1.Classification of Titanium Alloys by Structure
The microstructure is a method used to classify titanium alloys. The structure of these types of titanium alloys depends on the alloy composition and process used to make them.
Alpha Alloys
Alpha alloys are titanium alloys that are only purposely alloyed with oxygen. While other components such as carbon and iron can be found in small quantities, they only exist as impurities. As an interstitial alloying element, oxygen significantly boosts strength while decreasing ductility. The chemical and engineering industries are the primary users of alpha alloys.
Here, great corrosion behavior and deformability are more important than high (specific) strength. The main difference between commercially pure (cp) titanium grades is their oxygen concentration.
Near-Alpha Alloys
Near-alpha alloys of titanium are the most common high-temperature alloys. This alloy class is appropriate for high temperatures because it combines the superior creep behavior of alpha alloys with the high strength of alpha + beta alloys. However, their maximum working temperature is now limited to 500 to 550 ºC.
Beta and Near-Beta Alloys
Beta alloys are another type of titanium material. Manufacturers create all titanium alloys by adding enough beta-stabilizing elements to titanium. These materials have been available for many years but have only lately gained popularity. They are more easily cold workable than alpha-beta alloys, heat treatable to high strengths, and some have better corrosion resistance than commercially pure grades.
Alpha and Beta Alloys
These are typically medium to high strength materials with tensile strengths ranging from 620 to 1250 MPa and creep resistance ranging from 350 to 400°C. In addition to tensile properties, they also have low and high cycle fatigue and fracture toughness characteristics.
As a result, people developed thermomechanical and heat treatment procedures to ensure that the alloys provide an optimal balance of mechanical properties for various applications.
2.Classification of Titanium Alloys by Strength
When designing a part or product, it is important to know the strength characteristics of the material for the design and selection of the product. There are different types of titanium alloys available so it's important to have an understanding of all of these properties to use them effectively.
Low Strength
These are alloys of titanium with a yield strength of fewer than 73 KSI (500 MPa). They function in applications that need moderately strong materials. Examples include ASTM grades 1,2,3,7 and 11.
Moderate Strength
These are titanium alloys with yield strength between 73 and 131 KSI (500 and 900 MPa). They ASTM grades 4,5, and 9, Ti-2.5%Cu, Ti-8%Al-1%Mo-0.1%V.
Medium Strength
These are titanium alloys with yield strength between 131-145 KSI (900-1000 MPa). They function in critical applications requiring high-strength properties, good corrosion resistance, and notch toughness at elevated temperatures. Some 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.
Medium Strength
These are titanium alloys with yield strength between 131-145 KSI (900-1000 MPa). They function in critical applications requiring high-strength properties, good corrosion resistance, and notch toughness at elevated temperatures. Some 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
High-strength alloys of titanium have tensile strengths between 145 and 174 KSI(1000-1200 MPa). They are resistant to fatigue, creep, and corrosion, making them suitable for demanding applications such as aircraft parts and medical implants.
Very High Strength
Very high-strength alloys have tensile strengths exceeding 174 KSI (1200 MPa). This material class is expensive but offers exceptional performance in demanding applications such as jet engines, rocket motors, spacecraft, and nuclear reactors. Examples include Ti-10%V-2%Fe-3%Al and Ti-4%Al-4%Mo-4%Sn-0.5%Si.
