Titanium and titanium alloys have grown in popularity since their 1950s introduction. In short order titanium has become a mainstay in the aerospace, chemical and energy fields and is the optimal choice material for many critical applications such as military and civilian aviation components i.e. engine and airframe. It has been widely used in commercial applications such as tool parts or components and in sporting goods equipment i.e. golf club heads, tennis and racquetball racquet frames and climbing safety gear. Recently it has found its way into nuclear power plants, oil refineries, food processing plants, marine applications and even medical prosthesis and orthotics.
There are many advantageous properties of this once considered “exotic” metal. It has a good strength-to-weight ratio, resistance to erosion and corrosion, a surface that resists adhesions from foreign materials, and it contains a thin film of conductive oxide which allows the metal to re-heal itself when mechanically damaged when in the presence of oxygen or water.
There are multiple titanium net shape technologies available such as powder metallurgy, super plastic forming, precision forging, and precision casting. The most well developed of these is precision casting. It is also the most widely used and is the method in which Ti Squared Technologies has excelled.
It is the allotropic behavior of titanium that allows changes in microstructures through variations in the thermo mechanical processing. A vast range of properties and applications can be achieved with just a small number of different grades.
The titanium alloy that is most widely used is the Ti-6Al-4V alpha-beta because it is well understood and tolerant to variations in fabrication procedures even though it has a poor room-temperature forming and shaping property in comparison to that of steel or aluminum. Alloy Ti-6Al-4V is most commonly utilized in the annealed state. Slow cooling in a mold such as with investment casting, provides sufficient stress relief to avoid the need for subsequent annealing. Hipping (hot isostatic pressing) can substitute for annealing if required.
Proper welding techniques are important when working with titanium alloys in order to preserve useful ductility in the weldment and prevent negative affects to material properties. One major concern is contamination by interstitial impurities from oxygen and nitrogen.
To work successfully with titanium alloys not only is the correct alloy composition critical, but so are proper welding techniques and subsequent heat treatment. All of which can impact the material properties of welded joints. If done properly welding will increase strength and hardness and decrease tensile and bend ductility.
Unalloyed, alpha titanium grades 1 through 3 don’t require further treatment after welding unless the material is highly stressed.
Low temperature heat treatment for unalloyed titanium and titanium alpha-beta alloys are required in order to reduce any stresses that may occur during fabrication to improve ductility, machinabilty and structural stability. Strength, fracture toughness and high-temperature creep strength show little to no improvement by solution annealing from the as-cast condition for alpha or alpha-beta alloys.
So called beta alloys (alloys containing meta stable beta phase at room temp.), precipitation hardening similar to that of steel can be performed to increase strength. This is accomplished by solution annealing above the beta transus temperature followed by low temperature age hardening. Strengths equaling that of high strength stainless steels can be accomplished with these alloys. Beta alloys include Ti 15-3-3 and Beta C.