Last. Peter K. Liaw(UT: University of Tennessee)H-Index: 94
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The improvement of the creep properties of single-crystal superalloys is always strongly motivated by the vast growing demand from the aviation, aerospace, and gas engine. In this study, a static magnetic-field-assisted solidification process significantly improves the creep life of single-crystal superalloys. The mechanism originates from an increase in the composition homogeneity on the multiscales, which further decreases the lattice misfit of γ/γ′ phases and affects the phase precipitation. ...
It is well known that the growth and motion of equiaxed crystals govern important microstructural features, especially in larger castings such as heavy ingots. To determine the origin of the equiaxed crystals, heterogeneous nucleation, and/or fragmentation of dendrite arms from columnar regions are often discussed. In the present study, we demonstrate that under certain conditions relatively large areas of mushy regions slide downward and form spectacular crystal avalanches. These avalanches cru...
Experimental data for the validation of numerical models coupling solidification and hydrodynamics are very rare. Many experiments made in the field of solidifications are performed with pure metals or alloys (Al-Cu, Pb-Sn, etc) which are opaque and do not allow direct observation of the hydrodynamic. Only the results related to solidification such as grain size and orientation, or macro-segregation are usually used for the validation. The present paper is dedicated to the description of well-co...
In order to better understand the geometrical effect on freckle formation in superalloys, samples with uniform increases and decreases in their cross sections were directionally solidified in a Bridgman furnace. In comparison to our conventional knowledge, some new features of freckle appearance have been observed. Freckles could occur at sloped surfaces where the freckle pattern is no longer roughly parallel to the direction of gravity but has the same slope as the surface. At significantly ang...
Last. Menghuai Wu(University of Leoben)H-Index: 27
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A two-camera Particle Image Velocimetry (PIV) technique is applied to study the flow pattern and the equiaxed crystal motion during an equiaxed/columnar solidification process of Ammonium Chloride in a die cast cell. This technique is able to measure simultaneously the liquid and the equiaxed grain velocity pattern as already shown in Part I of this paper. The interaction between the equiaxed grains and the melt flow was explored by means of relative velocities. In single isolated configurations...
#1Yang-Cheng Shih(NTUT: National Taipei University of Technology)H-Index: 10
#2Su-Min Tu(NTUT: National Taipei University of Technology)H-Index: 1
Last. Cheng-Chi Chiu(NTUT: National Taipei University of Technology)H-Index: 2
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Abstract In the past, one main area of focus in the solidification of a liquid binary alloy has been the investigation of strategies for the elimination or minimization of the presence of “double-diffusive convection”, the main cause of poor quality alloys. In particular, “freckles” occurring in the solidification process cooled from the bottom can result in severe material defects in the final product. The objective of this study is to investigate the effect of a periodic lid-driven flow on the...
#2Peter D. Lee(University of Manchester)H-Index: 76
Abstract Freckle formation was directly simulated in three dimensions with a microstructure level model for unidirectional solidified Pb–Sn alloys. The microscale solidification model resolves the complex interaction of solute partition, interdendritic thermosolutal convection, dendrite formation and remelting. These simulations show that it is competition between all off these phenomena at the microstructural level that determines both the initiation and survival of solute channels and, hence, ...
A series of directional solidification experiments with superalloy CMSX-4 was carried out with various surface profiles. The results obtained clearly demonstrate the influence of surface features on the occurrence of freckles. The rough surfaces exhibit less freckling tendencies than smooth surfaces. For a notch depth larger than the critical layer beneath the surface, the freckle formation can be completely suppressed. The freckle formation is not only a surface defect but can initiate the occu...
Abstract This study focuses on the flow-solidification interaction during the solidification of NH4Cl – 70.43 wt.%H2O solution in a water-cooled mould with a large sample thickness (100 × 80 × 10 mm3). First part of the paper is to use a volume-average-based dendritic solidification model to reproduce an experiment in which transient flow is monitored in-situ using particle image velocimetry, and the solidification sequence is recorded with a light camera. The striking features of the solidifica...