Adding alloy elements to alter phase transition temperature and phase content to obtain different microstructures.
Classification of Alloy Elements:
α-stabilizing elements:
Stabilize α-phase, and increase phase transition temperature.
Examples: aluminum, magnesium, oxygen, and nitrogen.
Aluminum: improves room and high-temperature strength, reduces specific gravity, and increases elastic modulus.
β-stabilizing elements:
Stabilize β-phase, and decrease phase transition temperature.
Types:
Isomorphous: molybdenum, niobium, vanadium.
Eutectoid: chromium, manganese, copper, silicon.
Neutral elements:
Little effect on phase transition temperature.
Examples: zirconium, tin.
Classification of Titanium Alloys
Based on the structure of titanium alloys at room temperature, they can be classified into the following types:
α Titanium Alloy (TA)
Composed of a single-phase α solid solution.
Remains in the α phase at both general and higher application temperatures, ensuring stable structure.
Higher wear resistance than pure titanium.
Strong oxidation resistance.
Maintains strength and creep resistance at 500°C~600°C.
Cannot be strengthened by heat treatment.
Low strength at room temperature.
β Titanium Alloy (TB)
Composed of a single-phase β solid solution.
Has high strength without heat treatment.
Further strengthened by quenching and aging, with room temperature strength reaching 1372~1666MPa.
Poor thermal stability, not suitable for high-temperature use.
α + β Titanium Alloy (TC)
Dual-phase alloy with good overall performance.
Stable structure with good toughness, plasticity, and high-temperature deformation properties.
Suitable for hot-pressure processing.
Can be strengthened by quenching and aging, with post-heat treatment strength 50%~100% higher than in the annealed state.
High strength at high temperatures, capable of long-term operation at 400°C ~ 500°C.
Thermal stability is lower than that of α titanium alloys.
Usage Notes
The most commonly used alloys are α titanium alloys and α + β titanium alloys.
Machinability: α titanium alloys are the best for cutting and machining, followed by α + β titanium alloys, with β titanium alloys being the hardest to machine.
Aplikasi Paduan Titanium
Heat-resistant Alloys
High-strength Alloys
Corrosion-resistant Alloys: Including titanium-molybdenum and titanium-palladium alloys.
Low-temperature Alloys
Special Function Alloys: Including titanium-iron hydrogen storage materials and titanium-nickel memory alloys.
Typical Titanium Alloy Grades
TA2 (ASTM Grade 2): Industrial Pure Titanium
Known as the “workhorse” of the commercial pure titanium industry.
Similar qualities to TA1 grade titanium but is slightly stronger.
Corrosion-resistant and weldable.
Preferred in industries like construction, power generation, and medicine due to its good weldability, strength, ductility, and formability.
TA9 (ASTM Grade 7): Ti-0.2Pd
Equivalent to TA2 in mechanical and physical properties but alloyed with palladium.
Excellent weldability and corrosion resistance, the most corrosion-resistant among all titanium alloys.
Particularly resistant to corrosion in reducing acids.
Used in chemical processing and production equipment components, known for its exceptional corrosion resistance, especially in reducing acidic environments.
TA10 (ASTM Grade 12): Ti-0.3Mo-0.8Ni
Known for its superior weldability.
Durable alloy providing significant strength at high temperatures.
Similar properties to 300 series stainless steel.
Can be formed using various methods like hot or cold forming, hydroforming, stretching, or drop hammering.
High corrosion resistance makes it invaluable for manufacturing equipment where crevice corrosion needs to be considered.
TC4 (ASTM Grade 5): Ti-6Al-4V
Often referred to as the “workhorse” of titanium alloys, Ti6Al-4V or Grade 5 titanium is the most commonly used.
Accounts for 50% of the world’s total titanium usage.
Can be heat-treated to increase strength.
Used in various industries like aerospace, medis, marine, and chemical processing due to its lightweight, useful formability, high strength, and corrosion resistance.
Applications include aircraft turbine engines, engine components, aerospace structural components, aerospace fasteners, high-performance automotive parts, marine applications, and sports equipment.
TC6: Ti-6Al-1.5Cr-2.5Mo-0.5Fe-0.3Si
Performance of Titanium Alloys
High Strength:
Titanium alloys have a density of around 4.5g/cm³, which is only 60% of steel’s density.
Pure titanium exhibits strength comparable to ordinary steel, and some high-strength titanium alloys surpass the strength of many alloy structural steels.
The strength-to-density ratio of titanium alloys is much higher than that of other metal structural materials, making them suitable for manufacturing components with high strength, good toughness, and lightweight.
High Thermal Strength:
Titanium alloys have a higher service temperature compared to aluminum alloys by several hundred degrees.
They can maintain their required strength even at moderate temperatures and can operate long-term at temperatures of 450-500°C.
These alloys maintain high specific strength between 150°C and 500°C, whereas aluminum alloys experience a significant decrease in strength at 150°C.
Titanium alloys can operate at temperatures up to 500°C, while aluminum alloys operate below 200°C.
Excellent Corrosion Resistance:
Titanium alloys excel in working environments such as humid atmospheres and seawater, exhibiting superior corrosion resistance compared to stainless steel.
They have exceptional resistance to pitting, acid corrosion, and stress corrosion.
They also exhibit excellent corrosion resistance to alkalis, chlorides, chlorinated organic compounds, nitric acid, and sulfuric acid.
Namun, titanium’s corrosion resistance is poor in media containing reducing oxygen and chromium salts.
Good Low-Temperature Performance:
Titanium alloys maintain their mechanical properties at low and ultra-low temperatures, demonstrating excellent low-temperature performance.
Titanium alloys with low interstitial element content, such as TA7, can retain a certain level of ductility at -253°C, making titanium alloys important materials for low-temperature structures.
High Chemical Reactivity:
Titanium exhibits significant chemical reactivity, undergoing strong chemical reactions with O, N, H, CO, CO2, water vapor, and ammonia in the atmosphere.
When the carbon content exceeds 0.2%, hard TiC forms in titanium alloys.
At higher temperatures, TiN forms with nitrogen, creating a hard surface layer.
Above 600°C, titanium absorbs oxygen to form a highly hardened layer.
Increased hydrogen content leads to embrittlement.
The depth of the hard and brittle surface layer formed by absorbed gases can reach 0.1-0.15mm, with a hardness of 20%-30%.
Titanium also exhibits a strong chemical affinity, leading to adhesion phenomena with friction surfaces.
Low Thermal Conductivity and Elastic Modulus:
Titanium has a low thermal conductivity of approximately 15.2W/(m·K), about one-fourth that of nickel, five times that of iron, and one-fourteenth that of aluminum.
The thermal conductivity of various titanium alloys decreases by about 50% compared to pure titanium.
The elastic modulus of titanium alloys is about half that of steel, making them less rigid and prone to deformation.
This property makes them unsuitable for manufacturing slender rods and thin-walled components.
During cutting, the rebound of the machined surface of titanium alloys is large, approximately 2-3 times that of stainless steel, leading to severe friction, adhesion, and adhesive wear on cutting tool surfaces.
Poor Processability:
Titanium alloys have poor processability and are difficult to machine.
During heating, they readily absorb impurities such as hydrogen, oxygen, nitrogen, and carbon.
They also exhibit poor wear resistance, and their production processes are complex.