82 History

Titanium has been recognized as an element for more than 200 years since it was first identified in 1790 by a Cornish (UK) clergyman and named "titan" by a German chemist in 1795. Early reduction processes were both expensive and generally yielded a product of a purity level that was unsuitable for use of the metal itself, although the oxide was used from the early 1900s as a pigment. However, it is only in the last 50 years that metallic titanium has gained strategic importance since an economic extraction process was developed. In that time, commercial production of titanium and titanium alloys in the United States has increased from zero to a peak of more than 27 million kg/yr [1-9].

The catalyst for the remarkable growth of the metal was the development by Dr. Wilhelm J. Kroll of a relatively safe, economical method to produce titanium metal in the late 1930s. Kroll's process involved reduction of titanium tetrachloride (TiCl4), first with sodium and calcium, and later with magnesium, under an inert gas atmosphere [1]. Research by Kroll and many others continued through World War II. By the late 1940s, the mechanical properties, physical properties, and alloying characteristics of titanium were defined as the commercial importance of the metal was apparent. The first titanium for actual flight was ordered from Remington Arms (later Rem-Cru, and still later, Crucible Steel) in the United States by Douglas Aircraft in 1949. Other early U.S. entrants to the titanium field included Mallory-Sharon (later IMI) and TMCA (later Timet). In the United Kingdom, ICI Metals (later IMI and recently Timet Europe) began sponge production in 1948, with other involvement from continental Europe a few years later. Recognizing the military potential of titanium, the Soviets began sponge production in 1954. In Japan, sponge production was initiated by Osaka Titanium in 1952, generally to supply other countries and internal corrosion-resistant applications.

The U.S. government invested large sums of money to develop the science and technology of titanium and its alloys. This included an investment of in excess of a quarter of a billion dollars for a sponge stockpile up to 1964 and establishment of a titanium laboratory at Battelle, Columbus, in 1955 [1].

The vast influx of money resulted in rapid development of a sound technology with very good scientific underpinning. The double consumable vacuum arc melting (VAR) technique was developed by Armor Research Foundation in 1953. Problems relating to hydrogen embrittlement and hot salt stress corrosion cracking were recognized and circumvented.

Alloy development progressed rapidly from about 1948 with people at Remington Arms recognizing the beneficial effects of aluminum additions. The "workhorse" Ti-6AI-4V* alloy was introduced in 1954, with the disputed patent assigned to Rem-Cru. This alloy soon became by far the most important titanium alloy because of its excellent combination of mechanical properties and "forgiving" processability. The first beta titanium alloy (Ti-13V-11Cr-3AI) was developed by Rem-Cru in the mid-late 1950s, with this high-strength heat-treatable alloy seeing extensive use on the high-speed surveillance aircraft the SR71. Alloy development in the United Kingdom, driven by Rolls-Royce, was concentrated more on elevated temperature alloys for use in engines.

Aircraft manufacturers have used a generally increasing amount of titanium in airframe applications for heavily stressed demanding components. Engine components using titanium began in the United States with the Pratt and Whitney J57 in 1954, including discs, blades, and spacers in the compressor section, and in the United Kingdom with the Rolls-Royce Avon engine in 1954.

Work in the 1950s also indicated the excellent corrosion resistance of titanium and its alloys, and early commercial applications included use in anodizing, wet chlorine, and nitric acid equipment.

*Throughout the text, all terminal alloys are given in wt %, intermetallics in at %.

During the late 1950s the shipment of titanium mill products in the United States dropped from a high of 4.5 million kg (9.9 million lb) in 1957 with a change in emphasis from aircraft to missiles and concerns over the cost of titanium.

Mill shipments in the United States tripled during the 1960s from 4.5 million kg (9.9 million lb) in 1960, with aerospace use accounting for 90% of the market in 1970. This increase resulted mainly from use in nonmilitary engines and the wide-body jets, the Boeing 747, the DC-10, and the L-1011. Advances also occurred in melting practices and expanded use in nonaerospace markets such as ships and heat exchanger tubing. The 1971 cancellation of the March 3 Supersonic Transport (SST), which was slated to use considerable amounts of titanium, was a blow to the titanium industry with mill products in the United States dropping from 12 million kg (26.5 million lb) in 1970 to 9 million kg (19.8 million lb) in 1971.

Mill product shipments increased in the 1970's in large part due to increased use in the large commercial transports and their high bypass engines, new military airframes with 20-35% of their structural weight produced from titanium products, and nonaerospace use, a result of the corrosion resistance of titanium. The U.S. industry set a new record in 1980-81 of about 23 million kg (51 million lb), but this figure then dropped because of hedge buying by the aerospace industry. This cyclic nature of the titanium industry will only smooth out if nonaerospace use increases. In Europe, and to a greater extent in Japan, industrial applications exceed 50% of the total use (see Section 8.11)

Titanium mill shipments in the United States increased steadily during the Reagan years, and the early years of the Bush administration with the buildup in military hardware, peaking in 1990 at a record 25 million kg (55 million lb) [4-6]. When "peace broke out," symbolized by the dismantling of the Berlin Wall, titanium shipments fell precipitously soon thereafter to about 16 million kg (35 million lb) per year, a level that was suggested at the time to possibly be the "norm"; however, this has proved not to be true, see below. This left a great overcapacity in the United States and painful "right-sizing" by the titanium industry occurred.

In the past decade, a steady growth of titanium shipments in the United States has occurred [3-7] fueled by increased commercial aerospace orders (the Boeing 777 has almost 10% in its airframe) and the amazing golf club phenomenon, the latter helped by the appearance of the extremely popular Tiger Woods on the golf scene [4-6].

Further expansion of the titanium market is now very critically dependent on reducing cost for a variety of applications [3 -7]. Addressing this need, lower cost alloys are being introduced into the marketplace that utilize Al-Fe master alloys to reduce cost rather than the AI-V master alloy needed for alloys such as Ti-6AI-4V. These include the Ti-6AI-1. Fe-0. 1Si (Timetal 62S) and Ti-4. 5Fe-6.8Mo-1.5AI. [Timetal LCB (low-cost beta)] alloys (5.6). Attention is also being given to lower cost processes such as near-net-shape powder metallurgy (PM) and permanent mold casting approaches [4-7].

Recent realignments include the Allegheny-Technologies acquisition of Oremet Wah-Chang and that of IMI Titanium and Cezus by Timet. There are also rumblings of some "giants" getting into the titanium business, with some new approaches to reducing cost.

The effect of low-cost product from the former USSR, where the peak capacity is estimated to have been four times that of the United States [i.e., as much as 90 million kg (200 million lb) of mill products per year] has not yet caused any major problems with the U.S. production capacity, but this situation could change as VSMPO in Salda, Russia, strives to increase exports, particularly to the United States.

The current uses of titanium and its alloys are discussed in Section 8.11. 8.3 GENERAL CHARACTERISTICS

Titanium alloys may be divided into two major categories: corrosion-resistant and structural alloys [8, 9]. The corrosion-resistant alloys are generally based on the single-phase a with dilute additions of solid solution strengthening and a-stabilizing elements like oxygen, palladium, ruthenium, and aluminum. These alloys are used in the chemical, energy, paper, and food processing industries to produce highly corrosion-resistant tubings, heat exchangers, valve housings, and containers. The single-phase a alloys provide excellent corrosion resistance, good weldability, and easy processing and fabrication but at a relatively low strength.

The structural alloys can be divided into four categories: the near-a alloys, the a + P alloys, the P alloys, and the titanium aluminide intermetallics, which will be discussed later.

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