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  Beta-titanium alloy, method for the production of a hot-rolled product from an alloy of this type, and uses thereofRelated Patent Categories: Metal Treatment, Process Of Modifying Or Maintaining Internal Physical Structure (i.e., Microstructure) Or Chemical Properties Of Metal, Process Of Reactive Coating Of Metal And Process Of Chemical-heat Removing (e.g., Flame-cutting, Etc.) Or Burning Of Metal, Heating Or Cooling Of Solid Metal, Refractory Metal (i.e., Titanium(ti), Zirconium(zr), Hafnium(hf), Vanadium(v), Niobium(nb), Columbium(cb), Tantalum(ta), Chromium(cr), Molybdenum(mo), Tungsten(w)), Or Alloy Base Thereof, Titanium(ti) Or Titanium Base Alloy, With Working, With Ageing, Solution Treating (i.e., For Hardening), Precipitation Hardening Or StrengtheningThe Patent Description & Claims data below is from USPTO Patent Application 20070175552. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] Beta titanium alloys with high vanadium contents are distinguished by high strength and also effective toughness or ductility. They are conventionally processed in a hot-forming process to form semi-finished products such as metal sheets, rods, hollow or solid profile members, and wires, from which high-quality, light-weight components are then produced. [0002] The basic principles of the production and characteristics of beta titanium alloys are described in U. Zwicker, Titan-und Titanlegierungen ("Titanium and Titanium Alloys"), Springer: Berlin, Heidelberg, N.Y. (1974). In addition to titanium as the matrix metal, beta titanium alloys therefore conventionally contain, as principal alloys elements stabilising the .beta. mixed crystal, V, Nb, Ta, Mo, Fe and Cr, as well as certain contents of Zr, Sn, Al and additives of Si. [0003] A beta titanium alloy and a method for the production of components from this alloy are also known from DD 281 422 A5. In the known alloy, the contents of Cr and V are in total 1.5 to 4.5 mass %, while the content of Cr is limited to less than 2.5 mass %. In addition, the known alloy contains less than 2.0 mass % Fe, 3.8 to 4.8 mass % Al, 1.5 to 4.5 mass % Mo, as well as 1.5 to 2.5 mass % Sn, 2.8 to 4.8 mass % Zr and less than 0.3 mass % Si. According to the known method, a melt having a composition of this type is cast to form bars, which are then hot-formed, in a process carried out in two stages, to form a component. The component that is obtained is brought into solid solution by means of a heat treatment process, in which its temperature is maintained at 10.degree. C. to 40.degree. C. below a value designated in DD 281 422 A5 as the ".beta. transus" real value. After this heat treatment process, the part is then kept between 550.degree. C. and 650.degree. C. for 4 to 12 hours. The parts treated in this manner have a yield point R.sub.p0.2 of at least 1,100 MPa and tensile strength R.sub.m of at least 1,200 MPa. [0004] Further examples of beta titanium alloys are provided in AT-PS 272 677, EP 0 408 313 B1 and EP 0 600 579 B1. Common to the prior art documented in all of these documents is the endeavour to provide a titanium alloy that may be cast as easily as possible, while at the same time having good mechanical characteristics and being able to be produced cost-effectively. [0005] However, practical experience has shown that the known alloys, both with respect to their strength and with respect to their expansion behaviour, do not satisfactorily meet the requirements set by the processors and users. [0006] The object of the invention was therefore to provide a high-strength beta titanium alloy that has good plastic characteristics prior to curing, for the purposes of effective formability, and high fatigue strength after curing and may be produced cost-effectively. A method by means of which high-strength components may be produced cost-effectively from an alloy of this type is also to be indicated. [0007] With respect to the material, this object is achieved by a beta titanium alloy that contains (in mass %): V: 10 to 17%, Fe: 2 to 5%, Al: 2 to 5%, Mo: 0.1 to 3%, and optionally one or more alloy elements from the group of Sn, Si, Cr, Nb, Zr according to the following proportions: Sn: 0.1 to 3%, Si: 0.1.ltoreq.2%, Cr: .ltoreq.2%, Nb: .ltoreq.2%, Zr: .ltoreq.2%, wherein the beta titanium alloy may additionally comprise contents of C and of elements from the group of the lanthanides, and as the remainder Ti and inevitable impurities. [0008] At ambient temperature, a beta titanium alloy having the composition according to the invention easily achieves a yield point R.sub.p0.2 of at least 1,400 MPa, a tensile strength R.sub.m of at least 1,500 MPa, and a plastic strain E.sub.p0.2 of more than 4%. Its density .rho. does not exceed 4.8 g/cm.sup.3, so components that are not only extremely strong, but also weight-optimised, may be produced using a beta titanium alloy according to the invention. [0009] This is achieved, firstly, in that the alloy according to the invention comprises significantly higher vanadium contents than those provided in beta titanium alloys in the prior art. As a result of the high V contents, the .beta. phase of the structure is stabilised and the high-temperature strength increased. In an alloy according to the invention, the V content is therefore preferably in the range from 12 to 17 mass %, in particular in the range from 13 to 17 mass %. [0010] Contents of 2 to 5 mass % aluminium stabilise the a phase of the structure and cause effective mixed crystal hardening. [0011] The effect of the iron in the titanium alloy having the composition according to the invention consists in a stabilisation of the .beta. phase of the structure, an increase in the high-temperature strength and an improvement in the mixed crystal formation. [0012] Molybdenum in contents of 0.1 to 3 mass %, preferably at least 0.5 mass %, is contained in a titanium material according to the invention to stabilise the .beta. phase of the structure and to increase the high-temperature strength. [0013] A beta titanium alloy according to the invention optionally also contains one or more alloy elements from the group of Sn, Si, Cr, Nb, Zr. [0014] The presence of tin has a beneficial effect on the mixed crystal hardening and the high-temperature strength. The Sn contents are therefore preferably in the range from 0.5 to 3 mass %. [0015] In an alloy according to the invention, silicon increases the high-temperature strength and the oxidation resistance. [0016] Chromium may be added to the alloy to stabilise the .beta. phase of the structure and to increase the high-temperature strength. [0017] Adding niobium may also have a beneficial effect on the high-temperature strength and the oxidation resistance of the alloy. [0018] Finally, it may also be advantageous, for improving the mixed crystal formation and the oxidation resistance, to add zirconium to the alloy according to the invention. [0019] In addition to the components of which the effect has been described in detail above, the alloy according to the invention may contain further components, provided that they do not negatively affect the characteristics achieved according to the invention. These include, in particular, contents of carbon and contents of elements associated with the group of the lanthanides. [0020] Optimal characteristics of the beta titanium alloys according to the invention are achieved if the above-specified limit values are observed to within at least two decimal places. [0021] With respect to the method, the above-specified object is achieved in that the manufacturing of a product produced from a beta titanium alloy involves the following steps: [0022] melting a beta titanium melt having the composition according to the invention to form a preliminary product in block form, [0023] hot-forming the preliminary product, [0024] hot end forming the hot-formed preliminary product to form a hot end product, [0025] solution annealing the hot end product, [0026] cold-forming the hot end product to form an end product, [0027] curing treatment of the end product. [0028] The hot end forming process for the production of strips or metal sheets may be carried out as a hot-rolling process, which may, if necessary, be followed by a coiling process. [0029] The Ti alloy according to the invention may be produced in a particularly cost-effective manner in that the alloy elements V, Fe and Al are added by alloying, in a manner known per se, not individually, but rather in the form of a master alloy. Master alloys of this type are commercially available. [0030] The hot end product obtained by means of the method according to the invention after the hot-forming process consists of a single-phase, metastable beta titanium, the transus temperature T.sub.B of which is approximately 788.degree. C. If the hot end product is produced by means of a hot-rolling process, it comprises crystals stretched in the rolling direction and possesses a partially dynamically re-crystallised structure. Continue reading... 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