Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Reexamination Certificate
1995-07-05
2001-12-11
King, Roy (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
C148S675000, C148S677000, C148S564000
Reexamination Certificate
active
06328827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing sheets having superplastic properties from a nickel-based superalloy known by the name of “alloy 718”, and also to a method of forming parts by superplastic deformation of such sheets.
2. Summary of the Prior Art
Numerous applications of superplastic forming processes have been developed, particularly in aeronautics, for producing parts from titanium and aluminium based sheets. Some sandwich-type structures in particular are obtained by combining the processes of superplastic forming and diffusion welding. These applications have demonstrated the advantages, in terms of quality, cost, productivity and industrial expertise, of using a superplastic forming process for making parts from sheets.
In addition, the designer's preferred choice of material for numerous parts of casing or fixed structure type for aircraft engines, turbojets or turbo-machines is a nickel-based superalloy known by the name of “alloy 718”, and a typical composition of which is, by weight, 19% Cr, 18% Fe, 5% Nb+Ta, 3% Mo, 1% Ti, 0.5% Al, and mainly Ni as the remainder.
Currently, however, sheets of alloy 718 do not possess superplastic properties, and mechanical elongation characteristics as low as A%=12 are normally allowed for these sheets.
Consequently, the invention seeks to determine particular manufacturing and forming conditions which will enable parts to be made from sheets of alloy 718 by superplastic forming.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of manufacturing a sheet from a nickel-based superalloy known by the name of “alloy 718” and having a typical composition comprising, by weight, 19% Cr, 18% Fe, 5% Nb+Ta, 3% Mo, 1% Ti, 0.5% Al, and mainly Ni as the remainder, comprising a preliminary cycle including at least the steps of casting and hot rolling said sheet, and a final cycle comprising the following steps in order to impart properties of superplasticity to said sheet:
a) solution heat treatment at a temperature of substantially 1060° C. for substantially 15 minutes;
b) precipitation heat treatment at a temperature between 730° C. and 800° C. for a period of from one to two hours;
c) cold rolling at a rolling ratio greater than 60%; and,
d) recrystallization heat treatment at a temperature of substantially 900° C. for substantially 30 minutes.
According to a second aspect of the invention parts are formed from sheets of alloy 718 manufactured in accordance with the invention by superplastic deformation carried out at a temperature below 985° C., preferably at a temperature of 970°±10° C., and by applying pressures calculated to obtain stresses within the material of between 45 and 60 MPa.
Further preferred features and advantages of the invention will become apparent from the following more detailed description of embodiments of the invention, given by way of example, with reference to the attached drawings.
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Smith, Gaylord D & H. Lee Flower, “Superplastic Forming of Alloy 718” in Advanced Materials & Process 4/94 pp. 32-34.*
Ceschini, L; G. P. Cammarota, G. L. Garagnaniand A. Afrikantov, “Variazioi MicrostrulturaliNella Lega IN-718 Indotte da Trattamenti Termici E Meccanici” in LaMetallurgica Italiana, vol. 86, n6-7/1994 pp. 355-362.*
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Bouzidi Mohamed
Caburet Philippe
Clement Pierre
Collot André Claude Félix
Lebrun Jean-Lou
Coy Nicole
King Roy
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Societe Nationale d'Etude et de Construction de Moteurs d&a
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