Titanium Alloys Characteristics
Strength, ductility, corrosion resistance, and low density are what give titanium its popularity. Titanium and its alloys maintain good mechanical properties in environments with temperatures rising to 600°C, being this the reason why it’s known as a high-temperature engineering material.
Its high strength-to-weight ratio and the high-temperatures it can withstand are the main reasons why titanium is used for military and aerospace industries.
Titanium is also a non-toxic and biocompatible metal, making it perfect to be used as a prosthesis to replace human bones.
The most popular fabrication methods include casting, rolling, extrusion, CNC machining, and welding but it requires special process modifications to ensure that the final product complies with the customer’s needs.
Titanium Alloys and Their Manufacturability
Alloys having titanium as the primary element are categorized in grades. Titanium grades 1, 2, 3, 4, 7, 11, and 12 are considered to be commercially pure titanium, having a titanium concentration starting at 97%. Commercially pure titanium is very ductile meaning that can be easily cold formed. It has excellent impact and corrosion resistance and can be welded with ease.
Alloy titanium has a slightly lower amount of titanium in its composition. They can be classified as Alpha and Beta titanium grades; the latter being heat treatable. Titanium alloys are known for their amazing strength and ductility, corrosion resistance, and high strength-to-weight ratio.
Here we present some of the most popular titanium alloys:
1. Titanium Grade 3
Grade 3 is composed of almost 99% titanium with minor quantities of carbon, oxygen, and iron. Its high ductility makes it suitable for most manufacturing processes, being extrusion, cold forming, sheet metal, and welding the most popular. It has intermediate strength compared to other titanium’s grades, but has very good corrosion resistance and weldability, making it suitable for applications in the medical industry, cryogenic vessels, exhaust pipes, and heat-exchanger tubing.
√ Mechanical Properties
| Tensile Ultimate Strength | Tensile Yield Strength | Hardness | Fatigue Strength | Density | Melting point |
|---|---|---|---|---|---|
| 560 MPa | 450 MPa | 225 HB | 315 MPa | 4,5 g/cc | 1660°C |
√ Manufacturing Processes Performance
| Machinability | Formability | Weldability | Workability | Corrosion resistance | Wear resistance |
|---|---|---|---|---|---|
| Good (low speeds and properly cooled) | Excellent | Excellent | Excellent | Excellent | Very Good |
2. Titanium Grade 5
With an aluminum concentration of up to 6% and vanadium up to 4%. Grade 5 titanium is lighter and shows and amazing biocompatibility.
It has higher strength, and its biocompatibility makes it suitable for the prosthetic industry and medical implants. This alloy can be both colds, and hot-formed, has fair machinability and welding properties, and it is heat-treatable.
Other applications include the aerospace industry, offshore power generation, and the marine industry. It requires a nitriding and oxidation surface treatment to increase its wear resistance. Properties for the annealed Grade 5 are given below.
√ Mechanical Properties
| Tensile Ultimate Strength | Tensile Yield Strength | Hardness | Fatigue Strength | Density | Melting point |
|---|---|---|---|---|---|
| 950 MPa | 880 MPa | 334 HB | 510 MPa | 4,43 g/cc | 1600°C |
√ Manufacturing Processes Performance
| Machinability | Formability | Weldability | Workability | Corrosion resistance | Wear resistance |
|---|---|---|---|---|---|
| Fair | Excellent | Fair | Excellent | Excellent | Poor |
3. Titanium Grade 9
Grade 9 is one of the strongest titanium alloys, composed of 80% titanium with vanadium, molybdenum, and chromium. These alloying materials enhance the mechanical properties and corrosion resistance of titanium, making this one of the favorite alloys when high strength and relatively low weight are needed. This alloy can be easily formed, making extrusion one of the favorite manufacturing processes. Other applications include springs, fasteners, and tubing for the marine and offshore industries.
√ Mechanical Properties
| Tensile Ultimate Strength | Tensile Yield Strength | Hardness | Fatigue Strength | Density | Melting point |
|---|---|---|---|---|---|
| 1450 MPa | 1380 MPa | 381 HB | 620 MPa | 4,81 g/cc | 1900°C |
√ Manufacturing Processes Performance[table “47” not found /]
Surface Finishing For Titanium Alloys
Titanium surface finishing aims to increase its strength, wear resistance. Processes used to enhance titanium are expensive, compared to those used for other materials such as aluminum and steel. The additional costs come from the special equipment required to perform these processes. Surface finishing processes are listed below:
1. Nitriding and oxidation
This plasma-based treatment is performed to increase the wear resistance of titanium alloys. When applied to the surface, plasma thermochemically adds nitrogen to the material’s surface, enhancing its corrosion, fatigue, and wear resistance. It is a costly process, being performed only on few applications such as biomedical implants, in which wear and corrosion are not allowed.
2. Anodizing
The anodizing finishing increases the oxide layer on a material’s surface, improving strength, and wear resistance. It is one of the preferred finishing methods for the aerospace industry because of its low cost and the fact that it doesn’t imply the dimensional change of the product. Anodizing also changes the surface’s color, improving its appearance. This process is mostly used in tubular profiles used for exhausts and heat-exchangers.
3. Electro-polishing
This electrochemical process is used to remove a controlled amount of material from the product’s surface, eliminating surface imperfections while improving corrosion resistance, and cleaning the surface giving it a better appearance. Compared to other processes, electro-polishing is cheaper, and due to the number of benefits related to it, it’s one of the preferred finishing methods for titanium.
Titanium Alloys Materials: Design and Engineering Tips
Titanium is a versatile element; it is widely used as a primary or alloying constituent for multiple materials. It can be used for both low and high-temperature applications, it has excellent mechanical properties, and its low weight makes it an excellent option for the automotive, aerospace, and marine industries. Here are some tips to help you out with your titanium designs.
1. If increased wear resistance is required, an anodizing treatment is preferred over an NO process. Anodizing costs less and gives excellent corrosion and wear resistance while improving the material’s strength. NO treatment is only applied when the product is to be used in a biomedical implant.
2. Using titanium alloys for the critical components of your design can help you reducing weight and increasing the factor of safety.
3. Titanium is widely used in sheet-metal and extrusion applications. Titanium profiles are very popular for their high strength and corrosion resistance, making them suitable for tubing in the chemical industry.