General Electric Company

Charles P Blankenship, Jr

Michael F Henry

Mark Gilbert Benz

Eric Scott Huron

Edward Lee Raymond

Aldo Enrique Murut

Duk Y Yoon

John Michael Hyzak

Renee M Rohling

Robert Donald Kissinger

Duk N Yoon

A method combining isothermal and high retained strain forging is described for Ni-base superalloys, particularly those which comprise a mixture of .gamma. and .gamma.' phases, and most particularly those which contain at least about 40 percent by volume of .gamma.'. The method permits the manufacture of forged articles having a fine grain size in the range of 20 .mu.m or less. The method comprises the selection of a fine-grained forging preform formed from a Ni-base superalloy, isothermal forging to develop the shape of the forged article, subsolvus forging to impart a sufficient level of retained strain to the forged article to promote subsequent recrystallization and avoid critical grain growth, and annealing to recrystallize the microstructure. The method permits the forging of relatively complex shapes and avoids the problem of critical grain growth. The method may also be used to produce location specific grain sizes and phase distributions within the forged article.

Isothermal and high retained strain forging of Ni-base superalloys

A method for forming nickel base superalloy articles of manufacture by a combination of hot die forging, isothermal forging and heat treatment below and above the solvus.

Grain size control in nickel base superalloys

A method of high retained strain forging is described for Ni-base superalloys, particularly those which comprise a mixture of .gamma. and .gamma.' phases, and most particularly those which contain at least about 30 percent by volume of .gamma.'. The method utilizes an extended subsolvus anneal to recrystallize essentially all of the superalloy and form a uniform, free grain size. Such alloys may also be given a supersolvus anneal to coarsen the grain size and redistribute the .gamma.'. The method permits the manufacture of forged articles having a fine grain size in the range of about ASTM 5-12 (5-60 .mu.m).

Method for controlling grain size in Ni-base superalloys

A method of supersolvus forging is described for Ni-base superalloys, particularly those which comprise a mixture of .gamma. and .gamma.' phases, and most particularly those which contain at least about 40 percent by volume of .gamma.'. The method permits the manufacture of large grain size forged articles having a grain size in the range of 50-150 .mu.m. The method comprises the selection of a fine-grained forging preform of a Ni-base superalloy. Supersolvus forging in the range of 0.degree.-100.degree. F. above the alloy solvus temperature then performed at slow strain rates in the range of 0.01-0.001 s.sup.-1. Subsequent supersolvus annealing followed by controlled cooling may be employed to control the distribution of the .gamma.', and hence influence the alloy mechanical and physical properties. The method may also be used to produce location specific grain sizes and phase distributions within the forged article.

Supersolvus forging of ni-base superalloys

A method of forging Ni-base superalloys is described which avoids the growth of abnormally large grains in the surface region of a forged article. The method involves forging and/or annealing a Ni-base superalloy in a carburizing environment. Forging and/or annealing in a carburizing environment is done to maintain the carbon concentration in the surface region at a level that is sufficient to prevent the depletion of carbides and carbonitrides. The carburizing environment may also be selected so that it is non-oxidizing with respect to aluminum, in order to prevent the depletion of aluminum and the reduction of the .gamma.' phase in the surface region.

Method for reducing abnormal grain growth in Ni-base superalloys

A method of forging to impart a critical amount of retained strain is described for Ni-base superalloys, particularly those which comprise a mixture of .gamma. and .gamma.' phases, and most particularly those which contain at least about 40 percent by volume of .gamma.'. This forging method harnesses nucleation-limited recrystallization, a phenomenon which has been known in the past to produce uncontrolled, non-uniform Critical grain growth, to produce forged articles having a uniform average grain size in the range of about 90-120 microns. The method comprises the selection of a forging preform formed from a Ni-base superalloy. Isothermal subsolvus forging is then used to form a precursor forging which has a near-net shape. The precursor forging is then forged using relatively high strain rate techniques, such as hammer forging, hot die forging or room temperature forging, to impart all or some portion of it with a critical amount of retained strain energy. The forging is then given a final subsolvus soak and supersolvus anneal to form the uniform grain structure.

Retained strain forging of ni-base superalloys

A method is provided for obtaining uniform grain growth within .gamma.' precipitation strengthened nickel-base superalloys. The method includes forming a billet having a very fine grain size in order to achieve optimum superplasticity of the superalloy during forging. The article is then heated to a pre-working hold temperature in a manner which prevents coarsening of the microstructure and a loss of superplasticity. The article is then worked, such as by forging, at a temperature below the .gamma.' solvus temperature of the alloy, so as to maintain local strain rates within the article below a critical strain rate for random grain growth, and so as to maintain the strain rate gradient throughout the article below a critical upper limit. After working, the article is subjected to annealing at a temperature which is less than the .gamma.' solvus temperature of the alloy, and for a duration which is sufficient to remove accumulated metallurgical strain in the article. A supersolvus heat treatment is then performed by further heating the article to a temperature above the .GAMMA.' solvus temperature of the superalloy for a duration sufficient to uniformly coarsen the grains of the article.

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Niskayuna, NY, United States of America

Charles P Blankenship, Jr