The Experts below are selected from a list of 816 Experts worldwide ranked by ideXlab platform
Antonios Zavaliangos - One of the best experts on this subject based on the ideXlab platform.
-
a comparative characterization of near equiaxed microstructures as produced by spray casting magnetohydrodynamic casting and the stress induced melt activated process
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: Evangelos Tzimas, Antonios ZavaliangosAbstract:The near-equiaxed microstructure of wrought and cast aluminum alloys as produced by the most common methods used to provide material for subsequent Semisolid Processing, is examined. More specifically, the grain size and degree of spheroidization of alloys produced by spray casting, magnetohydrodynamic (MHD) casting and the stress induced, melt activated (SIMA) process are characterized and compared. It is shown that the microstructure of alloys with the same composition differs significantly when produced by the three methods, showing the influence of the production method. Spray casting and the SIMA process result in a microstructure with perfectly equiaxed grains that is inherently suitable for Semisolid Processing, while MHD-cast alloys exhibit a non-uniform initial microstructure, with dendritic features dominant at the perimeter of the casting. Finally, the mechanisms responsible for the formation of near-equiaxed microstructure for each method are investigated.
-
Evaluation of volume fraction of solid in alloys formed by Semisolid Processing
Journal of Materials Science, 2000Co-Authors: Evangelos Tzimas, Antonios ZavaliangosAbstract:Three of the methods used to determine the volume fraction of solid as a function of temperature in alloys in the Semisolid state, namely utilization of thermodynamic data, thermal analysis, and quantitative metallography on quenched microstructures, are studied. The accuracy of each method is evaluated and the advantages and limitations are recognized. It is demonstrated that, while all methods are approximate, they offer distinct and different advantages.
-
Materials Selection for Semisolid Processing
Materials and Manufacturing Processes, 1999Co-Authors: Evangelos Tzimas, Antonios ZavaliangosAbstract:Abstract The mechanical behavior of alloys in the Semisolid state is very sensitive to the volume fraction of solid. In this paper, a simple criterion for processability in the Semisolid range is introduced, based on the sensitivity of the volume fraction of solid with respect to minor temperature variations. In addition it is proposed that the processability in the Semisolid state can be enhanced using microsegregated material.
-
Modeling of the mechanical behavior of Semisolid metallic alloys at high volume fractions of solid
International Journal of Mechanical Sciences, 1998Co-Authors: Antonios ZavaliangosAbstract:A two-phase strain rate and pressure-dependent model that describes the mechanical behavior of Semisolid materials at high volume fractions of solid as an interpolation between the limits of fully cohesive and fully cohesionless materials is presented. An internal variable that describes the degree of cohesion in the material is introduced. The proposed model predicts a reduction of the stress required to sustain undrained constant strain rate deformation. From numerical simulations it is shown that high strain rates result in near-undrained conditions and minimal phase segregation. This effect has important consequences in Semisolid Processing operations.
Helen V. Atkinson - One of the best experts on this subject based on the ideXlab platform.
-
Does Shear Thickening Occur in Semisolid Metals?
Metallurgical and Materials Transactions A, 2016Co-Authors: Helen V. Atkinson, Veronique FavierAbstract:In the various forms of Semisolid Processing such as thixoforming and thixoforging, the entry into the die occurs in a fraction of a second so it is the transient rheological behavior which governs the initial stages of flow. In experiments in the literature, this rheological behavior is probed through applying rapid transitions in shear rate under isothermal conditions. There is contradictory evidence as to whether the behavior during these transitions is shear thinning or shear thickening, although it is clear that once in the die the material is thinning. Here the data in the literature are reanalyzed to obtain a rationalization of the contradictions which has not previously been available. It is argued that if a suspension is initially in a disagglomerated state ( i.e., one which is initially sheared), the instantaneous behavior with a jump-up in shear rate is shear thickening (even if the long-term steady-state behavior is shear thinning) provided the fraction solid is greater than about 0.36 and the final shear rate at the end of the jump is greater than about 100 s^−1. If the jump-up in shear rate is made from rest then yield masks the shear thickening.
-
Semisolid Processing of metallic materials
Materials Science and Technology, 2010Co-Authors: Helen V. AtkinsonAbstract:AbstractSemisolid Processing involves forming metallic alloys between the solidus and the liquidus. For the process to operate, the microstructure must consist of solid spheroids in the liquid matrix, rather than dendrites. The material then flows when it is sheared but thickens again when allowed to stand, i.e. it behaves thixotropically. This type of behaviour was first discovered by Flemings and co-workers in the 1970s and is utilised in a family of processes, some now applied commercially. Here, the current status of Semisolid Processing, both technologically and from a research point of view, will be reviewed.
-
Semi-solid Processing of Alloys
2009Co-Authors: D. H. Kirkwood, Helen V. Atkinson, Michel Suéry, Plato Kapranos, Kenneth P. YoungAbstract:EVOLUTION AND DESIGN OF MICROSTRUCTURE IN Semisolid ALLOYS.- Fundamental Aspects.- Characterization of Microstructure in Semisolid Slurries.- Evolution of Microstructure in Semisolid Alloys During Isothermal Holding (Soaking).- Recent Developments in Slurry Formation.- RHEOLOGY AND MODELING.- and Definitions for Rheology and Modeling.- Experimental Determination of Rheological Behavior.- Modeling of Semisolid Processing.- General Conclusions on Rheology and Modeling.- INDUSTRIAL APPLICATIONS OF Semisolid Processing.- to Industrial Applications of Semisolid Processing.- Raw Material.- Process Control in Die Filling and Die Design.- Component Design Rules.- Practical Applications in Use Today.- The Future.
-
Modeling of Semisolid Processing
Semi-solid Processing of Alloys, 2009Co-Authors: D. H. Kirkwood, Helen V. Atkinson, Michel Suéry, Plato Kapranos, Kenneth P. YoungAbstract:Computational fluid dynamics (CFD) can be used to predict die filling. However, input parameters must be obtained from rheological experiments (see Chap. 6. In some cases, the data that has been used is from steady state experiments, where the material has been maintained at a particular shear rate for some time. In cases where the process involves taking material from rest into the die in a fraction of a second, it is difficult to see how this can be appropriate. The material changes viscosity by several orders of magnitude in that fraction of a second [23, 32]. Observations of transient rheological behavior under rapid changes in shear rate are therefore more relevant for input data for modeling. Modeling of Semisolid Processing is generally continuum modeling, where the macroscopic behavior is predicted with the internal structure represented by a few internal variables. Continuum modeling for Semisolid can be categorized into onephase or two-phase and as finite difference or finite element. In one-phase modeling, a single non-Newtonian equation of state for the viscosity takes into account the interrelationship between the liquid and the solid through the way in which they behave when they are in combination. In two-phase modeling, each individual phase (the liquid matrix or the solid particles) is characterized with separate equations. The two-phase approach is more complicated, requires significantly higher computational time and much higher effort on obtaining the experimental parameters for input. It is, however, more physically realistic and does allow for important (and undesirable) phenomena, such as liquid segregation to be modeled. Liquid segregation is where liquid gathers in one part of the component in preference to another during Processing. Figure 7.1 shows a classic but extreme example. The material is being forced vertically upwards into a die and has to flow around a corner to reach the end of the die. The sharp corner (the dotted line in the inset shows the die shape) causes the liquid to separate from the solid and to gather in one place. In the micrograph, the quenched liquid is dark gray in comparison with the solid. The die has not filled properly. Liquid segregation is deleterious, leading, for example, to inhomogeneous mechanical properties after solidification.
-
Introduction to Industrial Applications of Semisolid Processing
Semi-solid Processing of Alloys, 2009Co-Authors: D. H. Kirkwood, Helen V. Atkinson, Michel Suéry, Plato Kapranos, Kenneth P. YoungAbstract:Semisolid metal (SSM) Processing is a hybrid technology combining features of both casting and forging that enables the production of near net-shape components of superior properties and surface finish. It was developed, from a discovery made at the Massachusetts Institute of Technology in the early 1970s, by Spencer et al. [1] that stirring of alloys during solidification led to a change in the solidifying microstructure resulting not only in a dramatic lowering of the apparent viscosity of the Semisolid slurry, but also facilitating two-phase homogeneous flow at quite high fractions solid. More detail of this discovery and the effects of shear rate cooling rate and fraction solid can be found in Part II. The process of stirring alloys during solidification to produce non-dendritic solid within a slurry, and then injecting this slurry directly into a die as in liquid metal die casting, was called “rheocasting” by the MIT researchers and that name has largely stuck. Rheocasting started out as the preferred process route for industrial production and a new company formed byMIT and a group of industrial partners “Rheocast Corp.” designed and built several large-scale rheocasters for production of both aluminium and copper-base alloys. The first major customer of the technology and for the large-scale rheocasters produced by Rheocast Corp. was International Telephone and Telegraph (ITT) Corp.
Rubens Caram - One of the best experts on this subject based on the ideXlab platform.
-
Observations on the compression properties of Semisolid Ti–Cu alloys
Journal of Materials Research and Technology, 2020Co-Authors: Kaio Niitsu Campo, Caio Chaussê De Freitas, Dalton Daniel De Lima, Rubens CaramAbstract:Abstract Ti–Cu alloys are considered viable candidates for thixoforming (Semisolid Processing) due to their solid–to–liquid transitions and good microstructural properties. In the present study, the deformation behavior of these alloys in the Semisolid state has been investigated by performing hot compression tests on Ti–(25, 27, 29)Cu samples isothermally treated at 1035 °C for 300 s. In general, relatively low loads were applied to deform samples with globular microstructure, which decreased with increasing liquid fraction (Cu content). In contrast, dendritic samples required much higher loads; the resulting materials were significantly more heterogeneous and contained large numbers of microstructural defects. At applied compression velocities of 4, 8, and 16 mm s−1, the strain rate had little effect on the response of the globular material; however, longer isothermal heat treatments significantly reduced the compression load due to globularization enhancement. The obtained results suggest potential applicability of Ti–Cu alloys for Semisolid Processing.
-
rapid quenching of Semisolid ti cu alloys insights into globular microstructure formation and coarsening
Acta Materialia, 2017Co-Authors: Kaio Niitsu Campo, Catherine J Parrish, E S N Lopes, Rubens CaramAbstract:Abstract Thixoforming is a typical Semisolid Processing route for the production of affordable near-net shape metallic components. In this study, Ti-Cu alloys specifically designed for thixoforming were evaluated to determine their microstructural evolution in the Semisolid state. Ti-(25, 27, 29)Cu (wt.%) alloys were prepared by voltaic arc melting, homogenized, and then hot worked prior to isothermal heat treatment at 1035 °C. Rapid quenching allowed for the investigation of “frozen” Semisolid microstructures. The results indicated the formation of fine grained globular microstructures in all the alloys under study. This was attributed to the deformation process, which was able to break up the dendrites resulting from solidification. The liquid fraction increased with Cu content and its values were consistent with those predicted under equilibrium, although evidence of some nonequilibrium liquid was still present during the time period of analysis. Lastly, coarsening rate constants ( K ) exhibited low values, indicating stable Semisolid microstructures.
Kaio Niitsu Campo - One of the best experts on this subject based on the ideXlab platform.
-
Observations on the compression properties of Semisolid Ti–Cu alloys
Journal of Materials Research and Technology, 2020Co-Authors: Kaio Niitsu Campo, Caio Chaussê De Freitas, Dalton Daniel De Lima, Rubens CaramAbstract:Abstract Ti–Cu alloys are considered viable candidates for thixoforming (Semisolid Processing) due to their solid–to–liquid transitions and good microstructural properties. In the present study, the deformation behavior of these alloys in the Semisolid state has been investigated by performing hot compression tests on Ti–(25, 27, 29)Cu samples isothermally treated at 1035 °C for 300 s. In general, relatively low loads were applied to deform samples with globular microstructure, which decreased with increasing liquid fraction (Cu content). In contrast, dendritic samples required much higher loads; the resulting materials were significantly more heterogeneous and contained large numbers of microstructural defects. At applied compression velocities of 4, 8, and 16 mm s−1, the strain rate had little effect on the response of the globular material; however, longer isothermal heat treatments significantly reduced the compression load due to globularization enhancement. The obtained results suggest potential applicability of Ti–Cu alloys for Semisolid Processing.
-
rapid quenching of Semisolid ti cu alloys insights into globular microstructure formation and coarsening
Acta Materialia, 2017Co-Authors: Kaio Niitsu Campo, Catherine J Parrish, E S N Lopes, Rubens CaramAbstract:Abstract Thixoforming is a typical Semisolid Processing route for the production of affordable near-net shape metallic components. In this study, Ti-Cu alloys specifically designed for thixoforming were evaluated to determine their microstructural evolution in the Semisolid state. Ti-(25, 27, 29)Cu (wt.%) alloys were prepared by voltaic arc melting, homogenized, and then hot worked prior to isothermal heat treatment at 1035 °C. Rapid quenching allowed for the investigation of “frozen” Semisolid microstructures. The results indicated the formation of fine grained globular microstructures in all the alloys under study. This was attributed to the deformation process, which was able to break up the dendrites resulting from solidification. The liquid fraction increased with Cu content and its values were consistent with those predicted under equilibrium, although evidence of some nonequilibrium liquid was still present during the time period of analysis. Lastly, coarsening rate constants ( K ) exhibited low values, indicating stable Semisolid microstructures.
Yucel Birol - One of the best experts on this subject based on the ideXlab platform.
-
Testing of a novel CrNiCo alloy for tooling applications in semi-solid Processing of steels
International Journal of Material Forming, 2010Co-Authors: Yucel BirolAbstract:Semisolid Processing which has become a well established manufacturing route for the production of intricate, thin-walled aluminium and magnesium parts with mechanical properties as good as forged grades, faces a major challenge in the case of steels. The tool materials must withstand the complex load profile and relatively higher forming temperatures which promote chemical interaction with steel slurries. Thixoforming tools ought to last thousands of forming cycles for industrial application to be attractive. Hot work tool steel dies proved to be entirely inadequate when thixoforming steels. In spite of extensive research on tool materials for the Semisolid Processing of steels, there is yet no material to fulfil this critical role. The present work was undertaken to explore the potential of a novel CrNiCo alloy as the tooling material in Semisolid Processing of steel.
-
A CrNiCo Alloy as a Potential Tool Material in Semi‐solid Processing of Steels
Steel Research International, 2009Co-Authors: Yucel BirolAbstract:Semisolid Processing of aluminium and magnesium alloys has matured to become a well established manufacturing route for the production of intricate, thin-walled parts with mechanical properties as good as forged grades. However, this innovative forming technology faces a major challenge in the case of steels. The tool materials must withstand the complex load profile and relatively higher forming temperatures which promote chemical interaction with steel slurries. Thixoforming tools ought to last thousands of forming cycles for industrial application to be attractive. Hot work tool steel dies proved to be entirely inadequate when thixoforming steels. In spite of extensive research on tool materials for the Semisolid Processing of steels, there is yet no material to fulfil this critical role. The present work was undertaken to explore the potential of a novel CrNiCo alloy as the tooling material in Semisolid Processing of steel.
-
Semisolid Processing of near-eutectic and hypereutectic Al-Si-Cu alloys
Journal of Materials Science, 2008Co-Authors: Yucel BirolAbstract:Semisolid Processing of near-eutectic and hypereutectic versions of alloy 380 offers to overcome the problems encountered in casting hypereutectic Al–Si alloys and was thus explored in the present work. Experimental near-eutectic and hypereutectic Al–Si–Cu alloys obtained by adding elemental silicon to the 380 alloy were melted and were cooled to within 5 to 15 °C of their liquidus points before they were poured into a permanent mould in order to produce non-dendritic feedstock for thixoforming. This low superheat casting (LSC) process largely replaced α-Al dendrites with relatively smaller α-Al rosettes in all alloys. The slugs machined from the LSC ingots thus obtained were thixoformed after they were heated in situ in the Semisolid range, between 568 and 573 °C, for 5 min in a laboratory press. Semisolid soaking sufficed to produce the required globular structure even when some dendritic features were retained in the starting feedstock. The hardness of the thixoformed parts which ranged between 84 and 96 HB have increased to 121–131 HB after the T6 heat treatment, implying a considerable age-hardening potential. The T6 treatment also improved the morphology of the eutectic silicon with potential benefits regarding the ductility of the thixoformed part.
-
Microstructural Evolution of ETIAL 160 Aluminium Alloy Feedstock Produced by Cooling Slope Casting
Solid State Phenomena, 2008Co-Authors: Nursen Saklakoglu, Yucel Birol, Şefika KasmanAbstract:Owing to its superior flow and mould-filling capability, a fully globular structure is essential for Semisolid Processing technologies. The present work was undertaken to identify the cooling slope casting process parameters that, upon heating to the Semisolid state, gives the required globular structure for the ETIAL 160 alloy. Of the two pouring temperatures investigated, 605 °C and 615 °C, the lower pouring temperature was found to provide more globular grains surrounded by liquid phases.
