Titanium Alloys are characterized by high strength, moderate density (half the density of the steel nd 70% higher than aluminium) and excellent corrosion resistance. Titanium alloys have high strength, rating form 175MPa (25,000 psi)for commercially pure titanium up to 1380 MPa (200 000 psi) for more complex wrought alloys. Corrosion resistance is excellent in oxidizing conditions, such as general atmosphere, marine and biological environments, but titanium alloys are generally not resistant to attack from reducing acids, such as sulfuric, hydrochloric and phosphoric acids.Oxidation resistance is effective up toa working temperature of 480ºC (900ºF), but higher thermal exposure will lead to the growth of a brittle surface oxide, know as "alpha case" which can be detrimental to mechanical properties.
Wrought and cast titanium alloys have similar compositions. Typically, two or more metallic elements - the list includes aluminium, vanadium, molybdenum, iron, zirconium, chromium, silicon and tin- are alloyed with titanium, along with small amounts of oxygen, nitrogen and carbon, to improve strength, fatigue(cyclic loading) and fracture toughness properties. Typical applications of titanium alloys include aircraft engines rotating components, aircraft primary structure, land-based turbine components, chemical processing equipment and medical implants.
The strength of titanium is comparable to that of steel and because of the additional properties of its relative light weight, combined with corrosion and heat resistance, it has been a prime metal for aerospace applications
The medical industry has also benefited from the low-weight/high strength properties of titanium in products including surgical instruments and patient-assist products. Another property that is invaluable is the biocompatibility. This enables the metal to be readily available for implants as it will not be rejected by the body.Titanium is one of the most common elements and is found in the Earth`s crust. It is the ninth most abundant element and the seventh most metal. Titanium alloys usually consist of titanium mixed with small quantities of other metals, which help to provide improved properties over pure titanium, such as corrosion resistance, shapability, stability and strength at elevated temperatures.
The principal challenges of titanium, other than the relatively high cost of refining the pure metal from titanium oxide bearing ores, are related to its crystalline structure. Titanium, like magnesium and zirconium, is one of the few industrial metals having a close-packed hexagonal crystallographic structure. Characteristics of these metals is a high rate of strain hardening, which limits the amount of cold working that can be done without a recrystallization heat treatment.The high rate of strain hardening also results in the discontinuity called Notch sensitivity. At a stress concentration point, such as the base of the notch in an impact test specimen, the load-carrying ability of a material depends on its ability to permit some plastic flow to enlarge the radicand relive the stress concentration.