Directional and single-crystal solidification of Ni-base superalloys: Part I. The role of curved isotherms on grain selection

D’Souza, N.; Ardakani, M.G.; McLean, M.; Shollock, Barbara A.

doi:10.1007/bf02830351

Cited by 89 publications

(36 citation statements)

References 9 publications

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“…The schematic diagram in Figure 9(a) shows the initial profile at melt-back that corresponds to Figure 8. During the initial withdrawal stage, the heat-transfer mode changes from chill conduction to mold-wall radiation, as experimentally observed by D'Souza et al for a similar geometry in a Bridgman apparatus [19] (Figure 9(b)). Therefore, a transient thermal field was imposed upon the domain to simulate the initial stage following melt-back.…”

Section: Structure Evolution and Undercooling During The Initial Thersupporting

confidence: 72%

Seeding of single-crystal superalloys—Role of constitutional undercooling and primary dendrite orientation on stray-grain nucleation and growth

D’Souza

Jennings

Yang

et al. 2005

Metall Mater Trans B

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An experimental study, together with a two-dimensional numerical simulation of solute segregation, was conducted to investigate (1) the mechanism for stray-grain nucleation following seed melt-back and initial withdrawal and (2) the role of the primary dendrite disposition of the seed crystal in relation to the mold wall during growth. It is proposed that the factors contributing to stray-grain nucleation during initial withdrawal are (1) the magnitude of local, solute-adjusted undercooling and (2) the rapidly changing curvature of the solidification front close to the mold walls during the initial solidification transient. Based upon the calculated local undercooling and experimentally observed stray-grain morphologies, it was concluded that stray grains nucleate near the mold wall around the seed perimeter and behind the columnar dendrites that advance into the bulk liquid ahead of the melt-back zone. These grains then compete during growth with the dendrites originating from the seed. Therefore, the morphological constraints arising from the inclination of the primary dendrites from the seed crystal with respect to the mold wall (converging/diverging/axial Ͻ001Ͼ) determines the probability of the stray-grain nuclei developing into equiaxed/columnar grains following competitive growth.

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Section: Structure Evolution and Undercooling During The Initial Thersupporting

confidence: 72%

Seeding of single-crystal superalloys—Role of constitutional undercooling and primary dendrite orientation on stray-grain nucleation and growth

D’Souza

Jennings

Yang

et al. 2005

Metall Mater Trans B

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“…Pollock et al [2][3][4] reported refractory alloying additions to promote the formation of freckle-type defects. McLean et al [5][6][7] found that the high-refractory superalloys yield a wider range of crystal orientations. The present article studies hot tearing susceptibility of these alloys.…”

Section: Introductionmentioning

confidence: 99%

Effect of grain boundary characteristics on hot tearing in directional solidification of superalloys

2006

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The effect of grain boundary (GB) misorientation on hot tearing susceptibility of directionally solidified (DS) nickel-based superalloys was explored. We found that the castability of second generation nickel-based superalloy CMSX-4 is inferior to DS superalloy IN792, an alloy well known for bad castability. The castability of CMSX-4 is somewhat improved at a higher solidification rate. The hot tearing tendency increases with increasing GB misorientation angle. As feeding tendency becomes greater with increasing misorientation, this points to the importance of GB cohesion for solidification cracking in the alloy. Microstructure investigation reveals that hot tearing is associated with formation of continuous gamma and gamma prime eutectic films at the GB in CMSX-4. We assume that the gamma and gamma prime eutectic, which reflects the remaining liquid at the end of solidification, prevents the impinging dendrite arms from touching and in this way decreases cohesion.

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“…These alloys also find a wide variety of corrosion and elevated temperature oxidation environment applications, especially CUSTOM-AGE 625* plus and ALLOY 625**, which are superior to INCONEL 718 , [2] and used in refinery and chemical process industries. [3][4][5][6][7][8][9] Directional (or unidirectional) solidification processing [10] was extensively applied in the production of aligned eutectic structures, directional columnar structures, and single-crystal Ni-base superalloy turbine blades. These single-crystal turbine blades solidify with a dendritic structure containing microsegregation and second-phase (c¢) particles formed by eutectic reactions.…”

mentioning

confidence: 99%

Microstructural Architecture, Microstructures, and Mechanical Properties for a Nickel-Base Superalloy Fabricated by Electron Beam Melting

Murr

Martínez

Gaytan

et al. 2011

Metall Mater Trans A

251

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Microstructures and a microstructural, columnar architecture as well as mechanical behavior of as-fabricated and processed INCONEL alloy 625 components produced by additive manufacturing using electron beam melting (EBM) of prealloyed precursor powder are examined in this study. As-fabricated and hot-isostatically pressed (''hipped'') [at 1393 K (1120°C)] cylinders examined by optical metallography (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive (X-ray) spectrometry (EDS), and X-ray diffraction (XRD) exhibited an initial EBM-developed c¢¢ (bct) Ni 3 Nb precipitate platelet columnar architecture within columnar [200] textured c (fcc) Ni-Cr grains aligned in the cylinder axis, parallel to the EBM build direction. Upon annealing at 1393 K (1120°C) (hot-isostatic press (HIP)), these precipitate columns dissolve and the columnar, c, grains recrystallized forming generally equiaxed grains (with coherent {111} annealing twins), containing NbCr 2 laves precipitates. Microindentation hardnesses decreased from~2.7 tõ 2.2 GPa following hot-isostatic pressing (''hipping''), and the corresponding engineering (0.2 pct) offset yield stress decreased from 0.41 to 0.33 GPa, while the UTS increased from 0.75 to 0.77 GPa. However, the corresponding elongation increased from 44 to 69 pct for the hipped components.

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Directional and single-crystal solidification of Ni-base superalloys: Part I. The role of curved isotherms on grain selection

Cited by 89 publications

References 9 publications

Seeding of single-crystal superalloys—Role of constitutional undercooling and primary dendrite orientation on stray-grain nucleation and growth

Seeding of single-crystal superalloys—Role of constitutional undercooling and primary dendrite orientation on stray-grain nucleation and growth

Effect of grain boundary characteristics on hot tearing in directional solidification of superalloys

Microstructural Architecture, Microstructures, and Mechanical Properties for a Nickel-Base Superalloy Fabricated by Electron Beam Melting

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