Materials for engineering, 3rd Edition - (Malestrom)

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Materials for engineering
β
α + β
Temperature
α
α 2
α + α 2
3.11 Schematic phase diagram for near-α alloys of titanium.
leading to precipitation of a fine dispersion of the Ti 2 Cu phase, as indicated
in the phase diagram of Fig. 3.12. The strength is increased further if the
alloy is cold worked before ageing. This, coupled with ready weldability
makes it appropriate for use in, for example, gas turbine engine casing
assemblies.
β-alloys
β-alloys require the addition of sufficient β-stabilizing elements, such as
vanadium, as indicated in the phase diagram of Fig. 3.13. The resulting
body-centred cubic (bcc) structure is much more readily cold-formed than
the hexagonal α–Ti. One example of this group is Ti–13V–11Cr–3Al, and
final strengthening is achieved by age-hardening, which, together with solution
hardening by the β-stabilizing elements can give tensile strengths in excess
of 1300 MPa.
A remarkable new β-alloy containing Ta and Nb has been developed,
known as ‘Gum Metal’, which has unique characteristics: a low Young’s
modulus and extremely high strength. Gum metal exhibits elastic strains of
up to 2.5%, an order of magnitude greater than that observed in other metals
and alloys. Present applications include its use in spectacle frames and precision
screws, but it is potentially widely applicable for automotive parts, medical
equipment etc.