Titanium alloys - when titanium goes out to form a bond


Titanium alloys were originally developed in the early 1950s for aerospace applications due their unusually high strength-to-density ratio, meaning, they are light, yet strong. Nowadays, though they are still vital to the aerospace industry for the exactly the same properties, the recognition of titanium excellent resistance in highly corrosive environments has led to widespread non-aerospace industrial applications. Stemming from decreasing cost and increasing availability of mill and fabricated products, titanium alloys have become standard engineering materials for a host of common consumer products too.

In order to better understand the composition of an alloy containing titanium, you first need to understand the common titanium structure. Titanium atoms are arranged in regular patterns, extending in all three dimensions. The shape of these patterns determine two possible forms for pure titanium:

α (alpha)-titanium - in which atoms are arranged in a somewhat hexagonal pattern, and,

β (beta) -titanium - in which atoms are arranged in a cubic (square) pattern;

Pure titanium atoms are arranged as of α-phase at temperatures up to1621°F (883°C). When this temperature (Beta Transus Tempereture) is reached they transform in β-phase.

TI alloys are classified according to the alloying elements that may stabilize either α-phase or β-phase of titanium.

Aluminum (Al), gallium (Ga), Nitrogen (N), Oxygen (O) stabilize α-phase.

Molybdenum (Mo), vanadium (V), tungsten (W), tantalum (Ta), silicon (Si) stabilize β-phase.

Commercially pure titanium consist mainly of α-phase and some dispersed β-phase. There are five titanium grades of what is known as commercially pure (CP) or unalloyed titanium - ASTM Grades 1 through 4, and 7. Each grade has a different amount of impurity content, with Grade 1 being the most pure. Usually, titanium jewelry is made of Grade 2.A special note is to be made for the black titanium alloy, which is a special patented alloy used in the jewelry industry, especially in wedding bands.

Titanium alpha and near-alpha alloys consist entirely of α-phase. They contain aluminum as the major alloying element, stabilizing α-phase. Alpha alloys do not generally respond to heat treatment, but they are weldable and are commonly used for cryogenic applications, airplane parts, and chemical processing equipment.

Titanium alpha-beta alloys contain 4-6% of β-phase stabilizers; therefore they consist of a mixture of α and β phases. α-β titanium alloys are heat-treatable. They have high mechanical strength and good hot formability.Alpha-beta titanium alloys can be strengthened by heat treatment and aging, and therefore can undergo manufacturing while the material is still ductile, then undergo heat treatment to strengthen the material, which is a big advantage. The alloys are used in aircraft and aircraft turbine parts, chemical processing equipment, marine hardware, and prosthetic devices.

Ti-6Al-4V is the most popular Titanium α-β Alloy - its total production is about half of all TI alloys. Aluminum (Al) is added to the alloy as α-phase stabilizer and hardener due its solution strengthening effect. Vanadium (V) stabilizes ductile β-phase, providing hot workability of the alloy.

Titanium beta alloys are rich of β-phase. They are the smallest group of all, have good hardenability, good cold formability when they are solution-treated, and high strength when they are aged. Beta alloys are slightly denser than other titanium alloys. They are used for heavier duty purposes on aircraft, aerospace components, high-strength fasteners, torsion bars, high-strength aircraft sheets, burn-resistant aircraft engine parts because of their superior melting point.

Maraging steel is a special ferro-alloy for which titanium is a critical component, though titanium is the main constituent.

Titanium also is part of the most widely used shape memory alloy when it is alloyed with nickel to become NITINOL. There are also other titanium compounds with different non-metal element that are of industrial importance, such as nitrides used in coatings.

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