A transmission electron microscopic investigation of phase transformations in MP35N

Raghavan, M.; Berkowitz, B. J.; Kane, Russell D.

doi:10.1007/bf02700461

Cited by 38 publications

(26 citation statements)

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“…In the case of alloy MP35N ( 3 5 C o -3 5 N i -2 0 C r10Mo, in wt %), the strengthening associated with cold working is attributed to a face-centred cubic (fc c) -~ hexagonal close-packed (h c p) transformation and/or formation of mechanical twins depending on the deformation temperature relative to the Md temperature [3,4] (Md is the temperature below which the f c c --* h c p transformation can be stressinduced). The strengthening which results from subsequent ageing heat treatments is correlated with the f c c ~ h c p transformation [4] or the formation of intermetallic compounds [6].Haynes alloy No. 25 (Haynes is a registered trademark of Cabot Corporation) is a cobalt-base superalloy with a nominal chemical composition of C o10Ni-20Cr-15W.…”

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On the fcc → hcp transformation in a cobalt-base superalloy (Haynes alloy No. 25)

1986

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It is known that the cobalt-based family of Multiphase alloys (Multiphase is a registered trademark of SPS Technologies, Inc.) derive their strength, in part, from cold working and that additional strengthening can be obtained by subsequent ageing heat treatments [1][2][3][4][5][6][7][8][9]. In the case of alloy MP35N ( 3 5 C o -3 5 N i -2 0 C r10Mo, in wt %), the strengthening associated with cold working is attributed to a face-centred cubic (fc c) -~ hexagonal close-packed (h c p) transformation and/or formation of mechanical twins depending on the deformation temperature relative to the Md temperature [3,4] (Md is the temperature below which the f c c --* h c p transformation can be stressinduced). The strengthening which results from subsequent ageing heat treatments is correlated with the f c c ~ h c p transformation [4] or the formation of intermetallic compounds [6].Haynes alloy No. 25 (Haynes is a registered trademark of Cabot Corporation) is a cobalt-base superalloy with a nominal chemical composition of C o10Ni-20Cr-15W. Typically, 'the alloy is heat treated at 1205 ° C for 15 min followed by rapid air cooling. In this condition, the matrix is a fc c solid solution with a lattice constant of 0.357 nm. In view of the behaviour of alloy MP35N, it may be expected that alloy 25 is also susceptible to the fc c ~ h c p transformation particularly as it contains less nickel than alloy MP35N. Therefore, the present investigation was undertaken to determine the susceptibility of alloy 25 to the fc c ~ h c p transformation with emphasis on the role of cold working and ageing heat treatments.Sheet samples (1.3 mm thick) were cold reduced by up to 20%. Ageing heat treatments were conducted at temperatures in the range 370 to 760 ° C. The effect of cold working on the mechanical properties was determined from tensile tests. Light optical metallography and thin-foil transmission electron microscopy were used for the microstructural characterizations. Samples for light optical metallography were etched in a solution consisting of 95% HC1 and 5% H202 by volume. Thin foils for transmission electron microscopy and diffraction work were prepared by the jet polishing technique in a solution of 30vol % nitric acid in methanol at about -20 ° C. All foils were examined at 100 kV. Fig. I shows characteristic optical microstructures of alloy 25 in the annealed condition ( Fig. la) and after ageing for 48h (Fig. lb) and 500h (Fig. lc) at 760 ° C. It can be seen that after ageing at 760 ° C, the microstructure contains a phase with a widmanst~iten-type morphology. This phase was identified by electron diffraction as h c p s-phase with lattice constants of a = 0.25nm and c = 0.41 nm. The electron diffraction pattern of Fig. 2 illustrates the coexistence of

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On the fcc → hcp transformation in a cobalt-base superalloy (Haynes alloy No. 25)

1986

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“…1-Co-Cr binary phase diagram (the approximate chemistry of the ULTIMET alloy is indicated by the vertical dashed line). [7] However, for the MP35N alloy [13][14][15][16][17][18] (a Co-35Ni-20Cr-10Mo alloy) and the MP159 alloy [19] (a Co-25.5Ni-19Cr-7Mo alloy), the stress-(or strain-) induced fcc-to-hcp transformation did not occur at room temperature. It can be seen that the M d temperature decreased with the increase of Ni content in the alloys.…”

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Low-cycle fatigue behavior of ULTIMET® alloy

Jiang

Brooks

Liaw

et al. 2004

Metall Mater Trans A

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The low-cycle fatigue behavior of ULTIMET ® , a wrought cobalt-based alloy, was studied at the temperatures of 294, 873, and 1,173 K under isothermal conditions. A constant strain rate of 3.0 ϫ 10 Ϫ3 s Ϫ1 was used with fully reversed strain ranges between 0.4 and 2.5 pct. Observations on the strain vs fatiguelife curves, cyclic stress-strain responses, and fatigue fracture modes were obtained. The microstructure evolution of the ULTIMET alloy was characterized using X-ray diffraction, scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM). For fatigue tests performed at 294 and 873 K, plastic-strain-induced, fcc-to-hcp phase transformations were observed. Twinning and carbide precipitation were found to contribute to the significant cyclic hardening observed at 1,173 K.

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“…When fully annealed, the alloy is a single phase material with fcc structure. Previous studies [1][2][3][4] on the strengthening mechanisms of MP35N have shown that the alloy with 30-40 m grain size gains its strength through work hardening and a second mechanism known as secondary hardening. These strengthening mechanisms have been recently investigated [5,6].…”

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Anomalous plastic behavior of fine-grained MP35N alloy during room temperature tensile testing

Asgari¹

2004

Journal of Materials Processing Technology

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A transmission electron microscopic investigation of phase transformations in MP35N

Cited by 38 publications

References 2 publications

On the fcc → hcp transformation in a cobalt-base superalloy (Haynes alloy No. 25)

On the fcc → hcp transformation in a cobalt-base superalloy (Haynes alloy No. 25)

Low-cycle fatigue behavior of ULTIMET® alloy

Anomalous plastic behavior of fine-grained MP35N alloy during room temperature tensile testing

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