Method for controlling grain size in Ni-base superalloys
AssigneeGeneral Electric Company
InventorsCharles Philip Blankenship, Michael Francis Henry, Eric Scott Huron, John Michael Hyzak
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Abstract
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).
Claims20
A method of making an article having a controlled grain size from a Ni-base superalloy, comprising the steps of:
- providing a Ni-base superalloy having a recrystallization temperature, a .gamma.' solvus temperature and a microstructure comprising a mixture of .gamma. and .gamma.' phases, wherein the .gamma.' phase occupies at least 30% by volume of the Ni-base superalloy;
- working the superalloy at preselected working conditions, comprising a working temperature less than the .gamma.' solvus temperature and a strain rate greater than a predetermined strain rate, .epsilon..sub.min sufficiently to store a predetermined minimum amount of retained strain, .epsilon..sub.min, per unit of volume throughout the superalloy, to form an article, wherein .epsilon..sub.min is sufficient to promote subsequent recrystallization of a uniform grain size microstructure throughout the article;
- subsolvus annealing the article at a subsolvus temperature for a time sufficient to cause recrystallization of a uniform grain size throughout the article;
- and
- cooling the article from the subsolvus annealing temperature at a predetermined rate in order to cause the precipitation of .gamma.'.
A method of making an article having a controlled grain size from a Ni-base superalloy, comprising the steps of:
- providing a Ni-base superalloy having a recrystallization temperature, a .gamma.' solvus temperature and a microstructure comprising a mixture of .gamma. and .gamma.' phases, wherein the .gamma.' phase occupies at least 30% by volume of the Ni-base superalloy;
- working the superalloy at preselected working conditions, comprising a working temperature less than the .gamma.' solvus temperature and a strain rate greater than a predetermined strain rate, .epsilon..sub.min sufficiently to store a minimum amount of retained strain, .epsilon..sub.min, per unit of volume throughout the superalloy, to form an article, wherein .epsilon..sub.min is sufficient to promote subsequent recrystallization of a uniform grain size microstructure throughout the article;
- subsolvus annealing the article at a subsolvus temperature for a time sufficient to cause recrystallization of a uniform grain size throughout the article;
- and
- supersolvus annealing the article at a supersolvus temperature for a time sufficient to cause the dissolution of at least a portion of the .gamma.' and the coarsening of the recrystallized grain size to a larger solutionized grain size;
- cooling the article from the subsolvus annealing temperature at a predetermined rate in order to cause the precipitation of .gamma.'.
Dependencies are inferred from the claim text.