Showing papers on "Equiaxed crystals published in 2015"
TL;DR: In this paper, columnar to equiaxed transitions during solidification were used to promote the growth of highly misoriented micron scale grains outlining the letters D, O and E, through the thickness of a 25·4 mm tall bulk block comprised of primarily columnar oriented grains made of the nickel base superalloy Inconel 718.
Abstract: Site specific control of the crystallographic orientation of grains within metal components has been unachievable before the advent of metals additive manufacturing (AM) technologies. To demonstrate the capability, the growth of highly misoriented micron scale grains outlining the letters D, O and E, through the thickness of a 25·4 mm tall bulk block comprised of primarily columnar [001] oriented grains made of the nickel base superalloy Inconel 718 was promoted. To accomplish this, electron beam scan strategies were developed based on principles of columnar to equiaxed transitions during solidification. Through changes in scan strategy, the electron beam heat source can rapidly change between point and line heat source modes to promote steady state and/or transient thermal gradients and liquid/solid interface velocity. With this approach, an equiaxed solidification in the regions bounding the letters D, O and E was achieved. The through thickness existence of the equiaxed grain structure outlinin...
424 citations
TL;DR: In this paper, the grain morphology evolution behaviors of laser-deposition titanium alloy components were investigated via basic study on solidification nucleation and growth mechanisms of the local melt pool during the layer-by-layer deposition process.
373 citations
TL;DR: In this paper, a polycrystalline Ni (99.882% purity) bar sample was subjected to surface mechanical grinding treatment (SMGT) at ambient temperature, and 2-dimensional laminated structures with low angle boundaries and strong deformation textures were formed of which the average thickness is ∼20nm.
152 citations
TL;DR: In this article, the anisotropy of laser melting deposition additive manufacturing Ti−6.5Al−3.5Mo−1.5Zr−0.3Si was studied by microstructure observation and room tensile properties testing.
127 citations
TL;DR: In this article, the role of constitutional supercooling in grain nucleation and grain formation is discussed and a comprehensive description of the mechanisms affecting grain formation and prediction of grain size is presented with reference to the influence of the casting conditions applied during the practical casting of an alloy.
Abstract: The concept of constitutional supercooling (CS) including the term itself was first described and discussed qualitatively by Rutter and Chalmers in order to understand the formation of cellular structures during the solidification of tin, and then quantified by Tiller et al. On that basis, Winegard and Chalmers further considered ‘supercooling and dendritic freezing of alloys’ where they described how CS promotes the heterogeneous nucleation of new crystals and the formation of an equiaxed zone. Since then the importance of CS in promoting the formation of equiaxed microstructures in both grain refined and unrefined alloys has been clearly revealed and quantified. This paper describes our current understanding of the role of CS in promoting nucleation and grain formation. It also highlights that CS, on the one hand, develops a nucleation-free zone surrounding each nucleated and growing grain and, on the other hand, protects this grain from readily remelting when temperature fluctuations occur due to convection. Further, due to the importance of the diffusion field that generates CS, recent analytical models are evaluated and compared with a numerical model. A comprehensive description of the mechanisms affecting nucleation and grain formation and the prediction of grain size is presented with reference to the influence of the casting conditions applied during the practical casting of an alloy.
114 citations
TL;DR: In this article, a multiple-layer laser cladding of 308L stainless steel was obtained by a fiber laser using a way of wire feeding to repair the surface scrapped or erosive parts of 316 l stainless steel.
101 citations
15 Jul 2015-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the 1.8mm thick cold-rolled sheets of 2198-T8 Al-Li alloy were manufactured by friction stir welding (FSW) at a rotation rate of 800 rpm and a travel speed of 300 mm/min.
Abstract: In this study, the 1.8 mm thick cold-rolled sheets of 2198-T8 Al–Li alloy were manufactured by friction stir welding (FSW) at a rotation rate of 800 rpm and a travel speed of 300 mm/min. The microstructure and mechanical properties of different regions of the produced joint were evaluated by means of optical microscopy (OM), transmission electron microscopy (TEM), hardness testing and tensile testing. Results show that the original “pancake” grains became coarser in the heat affected zone (HAZ), transformed into equiaxed grains in the stir shoulder zone (SsZ) and stir pin zone (SpZ), and formed mixed grains with both “pancake” and equiaxed shapes in the thermo-mechanical affected zone (TMAZ). The hardness distribution in the cross-section of the FSW joint exhibited a “basin” shape. When approaching the weld centre, the hardness gradually decreased compared to the base metal (BM). The BM exhibited the highest strength due to the presence of fine T1 phase. In the HAZ, the strength decreased as T1 phase was partially dissolved. In the SsZ and SpZ, in spite of strength contribution from grain refinement, the strength further decreased as T1 phase was fully dissolved. The minimum strength in the TMAZ was related to the reduced amount of T1 phase and the presence of transition layer with sharp gradient of grain size.
85 citations
TL;DR: In this paper, high-resolution electron-backscatter diffraction was used to study the effect of welding temperature on the microstructure, texture, and strength of friction-stir welded aluminum.
Abstract: High-resolution electron-backscatter diffraction was used to study the effect of welding temperature on the microstructure, texture, and strength of friction-stir welded aluminum. In all cases, the grain structure development was shown to be primarily governed by continuous recrystallization, although discontinuous recrystallization may also play a role at relatively high temperatures. An increase in welding temperature was shown to lead to transformation of the morphology of the deformation-induced substructure from lamellar type to equiaxed type. This was deduced to alter strain compatibility requirements and thus change the texture from $$ C\{ 001\} \langle 110\rangle $$
to $$ B/\bar{B}\{ 112\} \langle 110\rangle $$
.
82 citations
TL;DR: In this paper, an ultrafine grained Ti-based composites with equiaxed microstructure were fabricated by sintering and crystallizing from glassy powder precursors.
82 citations
TL;DR: In this paper, the microstructures and mechanical properties of homogenized-rolled AA5052 aluminum alloys with different rolling reductions and following annealing treatments were investigated by optical microscope, scanning electron microscope, X-ray diffractometer, micro-hardness and tensile tests.
78 citations
TL;DR: An approach involving grain refinement through three-stages of cold rolling and annealing was explored with 304 austenitic stainless steel to obtain ultrahigh strength as mentioned in this paper, which was obtained with a desirable combination of strength and moderate ductility.
TL;DR: In this paper, the effect of Mo content on the microstructures and mechanical properties of Al2CrFeNiMo fixme x¯¯ coatings was studied and the results showed that the laser clad layer consists of the cladding zone, bonding zone, and heat-affected zone.
Abstract: A series of Al2CrFeNiMo
x
(x = 0 to 2.0 at.%) high-entropy alloys coatings was synthesized on stainless steel by laser cladding. The effect of Mo content on the microstructures and mechanical properties of Al2CrFeNiMo
x
coatings was studied. The results show that the laser clad layer consists of the cladding zone, bonding zone, and heat-affected zone. The Al2CrFeNiMo
x
coatings are composed of two simple body-center cubic phases and the cladding zone is mainly composed of equiaxed grains. When the content of Mo reaches 2 at.%, a eutectic structure is found in the interdendritic regions. The surface microhardness of the Al2CrFeNiMo2 coating is 678 HV, which is about three times higher than that of the substrate (243 HV). Compared with stainless steel, the wear resistance of the coatings has been improved greatly. The wear mass loss of the Al2CrFeNiMo alloy is 9.8 mg, which is much less than that of the substrate (18.9 mg) and its wear scar width is the lowest among the Al2CrFeNiMo
x
coatings, indicating that the wear resistance of the Al2CrFeNiMo is the best.
05 Jan 2015-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of heating rate on the mechanical properties, microstructure and texture of Al-Mg-Si-Cu alloy during solution treatment was investigated through tensile testing, scanning electron microscope, scanning transmission electron microscope and metallographic observation and EBSD measurement.
Abstract: The effect of heating rate on the mechanical properties, microstructure and texture of Al–Mg–Si–Cu alloy during solution treatment was investigated through tensile testing, scanning electron microscope, scanning transmission electron microscope, metallographic observation and EBSD measurement. The experimental results reveal that there are great differences in the mechanical properties, microstructures and textures after the solution treatment with two different heating rates. Compared with the alloy sheet solution treated with slow heating rate, the alloy sheet solution treated with rapid heating rate possesses weak mechanical property anisotropy and higher average r value. The equiaxed grain is the main recrystallization microstructure for the case of rapid heating rate, while the elongated grain appears in the case of slow heating rate. The texture components are also quite different in the two cases, Cube ND orientation is the main texture component for the former case, while the latter one includes Cube, R, Goss, P and Brass orientations. The relationship between r value, texture components and microstructure has also been established in this paper.
TL;DR: In this article, the authors reported a novel microstructure consisting of fine and oxygen hardened equiaxed α grains, formed by solution treatment, quenching and aging of a Ti-6Al-4V (wt.%) alloy with a relatively high oxygen content of 0.52% and produced by powder compact forging.
TL;DR: In this paper, the crystallization behavior of Zr55Cu30Al10Ni5 bulk amorphous alloy during laser solid forming (LSF) was analyzed, and it was found that the as-deposited microstructure exhibited a series of phase evolutions from the molten pool to the HAZ.
TL;DR: In this article, the effect of buoyancy on grain motion, nucleation density, and average grain size was investigated in situ with laboratory-based radiography, where the ability to align the X-ray beam axis both perpendicular and parallel to the gravity vector provided limited control over buoyant grain motion normally associated with terrestrial solidification.
TL;DR: In this article, the microstructure of the stir zone exhibited inhomogeneous distribution along the plate thickness due to the temperature gradient caused by the lower thermal conductivity, and the change in texture is also quite consistent with the micro-structure distributions.
TL;DR: In this article, the performance characteristics of VO2 films with different microstructures in an oxidation environment were analyzed and the results reveal the correlation of micro-structures and performances of the VO2 materials.
TL;DR: In this paper, the authors studied the hot deformation behavior of in situ 5-wt.% nano ZrB 2 /2024Al composite at deformation temperatures of 350-450°C and strain rates of 0.001-10−s −1.
TL;DR: The non-equiatomic FeCoNiAlSi alloy is prepared by the Bridgman solidification (BS) technique at different withdrawal velocities (V = 30, 100, and 200μm/s) as discussed by the authors.
TL;DR: In this article, three types of initial microstructures, which have different densities of the high angle boundaries, were joined by friction stir welding (FSW), and the microstructure evolution in the stir zone by the FSW was clarified.
TL;DR: In this paper, the authors investigated the relationship between the failure mechanism and the microstructural features of the Ti-6Al-4V targets and found that in the equiaxed microstructure, the regularly spaced propagating features of adiabatic shear bands facilitated ductile hole enlargement.
TL;DR: In this paper, the effect of ultrasonic irradiation on the solidification microstructure of hypo- and hyper-eutectic Al-Si alloys was investigated.
TL;DR: In this paper, a 3D numerical model coupling the electromagnetic field, fluid flow, heat transfer and solidification phenomena was developed to simulate the 160mm × 160mm billet continuous casting process of SWRT82B steel with dual electromagnetic stirrings of mold and the final solidification.
Abstract: A 3D numerical model coupling the electromagnetic field, fluid flow, heat transfer and solidification phenomena was developed to simulate the 160 mm × 160 mm billet continuous casting process of SWRT82B steel with dual electromagnetic stirrings of mold and the final solidification. The columnar region was treated as a porous zone and a generalized approach was used to calculate permeability, while for the equiaxed zone, a variable apparent viscosity model was applied to simulate the fluid flow at the initial growing stage of equiaxed dendrite. The model was validated by the measured data of magnetic induction intensity in the stirrer center and strand surface temperature. The results show that it is indispensable to consider the solidification phenomenon in the mold zone with EMS, as the fluid flow mechanism near the meniscus is quite different. With the current intensity of M-EMS and F-EMS increasing, the tangential velocity of molten steel rises and the central temperature decreases. As the F-EMS is applied, the nature convection mechanism is destroyed and the temperature is promoted to distribute evenly in the mushy zone. Moreover, the results show that the coherent solid fraction has a significant effect on the temperature distribution and the fluid flow in F-EMS zone.
TL;DR: In this paper, the effect of trace TiB2 addition on the solidification microstructure of Ti-48Al-2Cr-2Nb+(0.18, 0.54, 09) wt.% alloys was investigated by arc melting and electromagnetic levitation melting.
TL;DR: In this article, grain refinement was achieved in aluminium welds through additions of grain refiner to the weld metal, which led to a decrease of the welding metal mean grain size.
Abstract: Grain refinement is an important opportunity to improve mechanical properties of fusion welds and the weldability (susceptibility to solidification cracking) of the base metal. In this study, grain refinement was achieved in aluminium welds through additions of grain refiner to the weld metal. Increasing grain refiner additions led to a decrease of the weld metal mean grain size (down to −86 %). The grain refinement efficiency was the highest in commercial pure Al (Alloy 1050A, Al 99.5), followed by Alloy 6082 (Al Si1MgMn) and Alloy 5083 (Al Mg4.5Mn0.7). To investigate this clear influence of alloy content on grain size, the undercooling parameters P and Q were calculated. Temperature measurements revealed that solidification parameters such as solidification growth rate or cooling rate vary significantly along the solidification front, dependent upon torch speed and alloy. On the basis of this comparison, an analytical approach was used to model the columnar to equiaxed transition (CET). Moreover, wavelength dispersive X-ray spectroscopy (WDS) and transmission electron microscopy (TEM) analyses revealed particles rich in Ti and B that are probably TiB2 particles coated by Al3Ti nucleating Al grains during solidification. Also, Ti/B contents needed in commercial filler wires to allow optimum weld metal grain refinement were calculated dependent upon base alloy and welding process.
TL;DR: The results indicate that the proposed ultrasonic vibration-assisted laser processing can be designed for efficient material removal (laser machining) and improved equiaxed microstructure (l laser surface modifications) during materials processing.
TL;DR: The numerical study of grid sensitivity indicates that the global segregation pattern and CET are not significantly affected by grid size; however, some fine details of the segregation map which are predicted by fine grid are smeared or locally averaged by the coarse grid.
TL;DR: The microstructure of cold-sprayed Ti-6Al-4V is unlike the structure resulting from any other processing technique as mentioned in this paper, which is derived from the solid state thermomechanical processing of predominantly martensitic feedstock powders.
Abstract: The microstructure of cold-sprayed Ti-6Al-4V is unlike the structure resulting from any other processing technique. The unique characteristics are derived from the solid state thermomechanical processing of predominantly martensitic feedstock powders. During deposition, these powders undergo high strain rate deformation, leading to shear band-induced transformation of martensitic grains into nano-scale martensite, equiaxed alpha structures, and nanostructured alpha grains. The resultant microstructure evolution is dependent on the magnitude and direction of shear undergone by the particles. The specific structure and mechanism for formation of these regions will be discussed in detail using nanohardness mapping, scanning electron microscopy, and transmission electron microscopy.
TL;DR: In this article, a new type of Al-Zn-Mg-Cu alloy sheets with T6 temper were welded by laser beam welding (LBW), and microstructure characteristics and mechanical properties of the joints were evaluated.