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Nucleation and growth conditions of single-crystallinity control are convincingly elaborated by multi-scale mathematical modeling of heat and mass transport to totally abate undesirable weld defects, e.g. disoriented crystal and hot cracking inside molten pool of nonequilibrium crystallization, in order to illustrate the usefulness of predictive capability through theory and experiment procedures. Crystal growth is complicated by crystallinity-dependent thermal and chemical driving forces in front of dendrite tip during viable laser surface modification of Ni-based single-crystal superalloy. These two thermal metallurgical determinants play crucial role in crack-insusceptible columnar crystal growth, which is favorably oriented throughout weld depth. There is particular challenge in complete elimination of disoriented crystal, i.e. stray grain formation, for acceptable surface quality. Conservative (001)/[100] crystalline orientation is desired to diminish Al concentration and supersaturation, and morphologically satisfy epitaxial growth kinetics to successfully lessen central cracking with satisfactory variability of laser power and welding speed. Comparatively, (001)/[110] crystalline orientation is disadvantageous to asymmetrically augment Al concentration and supersaturation and aggressively increase interface instability, microstructure heterogeneity and hot cracking vulnerability along disoriented crystal boundaries. Disoriented crystal is increasingly withstood if the Al concentration and supersaturation in front of dendrite tip are low enough and crack-unsusceptible part is relatively large enough in case of attractive (001)/[100] crystalline orientation with optimal range of heat input to ameliorate microstructure homogeneity. Crystalline orientation region varies with diverse welding configurations, and epitaxy across solid/liquid interface is also sensitive to heat input of laser processing, which necessitate high efficient welding conditions optimization. Considerable effort is made to distinguish diffusion-driven crystal growth between a series of combinations of multiple welding conditions, such as critical welding configuration and heat input. Metallographically, the morphologies of crystal growth and hot cracking are experimentally observed to consistently support kinetics calculation result and well explain correlation between solidification behavior and crystal growth.

When multicomponent molten pool nonequilibrium solidification, the interrelationship of location-dependent dendrite tip undercooling on low heat input and optimal growth crystallography is progressively discussed over planar interface morphology stability range to unidirectionally facilitate epitaxial growth by single-crystallinity control during laser repair of nickel-based superalloy to inhibit microstructure heterogeneity. Suppression of disoriented dendrite growth and crystallography orientation deviation along columnar interface is necessary for crackless repair. Axis-symmetrical (001)/[100] welding configuration kinetically reduces dendrite tip undercooling, nucleation and subsequent disoriented dendrite growth rather than unsymmetrical (001)/[110] welding configuration. When comparison between low heat input, within which laser power is limited and welding speed is rapid, and high heat input, within which laser power is considerable and welding speed is insignificant, the former attenuates dendrite tip undercooling and morphology transition between columnar and equiaxed dendrites to stabilize epitaxy and ameliorate dendrite growth with advantageous solidification conditions, especially drastic temperature gradient and small dendrite growth velocity. Axis-symmetrical growth crystallography and low heat input are favored to mitigate size of high-undercooling region, where stray grain formation are dominant, for homologous single-crystallization of epitaxial growth with satisfactory growth kinetics of dendrite tip, and are capable of elimination of undercooling-induced overgrowth for high quality weld, instead of aggressive unsymmetrical growth crystallography and high heat input. Additionally, the achievement of low heat input with axis-symmetrical welding configuration possesses stronger resistance to unstable interface morphology and solidification cracking. When comparison between growth regions of [100] and [010] crystalline orientation, where identical heat input is kept on both sides, wider dendrite tip undercooling is mainly located on the right side than left side to insidiously exacerbate crack-vulnerable dendrite growth, which is a ubiquitous phenomenon in the adverse (001)/[110] welding configuration. The effect of low heat input on dendrite tip undercooling is spontaneously smaller than growth crystallography. Hence, during nonequilibrium solidification of weld pool, the important mechanism of crystallography-induced microstructure heterogeneity obviation due to undercooling-limited epitaxial growth is consequently provided. The theoretical predictions cogently explain the experiment results in a concise way to properly illustrate microstructure degradation phenomena in the both sides of weld by reproducible calculation of mathematical modeling.

To pertinently balance growth kinetics, solidification thermodynamics and dendrite expitaxy of multicomponent nickel-based single-crystal supralloy during laser processing, effect of thermometallurgy determinant factors, including laser power, welding speed and welding configuration, on solidification behavior, such as nonequilibrium solidification temperature range, and dendrite growth, such as dendrite trunk spacing, are progressively advanced to forestall solidification cracking phenomena. Symmetric developments of dendrite trunk spacing and solidification temperature range alongside solid/liquid interface are crystallographically driven by useful (001)/[100] welding configuration to auspiciously bring about crack-insusceptible and well-oriented dendrite growth. Dissimilarly, unsymmetrical developments of dendrite trunk spacing and solidification temperature range alongside solid/liquid interface are crystallographically driven by (001)/[110] welding configuration to insidiously favor crack-unresistant and disoriented dendrite growth. Higher heat input thermodynamically and kinetically boosts wide solidification temperature range, appalling stray grain growth with excess of solute ahead of dendrite tip and large size of crack-unresistant region to thermometallurgically disintegrate epitaxial growth for untoward solidification cracking, and therefore should be strictly withstood. Although geometry of symmetrical weld pool both sides is the same in infelicitous (001)/[110] welding configuration, [100] region of dendrite growth is more liable to ruinous stray grain growth and extensive solidification temperature range than [010] region of dendrite growth to complicate dendrite growth and exacerbate weld integrity. The determinant mechanism of crystallography-aided amelioration of solidification cracking resistance as result of kinetics-and thermodynamics-driven dendrite growth is propitiously proposed. Furthermore, the credible and understandable theoretical predictions are in conformity with the experiment results.

The effect of thermo-metallurgical factors, such as heat input and welding configuration, on solidification cracking driving forces nearby dendrite tip, such as solidification temperature range and columnar/equiaxed transition (CET) was thermodynamically and kinetically discussed with aid of comprehensive numerical analysis for multicomponent melt-pool solidification during laser processing under non-equilibrium solidification conditions to better understand problematical solidification cracking phenomena. By using (001)/[100] welding configuration, axisymmetrical distributions of columnar/equiaxed transition and solidification temperature range alongside solidification interface are homogeneously produced on both sides of weld pool. By using (001)/[110] welding configuration, nonaxisymmetrical distributions are heterogeneously produced, and are able to bring about infelicitous microstructure degradation. Unidirectional region of [001] columnar dendrite is more prone to epitaxial growth without morphology transition to conservatively better crystallography-assisted single-crystal growth. Unidirectional epitaxial growth is collapsed, and onset of stray grain nucleation and solidification cracking eventuates in [100] region of equiaxed dendrite growth. Low heat input relatively broadens portion of unidirectional columnar dendrite, where stray grain is infrequently nucleated and grown, and thus morphology transition seldom happens, as long as undercooling and solidification temperature range alongside dendrite tip are sufficient low to challengingly develop crackless dendrite growth and high-quality weld by thermometallurgy-aided single-crystallinity control. Auspicious (001)/[100] welding configuration simultaneously abates overall stray grain nucleation and constricts solidification temperature range nearby fusion boundary to wane microstructure heterogeneity. Conversely, plenteous stray grain formation is kinetically attained and extensive solidification temperature range nearby fusion boundary is thermodynamically obtained by problematical (001)/[110] welding configuration to metallurgically induce pernicious equiaxed dendrite and disintegrate dendrite growth. Moreover, the mechanism of solidification cracking diminution as consequence of appropriate optimization of thermo-metallurgical determinants during multicomponent nickel-based single-crystal superalloy melt-pool non-equilibrium solidification is also proposed. The potent consistency between the predicted and experimented results is exceedingly tenable.

The dependency of morphology development and dendrite growth on welding conditions (laser power, welding speed and welding configuration) is numerically analyzed to decrease nucleation and growth of stray grain formation during laser processing aerospace component surface of ternary Ni-Cr-Al single-crystal superalloy. Proper (001)/[100] welding configuration crystallographically initiates three axisymmetrical distributions of microstructure development, i.e. stray grain formation, morphology development and dendrite trunk spacing, alongside the advancing solid/liquid interface of molten pool, whereby metallurgical properties are increased. Unpromising (001)/[110] welding configuration tends to crystallographically possesses unaxisymmetrical microstructure development to favor substantial crack-vulnerable dendrite size and morphology. Epitaxial [001] columnar dendrite growth region is favored for single-crystal dendrite growth, while vulnerable [100] equiaxed dendrite growth region is more susceptible to solidification cracking. The lower heat input is used, the smaller stray grain formation, negligible columnar/equiaxed transition (CET) and finer dendrite trunk spacing are consistently promoted by narrower constitutional undercooling ahead of solid/liquid interface to improve crack-resistant microstructure development and weld integrity. When comparing between [100] dendrite growth region on the right side and [010] dendrite growth region on the left side, (001)/[110] welding configuration spontaneously engenders severer stray grain formation, insidious columnar/equiaxed transition and coarser dendrite trunk spacing on the right side to deteriorate microstructure development with restriction of the same heat input on both sides of weld pool. The mechanism of asymmetrical solidification cracking as result of crystallography-induced microstructure degradation is therefore proposed. The theoretical predictions of asymmetrical solidification cracking susceptibility are comparable with experiments.

When three welding conditions, including welding configuration, welding speed and laser power, are sequentially altered, supersaturation of liquid aluminum is crystallography-dependently determined to limit growth kinetics of dendrite tip with decease of thermo-metallurgical factors for solidification cracking to salvage the weld properties during emerging laser welding repair of multicomponent nickel-based single-crystal superalloy. After comparing growth crystallography between right side and left side of weld, the distribution of supersaturation of liquid aluminum is axis- symmetrically developed by favorite (001)/[100] dendrite growth kinetics, while the distribution is nonaxisymmetrically developed by detrimental (001)/[110] dendrite growth kinetics. High heat input is inappropriately procured by either high laser power or slow welding speed to insidiously boost supersaturation of liquid aluminum, worsen alloying partition and solute copiousness, heterogeneously exacerbate morphology and size of dendrite growth, whereby stray grain formation is strongly produced. In order to ameliorate dendrite growth, low heat input is usefully rendered by either low laser power or high welding speed to attenuate supersaturation of liquid aluminum, narrow solidification temperature range and obviate dendrite tip undercooling alongside columnar interface in order to augment crack-resistant dendrite of epitaxial growth. The overall supersaturation of liquid aluminum is crystallography-dependent. During across whole melt-pool solidification interface, supersaturation of nonsymmetric (001)/[110] welding configuration is not as small as symmetric (001)/[100] welding configuration under well-controlled heat input, thereby fosters the kinetic factors for stray grain development to obstruct columnar dendrite and consequently weaken unidirectional morphology. It is crystallographically favorable for relief of supersaturation with axis- symmetrical dendrite growth. The mechanism of crack-vulnerable dendrite growth elimination through circumspect improvement of supersaturation-controlled growth kinetics is constructively proposed for feasible crackless rejuvenation of laser welding or laser cladding. The theoretical predictions are scrupulously supported by corroborative metallograph observation.

Two important thermometallurgical factors, i.e. aluminum redistribution and dendrite tip undercooling, are numerically analyzed to better understand growth kinetics of microstructure development with favorable and unfavorable crystallographic orientations in three dimensions during advancement of Ni-Cr-Al ternary single-crystal melt-pool solidification interface to optimize microstructure stability within gamma γ phase. Inappropriate growth crystallography dominates profiles of aluminum redistribution and undercooling of dendrite tip in the crack-susceptible region, simultaneously. For beneficial (001)/[100] growth crystallography, the profiles of solid aluminum concentration and undercooling ahead of dendrite tip are clearly symmetrical throughout solidification interface. For detrimental (001)/[110] growth crystallography, the profiles of solid aluminum concentration and undercooling ahead of dendrite tip are quite asymmetrical within two sides of weld, and this asymmetrical phenomenon is of particular interest. The same energy of heat input is accessible to each half of molten pool, however, the difference of dendrite growth driving forces between right side and left side of weld pool kinetically exacerbates microstructure development. The complexity of (001)/[110] welding configuration is consistently attributable to larger overall solid aluminum concentration and undercooling of dendrite tip in [100] dendrite region than that of [010] dendrite region. In the two welding configurations, the size and shape of [001] dendrite growth region modifies growth kinetics of dendrite tip to extend columnar morphology of epitaxial growth for crack-resistant microstructure development with smaller solid aluminum concentration and narrower dendrite tip undercooling by either decrease of laser power or further increase of welding speed, while [100] dendrite growth region preferentially aids columnar/equiaxed transition (CET) with severe aluminum redistribution and wider dendrite tip undercoolig. The smaller heat input is imposed, the smaller solid aluminum concentration and narrower dendrite tip undercooling are crystallographically induced that is capable of elimination of metallurgical contributing factors for microstructure anomalies and vice versa. Optimum (001)/[100] growth crystallography and low heat input with decrease of laser power and increase of welding speed minimize columnar/equiaxed transition and stray grain formation, improve resistance to solidification cracking and ameliorate weld integrity, while (001)/[110] growth crystallography and high heat input with increase of laser power and decrease of welding speed significantly contribute to weldability exacerbation and microstructure degradation. The crystallography-dependent mechanism of efficient microstructure anomalies reduction, which is attributed to decreasing aluminum enrichment and undercooling ahead of dendrite tip, is therefore proposed. Consequently, comparison between calculation results and experiment results is plausible and acceptable. The usefulness application of this numerical analysis improves predictive capability and enables attractive microstructure control of single-crystal superalloys with similar materials properties.

Correlation between welding conditions, such as laser power, welding speed and welding configuration, microstructure anomalies, including columnar/equiaxed transition (CET) and stray grain formation, and metallurgical factors, such as aluminum redistribution and supersaturation near dendrite tip, is elucidated by thorough numerical analysis to explain prevalent phenomenon of insidious microstructure development and face the challenge of microstructure amelioration as well as solidification cracking resistance improvement during course of ternary single-crystal Nickel-Chromium-Aluminum superalloy melt-pool solidification for crack-free laser surface modification. Metallurgical factors of γ gamma phase microstructure development strongly depend on welding configuration, and heat input is not as important as welding configuration. Although melted-pool center region is susceptible to microstructure anomalies, (001)/[100] welding configuration possesses auspicious growth crystallography under which the bimodal profiles of solid aluminum concentration and liquid aluminum supersaturation ahead of dendrite tip are symmetrically distributed to potentially decrease solute redistribution and increase resistibility to solidification cracking. Dissimilarly, (001)/[110] welding configuration possesses insidious growth crystallography under which the profiles of solid aluminum concentration and liquid aluminum supersaturation ahead of dendrite tip are asymmetrically distributed to preferably facilitate alloying plentiful enrichment and differentiate problematical microstructure instability on half side of molten pool. In the bottom of molten pool, beneficial Al-barren [001] dendrite is kinetically driven by homologous single-crystal epitaxial growth without columnar/equiaxed transition. On the right side of molten pool, detrimental Al-rich [100] dendrite is spontaneously susceptible to stray grain formation with equiaxed morphology. Symmetrical microstructure development is more enrichment-resistant than asymmetrical microstructure development, which is crystallographically ascribable to favorable thermo-metallurgical factors, i.e. aluminum redistribution mitigation and supersaturation relief, and substantially reduce metallurgical degradation and microstructure failure. The faster welding speed and the lower laser power are used, the smaller aluminum concentration and supersaturation ahead of dendrite tip are kinetically incurred to suppress columnar/equiaxed transition and stray grain formation with a number of thermometallurgical factors contribution to considerable microstructure amelioration and increasingly improve solidification cracking resistance and vice versa. Shallow molten-pool shape with symmetrical growth crystallography efficiently advances anomalies-resistant microstructure development with diminution of partition driving forces for solute redistribution and supersaturation during nonequilibrium solidification instead of deep molten-pool shape with asymmetrical growth crystallography. The latter importantly aggravates stray grain formation. Useful combination of optimum solidification conditions and favorable growth crystallography predominantly minimizes diffusion-controlled solute deviation and microstructure anomalies for excellent single-crystal superalloy laser processing without cracking, and possesses tenable relationship between welding conditions, solute redistribution and microstructure anomalies. The mechanism of crystallography-aided concentration fluctuation and copious supersaturation behind prominent phenomenon of microstructure anomalies, where nucleation and growth of stray grain formation near dendrite tip are activated, is consequently proposed. The comparison between numerical analyses and experiment results are valid and satisfactory. Microstructure anomalies are predictable for proper understanding of multicomponent microstructure development in the interior of fusion zone. The theoretical methodology is reproducible as consequence of availability of thermodynamic and kinetic properties of Nickel-based or Iron-based single-crystal superalloys.

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.

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.

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.

The thermal metallurgical modeling of alloying aluminum redistribution was further developed through couple of heat transfer model, dendrite selection model, multicomponent dendrtie grwoth model and nonequilibrium solidification model during three-dimensional nickel-based single-crystal superalloy weld pool solidification over a wide range of welding conditions (laser power, welding speed and welding configuration) to facilitate understanding of solidification cracking phenomena. It is indicated that the welding configuration plays more important role than heat input in aluminum redistribution. The bimodal distribution of solid aluminum concentration along the solid/liquid interface is crystallographically symmetrical about the weld pool centerline for (001) and [100] welding configuration, while the distribution of solid aluminum concentration along the solid/liquid interface is crystallographically asymmetrical throughout the weld pool for (001) and [110] welding configuration. The size of vulnerable [100] dendrite growth region is beneficially suppressed in favor of epitaxial [001] dendrite growth region through optimum low heat input (low laser power and high welding speed) to facilitate single-crystal dendrite growth for successful crack-free weld at the expense of shallow weld pool geometry. The overall aluminum concentration in (001) and [100] welding configuration is significantly smaller than that of (001) and [110] welding configuration regardless of heat input. Severe aluminum enrichment is confined to [100] dendrite growth region where is more susceptible to solidification cracking. Heat input and welding configuration are optimized in order to minimize the solidification cracking susceptibility and improve microstructure stability. The relationship between welding conditions and alloying aluminum redistribution are established for solidification cracking susceptibility evaluation. The higher heat input is used, the more aluminum enrichment is monotonically incurred by diffusion with considerable increase of metallurgical driving forces for morphology instability and microstructure anomalies to deteriorate weldability and vice versa. The mechanism of asymmetrical solidification cracking because of crystallography-dependent alloying redistribution is proposed. The theoretical predictions agree well with the experiment results. Moreover, the useful modeling is also applicable to other single-crystal superalloys with similar metallurgical properties during laser welding or laser cladding.

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.

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.

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.

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.

This paper designed a novel shared aperture dual-band slot array. The array is a planar mono pulse antenna. The Ku band slot array is interlaced to the C band slot array to make the dual-band antenna radiate in the same plane. The Ku band slot array is fed by waveguide, and the C band slot array is fed by strip line, which not only ensures high antenna efficiency but also reduces the weight and size of the antenna. Antenna simulation and prototype measurement results are presented.

Effects of cooling rate on metallographic structure of boron-bearing steel were investigated in present research. The results showed it consists of ferrite and pearlite formed in the initial stage of the transformation in the studied boron-bearing steels cooled at the rate from 1 to 10°C/s. For the higher cooling rate than 15 to 33°C/s, it consisted of bainite formed in the second stage of the transformation. For increasing presently cooling rate than 66°C/s, it consisted of martensite formed in the third stage of the transformation. All the transformation of metallographic structure was proved by CCT diagram.

Split Hopkinson pressure bar setup was used as experimental method for dynamic impacted testing at 573K at the strain rate of 7030s-1. The microstructure of Al-5.8Cu aluminum alloy impacted plate was characterized by transmission electron microscopy (TEM). The findings indicated that dislocation network of Al matrix was observed, which was attributed to isothermal and adiabatic process during impaction. The researched results indicated the dislocation network of Al matrix was inhabited by coarsened precipitate in Al-5.8Cu alloy impacted plate.

Recrystallization law was investigated at different annealing processes. The results showed that the annealing temperature was a main effect factor on the properties of Ti-IF steel. Nominal recrystallization temperature of the samples was evaluated as 620 °C. Simulated batch annealing was performed by two-stage heating. Determined recrystallization temperature was 660 °C, the recrystallization of samples heated at 660 °C was completed in 68min. For 800 °C, the equiaxial recrystallized grains were obtained. Simulated continuous annealing by rapidly heating to different temperatures, samples were held for 100s and then cooled in air. Recrystallization nucleation was not observed until 660 °C. The occurrence of secondary recrystallization was observed at 900 °C.

Steel-bonded cemented carbide sheet considered as cladding was successfully bonded with carbon steel plate by a technological combination of powder explosive compaction and liquid sintering. The microstructural interface between steel-bonded cemented carbide cladding and carbon steel plate was characterized by SEM, EDS analysis and hardness testing. The results showed that the gradient distributions of the elements Fe, C and W were found in the normal direction of the interface. The element W permeated about 100μm in depth through the side of carbon steel. The improved hardness of about 600～700HV of cladding was attributed to multiple carbides.

An 3D mathematical model was established to illustrate weld pool development in the ASHPW (Automated Submerged Horizontal Position Welding) process. This model takes into consideration the spatial position characteristic of ASHPW, and used the heat transfer and mass transfer phenomena during welding process to explain the weld geometry mechanism in order to correctly design the bevel geometry. The final results show that the predicted geometry , such as the weld cross-section, weld width and weld cross section area, are in good agreement with experimental measurements.

In order to better understand heat transfer and fluid flow pattern in the weld pool of laser-metal inert gas (MIG) hybrid welding aluminum-alloy process, weld formation mechanism and weld pool dynamic behavior were analyzed by a three-dimensional mathematical model for moving laser- MIG hybrid welding. The temperature and velocity distribution of weld longitudinal section for laser-MIG moving hybrid welding at different moment were discussed to explain flow dynamic behavior in the weld pool. In addition, weld formation mechanism was illustrated by a transverse section heat history evolvement. Moreover, the effects of laser welding parameter and MIG welding parameter on important weld geometry characteristic were quantitatively studied using the mathematical model, and the simulated weld bead geometry parameters were in good agreement with experimental measurements.

The effects of Yb content on the microstructures and mechanical properties of 2519A aluminum alloy plate were investigated by means of tensile test, optical microscopy, transmission electron microscopy, scanning electron microscopy and X-ray diffractometer. The results show that addition of 0.17% (mass fraction) Yb increases the density of θ ' particles of the 2519A alloy plate and reduces the coarsening speed rate of θ ' phase at 300 °C. Therefore, tensile strength is enhanced from 483.2 MPa to 501.0 MPa at room temperature and is improved from 139.5 MPa to 169.4 MPa at 300 °C. The results also show that with the addition of 0.30% (mass fraction) Yb, the mechanical properties increase at 300 °C and decrease at room temperature. With Yb additions, the Al 7.4 Cu 9.6 Yb 2 phase is found whilst the segregated phases of as-cast alloys along grain boundaries become discontinuous, thin and spheroidized.

The precipitation hardening response, microstructures and mechanical properties of 2519A aluminum alloy plates with additions of 0, 0.2 and 0.4 wt.% Ce were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), X-ray diffractometer (XRD), Vickers hardness test and tensile tests. The results show that 0.2 wt.% Ce promotes the precipitation of denser and finer θ′ phase, which improves the tensile strength of the alloy at both room and elevated temperatures. High melting point Al8Cu4Ce phase particles are found in alloys with additions of Ce up to 0.4 wt.%, which contributes to the mechanical properties at elevated temperature.

The commercial 2519 aluminum alloy is a primary material for structural components of aircrafts, helicopters, and amphibians because of its low specific density, which favors the selection of aluminum alloys in weight-critical applications [1, 2]. To promote the mechanical properties of the alloys, severe plastic deformation (SPD) processes were explored such as equal channel angular pressing and severe cold rolling (SCR) [3–8]. However, 2519A aluminum alloy for a new version of Al–Cu alloy was developed as armor material and scarcely fabricated by SPD processes. Valiev has reported that alloys produced by the SPD processes have increased strength with limited ductility [9]. The increase in strength of 5083 aluminum alloy is always accompanied by a loss in ductility [10]. A combination of equal channel angular pressing and lowtemperature aging resulted in significant improvements in both ultimate tensile strength (UTS) and ductility in AA6061 and Al–10%Ag alloy [11, 12]. Short age was scarcely utilized for improving the mechanical properties of the aluminum alloy plate. In this letter, for the first time, short aging treatments are performed to balance UTS and ductility of severe cold-rolled (SCRed) 2519A aluminum alloy. The 2519A alloy plates quenched were rolled from 10 mm to no more than 3 mm in thickness. The total thickness reduction (70–90%) was achieved in multiple passes, with about 10% reduction per pass. The aging temperature of the SCRed aluminum alloy was identified using a differential scanning calorimeter (DSC). Uniaxial tensile tests were conducted at an initial strain rate of 3 9 10 s on SCRed and short-aged (SA) samples along rolling direction. Microstructural observations were carried out using Tecnai G 20 TEM and Sirion 200 SEM. Transmission electron microscopic (TEM) images corresponding to three considered rolling reduction rates are shown in Fig. 1. Cellular structure is observed due to high dislocation density deformed during SCR process regardless of the reduction rate. Dislocation tangle is found in SCRed plates, which were attributed to cross slide (Fig. 1a–c). In fact, there is no obvious difference between three images corresponding although to three different rolling reduction assignments of SCRed plates. However, the fracture surfaces of SCRed plates showed significant differences between each others. The increased sizes of microdimples were found with the increasing rolling reduction rates although in the existence of large dimples (Fig. 2a–c), which could be correlated to the effects of reduction rate on particle sizes. To identify an appropriate aging temperature, DSC experiments were carried out. Figure 3 shows the DSC trace for the SCRed aluminum alloy. From the DSC curve, the onset of aging temperature has been estimated to be 458 and 503 K. For achieving stable microstructures, the SCRed samples underwent short aging treatments for 20 min. TEM images of 2519A alloy short aged at 458 K corresponding to the three different rolling reduction rates are shown in Fig. 4. Only in the sample short aged at 458 K for 20 min corresponding to the rolling reduction rate of 70% (Fig. 4a), thickening anisotropy of h0 precipitate on {100}Al is observed. A similar result is not found in Fig. 4b and c, corresponding to the rolling reduction rate of 80 and X. Zhang (&) Z. Gao Y. Zhao School of Materials Science and Engineering, Central South University, Changsha 410083, People’s Republic of China e-mail: xmzhang_cn@yahoo.cn

A new parallel kinematic machine UPS-2RPS with serial input limb is presented, the topological structure characteristics are described. The mathematic model of inverse position solution is derived. The workspace of the mechanism is analyzed and researched by results of MATLAB and Pro/E simulation, The research will be of great significance to promote its novation, application and spread .

The effect of strain rate on the microstructure of 2519A aluminium alloy plate impacted at 573 K was characterized by optical microscopy (OM) and transmission electron microscopy (TEM). Adiabatic shear lines, arc-like shearing bands and DRX grains due to the concentrated stress and heat were observed in impacted aluminum alloy plate. Highly regular dislocation networks due to dislocation climb and irregular dislocation networks pinned by the coarsened precipitates were obtained with the increasing strain rate.

The influence of high strain rate on the precipitate microstructure in impacted aluminum alloy was revealed by transmission electron microscopy. The estimated aspect ratio and the area fraction of θ′ precipitate in impacted aluminum alloy specimens were not dramatically changed until impact testing at 5730 s−1 or higher at ambient temperature although the hardness of specimens impacted at 667–7050 s−1 was decreased. High strain rates are thus a simple way to lower the transformation temperature of θ′ phase in impacted aluminum alloy.

For many years, rivet joint technology has been applied in the automotive and aerospace industry. Recently, it began to apply laser welding technology to lap joints instead of rivet joining. Laser spot welding has some potential advantages including time saving, cost reduction, material saving and weight reducing. A lap joint of aluminum alloy LY12 with different plate thickness, namely 2mm and 1mm, was spot-welded by CO2 laser. For the welding, laser power in pulse form with ramping-up and cooling-down shape was used, and pure helium gas served as shielding gas to fill around welding area. In this study transient three-dimensional non-linear finite element modeling was used to analyze heat flow and residual stress of the laser spot welding of aluminum alloy LY12. In modeling the temperature dependence of material properties, influence of contact surfaces are taken into account. To analyze, Gaussian distributed heat source model and thermo-elasto-plastic behavior were applied. Weld dimensions and residual stress at the weld surface were calculated numerically and compared with the experimental results.

Impact behavior of aluminum alloy 2519A was investigated at strain rates of 600–7 000 s −1 and temperatures of 20–450 °C by a split Hopkinson pressure bar. The results show that the flow stress is dominated by temperature, and it increases with strain rate and decreases with deformation temperature. The serrated flow curves show the dynamic recrystallization occurs. The strain rate sensitivity exponents m determined are 0.066, 0.059 4, 0.059 0 and 0.057 3 at 20, 150, 300 and 450 °C, respectively. Cowper-Symonds constitutive equation expressing the plastic flow behavior was calculated by analysis and regression of the experimental results. The fracture characteristics under the experimental conditions were observed by optical microscopy(OM) and scanning electron microscopy(SEM). It is determined that the tested material fails as a result of adiabatic shearing.

The research about effects of Nb on martensite size and mechanics in B-bearing steel was completed. The results show that both steels have similar martensite due to high hardenability of B element which is responsible for high mechanical properties. However, there are differences in the microstructures between A steel (Nb-containing steel) and the B steel (Ti-containing steel). Microstructural observation of the quenched specimen shows that the formation of fine martensite is dominant in the A Steel than B steel due to Nb element. Martensite size in B-bearing steel was refined by Nb element for high fatigue property and toughness.

The law of phase change of bearing-B steel during continual cooling was studied by adopting dilatometer. The CCT curves of bearing-B steel were drawn, and the effects of RE on critical cooling rates were studied. The experimental results show that the start temperatures of martensite TM was decreased from 438 to 404°C. The critical cooling rate was simultaneously decreased from 33 to 15°C/s.

Split Hopkinson pressure bar setup was used as experimental method for dynamic impacted testing at 723 ± 5 K at the nominal strain rate of 2400 ± 100 to 7000 ± 100 s−1. The microstructure of 2519A-T87 aluminum alloy plate impacted was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The findings indicated that the thickness of θ′ precipitate could be manipulated by adjusting the strain rate of impacted specimens, and its thickening became obvious gradually when the strain rate was above 2400 ± 100 s−1. Most of the semi-coherent plate-like θ′ precipitates were consequentially transformed to incoherent spherical θ′ precipitates only when the strain rate was up to 7000 ± 100 s−1, which was attributed to more adiabatic energy absorbed by Al matrix and precipitates.

To compare the efficacy differences between acupoint catgut-embedding combined western medicine (ACCWM) and simple western medicine (WM) for treatment of epilepsy of generalized seizures type.Fifty-two patients with epilepsy of generalized seizures type were randomly divided into an ACCWM group (n=30) and a WM group (n=22). Dazhui (GV 14), Yaoshu (GV 2), Jiuwei (CV 15), Qihai (CV 6) were selected in the ACCWM group as the main acupoints combined with routine antiepileptic drugs, Valpromide was taken orally, 2.0 g/d for adult, 50 mg/kg x d for child. The WM group was treated with routine antiepileptic drugs. The epilepsy score and the attack frequency one year before the treatment and one year during treatment were observed and the therapeutic effects in the two groups were compared.The epilepsy score and the attack frequency were both decreased in the two groups (P0.01, P0.05), and the epilepsy score in the ACCWM group decreased significantly (6.57 +/- 3.29 vs 10.73 +/- 2.54, P0.05). The total effective rate of 90.0% (27/30) in the ACCWM group was superior to that of 68.2% (15/22) in the WM group (P0.05).The therapeutic effect of ACCWM is superior to that of simple western medicine in treating epilepsy of generalized seizures type. It can improve significantly the attack symptoms so as to enhance life quality of the patients with epilepsy.

Tourniquets used during total knee arthroplasty may lead to many complications. The aim of this study was to determine perioperative blood loss and its clinical relevance in total knee replacement surgery after applying a tourniquet.From June 2009 to October 2009, 60 consecutive patients who underwent routine total knee arthroplasty were randomly divided into two groups and were treated with or without a tourniquet (30 patients/group). There were no significant differences in patient baseline characteristics between the two groups. We compared the two groups of patients in terms of intra- and postoperative bleeding, invisible or visible bleeding, and total blood loss.None of the patients showed poor wound healing, lower extremity deep venous thrombosis or other complications. The amount of blood loss during surgery was lower in the tourniquet group than in the control group (P0.01). However, postoperative visible bleeding (P0.05) and occult bleeding (P0.05) were significantly greater in the tourniquet group than in the control group. There was no significant difference in the total amount of blood loss between the two groups (P0.05).Tourniquet can reduce bleeding during total knee replacement surgery, but is associated with greater visible and invisible blood loss.