Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon

Definitions

• the nickel-base superalloys such as Inconel Incoloy 901 are strengthened by thermomechanical processing, usually including solutioning, cold work, precipitation aging and warm working. The processing results in a fine-grained microstructure containing dispersed intermetallic particles and a dense dislocation substructure which may be stabilized by post-deformation precipitation aging.
• the present invention relates in general to the nickel base alloy field and, more particularly, to the thermomechanical processing of the intermediate service temperature nickel-base superalloys for improved strength.
• both Inconel 718 and Incoloy 901 are strengthened by metastable coherent 'y'-type precipitates which are formed by aging in the 1100'1500 F. temperature range.
• Incoloy 901 a face-centercd-cubic Ni Ti 7 phase forms, while in Inconel 718 both face-centered-cubic Ni (Al, Ti) 7' and body-centered-tetragonal Ni Cb 'y" are present.
• a stable intermetallic phase forms at higher temperatures (1400- 1800 F.) at the expense of the ordered strengthening 7' and/or 7" phases.
• Udimet 700 has no analogous intermetallic phase. These stable phases are a hexagonal Ni Ti (901) and orthorhombic Ni Cb (718) and, as these alloys are conventionally processed, both are generally considered to be detrimental to the strength and toughness of the alloy if present in substantial quantities.
• This invention contemplates the duplex processing of certain precipitation-hardened nickel-base superalloys for strength improvements. It is applicable to the intermediate service temperature nickel-base superalloys of the type characterized by Inconel 718 and Incoloy 901. v
• the alloys are first thermomechanically processed to refine the morphology of the intermetallic phase, utilizing it for a grain boundary pin-- ning function, and are subsequently thermomechanically processed to introduce and stabilize dislocation arrays within the microstructure.
• a particularly preferred processing of the Incoloy 901 alloy comprises: heat'trea'tmeiitat'about 2000 F. for 2 hours'with water” quench; cold working to reductions in area of percent; precipitation aging at 1700 F. for about 16 hours with fast air cool; 7 and .warm working at about 17 25 F.
• the alloys are solution annealed and cooled sufficiently rapidly from the solution temperature to suppress the formation of the strengthening precipitate phase.
• the material is then cold-worked to in troduce a dislocation substructure, the deformation generally varying over a wide range (15-75%).
• the material in the absence of the strengthening precipitate, the material can be cold worked to reductions in excess of 75 percent reduction-in-a'rea (1.39 true strain) without difficulty.
• the dislocation substructure may be stabilized when there is an interaction between the dislocations and the formation of the precipitating phase.
• a high temperature age is utilized, subsequent to the cold working sequence, to precipitate the eta phases.
• the cold worked substructure provides intragranular nucleation sites which lead to a favorable morphology and distribution of precipitate when subsequently heat treated above the 'y' solvus for eta phase precipitation.
• the alloys are then warm worked at a temperature where recrystallization can take place, utilizing the precipitate to establish a fine grain size. Generally, deformations within the range of 15-75 percent (about .2-1.4 true strain) are utilized.
• the warm work operation provides compatibility with subsequent processing wherein the dislocation substructure is stabilized by normal precipitation aging.
• fast cooling is required to preserve the dislocation substructure during the cooling sequence.
• the degree of deformation is preferably restricted to the 15-75 percent deformation band.
• the 'y Ni Ti interacts with dislocations to form stacking faults within the precipitate particles.
• the dislocation substructure is stabilized since motion of a dislocation away from a particle would require a high energy defect within the 'y'.
• the duplex-processed alloys exhibit higher hardnesses than those conventionally processed. This can be attributed to the stabilized warm worked dislocation substructure. In utilizing this strengthening elfect care must be taken to cool sufiiciently rapidly from the warm working temperature to limit recovery. However, in applications where only grain size is of concern, rapid cooling is not necessary.
• thermomechanical treatments thus appear to be a suitable and practical method for strengthening the low 7' volume fraction superalloys such as Inconel 718 and Incoloy 901.
• One such strengthening treatment is simply to solution cold work and age for the strengthening precipitate.
• a second thermomechanical treatment, duplex-processing consists of solution, cold Work, high temperature age and warm work. This results in a fine grained microstructure, ASTM 11-14, containing dispersed intermetallic particles (eta) along with a dense dislocation structure. This may be stabilized by aging for the strengthening 7' precipitate. While dislocation recovery occurs above the 'y' solvus, the fine grain size is maintained at higher temperatures.
• thermomechanical treatments presented are convenient from a view point of suitability to engineering application. All working operations may realistically be incorporated into a rolling or forging process. Also, the eta phase precipitation sequence and warm working operation may be combined.
• thermodynamically metastable 'y'-type precipitate whichcomprises:
• the alloy is subjected to post deformation aging to precipitate the 'y-type precipitate in a homogeneous distribution.
• the alloy is subjected to post deformation aging at a temperature of 1000-1400 F.
• the alloy is aged at about 1300-1350 F. for a minimum of about 6 hours;
• the alloy is subjected to post deformation aging at a temperature of about 1000-1400 F.
• the alloy is aged as follows: 1300-1350 F. for a minimum of about 6 hours; and 1l25-1175 F., the total aging time being about 18 hours.

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• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

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Cited By (27)

Families Citing this family (1)

• 1970
  • 1970-06-25 US US49957A patent/US3676225A/en not_active Expired - Lifetime
• 1971
  • 1971-02-09 CA CA104,941A patent/CA940806A/en not_active Expired
  • 1971-05-07 GB GB1378471*[A patent/GB1342831A/en not_active Expired
  • 1971-05-26 SE SE7106790A patent/SE379212B/xx unknown
  • 1971-06-14 FR FR7122753A patent/FR2099818A5/fr not_active Expired
  • 1971-06-19 DE DE19712130518 patent/DE2130518A1/de active Pending

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