Titanium is a metal whose demand is increasing. This is because it has excellent corrosion resistance and a wide range of desirable mechanical properties. To take advantage of titanium's unique properties, manufacturers add smaller amounts of other elements to pure titanium to alter the metal's physical properties.
Therefore, there are many types of titanium alloys to choose from as they offer different properties and costs. In this article, we discuss the different classifications of titanium alloys and the applications of each of these classifications.
Classification of titanium alloys by structure
Microstructure is a method for classifying titanium alloys. The structure of these types of titanium alloys depends on the alloy composition and manufacturing process.
Alpha leagues
Alpha alloys are titanium alloys that are only selectively bound to oxygen. Other components, such as carbon and iron, are contained in small amounts but occur only as impurities. As an interstitial alloying element, oxygen significantly increases strength and reduces ductility. Alpha alloys are mainly used in the chemical and mechanical engineering industries.
Here, good corrosion behavior and deformability are more important than high (specific) strength. The main difference between commercially pure (cp) titanium grades is the oxygen concentration.
Near alpha leagues
Near-alpha titanium alloys are the most common high-temperature alloys. This class of alloys is suitable for high temperatures because it combines the superior creep behavior of alpha alloys with the high strength of alpha and beta alloys. However, its maximum working temperature is now limited to 500 to 550 ºC.
Beta and near-beta leagues
Beta alloys are another type of titanium material. Manufacturers make all titanium alloys by adding sufficient beta stabilizing elements to the titanium. These materials have been available for many years, but have only recently gained popularity. They are easier to cold work than alpha-beta alloys, can be heat treated to high strengths, and some have better corrosion resistance than commercially pure grades.
Alpha and Beta Leagues
These are typically medium to high strength materials, with tensile strength of 620 to 1250 MPa and creep strength of 350 to 400 °C. In addition to tensile strength properties, they also exhibit low and high cycle fatigue strength and fracture toughness properties.
Therefore, thermomechanical processes and heat treatment processes have been developed to ensure that alloys have an ideal balance of mechanical properties for various applications.
Classification of titanium alloys by strength
When designing a part or product, it is important to understand the strength properties of the material for product design and selection. There are different types of titanium alloys. Therefore, it is important to know all these properties to use them effectively.
Low resistance
These are titanium alloys with a yield strength of less than 73 KSI (500 MPa). They are suitable for applications requiring medium strength materials. Examples include ASTM Classes 1, 2, 3, 7, and 11.
Moderate strength
They are titanium alloys with yield strengths between 73 and 131 KSI (500 and 900 MPa). They have ASTM grades 4, 5 and 9, Ti-2.5% Cu, Ti-8% Al-1% Mo-0.1% V.
Medium strength
They are titanium alloys with yield strengths between 131 and 145 KSI (900-1000 MPa). They are suitable for critical applications requiring high strength properties, good corrosion resistance and notched impact resistance at elevated temperatures. Some examples are 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 titanium alloys 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 resistance
Very high strength alloys have tensile strength greater than 174 KSI (1200 MPa). This class of materials is expensive but offers exceptional performance in demanding applications such as jet engines, rocket engines, spacecraft and nuclear reactors. Examples are Ti-10%V-2%Fe-3%Al and Ti-4%Al-4%Mo-4%Sn-0.5%Si.
Titanium alloys with properties and applications
Titanium alloys are available in several grades, each with its own specific properties. Below are some of the most common Titanium alloy grades .
Grade 5 titanium alloy
Due to its high strength, Grade 5 titanium is the most commonly used alloy. It is a commonly used welding alloy that can be used in structural and pressure-bearing components. It presents high resistance to corrosion in oxidizing and reducing environments.
Furthermore, it is also used in the chemical and petroleum industries, as well as in the manufacture of offshore drilling platforms. The alloy is used in the construction of water treatment plants, nuclear reactors and other critical environments that require a high-strength, low-cost material.
Grade 6 titanium alloy
Grade 6 is a commonly welded titanium alloy made from aluminum and tin, often used for components exposed to high temperatures. In addition to high resistance, the alloy has excellent stability, making it a good option for aircraft and engines.
Grade 7 titanium alloy
Grade 7 titanium alloys are particularly suitable for low temperature and high pH applications. This is due to its extreme resistance to corrosion.
Grade 11 titanium alloy
Grade 11 is a titanium alloy with good high temperature resistance and high corrosion resistance. The alloy is a raw material for components that are used at high temperatures, such as: B. Chemical and petroleum processing plants, as well as the production of aircraft engines and fuselages. Grade 11 is also used to manufacture turbines, liquid hydrogen storage tanks and other important equipment. The alloy is easily manufactured by machining, forging, rolling and extrusion.
Grade 12 titanium alloy
It applies to the manufacturing of aircraft components such as engine parts, fuselages, landing gear, fuel systems and other critical equipment. The alloy is also used in the manufacture of cryogenic containers, heat exchangers, distillation columns and other equipment that operate at high temperatures.
Furthermore, Grade 12 is easily manufactured through machining, forging, rolling and extrusion. This makes it ideal for manufacturing valves, fittings and other devices that require corrosion-resistant materials.
Grade 23 titanium alloy
Grade 23 is a titanium alloy with good ductility and fracture resistance. It is mainly used to make medical implants.
Why is machining titanium alloy difficult?
Titanium alloys are difficult to machine because they are hard and have a low coefficient of friction. Titanium's hardness comes from its high strength and density, making it difficult to cut and shape. High strength also means the material is less malleable and susceptible to cracking that can occur during machining, heat treatment or welding.
The low coefficient of friction can cause problems when cutting or milling titanium with traditional tool materials. Titanium chips make it difficult for the tool to easily remove material from the workpiece. Chips also tend to stick to the tooth surface of the tool because there is no lubrication between them and the tool. This results in chip accumulation on the tool surface at high feed rates, resulting in poor surface finishes, reduced tool life, and excessive vibration during machining.
Another difficulty in machining titanium alloys is their low thermal conductivity, which means they do not cool quickly enough when machining with cutting fluids or water cooling. This causes the workpiece material to become soft and tool life to be reduced due to tool chatter or breakage.
Tips for Effective Machining of Titanium Alloys
Due to the special properties of titanium alloys, machining these metals can be somewhat difficult. To edit these components effectively, you need to know which tools and techniques to use. We've put together a list of helpful tips on how to machine titanium alloys effectively.
Use the right tools and equipment
Firstly, you need to make sure you are using the right tools and equipment for the job. This may seem pretty obvious, but it's a crucial step in any editing process. Titanium alloys are more difficult to machine due to their greater hardness. Always use high-speed steel tools and carbide drill bits when cutting titanium. Steel tools dull quickly with this material, while carbide bits cut cleanly and last longer.
Transfer the heat generated to the chip
An important aspect of efficiently machining titanium is the transfer of generated heat to the chip. This helps keep the part, tool and coolant at a relatively constant temperature. The most effective way to do this is to use a machine with a horizontal spindle for machining titanium.
Another way to direct the heat generated to the chip is to increase the feed rate of the part. A higher feed rate can help maintain a constant temperature during the machining process. This can be particularly useful when machining large part sizes.
Increase coolant concentration and pressure
As already mentioned, titanium alloys have higher thermal conductivity than other metals. Therefore, when processing these materials, the concentration and pressure of the coolant must be increased. Increasing the coolant concentration can help reduce the heat generated in the engine. It can also help keep the part and tool at a relatively constant temperature, allowing the part's feed rate to increase.
If you use a water-based coolant, you can increase the concentration of that fluid by adding an antifoaming agent. A good option for an anti-foaming agent is sodium salts, which help to increase the boiling point and viscosity of water.
Avoid seizing
Titanium alloys typically have lower lubricity than other metals. This means they are more likely to eat it while processing. Seizure is a phenomenon that occurs when two opposing metal parts come into contact and one part becomes trapped between the two. Seizing can make the machining process significantly more difficult and significantly reduce tool life.
You can avoid galling when machining titanium alloys by using a lower feed rate and lower spindle speed. If you already notice seizing, you can often correct the problem by increasing the coolant concentration. This can help break through the existing irritation and continue the editing process.
Titanium Alloy Applications
aerospace industry
Titanium alloys are widely used in the aerospace industry due to their high strength-to-weight ratio. They are used to make fasteners, aircraft structures, landing gear assemblies, and engines because they can withstand extreme temperatures without corroding or cracking under pressure.
Medical industry
Titanium alloys are used in medical devices such as artificial joints and hip replacements because they are biocompatible and resistant to corrosion. The metal can take on complex shapes without breaking or cracking, making it ideal for surgical instruments such as scalpels or pliers. It is also used in dental implants because it does not irritate soft tissue like stainless steel when inserted into the oral cavity.
Electronics industry
Titanium alloys are widely used in electronics because they have high conductivity and are corrosion resistant to most acids and bases. This makes them ideal as connecting elements in batteries or other electrical components that require electrical contact with each other, but should not corrode over time due to contact with corrosive substances such as salt water.
Concluding
So, which titanium alloys have the best properties for your application? That's hard to say. It depends on your requirements and the intended use of the alloy. For example, if you are manufacturing a type of eyeglasses, it would be better to use purer titanium as the strength of an alloy is not necessary for this specific application.
However, we could take this discussion in a million different directions. Therefore, you may want to consult an expert to determine which type of titanium alloy is best for your project.
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