can maintain a certain plasticity under -253 ℃. Therefore, titanium is also an important low-temperature structural materials.

large Chemical activity

Large chemical activity of titanium, and have a strong chemical reaction with atmospheric O, N, H, CO, CO2, water vapor, ammonia, etc. Greater than 0.2% carbon, titanium formed in the hard TiC; temperature is higher, the role will be to form TiN with N.

Hard surface; above 600 ℃, the high hardness of titanium to absorb oxygen to form the hardened layer; Hydrogen content increased will form a brittle layer. Absorption of gases arising from hard and brittle surface depth of up to 0.1 ~ 0.15 mm, sclerosis of 20% to 30%. The chemical affinity of titanium is also large, easy-surface adhesion and friction phenomena.

Low thermal conductivity, modulus of elasticity
Thermal conductivity of titanium λ = 15.24W / (mK), about 1 / 4 of nickel, 1/5 of iron, 1 / 14 of Al, While the thermal conductivity of titanium alloy can be declined by about 50% than titanium. The elastic modulus of titanium is about 1 / 2 of steel, so the poor rigidity, deformation, not making slender rods and thin-walled parts, cutting the surface of the rebound process a large volume of about 2 to 3 stainless steel times, resulting in a sharp cutting tool flank friction, adhesion, adhesive wear.

Application

Titanium alloy have high strength and small density, good mechanical properties, good toughness and corrosion resistance. In addition, the titanium process performance is poor, cutting hard, in the heat processing, very easy to absorb hydrogen nitrogen carbon and other impurities. Have poor abrasion resistance, complex production process. The industrial production of titanium was begun from 1948. Aviation industry needs to make titanium industry at an average annual growth rate of about 8% of the development. World annual production of titanium processing material has reached 40,000 tons, nearly 30 kinds of titanium alloy grade. The most widely used titanium alloy is Ti-6Al-4V (TC4), Ti-5Al-2.5Sn (TA7) and commercially pure titanium (TA1, TA2 and TA3).

Mainly for the production of titanium aircraft engine compressor components, followed by rockets, missiles and high-speed aircraft structural parts. In the mid of 1960s, titanium and its alloys applied in general industrial applications, for the production of electrolytic electrode industry, power plant condensers, oil refining and desalination of the heater and environmental pollution control devices. Titanium and its alloys have become corrosion resistant structural materials. In addition, for the production of hydrogen storage materials and shape memory alloys.

China began studies of titanium and titanium alloys in 1956; in the mid of 1960s began the development of industrial production and produced the TB2 alloy.

Titanium is an important new structural materials used in the aerospace industry, the specific gravity, strength and temperature range between aluminum and steel, but high strength and excellent resistance to seawater corrosion and ultra-low temperature performance. In 1950 the United States for the first time in F-84 fighter-bombers used on the rear fuselage insulation panels, wind guide cover, tail cover and other non-load-bearing components. 1960s the use of titanium alloy parts of the body toward the fuselage from the rear, in part, instead of structural steel bulkheads, beams, rails and other important bearing flap components. The amount of titanium used in military aircraft the rapid increase, to the aircraft structural weight of 20% to 25%. 70's, began extensive use of civilian machine titanium alloys, such as the Boeing 747 with capacity of 3640 kg or more. Less than Mach 2.5 aircraft is mainly used titanium instead of steel in order to reduce structural weight. Again, the United States SR-71 high-altitude high-speed reconnaissance aircraft (flight Mach 3 at an altitude of 26,212 meters), titanium accounted for 93% of the weight of the aircraft structure, known as "the all-titanium" aircraft. When the aircraft engine thrust-weight ratio from 4~6 to 8~10, corresponding to the compressor outlet temperature from 200 ~ 300 ° C to 500 ~ 600 ° C, the original low-pressure compressor disk made of aluminum and the blades must be use titanium, or us titanium alloy instead of stainless steel high-pressure compressor disk and blades, to reduce the structural weight. In the 1970s, the amount of titanium used in aviation engines general accounted for 20%~30% of the total weight of the structure, mainly for the manufacture of compressor parts, such as forging titanium fan, compressor discs and blades, cast titanium compressor casing, intermediate casing, bearing housing and so on. The main use of titanium spacecraft is its high specific strength, corrosion resistance and low temperature performance to produce a variety of pressure vessels, fuel tanks, fasteners, instruments straps, and architecture and rocket shells. Man-made earth satellite, lunar module, manned spacecraft and space shuttle are also using titanium plates welded.
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