Panoramic Analysis of Titanium Alloys: Classification, Characteristics and Applications
As an important structural metal since the 1950s, titanium alloys have become key materials in the fields of biomedicine, ocean engineering and so on due to their unique physical and chemical properties. To fully understand titanium alloys, it is necessary to systematically analyze them from three dimensions: its classification system, core characteristics and diversified applications.
Classification System of Titanium Alloys
Titanium alloys are mainly divided into three categories: α-type, β-type, and α-β-type according to the microstructure at room temperature.
Alpha titanium alloy
It has good heat resistance, corrosion resistance and weldability, but its strength is low at room temperature and cannot be strengthened by heat treatment. Alpha-titanium alloy is one of the basic categories of titanium alloys, and its micro-structure is mainly composed of α-phase solid solution. This type of alloy achieves phase structure stabilization by adding α-stable elements such as aluminum, tin, and zirconium, and still has excellent strength, creep resistance, and oxidation resistance at high temperatures of 500 °C to 600 °C. Because it cannot be strengthened by heat treatment and has relatively low room temperature strength, α titanium alloys are mainly used in high-temperature structural components and low-temperature extreme fields.
Beta titanium alloy
It has high strength and can be strengthened by heat treatment, but the production process is complex, the cost is high, and the welding performance is poor.
β-titanium alloys are titanium alloys with β-stable elements as the main elements and quenched above the β-phase transformation point to obtain a full β-phase structure. According to molybdenum equivalence, they are divided into three categories: near-β, metastable β and stable β. The main components are molybdenum, vanadium, chromium and other elements. Typical grades include Ti-10V-2Fe-3Al, Ti-5Al-5Mo-5V-3Cr, etc. The tensile strength can reach 1100-1532MPa, and the minimum elastic modulus is 50GPa.
α + β type titanium alloy
It has the best comprehensive properties, adjusts strength and plastic properties, and is widely used, such as the common TC4 alloy. α β titanium alloy is one of the three categories of titanium alloy, and the grade is indicated by TC. The alloy is a dual-phase alloy with good microstructure stability, good toughness, plasticity and high-temperature deformation properties, and can be hot-pressed and heat-treated to strengthen. Its mechanical properties have a wide range of changes and can be adapted to a variety of purposes, accounting for more than 70% of industrial use. At present, the most widely used α + β titanium alloy is Ti-6Al-4V (TC4/Gr5).
Core Characteristics of Titanium Alloys
The excellent properties of titanium alloys are derived from their unique physical and chemical nature, which are mainly reflected in the following aspects:
I. Advantage of high specific strength
1. The density is only 60% of that of high-strength steel and about 1.2 times that of aluminum alloy. The specific strength (ratio of strength to density) far exceeds that of steel and aluminum alloy. The core material for high-speed rail transit parts.
2. At the same time, it has excellent toughness and fatigue resistance, can adapt to complex alternating load conditions, and is not easy to cause fatigue fracture in service.
II. Excellent corrosion resistance
1. The surface will naturally form a dense TiO ₂ passivation film with a thickness of about 10nm, which is extremely stable in seawater, atmosphere, and most acid-alkali media. It has outstanding resistance to pitting corrosion and crevice corrosion, and will not cause stress corrosion cracking. Corrosion resistance Far superior to ordinary stainless steel and aluminum alloys.
2. It can serve in harsh marine, chemical, nuclear power and other corrosion without additional anti-corrosion coating maintenance.
III. Strong adaptability to high and low temperature
1. Excellent low-temperature performance, good toughness and strength under liquid nitrogen of-253 °C, and will not have low-temperature brittle fracture problems like most metals, suitable for low-temperature storage tanks and low-temperature fuel pipeline scenarios.
2. The high-temperature performance is stable. The conventional TC4 titanium alloy can be used stably at 500 °C, and the new high-temperature titanium alloy can be used for a short period of time above 600 °C. It is suitable for engine turbine blades and high-temperature industrial furnace components.
IV. Excellent bio-compatibility
1. Chemical properties are stable, electrolysis and corrosion reactions will not occur in human body fluids, and no toxic metal ions will be precipitated;
2. It has good biocompatibility with human bones and soft tissues, strong osseointegration ability, and will not cause immune rejection. It is the mainstream medical metal material for medical orthopedic implants, dental implants, and artificial joints.
V. Low magnetism and non-magnetism
1. Most titanium alloys are paramagnetic materials with extremely low permeability, will not be absorbed by strong magnetic fields, will not generate residual magnetism, and will not interfere with electromagnetic signals.
2. Adapt to electromagnetic compatibility equipment, seabed detection instruments, medical nuclear magnetic resonance supporting components and other scenarios that have strict requirements on electromagnetic performance.
VI. Diversified Applications of Titanium Alloys
Aviation & The Deep Sea
It is used for fuselage structural parts (Boeing 787 uses 15 tons per unit), engine compressor blades/disks, rocket fuel tanks and satellite brackets to achieve extreme weight reduction and high temperature/low temperature balance.
Biomedical
Orthopedic implants (joint replacement, bone nails), dental implants, cardiovascular stents and surgical instruments rely on their "osseointegration" ability and non-magnetic and non-toxic properties.
Marine Chemical Industry and Energy
The pressure-resistant shell of the deep-sea detector, the seawater desalination heat exchange tube, the inner lining of the chlor-alkali industrial electrolyzer and the hydrogen energy storage tank solve the pain points of strong corrosion and high pressure.
