Microscale simulation of stray grain formation in investment cast turbine blades

Yang, Xinliang; Dong, Haibo; Wang, W.; Lee, Peter

doi:10.1016/j.msea.2004.07.007

Cited by 28 publications

(16 citation statements)

References 19 publications

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“…Finally, there is another possibility for the formation of the intermediate layer containing Re-rich particles. The stray grain in this study was probably formed through either a thermal or compositional cause, such as nucleation from the corner of the platform region [15][16][17][18] or the remelting of dendrite fragments 19,20) . During casting, the Re-rich particles formed early in the solidi cation process and were pushed ahead of each solidi cation front present; those of the stray grain and the matrix grain, and were piled up at the boundary of the matrix/ stray grain.…”

Section: Resultsmentioning

confidence: 81%

“…A typical commercial foundry specializing in the casting of single crystal turbine blades has an overall yield of 67% 4) with grain related defects being a major cause of non-conformance. Several kinds of defects, such as stray grains, equiax grains, freckle chain grains, low angle grain boundaries and recrystallized grains have been detected on the surface of turbine blades 3,4,11,[14][15][16][17][18][19][20][21] . Of these defects, it is well known that stray grains are formed through nucleation from the extremity of a platform region due to undercooling [15][16][17][18] , remelting of dendrite frag-ments 19,20) , and heterogeneous nucleation of grains from TiN particles ahead of the solidi cation front 21) .…”

Section: Introductionmentioning

confidence: 99%

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Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

Kim

Withey

2016

Mater. Trans.

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Ni-base single crystal superalloy turbine blades containing defect grains were investigated by high resolution electron microscopy. Several different types of defects, such as, stray grains, equiax grains and freckle chains which formed during casting, and recrystallized grains which formed during subsequent heat treatment, were selected. Regardless of the region of the turbine blade, many particles with large amounts of rhenium were detected at the boundary of the stray grain and matrix. The Re-rich particles were also detected at the boundary of the matrix and other defect grains, such as, equiax grains and freckle chain grains, and even at a low angle grain boundary. However, the boundary of the recrystallised grain and matrix which was formed after solution heat treatment showed just one Re-rich particle. Also, the composition of these Re-rich particles is different from any topologically close packed phases which have been reported in Ni-base superalloys. The results suggest that during solidi cation, the particles are formed from the melt and pushed ahead of each solidi cation front of the defect grain and the matrix, and piled up at the boundary of the matrix/defect grain.

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Section: Resultsmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

Kim

Withey

2016

Mater. Trans.

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“…The stochastic nucleation is based on the undercooling of the melt locally relative to that location's liquidus temperature, accounting for any solute enrichment at that location. The theory, implementation, and validation of this model are detailed in prior publications [9][10][11][12][13][14] and are not repeated here. In this section, the simulation parameters used in this study are first described, and then the model is applied to the prediction of the microstructures as a function of the seed orientation relative to the wall.…”

Section: Modeling Investigationmentioning

confidence: 99%

“…Heterogeneous nucleation was implemented in the CA-FD model [14] during the seed melt-back. Nucleation in liquid occurs when its local undercooling (⌬T C ) exceeds the critical nucleation undercooling (⌬T N ).…”

Section: A Simulation Parametersmentioning

confidence: 99%

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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“…However, during the manufacture of complex structures such as turbine blades, grain defects would be generated in the SC superalloy casting by directional solidification [18 -24]. It has been shown that thermal condition and mold geometry have a significant impact on the formation of grain defects [25,26]. The disordered temperature distribution at geometric discontinuities, e. g. blade shrouds, turbine blade platforms and turbine blade rabbets, can result in distortions in the crystal lattice [27].…”

Section: Introductionmentioning

confidence: 99%

Effect of grain defects on the mechanical behavior of nickel-based single crystal superalloy

Tang

Guo

2017

International Journal of Materials Research

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Effect of grain defects on the mechanical behavior of nickel-based single crystal superalloyIn this paper, a single crystal (SC) partition model, consisting of primary grains and grain defects, is proposed to simulate the weakening effect of grain defects generated at geometric discontinuities of SC materials. The plastic deformation of SC superalloy is described with the modified yield criterion, associated flow rule and hardening law. Then a bicrystal model containing only one group of misoriented grains under uniaxial loading is constructed and analyzed in the commercial finite element software ABAQUS. The simulation results indicate that the yield strength and elastic modulus of misoriented grains, which are determined by the crystallographic orientation, have a significant effect on the stress distribution of the bicrystal model. A critical stress, which is calculated by the stress state at critical regions, is proposed to evaluate the local stress rise at the sub-boundary of primary and misoriented grains.Keywords: Nickel-based single crystal superalloy; Grain defects; Single crystal partition model; Local stress rise; Critical stress IntroductionIn the modern aviation industry, advanced materials applied in the hot section are a critical issue to ensure the economic and reliable performance of aeroengines. Nickel-based single crystal (SC) superalloys have been increasingly used to manufacture turbine blades in high performance aircraft and rocket engines [1 -5]. Compared with polycrystalline materials or directionally solidified alloys, SC superalloys have better mechanical properties at elevated temperature due to the absence of weak grain boundaries.SC superalloy is a two-phase material made of intermetallic c 0 precipitates and face-centered cubic c matrix, which results in high material anisotropy [6 -10]. In the last several decades two main approaches have been proposed to describe the mechanical properties of SC superalloy. The first approach is based on the crystallographic slip theory [6, 11 -13]. The texture changes inside the material can be tracked and therefore the texture-induced anisotropy can be evaluated accordingly. However, the requirement of enormous computational power and time limits its usage in engineering practice. An alternative approach is through use of a phenomenological yield criterion [14 -17], which is also paid high attention to in theoretical research and practical applications, due to simplicity and convenience.As for grain defects' effects on mechanical properties, only limited research work can be found. However, during the manufacture of complex structures such as turbine blades, grain defects would be generated in the SC superalloy casting by directional solidification [18 -24]. It has been shown that thermal condition and mold geometry have a significant impact on the formation of grain defects [25,26]. The disordered temperature distribution at geometric discontinuities, e. g. blade shrouds, turbine blade platforms and turbine blade rabbets, can result in distortio...

show abstract

Microscale simulation of stray grain formation in investment cast turbine blades

Cited by 28 publications

References 19 publications

Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

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

Effect of grain defects on the mechanical behavior of nickel-based single crystal superalloy

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