High-Purity Vanadium Remains a Critical Material For Defense Applications, Economic Development By Terry Perles
T
itanium alloys are alloys that contain a mixture of titanium and other chemical elements, such as vanadium. These alloys have very high tensile strength and toughness (even at extreme temperatures). They are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures. The high cost of both raw materials and processing limit their use to military applications, aircraft, spacecraft, industrial applications, bicycles, medical devices, jewelry, highly stressed components such as connecting rods on expensive sports cars and some premium sports equipment and consumer electronics. The addition of vanadium to titanium alloys improves the strength of titanium alloys and promotes thermal stability. Several important commercial titanium alloys contain between 2.5 and 15 percent
26
TITANIUMTODAY
vanadium. Although “commercially pure” titanium has acceptable mechanical properties and has been used for orthopedic and dental implants, for most applications titanium is alloyed with small amounts of aluminum and vanadium, typically 6 percent and 4 percent respectively, by weight. (The most familiar example of this is the aerospace workhouse alloy Ti6Al4V.) This Terry Perles mixture has a solid solubility that varies dramatically with temperature, allowing it to undergo precipitation strengthening. This heat treatment process is carried out after the alloy has been worked into its final shape but before it is put to use, allowing much easier fabrication of a high-strength product.
The alloying of titanium alloys involves the melting of commercial pure titanium (typically referred to as titanium sponge) with master alloys containing the alloying elements. Typically vanadium bearing titanium alloys also contain aluminum. Vanadium/aluminum master alloys containing 50-80 percent vanadium are typically used to produce a variety of titanium alloys. The master alloy is typically crushed to ¼ inch by 65 mesh and blended with titanium sponge to form a consumable electrode which is melted in a variety of vacuum furnaces, depending upon the product and grade being produced. Vanadium aluminum master alloys have similar melting point and density as titanium sponge allowing for the production of homogenous titanium alloy ingots, plates and other physical forms. Given the critical nature of the applications of titanium alloys, the quality of the vanadium used in this application is critical. The titanium alloys must contain very low residual impurities and must be free of any high or low density inclusions to avoid catastrophic failure. Strict quality controls including ISO-9001 and AS9100 certifications are required for producers of vanadium to supply the titanium alloy industry. Roughly 90 percent of the vanadium produced globally is used in the production of high strength
