Metal treatment – Stock – Titanium – zirconium – or hafnium base
Patent
1996-06-28
1998-08-11
Sheehan, John
Metal treatment
Stock
Titanium, zirconium, or hafnium base
148237, 148512, C22C 1400
Patent
active
057922896
DESCRIPTION:
BRIEF SUMMARY
This invention relates to titanium alloy products and methods for their production, and in particular relates to such products which are required to have good tribological properties.
Although titanium is strong and light, applications of titanium in general engineering are limited by its poor tribological properties. It has been proposed in, for example, WO 91/05072, EP-A-0246828, WO 86/02868 and Metal Science and Heat Treatment, vol 26, no. 5/6, May-June 1984, pages 335 and 336, to improve the tribological properties of titanium and titanium alloys by melting suitable alloying ingredients such as boron, carbon, nitrogen, oxygen, silicon, chromium, manganese, iron, cobalt, nickel, copper into a surface layer using localised high energy surface melting techniques such as laser beam melting or electron beam melting. However, it is difficult to ensure that the required alloying ingredients are introduced evenly and in the correct quantity into the melted surface layer. Additionally, it is difficult in a non-destructive test to check that the surface layer in the final product has the correct distribution and composition.
It is an object of a first aspect of the present invention to obviate or mitigate the above disadvantage.
According to said one aspect of the present invention, there is provided a method of forming an titanium alloy product having a hardened layer thereon, comprising the steps of: preferably by a casting and forging operation) from a titanium alloy consisting of (a) 2 to 15% (preferably 5 to 9%) by weight silicon or 5 to 15% (preferably 8 to 11%) by weight nickel, (b) 0 to 7% by weight of at least one of the alloying elements conventionally used to strengthen wrought titanium alloys (aluminium, tin, zirconium, vanadium, chromium, manganese, iron, molybdenum and niobium) and (c) 0 to 2% by weight of at least one alloying element added specifically for the purpose of improving the surface properties and selected from boron, carbon, nitrogen, oxygen and zirconium, the balance apart from impurities and incidental ingredients being titanium, and solidification operation so as to produce a hard wear-resistant surface layer without substantially affecting the bulk properties of the alloy.
It has now been found that contrary to previous expectation, the titanium-silicon alloy is quite easily forged at 1000.degree. C. and so can be made by casting and forging route, rather than having to cast it to shape. The use of a forging operation enables the structure of the alloy to be refined to permit an improvement in ductility of the bulk material (i.e., the core or substrate of the product as opposed to the surface case) by a sequence of working and heat treatment operations to produce a wrought product. A typical sequence of such operations for an alloy containing 8.5 wt % silicon would comprise casting an ingot, forging it at 1000.degree. C. so as to produce an appropriately shaped billet or preform, annealing it at 550 to 750.degree. C., precision die forging it at 1000.degree. C. to the required shaped component and machining it to approximate final dimensions.
The surface treatment step (2) gives rise to a microstructural change during rapid cooling which results in a fine-grained surface layer consisting predominantly of Ti-Si or Ti-Ni eutectic which is substantially harder than the substrate.
It will thus be appreciated that there is no need to make specific additions to the surface and that surface hardening takes place automatically upon surface melting as a direct result of the alloy material chosen.
With regard to the optional strengthening alloying elements and optional surface-improving elements, it will be noted that zirconium can be used both for strengthening and for surface-improving. In the case where it is included for both purposes, it will normally be present in an amount of up to 7% by weight.
Also according to said first aspect of the present invention, there is provided a titanium alloy product, (preferably a cast or wrought titanium alloy product), formed of a titanium alloy cons
REFERENCES:
patent: 4902359 (1990-02-01), Takeuche et al.
patent: 5139585 (1992-08-01), Watanabe et al.
patent: 5466305 (1995-11-01), Sato et al.
patent: 5525165 (1996-06-01), Wu et al.
patent: 5573604 (1996-11-01), Gerdes et al.
Strength of Metals and Alloys, "Rapid Solidfication and Aging of a . . . ", Baeslack III et al, pp. 1633-1638, Aug. 1985.
Rapid Solidification Studies in Eutectoid . . . , L.S. Chumbley et al, Department of Materials Science. Mar. 1986.
Patent Abstracts of Japan, vol. 6, No. 24, Feb. 12, 1982.
Patent Abstracts of Japan, vol. 11, No. 39, Feb. 5, 1987.
Patent Abstracts of Japan, vol. 11, No. 251, Aug. 14, 1987.
2010 Le Vide, Les Couches Minces 43, "Traitments De Surface Par Laser", G. Coquerelle, pp. 545-563, 1988.
Bloyce Andrew
Dong Hanshan
Morton Peter Harlow
Sheehan John
The University of Birmingham
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