TABLE OF CONTENTS Stimulus for the development of titanium alloys during the past 40 years came initially from the aerospace industries when there was a critical need for new materials with higher strength: weight ratios at elevated temperatures. As mentioned in Chapter 1, the high melting point of titanium (1678 C) was taken as a strong indication that the alloys would show good creep strengths over a wide temperature range. Although subsequent investigations revealed that this temperature range was narrower than expected, titanium alloys now occupy a critical position in the materials inventory of the aerospace industries (see Fig. 1.6) and around 50% of titanium is used in this way. More recently the importance of these alloys as corrosion-resistant materials has been appreciated by the chemical industry as well as by the medical profession which uses titanium alloy prostheses for implanting in the human body. It is proposed to consider the alloys with respect to these applications and to concentrate on wrought products as titanium alloy castings amount to less than 2% of titanium metal.
Titanium has a number of features that distinguish it from the other light metals and which make its physical metallurgy both complex and interesting.
At 882.5 C, titanium undergoes an allotropic transformation from a low-temperature, hexagonal close-packed structure ( ?) to a body-centred cubic ( ?) phase that remains stable up to the melting point. This transformation offers the prospect of having alloys with ?, ? or mixed ?/ ?
