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J.m. Vitek - One of the best experts on this subject based on the ideXlab platform.
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the effect of welding conditions on stray Grain Formation in single crystal welds theoretical analysis
Acta Materialia, 2005Co-Authors: J.m. VitekAbstract:Stray Grain Formation during solidification of nickel-based single crystal superalloy welds leads to a degradation of mechanical properties and cracking. Based on the mechanism of constitutional supercooling ahead of the advancing dendritic growth front, the effect of welding conditions (weld speed and power) on the tendency to form stray Grains during solidification was evaluated. A simple 3D thermal model was combined with a geometric model to determine the extent of stray Grain Formation as a function of welding conditions and position in the weld pool, taking into account the influence of dendrite growth orientation. A parameter describing the degree of stray Grain Formation, averaged over the entire solidification front, was calculated. Processing maps that show the severity of stray Grain Formation as a function of weld speed, power and orientation were developed. It was found that low power and high weld speed were optimal for minimizing the stray Grain Formation potential. The effect of crystallographic orientation of the weld on the overall tendency to form stray Grains was minimal, although local variations based on orientation were quantified. The theoretical analysis was compared to earlier experimental work on laser welded nickel-based single crystals and all of the experimental observations could be reproduced in the calculations.
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The effect of welding conditions on stray Grain Formation in single crystal welds – theoretical analysis
Acta Materialia, 2005Co-Authors: J.m. VitekAbstract:Stray Grain Formation during solidification of nickel-based single crystal superalloy welds leads to a degradation of mechanical properties and cracking. Based on the mechanism of constitutional supercooling ahead of the advancing dendritic growth front, the effect of welding conditions (weld speed and power) on the tendency to form stray Grains during solidification was evaluated. A simple 3D thermal model was combined with a geometric model to determine the extent of stray Grain Formation as a function of welding conditions and position in the weld pool, taking into account the influence of dendrite growth orientation. A parameter describing the degree of stray Grain Formation, averaged over the entire solidification front, was calculated. Processing maps that show the severity of stray Grain Formation as a function of weld speed, power and orientation were developed. It was found that low power and high weld speed were optimal for minimizing the stray Grain Formation potential. The effect of crystallographic orientation of the weld on the overall tendency to form stray Grains was minimal, although local variations based on orientation were quantified. The theoretical analysis was compared to earlier experimental work on laser welded nickel-based single crystals and all of the experimental observations could be reproduced in the calculations.
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Stray Grain Formation, thermomechanical stress and solidification cracking in single crystal nickel base superalloy welds
Science and Technology of Welding and Joining, 2004Co-Authors: Jin Woo Park, J.m. Vitek, S. Suresh Babu, Stan A. DavidAbstract:In the present study, the effects of stray Grain Formation and thermomechanical stresses on solidification cracking in welds of single crystal Ni-base superalloys have been investigated. Welds were made in an asymmetric crystallographic orientation under three different processing conditions. As welding speed and power increased, stray Grain Formation became extensive, but only on one side of the weld. Solidification cracking also became more extensive and occurred mostly along the stray Grain boundaries. The three welding processes have been simulated using the finite element method (FEM). The calculation results showed that thermomechanical stresses increase with welding speed and power, leading to increased susceptibility to cracking. These results agree well with experimental observations.
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ANALYSIS OF STRAY Grain Formation IN SINGLE-CRYSTAL NICKEL-BASED SUPERALLOY WELDS
Superalloys 2004 (Tenth International Symposium), 2004Co-Authors: J.m. Vitek, S. Suresh Babu, Jin Woo Park, Stan A. DavidAbstract:The Formation of stray Grains during weld solidification of Rene N5, a single-crystal nickel-based superalloy, was studied. Experimental laser and electron-beam welds showed the extent of stray Grain Formation was sensitive to the welding conditions. It was also found that cracking is associated with the presence of stray Grains, and cracks follow along the stray-Grain high angle boundaries. Modeling was carried out to investigate the mechanism of stray Grain Formation and to predict the extent of stray Grains as a function of welding conditions and location within the weld. The effect of crystallographic orientation was also taken into account. It was found that the mechanism of constitutional supercooling for stray Grain Formation explained all of the experimental results. Modeling based on this mechanism indicated that welding conditions would have a very important influence on the extent of stray Grain Formation while crystallographic orientation had only a minor influence.
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To be presented at TMS2004, Solidification Processes and Microstructures: A Symposium in Honor of Prof. W. Kurz, March 14-18, 2004, Charlotte, North Carolina Stray Grain Formation in Nickel-Base Superalloy Single-Crystal Welds*
2004Co-Authors: J.m. Vitek, S. Suresh Babu, Stan A. DavidAbstract:During the welding of nickel-base superalloys, it is desirable to maintain the single crystal nature of the base material in the weldments. Stray Grain Formation during solidification destroys the single crystal structure and compromises properties. In addition, weld cracks form more easily along stray Grain boundaries. Kurz and Gaumann studied the stray Grain Formation tendencies in terms of the degree of constitutional supercooling ahead of the growing dendrites during weld solidification. Using the same ideas, the present work investigated the stray Grain Formation tendencies and cracking behavior in welds of Rene N5, a nickel-base single-crystal superalloy. The thermal behavior during welding was modeled and the extent of constitutional supercooling ahead of the growing interface was quantitatively evaluated. In addition, the dendrite orientation with respect to the moving solid-liquid interface was also taken into account. The results supported the mechanism proposed by Kurz for stray Grain Formation. The analysis provides insight into the conditions needed in order to minimize stray Grain Formation during welding of nickel superalloys.
Stan A. David - One of the best experts on this subject based on the ideXlab platform.
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Stray Grain Formation, thermomechanical stress and solidification cracking in single crystal nickel base superalloy welds
Science and Technology of Welding and Joining, 2004Co-Authors: Jin Woo Park, J.m. Vitek, S. Suresh Babu, Stan A. DavidAbstract:In the present study, the effects of stray Grain Formation and thermomechanical stresses on solidification cracking in welds of single crystal Ni-base superalloys have been investigated. Welds were made in an asymmetric crystallographic orientation under three different processing conditions. As welding speed and power increased, stray Grain Formation became extensive, but only on one side of the weld. Solidification cracking also became more extensive and occurred mostly along the stray Grain boundaries. The three welding processes have been simulated using the finite element method (FEM). The calculation results showed that thermomechanical stresses increase with welding speed and power, leading to increased susceptibility to cracking. These results agree well with experimental observations.
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ANALYSIS OF STRAY Grain Formation IN SINGLE-CRYSTAL NICKEL-BASED SUPERALLOY WELDS
Superalloys 2004 (Tenth International Symposium), 2004Co-Authors: J.m. Vitek, S. Suresh Babu, Jin Woo Park, Stan A. DavidAbstract:The Formation of stray Grains during weld solidification of Rene N5, a single-crystal nickel-based superalloy, was studied. Experimental laser and electron-beam welds showed the extent of stray Grain Formation was sensitive to the welding conditions. It was also found that cracking is associated with the presence of stray Grains, and cracks follow along the stray-Grain high angle boundaries. Modeling was carried out to investigate the mechanism of stray Grain Formation and to predict the extent of stray Grains as a function of welding conditions and location within the weld. The effect of crystallographic orientation was also taken into account. It was found that the mechanism of constitutional supercooling for stray Grain Formation explained all of the experimental results. Modeling based on this mechanism indicated that welding conditions would have a very important influence on the extent of stray Grain Formation while crystallographic orientation had only a minor influence.
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To be presented at TMS2004, Solidification Processes and Microstructures: A Symposium in Honor of Prof. W. Kurz, March 14-18, 2004, Charlotte, North Carolina Stray Grain Formation in Nickel-Base Superalloy Single-Crystal Welds*
2004Co-Authors: J.m. Vitek, S. Suresh Babu, Stan A. DavidAbstract:During the welding of nickel-base superalloys, it is desirable to maintain the single crystal nature of the base material in the weldments. Stray Grain Formation during solidification destroys the single crystal structure and compromises properties. In addition, weld cracks form more easily along stray Grain boundaries. Kurz and Gaumann studied the stray Grain Formation tendencies in terms of the degree of constitutional supercooling ahead of the growing dendrites during weld solidification. Using the same ideas, the present work investigated the stray Grain Formation tendencies and cracking behavior in welds of Rene N5, a nickel-base single-crystal superalloy. The thermal behavior during welding was modeled and the extent of constitutional supercooling ahead of the growing interface was quantitatively evaluated. In addition, the dendrite orientation with respect to the moving solid-liquid interface was also taken into account. The results supported the mechanism proposed by Kurz for stray Grain Formation. The analysis provides insight into the conditions needed in order to minimize stray Grain Formation during welding of nickel superalloys.
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Stray Grain Formation in single crystal Ni-base superalloy welds
Journal of Applied Physics, 2003Co-Authors: Jin Woo Park, J.m. Vitek, S. Suresh Babu, E. A. Kenik, Stan A. DavidAbstract:The effects of processing conditions and crystallographic orientation of growing dendrites on stray Grain Formation have been investigated in welds of single crystal Ni-base superalloys. The degree of constitutional supercooling (CS) at the solidification front has been used as a metric to quantify the effects. Numerical calculation results showed an appreciable effect of dendrite orientation on CS. For experimental verification, welds were made on a single crystal but in an asymmetric crystallographic orientation under three different processing conditions. Stray Grain Formation was observed to increase and become extensive on one side of the weld as power and welding speed increased. This result is in agreement with the calculated predictions and confirms that the degree of CS is a good metric.
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Mechanisms of equiaxed Grain Formation in ferritic stainless steel gas tungsten arc welds
Materials Science and Engineering: A, 1995Co-Authors: J.c. Villafuerte, H.w. Kerr, Stan A. DavidAbstract:Abstract Mechanisms of providing nuclei for equiaxed Grains in gas tungsten arc welds in ferritic stainless steel were examined. Tin-quenching of the solid-liquid interface revealed that TiN particles in commercial steels could act as heterogeneous nucleation sites. Direct additions of TiN also promoted an equiaxed region. However, no evidence for equiaxed Grain Formation by dendrite fragmentation was observed, despite the fact that titanium additions did produce a more branched dendritic structure.
Tianqi Huang - One of the best experts on this subject based on the ideXlab platform.
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Water and heat stresses during Grain Formation affect the physicochemical properties of waxy maize starch.
Journal of the science of food and agriculture, 2020Co-Authors: Jue Wang, Yuxiang Mao, Tianqi HuangAbstract:BACKGROUND Maize is frequently subjected to simultaneous water (drought or waterlogging) and heat (HS) stresses during Grain Formation in southern China. This work examined the effect of high temperature combined with drought (HD) or waterlogging (HW) during Grain Formation on the starch physicochemical properties of two waxy maize hybrids, namely Suyunnuo5 (SYN5) and Yunuo7 (YN7). RESULTS Heat stress enlarged the starch granule size, and water stresses aggravated this effect. Heat stress reduced the ratio of small molecular weight fractions for both hybrids, and HD aggravated this reduction only in SYN5. Relative crystallinity in SYN5 was increased by stresses but in YN7 it was unaffected by HD, reduced by HS, and increased by HW. Fourier-transform infrared (FTIR) spectrometry results showed that the 1045/1022 cm-1 ratio in SYN5 was not influenced by HW but was increased by other stresses, and that in YN7 it was increased by all stresses, with the highest value induced by HW. Peak viscosity was decreased, whereas gelatinization temperatures and retrogradation percentage were increased by all of these stresses. These effects were exacerbated by combined heat and water stresses. The maximum decomposition rate was severely increased by HW. CONCLUSION Drought or waterlogging at Grain Formation stage aggravated the detrimental effects of HS on the starch physicochemical properties of waxy maize. © 2020 Society of Chemical Industry.
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Effects of waterlogging at Grain Formation stage on starch structure and functionality of waxy maize
Food chemistry, 2019Co-Authors: Huan Yang, Zhangrong Wen, Tianqi HuangAbstract:Abstract The Grain Formation stage is a critical stage that affects Grain starch quality and frequently overlaps the rainy season in southern China for waxy maize production. Two waxy maize varieties were grown under control and waterlogging conditions during Grain Formation (1–15 days after pollination) to probe the effects of oversaturated soil moisture on starch structural and functional characteristics. Results indicated that waterlogging during Grain Formation decreased the size of starch granule, proportion of large granule (d > 15 μm) and ratio of medium-length chains (DP 10–24) in amylopectin, whereas the percentage of high-molecular-weight molecules were increased. Compared with the control, the percentage of ordered starch was increased by waterlogging for both varieties. The changes in starch internal structure under waterlogging had no influence on thermal stability, increased the maximum thermal decomposition ratio and pasting temperatures, and reduced pasting viscosity characteristics in both varieties.
Ruijun Long - One of the best experts on this subject based on the ideXlab platform.
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The cooperative relation between non-hydraulic root signals and osmotic adjustment under water stress improves Grain Formation for spring wheat varieties
Physiologia plantarum, 2008Co-Authors: Xian-wei Fan, You-cai Xiong, Ruijun LongAbstract:Non-hydraulic root signals (nHRS) and osmotic adjustment (OA) are two important adaptive responses of plants to water stress. There is little understanding of their relationships during water stress. The threshold range of soil water potential to occurrence of nHRS, the capacity for OA, Grain yield and water use efficiency (WUE) were examined in three spring wheat (Triticum aestivum L.) varieties (two bred after 1975 and one bred before 1900) under water stress conditions. The threshold range of nHRS was significantly correlated with the maintenance rate of Grain yield (MRGY) (r = 0.99, P < 0.05) under moderate drought (-0.49 to -0.55 MPa) but not under severe drought (-0.70 to -0.76 MPa). There were similar correlations between OA and the MRGY. However, regulation of nHRS precedes OA during gradual water stress. The threshold range of nHRS and OA was positively correlated (r = 0.93, P < 0.05), suggesting a mechanism for adapting to drought. WUE was higher for modern than for old varieties and was correlated with the root efficiency (full biomass weight including root per root weight, r = 0.78, P < 0.05) and the root water uptake efficiency (water consumption per root weight, r = 0.72, P < 0.05). However, there was a significant negative correlation between WUE and root weight (r = -0.84, P < 0.01). The cooperative relationship between the threshold range of nHRS and OA under water stress was beneficial for improving Grain Formation for spring wheat varieties.
A. Witztum - One of the best experts on this subject based on the ideXlab platform.
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The mechanism of spiral Grain Formation in trees
Wood Science and Technology, 2006Co-Authors: K. Schulgasser, A. WitztumAbstract:Spiral Grain in trees is formed during the process of cell division and maturation within the vascular cambium (sensu lato). Much effort in the past half century has been put into elucidating the mechanism(s) involved. The most accepted view is that the dominant factor involves the pseudotransverse cell divisions during anticlinal (multiplicative) division and subsequent intrusive growth of the daughter cells, the slant of the partition (S or Z) and the direction of the intrusion being statistically biased to the left or to the right. A strong correlation is known to exist between slant direction and its frequency of occurrence on the one hand and the rate of change of spiral Grain angle on the other hand. It is thus enticing to see the dominance of the orientation of the slant of the partition during pseudotransverse anticlinal cell division as the causative factor in the Formation of spiral Grain; the visual evidence seems clear. However, it will be shown that there is a constant, incessant tendency of all maturing cells (which are predominantly the result of periclinal divisions) to change their orientation in a given direction; this tendency will be modulated as to magnitude and direction by certain prevailing physical parameters of the system during the period of maturation. Thus it is concluded that neither the slant of pseudotransverse divisions nor other “isolated events” (imperfect periclinal division, biased intrusive growth) are causative, but that they rather result from the fact that there is a radial gradient of the inclination angle (in the tangential plane) of fusiform cells, i.e. from the general tendency of a maturing cell to take on a preferred inclination with respect to the cell which immediately preceded it in its file. Growth stress patterns in trees have also been extensively investigated in the past half century. It is shown that the development of these stresses and the Formation of spiral Grain are just two aspects of the same process occurring throughout the cambial zone during cell maturation. Models are presented to justify this claim which accord with reported patterns of growth stress and spiral Grain in conifers.
