By leveraging the distinct characteristics of alpha and beta titanium structures, alloying elements are added to gradually alter the phase transition temperature and phase composition.
This process results in titanium alloys with different microstructures, offering a range of properties suitable for various applications.
Titanium Alloys: Alloying Elements
Titanium alloyelements can be classified into three categories based on their influence on phase transition temperature:
Alpha-Stabilizing Elements (α-Stabilizers): These elements stabilize the α phase and increase the phase transition temperature. Examples include aluminum, magnesium, ออกซิเจน, and nitrogen. Aluminum is the primary alloying element in titanium alloys, significantly enhancing the alloy’s strength at both room and high temperatures, reducing density, and increasing elastic modulus.
Beta-Stabilizing Elements (β-Stabilizers): These elements stabilize the β phase and lower the phase transition temperature. They can be further categorized into isomorphous and eutectoid types. Examples of isomorphous β-stabilizers include molybdenum, niobium, and vanadium, while eutectoid β-stabilizers include chromium, manganese, copper, and silicon.
Neutral Elements: These elements have minimal influence on phase transition temperature. Examples include zirconium and tin.
Classification ofTitanium Alloys
Alpha Titanium Alloys (α-Ti Alloys):
These alloys consist of a single-phase α-phase solid solution.
They maintain stability at room temperature and higher practical application temperatures.
Superior wear resistance compared to pure titanium.
Retain strength and creep resistance at temperatures from 500°C to 600°C.
Cannot undergo heat treatment strengthening, resulting in moderate room temperature strength.
Beta Titanium Alloys (β-Ti Alloys):
These alloys consist of a single-phase β-phase solid solution.
Despite not undergoing heat treatment, they exhibit high strength.
Further strengthening can be achieved through quenching and aging.
Room temperature strengths range from 1372 to 1666 MPa.
Poor thermal stability, unsuitable for high-temperature applications.
Alpha + Beta Titanium Alloys (α + β-Ti Alloys):
Dual-phase alloys with good comprehensive performance and stable microstructure.
Possess good toughness, plasticity, and high-temperature deformation resistance.
Suitable for hot forging.
Heat treatment strengthens the alloy, increasing strength by approximately 50% to 100% compared to the annealed state.
Exhibit high-temperature strength, capable of operating for extended periods at temperatures from 400°C to 500°C.
Thermal stability is inferior to α-Ti alloys.
Classification and Usage:
Among titanium alloys, α-Ti alloys and α + β-Ti alloys are most commonly used, with α-Ti alloys being the most suitable for machining.
The designation for α-Ti alloys is TA, for β-Ti alloys is TB, and for α + β-Ti alloys is TC.
Titanium alloys can be classified according to their applications:
Heat-resistant alloys,
High-strength alloys,
Corrosion-resistant alloys (e.g., titanium-molybdenum and titanium-palladium alloys),
Low-temperature alloys,
Special function alloys (e.g., titanium-iron hydrogen storage materials and titanium-nickel memory alloys).
Heat Treatment of Titanium Alloys
Effect of Heat Treatment on Titanium Alloys:
By adjusting the heat treatment process, different phase compositions and microstructures can be achieved in titanium alloys.
Fine equiaxed microstructures are typically preferred due to their:
Better ductility,
Thermal stability, และ
Fatigue strength.
Needle-like microstructures offer advantages such as:
Higher creep strength, และ
Improved fracture toughness.
Mixed equiaxed and needle-like microstructures provide:
Good comprehensive performance.
Properties ofTitanium Alloys
High Specific Strength:Titanium alloys have a density of around4.5 g/cm34.5g/cm3, only 60% that of steel. Their specific strength (strength/density) far exceeds that of other metallic structural materials, making them ideal for lightweight components in aircraft engines, frameworks, skins, and landing gear.
High Temperature Strength:Titanium alloys maintain the required strength even at moderate temperatures, operating for extended periods between 450°C to 500°C.
Excellent Corrosion Resistance:Titanium alloys excel in humid atmospheres and seawater, exhibiting superior corrosion resistance compared to stainless steel. They resist pitting, acid, and stress corrosion exceptionally well.
Excellent Low-Temperature Performance:Titanium alloys maintain their mechanical properties at low and ultra-low temperatures, making them crucial for low-temperature structures.
High Chemical Reactivity:Titanium exhibits significant reactivity with atmospheric gases, forming various hard layers and exhibiting adhesion phenomena with friction surfaces.
Low Thermal Conductivity and Elastic Modulus:Titanium has low thermal conductivity and elastic modulus compared to other metals, resulting in poor rigidity and susceptibility to deformation. During cutting, titanium alloys exhibit significant spring-back, leading to severe friction and wear on the tool surface.
Summary
Titanium alloys possess high strength-to-density ratios, excellent mechanical properties, good toughness, and corrosion resistance. อย่างไรก็ตาม, they exhibit poor machinability and high susceptibility to absorbing impurities during heating processes.
The industrial production of titanium began in 1948, driven by aerospace industry needs, resulting in significant growth in the titanium industry.
The most widely used titanium alloys include Ti-6Al-4V (TC4), Ti-5Al-2.5Sn (ทีเอ7), and industrial pure titanium (TA1, TA2, and TA3).
Titanium alloys are primarily used in manufacturing aircraft engine compressor components, and structural components for rockets, missiles, and high-speed aircraft, as well as in various industrial applications such as electrodes, condensers, and heaters.