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Titanium Alloy

Titanium Alloy Introduction
Titanium alloys are non-ferrous metals with excellent corrosion resistance, fatigue properties, and high strength-to-weight ratios. Products are different in terms of composition, grade, shape, dimensions, and features. Commercially pure, unalloyed or very low alloy titanium does not contain or contains only very small amounts of elements. Titanium alloy contains significant amounts of added elements or constituents. Clad or bimetal titanium alloys consist of two different alloys that are bonded integrally together. Metal matrix composites have a composite or reinforced metal or alloy matrix filled with a second component, which may be in particulate, chopped fiber, continuous filament, or fabric form. Other unlisted, specialty or proprietary titanium and titanium alloys are also available. These materials are often based on a unique alloy system, use a novel processing technology, or have properties tailored for specific applications.   
 
We provide titanium and titanium alloy in many stock shapes and forms. Semi-finished stock shapes are suitable for part fabrication by machining, assembly, or other processes. They are also used as feedstock for casting, forging, and spinning. Common stock shapes and forms for titanium and titanium alloys include bars, rods, tubes, plates, profiles, sheets, strips, shims, spheres, foil, wire, billets, slabs, and blooms. Materials are also supplied as billets, ingots, powders, fillers, and reinforcements. Round, hexagonal, coil, and hollow stock are also available. There are two basic types of anodes. Plating anodes are in used in plating or electroplating processes. Sacrificial anodes are used to protect stainless steel or other metal structures from corrosion.   
 
Selecting titanium and titanium alloy requires an analysis of dimensions, production processes, and performance features. Outer diameter (OD), inner diameter (ID), overall length, and overall thickness are important dimensions. Most materials are cast, wrought, extruded, forged, cold-finished, hot-rolled, or formed by compacting powdered metals or alloys. Performance features for titanium and titanium alloys include resistance to corrosion, heat, and wear.

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

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

  1. 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.
  2. Alloys Ti-6242S, IMI 829, and Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) for creep resistance
  3. 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
  4. Alloy Ti-5Al-2,5Sn is designed for weldability, and the ELI grade is used extensively for cryogenic applications
  5. 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 such as oxygen and nitrogen must be minimized to maintain useful ductility in the weldment. Alloy composition, welding procedure, and subsequent heat treatment are highly important in determining the final properties of welded joints.

Some general principles can be summarized as follows:

  1. Welding generally increases strength and hardness
  2. Welding generally decreases tensile and bend ductility
  3. 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
  4. 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:
  1. To reduce residual stresses developed during fabrication
  2. To produce an optimal combination of ductility, machinability, and dimensional and structural stability (annealing)
  3. To increase strength (solution treating and aging)
  4. To optimise special properties such as fracture toughness, fatigue strength, and high-temperature creep strength.

 
addtime:2009-3-13 16:33:17   print
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