Influence of HIP processing on microstructure and mechanical properties of superalloy Udimet 720LI

Abstract

Inert gas (high purity argon) atomised powder of composition conforming to that of the superalloy Udimet 720 of low interstitial grade was hipped at 1200°C/120 MPa/3 h. The hipped alloy has shown near theoretical density and consisted of equiaxed grains with an average diameter of ∼45 μm. While primary γ′-Ni₃ (Ti, Al) precipitates with an acicular morphology were found at the grain boundaries, finer secondary γ′ precipitates with near cuboidal morphology were present in the austenite γ matrix. The yield strength (YS) of the as hipped alloy was found to be the same as that of the wrought alloy heat treated for creep applications (termed as creep resistant alloy) at room temperature (RT) as well as at 650°C. However, the ultimate tensile strength (UTS) and ductility were found to be higher than those of the wrought creep resistant alloy. On the other hand, the YS and UTS of the as hipped material were lower than those of the wrought alloy heat treated for high strength applications (termed as high strength alloy), although the ductility of the former was comparable to that of the latter. In order to improve the strength, the hipped alloy was subjected to a heat treatment consisting of solution treatment followed by two-step aging. Extensive precipitation of fine and coarse γ′ precipitates with cuboidal morphology during duplex aging treatment has led to a considerable improvement in YS and UTS of the alloy, although the corresponding ductility dropped moderately at RT and at 650°C. Fractography of the tensile tested specimens has shown ductile transgranular mode of fracture in the as hipped alloy at RT and at 650°C, while the hipped+heat treated alloy exhibited a mixed mode of fracture at those temperature. The stress rupture properties of the as hipped alloy compare well with those of the wrought alloy and have been found to improve significantly after heat treatment. The present investigation reveals that the hipped superalloy Udimet 720LI has substantial potential for use in the development of near net shaped components for aerospace applications.

Keywords

Powder metallurgy Hot isostatic pressing Superalloy Udimet 720

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References

Ren

and Nicholas

: Mater. Sci. Eng. A, 2002, A332, 236–248.

Sczernie

F. E.

Mancuso

S. O.

Keefe

P. W.

Maurer

G. E.

and Boesch

W. J.

: ‘Udimet® Alloy 720’, TR-88, Special Metals Corporation, Huntington, WV, USA, 1988.

Encinas-Oropesa

, Drew

G. L.

Hardy

M. C.

Leggett

A. J.

Nicholls

J. R.

and Simms

N. J.

: Proc. Conf. Superalloys 2008, (ed. Reed

R. C.

et al.), 609–618 2008, Warrendale, PA, TMS.

Bryant

D. J.

and Mclntosh

: Proc. Conf. Superalloys 1996, (ed. Kissinger

R. D.

et al.), 713–722 1996, Warrendale, PA, TMS.

Maurer

G. E.

Castledine

Schweitzer

F. A.

and Maucuso

: Proc. Conf. Superalloys 1996, (ed. Kissinger

R. D.

et al.), 645–652 1996, Warrendale, PA, TMS.

Lippard

H. E.

and Jones

R. F.

: Proc. Conf. Superalloys 2000, (ed. Pollock

T. M.

et al.), 151–157 2000, Warrendale, PA, TMS.

Bricknell

R. H.

: ‘Spray forming’, Report 85 CRD043, General Electric Corporate Research Centre, New York, USA, 1985.

Atkinson

H. V.

and Rikinson

B. A.

: ‘Hot isostatic processing’, 1st edn; 1991, Philadelphia/New York/Bristol, Adam Hilger.

‘Manufacture of near net shaped compoents by PM (HIP) route’, DRDL report no. 141-082-7006, Defence Research and Development Laboratory, Hyderabad, India, 1995.

10.

Bartos

J. L.

: Proc. Conf. on ‘Powder metallurgy in defence technology’, 1980; 85–113, Princeton, NJ, Metal Powder Industries Federation.

11.

Appa Rao

Sarma

K. S.

Murali

D. S. K.

and Kumar

: ‘Microstructure and tensile behaviour of hot isostaciallly pressed superalloy Udimet 720LI’, TR 2005 369, DMRL, Hyderabad, India, 2005.

12.

In ‘ASM metals handbook’, Vol. 7, 710–718 1998, Metals Park, OH, ASM.

13.

In ‘Annual book of ASTM standards’, Vol. 03(1); 1997, Philadelphia, PA, ASTM.

14.

Appa Rao

Srinivas

and Sarma

D. S.

: Mater. Sci. Eng. A, 2006, A435–A436, 84–96.

15.

Levi

C. J.

and Mehrabian

: Metall. Trans. B, 11B, 1980, 191.

16.

Sinha

A. K.

‘Powder metallurgy’, 2nd edn, 35–38 1982, Delhi, Danpat Rai and Sons/Technical and Educational Publishers.

17.

Chang

S. H.

Lee

S. C.

Tang

T. P.

and Ho

H. H.

: Int. J. Cast Met. Res., 2006, 19, (3), 181–187.

18.

Larson

J. M.

Volin

T. E.

and Larson

F. G.

: Microstruct. Sci., 1977, 5, (209).

19.

Sims

C. T.

and Hagel

H. C.

: ‘The superalloys’; 1972, New York, John Wiley and Sons, Inc.

20.

In ‘ASM metals handbook’, Vol. 7, 950–980 1990, Metals Park, OH, ASM.

21.

In ‘ASM metals handbook’, Vol. 1, 10th edn, 951; 1990, Metals Park, OH, ASM.

22.

Jackson

M. P.

and Reed

R. C.

: Mater. Sci. Eng. A, 1999, A259, 85–97.

23.

Heritier

and Petit

: ‘Evolution of Udimet 720 processing for advanced aero engine design’, Aubert and Duval-63770 LES, Ancizes-France, unpublished.

24.

Appa Rao

: ‘Inftuence of thermal and mechanical treatments on the structure and properties of HIPed superalloy 718’, PhD thesis, BHU, Varanasi, India, 2002.

25.

Gessinger

G. H.

: ‘Powder metallurgy of superalloys’, 1st edn; 1984, London, Butterworth and Co. Publishers.