An Atom Probe Tomography study of site preference and partitioning in a nickel-based superalloy

Bagot, Paul A.J.; Silk, O. B W; Douglas, James O.; Pedrazzini, S.; Crudden, D.J.; Martin, T.; Hardy, Mark; Moody, Michael P.; Reed, Roger C.

doi:10.1016/j.actamat.2016.11.053

Cited by 130 publications

(52 citation statements)

References 47 publications

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“…Besides, C and Si were found to segregate to the grain boundary up to 0.5 and 0.2 at.%, respectively, but no specific role on the hot cracking was observed from their presence at the grain boundary. The segregation behavior observed here is in agreement with previous reports [26,32,33]. Segregation of Zr and Hf at the grain boundary was not observed, instead they were found to partition within the γ', as shown in Supplementary Figure 1(a).…”

Section: Microstructural Characterization: Cracked Columnar Samplesupporting

confidence: 93%

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

et al. 2019

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There are still debates regarding the mechanisms that lead to hot cracking in parts build by additive manufacturing (AM) of non-weldable nickel-based superalloys. This lack of in-depth understanding of the root causes of hot cracking is an impediment to designing engineering parts for safety-critical applications. Here, we deploy a near-atomic-scale approach to investigate the details of the compositional decoration of grain boundaries in the coarse-grained, columnar microstructure in parts built from a non-weldable nickel-based superalloy by selective electron-beam melting. The progressive enrichment in Cr, Mo and B at grain boundaries over the course of the AM-typical successive solidification and remelting events, accompanied by solid-state diffusion, causes grain boundary segregation induced liquation. This observation is consistent with thermodynamic calculations. We demonstrate that by adjusting build parameters to obtain a fine-grained equiaxed or a columnar microstructure with grain width smaller than 100 μm enables to avoid cracking, despite strong grain boundary segregation. We find that the spread of critical solutes to a higher total interfacial area, combined with lower thermal stresses, helps to suppress interfacial liquation.

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Section: Microstructural Characterization: Cracked Columnar Samplesupporting

confidence: 93%

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

et al. 2019

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“…APT analysis revealed that these borides are mainly Cr-rich whereas W and Mo contribute in lower amounts, as shown in at.%. A similar observation was previously reported regarding the composition of these secondary precipitates from an APT analysis of a powder nickel-based superalloy [38].…”

Section: Primary Grain Boundary Phases After Heat Treatmentsupporting

confidence: 88%

Influence of composition and precipitation evolution on damage at grain boundaries in a crept polycrystalline Ni-based superalloy

et al. 2019

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The microstructural and compositional evolution of intergranular carbides and borides prior to and after creep deformation at 850 °C in a polycrystalline nickel-based superalloy was studied. Primary MC carbides, enveloped within intergranular γ' layers, decomposed resulting in the formation of layers of the undesirable  phase. These layers have a composition corresponding to Ni3Ta as measured by atom probe tomography and their structure is consistent with the D024 hexagonal structure as revealed by transmission electron microscopy. Electron backscattered diffraction reveals that they assume various misorientations with regard to the adjacent grains. As a consequence, these layers act as brittle recrystallized zones and crack initiation sites. The composition of the MC carbides after creep was altered substantially, with the Ta content decreasing and the Hf and Zr contents increasing, suggesting a beneficial effect of Hf and Zr additions on the stability of MC carbides. By contrast, M5B3 borides were found to be microstructurally stable after creep and without substantial compositional changes. Borides at 850 °C were found to coarsen, resulting in some cases into γ'depleted zones, where, however, no cracks were observed. The major consequences of secondary phases on the microstructural stability of superalloys during the design of new polycrystalline superalloys are discussed.

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“…A similar effect was observed for Ti, Ta, and Hf in the RR1000 alloy as seen by Bagot et al, [40] where it was attributed to the large lattice misfits for these elements as estimated using Vegard's Law. [1] Cr concentration profiles were also found to be non-uniform heading into the c matrix phase, showing a trend of rising to a plateau concentration of roughly 30 at.…”

Section: B Interface Chemistrysupporting

confidence: 65%

“…However, this study has shown that careful, methodical use of APT can play a key role in benchmarking the results from theoretical predictions, as also recently demonstrated on in-service alloys. [40] This combination of APT and modeling thus offers a robust, general methodology which should be considered in alloy design.…”

Section: Alloy Composition/phase Chemistrymentioning

confidence: 99%

Characterization of Phase Chemistry and Partitioning in a Family of High-Strength Nickel-Based Superalloys

Lapington

Crudden

Reed

et al. 2018

Metall Mater Trans A

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A family of novel polycrystalline Ni-based superalloys with varying Ti:Nb ratios has been created using computational alloy design techniques, and subsequently characterized using atom probe tomography and electron microscopy. Phase chemistry, elemental partitioning, and c¢ character have been analyzed and compared with thermodynamic predictions created using Thermo-Calc. Phase compositions and c¢ volume fraction were found to compare favorably with the thermodynamically predicted values, while predicted partitioning behavior for Ti, Nb, Cr, and Co tended to overestimate c¢ preference over the c matrix, often with opposing trends vs Nb concentration.

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An Atom Probe Tomography study of site preference and partitioning in a nickel-based superalloy

Cited by 130 publications

References 47 publications

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

Atomic-scale grain boundary engineering to overcome hot-cracking in additively-manufactured superalloys

Influence of composition and precipitation evolution on damage at grain boundaries in a crept polycrystalline Ni-based superalloy

Characterization of Phase Chemistry and Partitioning in a Family of High-Strength Nickel-Based Superalloys

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