Understanding Titanium Grading and Types

Titanium is a remarkable metal renowned for its exceptional strength-to-weight ratio, corrosion resistance, and versatility. These properties make it a preferred choice across various industries, including aerospace, medical, and automotive. However, the wide array of titanium alloys and grades can be overwhelming. This blog provides a detailed overview of titanium grading, types, and their applications to help you make informed decisions for your projects.

Classification of Titanium Alloys

Titanium alloys are broadly classified based on their microstructure and strength characteristics. Understanding these classifications helps in selecting the right alloy for specific applications.

1. Classification by Structure

Titanium alloys can be categorized into three main groups based on their predominant phase or phases:

• Alpha Alloys: These alloys are primarily stabilized by alpha-stabilizing elements such as aluminum, oxygen, and carbon. They exhibit a hexagonal close-packed (hcp) structure and are stable from room temperature up to approximately 882°C (1620°F). Alpha alloys are known for their excellent corrosion resistance and weldability but cannot be heat-treated for increased strength. They are commonly used in chemical processing and engineering industries.
• Alpha-Beta Alloys: These alloys contain a mixture of alpha and beta phases. They are achieved by adding controlled amounts of beta-stabilizing elements like chromium, niobium, and vanadium. The presence of both phases allows for a balance of strength and ductility. Alpha-beta alloys can be heat-treated to enhance their properties. They are versatile and used in applications ranging from aerospace to automotive.
• Beta Alloys: These alloys are predominantly stabilized by beta-stabilizing elements and have a body-centered cubic (bcc) structure. They are stable at higher temperatures but can be heat-treated to develop high strength. Beta alloys are often used in demanding applications like jet engines and aerospace components.

2. Classification by Strength

Titanium alloys are also classified based on their strength characteristics:

• Low Strength (≤ 73 KSI / 500 MPa): These alloys are suitable for applications requiring moderate strength. Examples include commercially pure titanium grades 1, 2, 3, and 7.
• Moderate Strength (73-131 KSI / 500-900 MPa): Alloys in this category offer higher strength and are used in critical applications. Examples include Ti-6Al-4V and Ti-8%Al-1%Mo-0.1%V.
• Medium Strength (131-145 KSI / 900-1000 MPa): These alloys are ideal for high-strength applications requiring good corrosion resistance and notch toughness. Examples include Ti-6%Al-2%Sn-4%Zr-2%Mo and Ti-5.5%Al-3.5%Sn-3%Zr-1%Nb-0.3%Mo-0.3%Si.
• High Strength (145-174 KSI / 1000-1200 MPa): High-strength alloys are used in demanding applications such as aircraft parts and medical implants. They offer excellent fatigue resistance and corrosion resistance. Examples include Ti-6Al-4V.
• Very High Strength (> 174 KSI / 1200 MPa): These alloys provide exceptional performance in extreme conditions, such as jet engines and spacecraft. They are expensive but offer unparalleled strength. Examples include Ti-10%V-2%Fe-3%Al.

Effects of Alloying Elements

The physical and mechanical properties of titanium alloys can be tailored by adding various alloying elements:

• Alpha Stabilizers: Elements like aluminum and interstitials (oxygen, nitrogen, carbon) increase the temperature at which titanium transforms from alpha to beta phase, enhancing high-temperature stability.
• Beta Stabilizers: Elements such as chromium, niobium, and vanadium lower the beta transus temperature, stabilizing the beta phase and improving cold workability and heat treatment response.
• Neutral Solutes: Elements like tin and zirconium strengthen the alpha phase without significantly affecting the transformation temperatures.

Applications of Titanium Alloys

The diverse properties of titanium alloys make them suitable for a range of applications:

• Aerospace: High-strength titanium alloys like Ti-6Al-4V are used in aircraft components and jet engines due to their excellent strength-to-weight ratio and fatigue resistance.
• Medical: Titanium alloys are used in implants and prosthetics due to their biocompatibility and corrosion resistance. For instance, Ti-6Al-4V is commonly used in orthopedic implants.
• Automotive: Lightweight and strong titanium alloys improve performance and fuel efficiency in high-performance vehicles.
• Chemical Processing: Alpha alloys with excellent corrosion resistance are used in chemical reactors and equipment.

Titanium Grades and Alloy Composition

To provide a clearer understanding of the different titanium grades and their applications, here's a table summarizing the key information about titanium alloys:

Alloy (ASTM Grade)	Composition	Description	Typical Forms	Applications
Commercially Pure Grades
Ti Grade 1	Unalloyed Titanium	Lowest strength, highest ductility, excellent corrosion resistance	Ingot, Bar, Billet, Plate, Sheet, Wire, Tubing	Chemical processing, desalination, medical, marine
Ti Grade 2	Unalloyed Titanium	Moderate strength, good corrosion resistance, weldable	Ingot, Bar, Billet, Plate, Sheet, Wire, Tubing	Chemical processing, marine, oil & gas, desalination
Ti Grade 3	Unalloyed Titanium	Higher strength than Gr. 2, good corrosion resistance	Ingot, Bar, Billet, Plate, Sheet, Wire, Tubing	Chemical processing, marine, aerospace
Ti Grade 4	Unalloyed Titanium	Strongest unalloyed titanium, moderate formability, excellent corrosion resistance	Ingot, Bar, Billet, Plate, Sheet, Wire, Tubing	Aerospace, chemical processing, marine, medical
Commercially Pure Grades Modified with Pd or Ru
Ti-0.15Pd (Grade 7)	Ti with 0.15% Pd	Excellent resistance to reducing acids and chlorides, equivalent to Gr. 2	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, desalination, marine, offshore
Ti-0.15Pd (Grade 11)	Ti with 0.15% Pd	Soft grade with enhanced corrosion resistance, equivalent to Gr. 1	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, desalination, marine, medical
Ti-0.05Pd (Grade 16)	Ti with 0.05% Pd	Lower-cost Pd alternative, corrosion resistance equivalent to Gr. 7	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, marine, offshore
Ti-0.05Pd (Grade 17)	Ti with 0.05% Pd	Lower-cost Pd alternative, corrosion resistance equivalent to Gr. 11	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, desalination, marine, medical
Ti-0.1Ru (Grade 26)	Ti with 0.1% Ru	Corrosion resistance equivalent to Gr. 7 with Ru addition	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, marine, offshore, oil & gas
Ti-0.1Ru (Grade 27)	Ti with 0.1% Ru	Corrosion resistance equivalent to Gr. 11 with Ru addition	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, marine, medical, oil & gas
Alpha and Near-Alpha Alloys
Ti-0.3Mo-0.8Ni (Grade 12)	Ti with 0.3% Mo, 0.8% Ni	Improved strength, weldable, resistance to brine and reducing acids	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, marine, geothermal, offshore
Ti-3Al-2.5V (Grade 9)	Ti with 3% Al, 2.5% V	Medium strength, high weldability, good cold formability	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Aerospace, marine, automotive, chemical processing
Ti-3Al-2.5V-Pd (Grade 18)	Ti with 3% Al, 2.5% V, Pd	Pd-enhanced for resistance to brine and reducing acids	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, marine, geothermal, offshore
Ti-3Al-2.5V-Ru (Grade 28)	Ti with 3% Al, 2.5% V, Ru	Ru-enhanced for brine resistance, approved for sour service	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Chemical processing, oil & gas, marine
Ti-5Al-2.5Sn (Grade 6)	Ti with 5% Al, 2.5% Sn	Good high-temperature strength and creep resistance	Ingot, Bar, Billet, Plate, Sheet	Aerospace, gas turbines, chemical processing
Alpha-Beta Alloys
Ti-6Al-4V (Grade 5)	Ti with 6% Al, 4% V	Heat-treatable, high strength, most widely used titanium alloy	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Aerospace, marine, automotive, chemical processing
Ti-6Al-4V ELI (Grade 23)	Ti with 6% Al, 4% V	Extra low interstitial version, improved ductility and fracture toughness	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Medical implants, marine, aerospace
Ti-6Al-4V-0.1Ru (Grade 29)	Ti with 6% Al, 4% V, 0.1% Ru	Improved fracture toughness, resistance to localized corrosion	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Oil & gas, marine, offshore, chemical processing
Ti-6Al-6V-2Sn (Grade 6-6-2)	Ti with 6% Al, 6% V, 2% Sn	Higher strength than Ti-6Al-4V, lower toughness, good hardenability	Ingot, Bar, Billet, Plate, Sheet	Aerospace, high-strength components, military applications
Ti-6Al-2Sn-4Zr-6Mo (Grade 6-2-4-6)	Ti with 6% Al, 2% Sn, 4% Zr, 6% Mo	Very high strength, deep hardenability, limited weldability	Ingot, Bar, Billet, Plate, Sheet	Aerospace, high-temperature components, gas turbines
Ti-4Al-4Mo-2Sn-0.5Si (Grade 550)	Ti with 4% Al, 4% Mo, 2% Sn, 0.5% Si	Good strength and creep resistance, high-temperature stability	Ingot, Bar, Billet, Plate, Sheet	Aerospace, industrial high-temperature environments
Near-Beta and Beta Alloys
Ti-10V-2Fe-3Al (Grade 10-2-3)	Ti with 10% V, 2% Fe, 3% Al	Heat-treatable, very high strength, excellent forgeability	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Aerospace, landing gear, high-strength, fatigue-resistant components
Ti-3Al-8V-6Cr-4Zr-4Mo (Grade 19)	Ti with 3% Al, 8% V, 6% Cr, 4% Zr, 4% Mo	Very high strength, good toughness, low elastic modulus	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	High-temperature, corrosive environments, aerospace
Ti-3Al-8V-6Cr-4Zr-4Mo-0.05Pd (Grade 20)	Ti with 3% Al, 8% V, 6% Cr, 4% Zr, 4% Mo, 0.05% Pd	Enhanced corrosion resistance, very high strength	Ingot, Bar, Billet, Plate, Sheet, Tubing, Wire	Oil & gas, marine, high-corrosion applications
Ti-5Al-4Cr-4Mo-2Sn-2Zr (Grade 17)	Ti with 5% Al, 4% Cr, 4% Mo, 2% Sn, 2% Zr	High strength, deep section hardenability, creep resistance	Ingot, Bar, Billet, Plate, Sheet	Aerospace, gas turbines, high-temperature components

Conclusion

In conclusion, titanium's exceptional properties, including its strength-to-weight ratio, corrosion resistance, and versatility, make it a highly sought-after metal across various industries. However, the vast array of titanium alloys and grades can be overwhelming. By understanding the classification of titanium alloys based on microstructure and strength characteristics, as well as the effects of alloying elements, you can make informed decisions for your specific applications.

From commercially pure titanium grades to alpha, alpha-beta, and beta alloys, each category offers unique properties and is suitable for different applications. Whether you require high strength, excellent corrosion resistance, or a combination of both, the titanium alloy landscape provides a diverse range of options. By carefully considering the specific requirements of your project, you can select the most appropriate titanium alloy to meet your needs and achieve optimal performance.

Reference

Veiga, C., Davim, J. P., & Loureiro, A. J. R. (2012). Properties and applications of titanium alloys: a brief review. Rev. Adv. Mater. Sci, 32(2), 133-148.

Welsch, G., Boyer, R., & Collings, E. W. (Eds.). (1993). Materials properties handbook: titanium alloys. ASM international.

Budinski, K. G. (1991). Tribological properties of titanium alloys. Wear, 151(2), 203-217.

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