Numerical Analysis of Aerospace Nickel-Based Single-Crystal Superalloy Weldability Part III: Solidification Cracking Susceptibility

2021 ◽  
Vol 1018 ◽  
pp. 23-32
Author(s):  
Zhi Guo Gao

The thermal-metallurgical model of primary γ gamma phase through couple of heat transfer model, dendrite selection model, columnar/equiaxed transition (CET) model, multicomponent dendrite growth model and nonequilibrium solidification model is further developed on the basis of criteria of minimum growth velocity, constitutional undercooling and marginal stability of planar front during nickel-based single-crystal weld pool solidification. It is clearly indicated that crystallographic orientation plays more important role than heat input in microstructure development and solidification behavior. The dendrite trunk spacing and solidification temperature range along the solid/liquid interface are symmetrically distributed about the weld pool centerline in (001) and [100] welding configuration, while they are asymmetrically distributed in (001) and [110] welding configuration. The dendrite size and solidification temperature range are beneficially smaller in (001) and [100] welding configuration than that of (001) and [110] welding configuration regardless of heat input. The mechanism of asymmetrical solidification cracking because of crystallography-dependent growth kinetics and solidification behavior is proposed. Optimum low heat input (low laser power and high welding speed) refines dendrite size and suppresses the solidification temperature range to minimize the solidification cracking susceptibility and ameliorate the weldability through microstructure control, while high heat input (high laser power and low welding speed) deteriorates the weldability and weld integrity. It is therefore imperative to optimize the welding conditions for successful defect-free laser welding. Moreover, the promising theoretical predictions agree well with the experiment results. The useful model is also applicable to other single-crystal superalloys with similar metallurgical properties by laser welding or laser cladding, and provide a more accurate and reliable way of solidification cracking susceptibility evaluation.

2021 ◽  
Vol 1018 ◽  
pp. 13-22
Author(s):  
Zhi Guo Gao

The thermal metallurgical modeling of liquid aluminum supersaturation was further developed through couple of heat transfer model, dendrite selection model, multicomponent dendrite growth model and nonequilibrium solidification model during three-dimensional nickel-based single-crystal superalloy weld pool solidification. The welding configuration plays more important role in supersaturation of liquid aluminum, morphology instability and nonequilibrium partition behavior. The bimodal distribution of liquid aluminum supersaturation along the solid/liquid interface is crystallographically symmetrical about the weld pool centerline in (001) and [100] welding configuration. The distribution of liquid aluminum supersaturation along the solid/liquid interface is crystallographically asymmetrical throughout the weld pool in (001) and [110] welding configuration. Optimum low heat input (low laser power and high welding speed) with (001) and [100] welding configuration is more favored to predominantly promote epitaxial [001] dendrite growth to reduce the metallurgical factors for solidification cracking than that of high heat input (high laser power and slow welding speed) with (001) and [110] welding configuration. The lower the heat input is used, the lower supersaturation of liquid aluminum is imposed, and the smaller size of vulnerable [100] dendrite growth region is incurred to ameliorate solidification cracking susceptibility and vice versa. The overall supersaturation of liquid aluminum in (001) and [100] welding configuration is beneficially smaller than that of (001) and [110] welding configuration regardless of heat input, and is not thermodynamically relieved by gamma prime γˊ phase. (001) and [110] welding configuration is detrimental to weldability and deteriorates the solidification cracking susceptibility because of unfavorable crystallographic orientations and alloying aluminum enrichment. The mechanism of asymmetrical solidification cracking because of crystallography-dependent supersaturation of liquid aluminum is proposed. The eligible solidification cracking location is particularly confined in [100] dendrite growth region. Moreover, the theoretical predictions agree well with the experiment results. The useful modeling is also applicable to other single-crystal superalloys with similar metallurgical properties for laser welding or laser cladding. The thorough numerical analyses facilitate the understanding of weld pool solidification behavior, microstructure development and solidification cracking phenomena in the primary γ phase, and thereby optimize the welding conditions (laser power, welding speed and welding configuration) for successful crack-free laser welding.


2021 ◽  
Vol 1018 ◽  
pp. 33-41
Author(s):  
Zhi Guo Gao

The thermal metallurgical modeling by coupling of heat transfer model, dendrite selection model, columnar/equiaxed transition (CET) model and nonequilibrium solidification model was further developed to numerically analyze stray grain formation and solidification temperature range on the basis of three criteria of constitutional undercooling, marginal stability of planar front and minimum growth velocity during multicomponent nickel-based single-crystal superalloy weld pool solidification. It is indicated that the primary γ gamma phase microstructure development and solidification cracking susceptibility along the solid/liquid interface are symmetrically distributed throughout the weld pool in (001) and [100] welding configuration. The microstructure development and solidification cracking susceptibility along the solid/liquid interface are asymmetrically distributed in (001) and [110] welding configuration. Appropriate low heat input (low laser power and high welding speed) simultaneously minimizes stray grain formation, grain boundary misorientation and solidification temperature range in the vulnerable [100] dendrite growth region and beneficially maintains single-crystal nature of the material in the [001] epitaxial dendrite growth region to improve the cracking resistance, while high heat input (high laser power and low welding speed) increases the solidification cracking susceptibility to deteriorate weldability and weld integrity. The solidification temperature range in (001) and [110] welding configuration is detrimentally wider than that of (001) and [100] welding configuration due to crystallographic orientation of dendrite growth regardless of heat input. The mechanism of asymmetrical crystallography-dependant solidification cracking because of nonequilibrium solidification behavior is proposed. The elliptical and shallow weld pool shape is less susceptible to solidification cracking for successful crack-free laser welding. Moreover, the promising theoretical predictions agree well with the experiment results. The useful modeling is also applicable to other single-crystal superalloys with similar metallurgical properties during laser welding or laser cladding.


2021 ◽  
Vol 1033 ◽  
pp. 40-48
Author(s):  
Zhi Guo Gao

The solidification temperature range was numerically analyzed to optimize nonequilibrium solidification behavior during ternary Ni-Cr-Al nickel-based single-crystal superalloy weld pool solidification with variation of laser welding conditions (either heat input or welding configuration). The distribution of solidification temperature range along the fusion boundary is beneficially symmetrical about the weld pool centerline in the (001)/[100] welding configuration. The distribution of solidification temperature range along the fusion boundary is detrimentally asymmetrical about the weld pool centerline in the (001)/[110] welding configuration. The stray grain formation and solidification cracking are preferentially confined to [100] dendrite growth region. [001] epitaxial growth region with columnar dendrite morphology is favored at the expense of undesirable [100] growth region with equiaxed dendrite morphology to facilitate essential single-crystal solidification with considerable reduction of heat input. The smaller heat input is used, the narrower solidification temperature range is thermodynamically promoted to reduce nucleation and growth of stray grain formation with decrease of constitutional undercooling ahead of dendrite tip and mitigate thermo-metallurgical factors for morphology instability and microstructure anomalies. Potential low heat input(both decreasing laser power and increasing welding speed) with (001)/[100] welding configuration decreases solidification temperature range to significantly minimize columnar/equiaxed transition (CET) and stray grain formation, and improve resistance to solidification cracking through microstructure control. On both sides of weld pool are imposed by the same heat input, while the solidification temperature range along the fusion boundary inside of [100] dendrite growth region on the right part of the weld pool is spontaneously wider than that of [010] dendrite growth region on the left part to increase solidification cracking susceptibility in the (001)/[110] welding configuration. Furthermore, another mechanism of solidification cracking as consequence of severe solidification behavior and anomalous microstructure with asymmetrical crystallographic orientation is therefore proposed. The theoretical predictions are well verified by experiment results. The useful and satisfactory numerical modeling is also available for other single-crystal superalloys during successful laser repair process without stray grain formation.


2021 ◽  
Vol 1041 ◽  
pp. 47-56
Author(s):  
Zhi Guo Gao

The contribution of crystallography-dependent metallurgical factors, such as supersaturation of liquid aluminum and minimum dendrite tip undercooling, to solidification behavior and microstructure development is numerically analyzed during Ni-Cr-Al ternary single-crystal superalloy molten pool solidification to better understand thermodynamic and kinetic driving forces behind solidification cracking resistance. The variation of supersaturation of liquid aluminum and minimum dendrite tip undercooling with location of solid/liquid interface is symmetrically consistent in (001)/[100] welding configuration. By comparison, the variation is asymmetrically consistent in (001)/[110] welding configuration. The different distribution is attributed to growth crystallography and dendrite selection. Significant increase of supersaturation of liquid aluminum and dendrite tip undercooling from [010] dendrite growth region to [100] dendrite growth region preferentially aggravates microstructure development as result of nucleation and growth of stray grain formation with the same heat input on each half of the weld pool in (001)/[110] welding configuration. High heat input (both increasing laser power and decreasing welding speed) exacerbates supersaturation of liquid aluminum and dendrite tip undercooling by faster diffusion to incur stray grain formation with severity of contributing thermometallurgical factors for susceptibility to solidification cracking, while low heat input (both decreasing laser power and increasing welding speed) ameliorates microstructure development and increases resistance to solidification cracking. Weld microstructure of optimum welding conditions, such as combination of low heat input and (001)/[100] welding configuration, is less susceptible to solidification cracking to suppress asymmetrical microstructure development and improve weld integrity potential rather than insidious welding conditions, such as combination of high heat input and (001)/[110] welding configuration. Severer supersaturation of liquid aluminum and wider dendrite tip undercooling occur in the [100] dendrite region as consequence of alloying enrichment, while smaller supersaturation of liquid aluminum and narrower dendrite tip undercooling occur in the [001] dendrite region as consequence of alloying depletion to spontaneously facilitate epitaxial growth of single-crystal essential. Symmetrical (001)/[100] welding configuration decreases growth kinetics of dendrite tip with smaller overall supersaturation of liquid aluminum and dendrite tip undercooling than that of asymmetrical (001)/[110] welding configuration regardless of combination of laser power and welding speed. Mitigation of supersaturation of liquid aluminum and dendrite tip undercooling simultaneously alleviate crack-susceptible microstructure development and solidification cracking. Additionally, the appropriate mechanism of solidification cracking resistance improvement through modification of crystallography-dependent supersaturation and undercooling of dendrite tip is proposed. Calculation analyses are sufficiently explained by experiment results in a reasonable way. The additional purpose of this theoretical analysis is to evaluate solidification cracking susceptibility of similar nickel-based or iron-based single-crystal superalloys.


2021 ◽  
Vol 1996 (1) ◽  
pp. 012004
Author(s):  
Zhiguo Gao

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.


Author(s):  
Steven L. McCracken ◽  
Boian T. Alexandrov ◽  
John C. Lippold ◽  
Jeffrey W. Sowards ◽  
Adam T. Hope

High chromium nickel-base weld filler metals 52 (ERNiCrFe-7) and 52M (ERNiCrFe-7A) have in recent years replaced filler metal 82 (ERNiCr-3) for new fabrication and for repair applications in commercial nuclear power plants. Filler metals 52 and 52M are selected because they have excellent resistance to primary water stress corrosion cracking (PWSCC). Unfortunately, filler metals 52 and 52M exhibit a higher susceptibility to ductility-dip cracking (DDC) compared to filler metal 82. Filler metal 52MSS (ERNiCrFe-13) is a new high chromium nickel-base alloy with Nb and Mo added to improve resistance to ductility-dip cracking. Increasing Nb has in previous research been shown to widen the solidification temperature range in nickel-base alloys. A wider solidification temperature range can potentially increase susceptibility to hot cracking. This study investigated the solidification behavior and hot cracking susceptibility of three heats of 52MSS and compared the results to a heat of filler metal 52M and a heat of filler metal 52i. The solidification behavior and hot cracking susceptibility were investigated by an optimized Transvarestraint test and by a next generation Cast Pin Tear Test (CPTT). The solidification temperature range and eutectic transformations were measured by a patented Single Sensor Differential Thermal Analysis (SS-DTA) technique. This study showed that filler metal 52MSS was slightly more susceptible to hot cracking than 52M and 52i. This study also demonstrated that the next generation CPTT and SS-DTA technique are effective methods for evaluating the solidification behavior and hot cracking susceptibility of high chromium nickel-base weld filler metals.


2021 ◽  
Vol 1020 ◽  
pp. 32-40
Author(s):  
Zhi Guo Gao

A thermal metallurgical coupling model was further developed for multicomponent dendrite growth of primary γ gamma phase during laser welding nickel-based single-crystal superalloys. It is indicated that welding configuration has a predominant role on the overall dendrite trunk spacing than heat input throughout the weld pool, and modifies the dendrite growth kinetics. The dendrite trunk spacing in (001) and [100] welding configuration is finer than that of in (001) and [110] welding configuration. In (001) and [100] welding configuration, the bimodal distribution of dendrite trunk spacing is symmetrical about weld pool centerline, the dendrite trunk spacing in [100] growth region near the weld pool center is coarser than [010], [0ī0] and [001] dendrite growth regions. In (001) and [110] welding configuration, the distribution of dendrite trunk spacing is crystallographically asymmetrical, and the dendrite trunk spacing in [100] growth region is severely coarser than that of [010] and [001] dendrite growth regions. (001) and [110] welding configuration is of particular interest, because dendrite trunk spacing decreases in [100] dendrite growth region and dendrite trunk spacing increases in [010] dendrite growth region from the maximum weld pool width to the end due to crystallography-dependent growth kinetics. Moreover, strict control of low heat input (low laser power and high welding speed) beneficially promotes fine dendrite trunk spacing and reduces the size of dendrite growth regions. High heat input (high laser power and low welding speed) monotonically coarsens dendrite trunk spacing. The dendrite trunk spacing is refined and [100] dendrite growth is suppressed by the optimum low heat input and (001) and [100] welding configuration to improve weldability. An alternative mechanism of solidification cracking because of asymmetrical dendrite trunk growth is proposed. The useful results facilitate understanding of single-crystal superalloys microstructure development and solidification cracking phenomena. The theoretical predictions agree well with the experiment results. Moreover, the model is also applicable to other single-crystal superalloys with similar metallurgical properties by feasible laser welding or laser cladding.


2021 ◽  
Vol 1033 ◽  
pp. 31-39
Author(s):  
Zhi Guo Gao

Multicomponent dendrite growth is theoretically predicted to optimize solidification cracking susceptibility during ternary Ni-Cr-Al nickel-based single-crystal superalloy weld pool solidification. The distribution of dendrite trunk spacing along the weld pool solidification interface is clearly symmetrical about the weld pool centerline in beneficial (001)/[100] welding configuration. The distribution of dendrite trunk spacing along the weld pool solidification interface is crystallography-dependent asymmetrical from bottom to top surface of the weld pool in detrimental (001)/[110] welding configuration. The smaller heat input is used, the finer dendrite trunk spacing is kinetically promoted by less solute enrichment and narrower constitutional undercooling ahead of solid/liquid interface with mitigation of metallurgical contributing factors for solidification cracking and vice versa. Vulnerable [100] dendrite growth region is predominantly suppressed and epitaxial [001] dendrite growth region is favored to spontaneously facilitate single-crystal columnar dendrite growth and reduce microstructure anomalies with further reduction of heat input. Optimum low heat input (both lower laser power and higher welding speed) with (001)/[100] welding configuration is the most favorable one to avoid nucleation and growth of stray grain formation, minimize both dendrite trunk spacing and solidification cracking susceptibility potential, improve resistance to solidification cracking, and ameliorate weldability and weld integrity through microstructure modification instead of inappropriate high heat input (both higher laser power and slower welding speed) with (001)/[110] welding configuration. The dendrite trunk spacing in the [100] dendrite growth region on the right side of the weld pool is considerably coarser and grows faster than that within the [010] dendrite growth region of the left side in the (001)/[110] welding configuration to deteriorate weldability, although the welding conditions are the same on the either side. Furthermore, the alternative mechanism of crystallography-dependent solidification cracking as consequence of asymmetrical microstructure development and diffusion-controlled dendrite growth of γ phase is therefore proposed. The theoretical predictions are comparable with experiment results. The reliable model is also useful for welding conditions optimization for crack-free laser processing.


2012 ◽  
Vol 445 ◽  
pp. 454-459 ◽  
Author(s):  
M.R. Nakhaei ◽  
N.B. Mostafa Arab ◽  
F. Kordestani

Laser welding of plastic materials has a wide range of applications in the packaging, medical, electronics and automobile industries provided it can predict high quality welds compared with other joining methods. Laser welding process parameters can affect the quality of welds. In this paper, Artificial Neural Network (ANN) is used to model the effects of laser power, welding speed, clamp pressure and stand-off distance on weld lap-shear strength in laser transmission welding (LTW) of acrylic (polymathy methacrylate). A set of experimental data on diode laser weld lap-shear strengths was used to train and test the ANN from which the neurons relations were gradually extracted to develop a model. The developed ANN model can be used for the analysis and prediction of the complex relationships between the above mentioned process parameters and weld lap-shear strength. The results indicated that increase in laser power and clamp pressure increases the weld lap-shear strength whereas welding speed and stand off distance had a decreasing affect on shear strength at high value.


Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3178 ◽  
Author(s):  
Wenbin Wang ◽  
Li Xiong ◽  
Dan Wang ◽  
Qin Ma ◽  
Yan Hu ◽  
...  

A new test method named “Trapezoidal hot” cracking test was developed to evaluate solidification cracking susceptibility of stainless steel during laser welding. The new test method was used to obtain the solidification cracking directly, and the solidification cracking susceptibility could be evaluated by the solidification cracking rate, defined as the ratio of the solidification cracking length to the weld bead length under certain conditions. The results show that with the increase in the solidification cracking rate, the solidification cracking susceptibility of SUS310 stainless steel was much higher than that of SUS316 and SUS304 stainless steels during laser welding (at a welding speed of 1.0 m/min) because a fully austenite structure appeared in the weld joint of the former steel, while the others were ferrite and austenitic mixed structures during solidification. Besides, with an increase in welding speed from 1.0 to 2.0 m/min during laser welding, the solidification cracking susceptibility of SUS310 stainless steel decreased slightly; however, there was a tendency towards an increase in the solidification cracking susceptibility of SUS304 stainless steel due to the decrease in the amount of ferrite under a higher cooling rate.


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