Metal treatment – Stock – Age or precipitation hardened or strengthened
Patent
1993-10-12
1995-06-06
Roy, Upendra
Metal treatment
Stock
Age or precipitation hardened or strengthened
148403, 148421, 4272552, C22C 2100
Patent
active
054219175
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a metastable solid solution titanium-based alloy produced by vapour quenching. Such alloys are amenable to age hardening by precipitation from the solid solution, but may also find application in the original solid solution form.
BACKGROUND OF THE INVENTION
Vapour quenching is a known process by which alloys having metastable supersaturated solid solutions can be produced. The process comprises evaporation of alloy constituents under vacuum from individual or combined sources to produce a flux of vapours and condensation of the vapours upon a temperature-controlled collector. The collector deposit may be mechanically worked in situ to consolidate the deposit and thus reduce any tendency towards porosity, or may be hot isostatic pressed after removal from the collector. Not all alloys require this subsequent consolidation step. Some are satisfactory in the as-deposited condition, depending on composition, deposition conditions and intended utilisation. A description of this process as applied to aluminium-based alloys is given in two articles by Bickerdike et al. in the International Journal of Rapid Solidification, 1985, vol. 1 pp. 305-325; and 1986, vol. 2, pp. 1-19.
Titanium alloys are well established in the field of aerospace structures and in aero engine applications because they possess a high strength-to-weight ratio at high temperatures. In these known alloys, titanium is commonly alloyed with one or more of the following elements in the indicated proportions by weight:
Al (up to 8%); Sn (up to 11%); Zr (up to 11%); Mo (up to 15%); V (up to 13%); Si (up to 0.5%), and Cr (up to 11%).
Commercial purity titanium may contain the following elements in addition to those strengthening ingredients found in titanium alloys:
O.sub.2 (up to 0.32%); N.sub.2 (up to 0.006%); C (up to 0.02%); H.sub.2 (0.002 to 0.004%), and Fe (up to 0.05%), together with trace quantities of other metals (0.05% or less). Proportions are again indicated by weight. Such elements are normally considered to be impurities but oxygen at least contributes to the hardness of the titanium material and is sometimes considered as a minor but significant alloying ingredient.
The present invention provides new alloys based on titanium incorporating an element from the group consisting of magnesium, calcium and lithium. Little published data is available regarding these three binary systems and it is virtually impossible to incorporate any of these into a titanium alloy made by mixing in the melt because all three elements boil at a temperature below the melting point of titanium. Certain limited data is available for these systems from the evidence of diffusion couples which reveals that all three of these elements have negligible equilibrium solid solubility in titanium (less than 0.5% by weight) and which further indicates that none of them form compounds when present in titanium.
We have discovered that it is possible to make binary alloys of titanium with magnesium, which alloys retain the magnesium constituent in solid solution within the titanium in quantities far greater than the equilibrium solid solubility limit, by producing these alloys using the vapour quenching route. Furthermore, we have found that these magnesium-containing alloys show an appreciable age hardening response which was previously unknown. It is believed that these findings will read across to the closely related elements calcium and lithium which can also be produced as binary alloys with titanium by means of vapour quenching, and that the findings will be valid to a greater or lesser extent when any of these three elements is introduced into a vapour-quenched titanium alloy containing any of the known alloying additions for titanium alloys.
The elements magnesium, calcium and lithium each have densities much lower than that of titanium. Since existing data indicates that none of these elements form compounds when present in binary titanium alloys, this leads to the conclusion that the density of the binary alloy may be predicted reliab
REFERENCES:
patent: 4469536 (1984-09-01), Forester
Materials Letters vol. 11, No. 8, 9 Jul. 1991 Ward-Close & Partridge p. 295 "The production of titanium-magnesium alloys by vapour quenching".
Partridge Peter G.
Ward-Close Charles M.
Roy Upendra
The Secretary of State for Defence in her Britannic Majesty's Go
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