Feb_March_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 1 8 1 9 T itanium and its alloys were in- troduced in the late 1940s. The main focus was on high specif- ic strength—including at elevated tem- peratures—which led to widespread use in aerospace applications. Further attention was paid to titaniumdue to its excellent flexibility, strong spring-back characteristics, corrosion resistance, and biocompatibility. However, titani- um alloys are inappropriate for use in many applications (e.g., in the auto in- dustry) due to high cost. The principal use for titanium (i.e., TiO 2 ) is paint filler, which takes advantage of its whiteness and high refractive index. Of all mined and synthetic titanium minerals, 95% go into the manufacture of TiO 2 , with just 5% used in the manufacture of tita- nium metal. Commercial production of titanium and Ti alloys in the U.S. has in- creased tomore than 27 × 10 6 kg/yr over the past 50 years [1-11] . The processing and behavior of ti- tanium and its alloys strongly depend on two allotropic forms of titanium (high-temperature body centered cu- bic, or bcc, beta phase; and low-tem- perature hexagonal close-packed, or hcp, alpha phase), with alloying el- ements stabilizing the alpha phase (Al, O, N) or beta phase (Mo, V, Nb, Fe, H) [12-17] . Titanium can be significantly strengthened by alloying. Of equal im- portance to the founding of the indus- try was development of titanium alloys, the most important being Ti-6Al-4V, or Ti64, an alpha-beta alloy introduced in 1954, which can be heat treated for hardenability and is weldable. It is still the workhorse of the titanium indus- try. There would have been no industry *Member of ASM International without it because commercially pure (CP) titanium is not useful in high- performance aerospace applications where great strength and the ability to withstand stress and fatigue are re- quired at high temperatures. The first beta alloy, Ti-13V-11Cr-3Al (Beta I) was introduced in the late 1950s. It has a high strength-to-density ratio and can be heat treated to a soft condition for fabrication. This alloy was used as the skin on the Lockheed SR-71 Blackbird. In the UK, alloy development was driv- en by Rolls-Royce and concentrated on high-temperature alloys for use in engines. Since the 1980s, R&D of new al- loys has diminished, with research ef- forts shifting to innovative production methodologies for sponge and ingot. It is a very costly procedure to introduce a new alloy and go through the lengthy process of having it certified for aero- space use, which is the only applica- tion that generates enough revenue to justify the R&D costs. The certification process typically lasts about two years in the U.S., during which time the com- pany must—at its own expense—manu- facture test products and validate their properties, which seriously dampens R&D. Titanium was predominantly used in military applications until the end of the Cold War, for aerospace in the West and for submarines in the USSR (Fig. 1). Use of titanium in commer- cial aircraft started during the 1950s TITANIUM: A HISTORIC AND CURRENT PERSPECTIVE—PART I Among the structural materials developed in the 20th century, titanium and its alloys have played a leading role in improving component performance. Francis H. (Sam) Froes, FASM,* Consultant Ashraf Imam, George Washington University Fig. 1 − Advanced F-35 U.S. fighter aircraft (top) and Russian submarine (bottom). Titaniumwas predominantly used in military applications until the end of the Cold War.