Effect of Boron on Solidification Microstructure in a Single Crystal Superalloy

Carbon and boron were mainly considered to strengthen grain boundaries formed during single crystal casting of complex shaped components. However, those elements cause segregation forming the phase with low melting temperature or with brittle nature. To determine the optimum amount of these elements, the effect of boron on solidification behavior was investigated in the C doped single crystal RR 2072 alloy. The solid/liquid interface morphologies and the solidification microstructures were studied at various solidification rates and with B addition by directional solidification.

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Numerical Analysis of Solidification Behavior during Laser Welding Nickel-based Single-crystal Superalloy Part IV: Optimization of Thermo-metallurgical Factors

Journal of Physics Conference Series ◽

10.1088/1742-6596/1996/1/012004 ◽

2021 ◽

Vol 1996 (1) ◽

pp. 012004

Author(s):

Zhiguo Gao

Keyword(s):

Single Crystal ◽

Welding Speed ◽

Laser Power ◽

Liquid Interface ◽

Solidification Behavior ◽

Dendrite Morphology ◽

Grain Formation ◽

Solid Liquid Interface ◽

Solid Liquid ◽

Stray Grain

Abstract Important metallurgical factors, such as alloying aluminum redistribution, supersaturation and undercooling of dendrite tip around solid/liquid interface, are separately optimized to alleviate stray grain formation and columnar/equiaxed transition (CET) with series of welding conditions and provide a very efficient method for microstructure control through modification of growth kinetics of dendrite tip under nonequilibrium solidification conditions of ternary Ni-Cr-Al molten pool. Asymmetrical (001)/[110] welding configuration is inferior to symmetrical (001)/[100] welding configuration, because overall area-weighted alloying redistribution, supersaturation and undercooling of dendrite tip throughout the solid/liquid interface of weld pool are consistently severer to exacerbate solidification behavior and microstructure development and incur morphology instability of columnar/equiaxed transition. High heat input, such as combination of higher laser power and slower welding speed, monotonically increases aluminum enrichment, supersaturation and undercooling of dendrite tip near solidification interface to simultaneously deteriorate nucleation and growth of stray grain formation and weaken columnar dendrite morphology, while low heat input, such as combination of lower laser power and faster welding speed, decreases solute buildup, relieves supersaturation and beneficially suppresses dendrite tip undercooling to minimize equiaxed dendrite morphology in the crack-susceptible region, and thereby facilitate single-crystal epitaxial growth with decrease of thermo-metallurgical factors for columnar/equiaxed transition in order to provide prerequisite for optimization of welding conditions. Favorable solidification conditions are obtainable with preferential crystallographic orientation to eliminate columnar/equiaxed transition under which the epitaxy of single-crystal metallurgical properties across fusion boundary of substrate is predominantly promoted to essentially reduce stray grain formation in (001)/[100] welding configuration, and is kinetically capable of significant reduction of microstructure anomalies and nonuniform solidification behavior. The useful relationship among welding conditions, alloying aluminum redistribution, supersaturation and undercooling of dendrite tip is properly established within dendrite stability range through thorough analysis. In addition, the validation of theoretical predictions is fairly reasonable by the experiment results. It is worth that the contributions of kinetics-related solidification phenomena with advancement of solid/liquid interface are imposed altogether to understand why stray grain formation occurs on the basis of controlling mechanism of minimum undercooling or minimum velocity by the reproducible methodology procedure.

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Morphological evolution of the solid-liquid interface near grain boundaries during directional solidification

Science China Physics Mechanics and Astronomy ◽

10.1007/s11433-011-4494-7 ◽

2011 ◽

Vol 54 (12) ◽

pp. 2174-2180 ◽

Cited By ~ 3

Author(s):

Hui Xing ◽

CaiFang Wang ◽

JianYuan Wang ◽

ChangLe Chen

Keyword(s):

Grain Boundaries ◽

Directional Solidification ◽

Morphological Evolution ◽

Liquid Interface ◽

Solid Liquid Interface ◽

Solid Liquid

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Role of the solid/liquid interface faceting in rapid penetration of a liquid phase along grain boundaries

Acta Materialia ◽

10.1016/s1359-6454(01)00039-8 ◽

2001 ◽

Vol 49 (7) ◽

pp. 1123-1128 ◽

Cited By ~ 41

Author(s):

D. Chatain ◽

E. Rabkin ◽

J. Derenne ◽

J. Bernardini

Keyword(s):

Liquid Phase ◽

Grain Boundaries ◽

Liquid Interface ◽

Solid Liquid Interface ◽

Solid Liquid

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Optical Fluorescence Microscopy for Spatially Characterizing Electron Transfer across a Solid-Liquid Interface on Heterogeneous Electrodes

MRS Advances ◽

10.1557/adv.2016.289 ◽

2016 ◽

Vol 1 (42) ◽

pp. 2867-2872

Author(s):

Eric Choudhary ◽

Jeyavel Velmurugan ◽

James M. Marr ◽

James A. Liddle ◽

Veronika Szalai

Keyword(s):

Fluorescence Microscopy ◽

Grain Boundaries ◽

Electrode Materials ◽

Liquid Interface ◽

Chemical Transformations ◽

Heterogeneous Catalytic ◽

Activity Measurements ◽

Optical Fluorescence ◽

Solid Liquid Interface ◽

Solid Liquid

ABSTRACTHeterogeneous catalytic materials and electrodes are used for (electro)chemical transformations, including those important for energy storage and utilization.1, 2 Due to the heterogeneous nature of these materials, activity measurements with sufficient spatial resolution are needed to obtain structure/activity correlations across the different surface features (exposed facets, step edges, lattice defects, grain boundaries, etc.). These measurements will help lead to an understanding of the underlying reaction mechanisms and enable engineering of more active materials. Because (electro)catalytic surfaces restructure with changing environments,1 it is important to perform measurements in operando. Sub-diffraction fluorescence microscopy is well suited for these requirements because it can operate in solution with resolution down to a few nm. We have applied sub-diffraction fluorescence microscopy to a thin cell containing an electrocatalyst and a solution containing the redox sensitive dye p-aminophenyl fluorescein to characterize reaction at the solid-liquid interface. Our chosen dye switches between a nonfluorescent reduced state and a one-electron oxidized bright state, a process that occurs at the electrode surface. This scheme is used to investigate the activity differences on the surface of polycrystalline Pt, in particular to differentiate reactivity at grain faces and grain boundaries. Ultimately, this method will be extended to study other dye systems and electrode materials.

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Solidification Front of Oriented Ledeburite

Archives of Foundry Engineering ◽

10.1515/afe-2016-0015 ◽

2016 ◽

Vol 16 (1) ◽

pp. 124-130 ◽

Cited By ~ 1

Author(s):

M. Trepczyńska-Łent ◽

E. Olejnik

Keyword(s):

Directional Solidification ◽

Solidification Front ◽

Liquid Interface ◽

Solid Liquid Interface ◽

Solid Liquid ◽

Interface Structures

Abstract Directional solidification of the Fe - 4,3 wt % C alloy was performed with the pulling rate equal to v=83 μm/s. Sample was frozen during solidification to reveal the shape of the solid/liquid interface. Structures eutectic pyramid and spherolitic eutectic were observed. The solidification front of ledeburite eutectic was revealed. The leading phase was identified and defined.

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Numerical Analysis of Aerospace Nickel-Based Single-Crystal Superalloy Weldability Part I: Crystallography-Dependent Dendrite Growth

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1018.3 ◽

2021 ◽

Vol 1018 ◽

pp. 3-12

Author(s):

Zhi Guo Gao

Keyword(s):

Single Crystal ◽

Weld Pool ◽

Dendrite Growth ◽

Liquid Interface ◽

Solidification Cracking ◽

Microstructure Development ◽

Growth Region ◽

The Right ◽

Solid Liquid Interface ◽

Solid Liquid

The thermal-metallurgical modeling of microstructure development was further advanced during single-crystal superalloy weld pool solidification by coupling of heat transfer model, columnar/equiaxed transition (CET) model and multicomponent dendrite growth model on the basis criteria of minimum dendrite velocity, constitutional undercooling and marginal stability of planar front. It is clearly indicated that heat input (laser power and welding speed) and welding configuration simultaneously influence the stray grain formation, columnar/equiaxed transition and dendrite growth. For beneficial (001) and [100] welding configuration, the microstructure development along the solid/liquid interface is symmetrically distributed about the weld pool centerline throughout the weld pool. Finer columnar in [001] epitaxial dendrite growth region is kinetically favored at the bottom of the weld pool. For detrimental (001) and [110] welding configuration, the microstructure development along the solid/liquid interface is asymmetrically distributed. The dendrite trunk spacing along the solid/liquid interface from the beginning to end of solidification morphologically increases on the left side of the weld pool, while it spontaneously decreases on the right side. The vulnerable location of solidification cracking is confined in the [100] dendrite growth region on the right side of the weld pool because of increasing metallurgical contributing factors of severe stray grain formation, centerline grain boundary formation and coarse dendrite size. The mechanism of crystallography-dependent asymmetrical solidification cracking due to microstructure anomalies is proposed. It is crystallographically favorable for predominant morphology instability to deteriorate weldability. Active [100] dendrite growth region is diminished in the shallow elliptical weld pool by optimum low heat input (low laser power and high welding speed) with (001) and [100] welding configuration to essentially facilitate single-crystal solidification conditions and provide enough resistant to solidification cracking. Moreover, the theoretical predictions agree well with the experiment results. The reliable weldability maps are therefore established to determine the prerequisite for successful crack-free laser welding or cladding. The useful model is also applicable for other single-crystal superalloys with similar metallurgical properties.

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