Titanium is the best material chosen for many critical applications because the combination of high strength-to-weight ratio, excellent mechanical properties, and corrosion resistance makes. Titanium alloys are used for demanding applications like static and rotating gas turbine engine components. Some of the most critical and highly-stressed civilian and military airframe parts are made of these alloys. And the use of it has expanded to include applications in nuclear power plants, food processing plants, oil refinery heat exchangers, marine components and medical prosthesis.

The high cost is often the result of the intrinsic raw material cost of metal, fabricating costs and the metal removal costs incurred in obtaining the desired final shape. So the high cost of titanium alloy components may limit their use to applications for which lower-cost alloys, such as aluminum and stainless steels.

These titanium net shape technologies include powder metallurgy (P/M), super plastic forming (SPF), precision forging, and precision casting. Precision casting is the most fully developed and the most widely used titanium net shape technology. In the United States between 1979 and 1989 the annual shipment of titanium castings increased by 260%.

Ti-6Al-2Sn-4Zr-2Mo andTi-6Al-2Sn-4Zr-6Mo are being specified more frequently As aircraft engine manufactures seek to use cast titanium at higher operating temperatures. Ti-1100 and IMI-834 are advanced high-temperature titanium alloys for service up to 595 o C, and are being developed as castings. They exhibit the same degree of elevated-temperature superiority, as their wrought counterparts over the more commonly used Ti-6Al-4V.

The wrought product forms of titanium and titanium-base alloys (include forgings and typical mill products) constitute more than 70% of the market in titanium and titanium alloy production. The wrought products are the most readily available product form of titanium-base materials, but also applications that require complex shapes or the use of P/M techniques to obtain microstructures not achievable by conventional ingot metallurgy uses cast and powder metallurgy (P/M) products that are available.

Powder metallurgy of titanium has not gained wide acceptance and is restricted to space and missile applications. Outstanding corrosion resistance of titanium and its useful combination of low density (4.5 g/cm 3 ) and high strength are the primary reasons for using titanium-base products. The strengths vary from 480 MPa for some grades of commercial titanium to about 1100 MPa for structural titanium alloy products and over 1725 MPa for special forms like wires and springs.

Another important characteristic of titanium- base materials is that when the temperatures exceed certain level a transformation of the crystal structure happened from alpha (?, hexagonal close-packed) structure to beta (?, body-centered cubic) structure witch is reversible. It depend on the type and amount of alloy contents, allows complex variations in microstructure and more diverse strengthening opportunities than those of other nonferrous alloys like copper or aluminum.

Pure titanium wrought products, which have minimum titanium contents ranging from about 98,635 to 99.5 wt%, are used primarily for corrosion resistance. Titanium products are also useful for fabrication but have relatively low strength in service.

Titanium has the following advantages:

• Good strength
• Resistance to erosion and erosion-corrosion
• Very thin, conductive oxide surface film
• Hard, smooth surface that limits adhesion of foreign materials
• Surface promotes drop wise condensation

Commercially pure titanium with minor alloy contents includes various titanium-palladium grades and alloy Ti-0, 3Mo-0,8Ni (ASTM grade 12 or UNS R533400). Give it improvements in corrosion resistance and strength.

In applications requiring excellent corrosion resistance in chemical processing or storage applications where the environment is mildly reducing or fluctuates between oxidizing and reducing, Titanium-palladium alloys with nominal palladium contents of about 0.2% Pd are used.

Alloy Ti-0, 3Mo-0,8Ni (UNS R533400, or ASTM grade 12) has applications similar to those for unalloyed titanium but has better strength and corrosion resistance. However, the corrosion resistance of this alloy is not as good as the titanium-palladium alloys. The ASTM grade 12 alloy is particularly resistant to crevice corrosion in hot brines.

Titanium alloy compositions of various titanium alloys

A broad range of properties and applications can be served with a minimum number of grades, because the allotropic behavior of titanium allows diverse changes in microstructures by variations in thermo mechanical processing. This is especially true of the alloys with a two-phase, ???, crystal structure.

The most widely used titanium alloy is the Ti-6Al-4V alpha-beta alloy. It is well understood, also is very tolerant on variations in fabrication operations, despite its relatively poor room-temperature shaping and forming characteristics compared to steel and aluminum. Alloy Ti-6Al-4V, which has limited section size harden ability, is most commonly used in the annealed condition.

Other titanium alloys are designed for particular application areas. For example:

• Alloys Ti-5Al-2Sn-2Zr-4Mo-4Cr (commonly called Ti-17) and Ti-6Al-2Sn-4Zr-6Mo for high strength in heavy sections at elevated temperatures.
• Alloys Ti-6242S, IMI 829, and Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) for creep resistance
• Alloys Ti-6Al-2Nb-ITa-Imo and Ti-6Al-4V-ELI are designed both to resist stress corrosion in aqueous salt solutions and for high fracture toughness
• Alloy Ti-5Al-2,5Sn is designed for weldability, and the ELI grade is used extensively for cryogenic applications
• Alloys Ti-6Al-6V-2Sn, Ti-6Al-4V and Ti-10V-2Fe-3Al for high strength at low-to-moderate temperatures.

Welding has the greatest potential for affecting material properties. In all types of welds, contamination by interstitial impurities like oxygen and nitrogen must be minimized to maintain useful ductility in the weldment. The highly important things in determining the final properties of welded joints are Alloy composition, welding procedure, and subsequent heat treatment.

Some general principles can be summarized as follows:

• Welding generally increases strength and hardness
• Welding generally decreases tensile and bend ductility
• Welds in unalloyed titanium grades 1, 2 and 3 do not require post-weld treatment unless the material will be highly stressed in a strongly reducing atmosphere
• Welds in more beta-rich alpha-beta alloys such as Ti-6Al-6V-2Sn have a high likelihood of fracturing with little or no plastic straining.

Titanium and titanium alloys are heat treated for the following purposes:

• To reduce residual stresses developed during fabrication
• To produce an optimal combination of ductility, mach inability, and dimensional and structural stability (annealing)
• To increase strength (solution treating and aging)
• To optimize special properties such as fracture toughness, fatigue strength, and high-temperature creep strength.