Numerical Simulations of Microstructural Evolution of Lamellar Alloys: Applications to Pb-Sn Solder

2002 ◽  
Vol 731 ◽  
Author(s):  
Rifa J. El-Khozondar ◽  
Vitcheslav S. Solomatov ◽  
Veena Tikare
Keyword(s):  
Microstructural Evolution ◽  
Lamellar Structure ◽  
Ostwald Ripening ◽  
Morphological Changes ◽  
Lamellar Spacing ◽  
Eutectic System ◽  
Initial Structure ◽  
Lamellar Structures ◽  
Power Law Function ◽  
Equiaxed Grains

AbstractUnderstanding the morphological changes of Pb-Sn solder alloys helps to improve their performance in electronic applications. The focus of our study is degeneration of lamellar structures at high temperatures. Microstructural evolution of the Pb-Sn eutectic lamellar structure is modeled numerically using Monte Carlo Potts approach. The initial structure consists of alternating layers of Pb-rich and Sn-rich phases, simulating the lamellar array in a near eutectic system. Faults are introduced to destabilize the system. After a short incubation period the shape of lamellae become irregular. The perturbations grow with time and eventually break the lamellae into nearly equiaxed grains. The grain size of the degenerated structure is 2-3 times the original lamellar spacing weakly depending on the spacing between the faults. This is consistent with the experimental observation of degeneration of Pb-62 wt% Sn solder. The duration of degeneration processes is comparable with the time it would take Ostwald ripening to produce grains of the same size. Eventually grain growth reaches the asymptotic regime of coarsening described by a power-law function of time.

Numerical Simulations of Coarsening of Lamellar Structures: Applications to metallic alloys

2002 ◽  
Vol 753 ◽  
Author(s):  
Rifa J. El-Khozondar ◽  
Hala J. El-Khozondar
Keyword(s):  
Lamellar Structure ◽  
Ostwald Ripening ◽  
Volume Fraction ◽  
Lamellar Spacing ◽  
Industrial Applications ◽  
Metallic Alloys ◽  
Lamellar Structures ◽  
Power Law Function ◽  
Discontinuous Coarsening ◽  
Equiaxed Grains

ABSTRACTUnderstanding the microstructural evolution in metallic alloys helps to control their properties and improve their performance in industrial applications. The emphasis of our study is the coarsening mechanisms of lamellar structures.Coarsening of lamellar structure is modeled numerically using Monte Carlo Potts method. The initial microstructure consists of alternating lamellae of phase A and phase B with the spacing proportional to their volume fraction. Faults are introduced to the lamellae to induce instability in the system. We find that an isotropic lamellar structure degenerates via edge spheroidization and termination migration into nearly equiaxed grains with a diameter which is 2 to 3 times larger than the original lamellar spacing. The duration of this process is comparable with the time it would take Ostwald ripening to produce grains of the same size. Eventually grain growth reaches the asymptotic regime of coarsening described by a power-law function of time. Lamellae with anisotropic grain boundaries coarsen more slowly and via discontinuous coarsening mechanism. This produces larger grains upon degeneration of lamellae. Discontinuous coarsening was observed in lamellar alloys as well as termination migration.

Microstructural Evolution of 7050 Aluminum Alloy Semisolid Billets Fabricated by RAP Process

2014 ◽  
Vol 217-218 ◽  
pp. 29-36 ◽  
Author(s):  
Ju Fu Jiang ◽  
Zhi Ming Du ◽  
Ying Wang ◽  
Shou Jing Luo
Keyword(s):  
Aluminum Alloy ◽  
Microstructural Evolution ◽  
Ostwald Ripening ◽  
Soaking Time ◽  
Isothermal Temperature ◽  
7050 Aluminum Alloy ◽  
Average Grain Size ◽  
Different Temperatures ◽  
Equiaxed Grains ◽  
Grain Coalescence

In the present study, 7050 supplied in extruded state was heated to different temperatures below solidus or the semisolid state and microstructural evolution and coarsening were investigated. The results showed that complete recrystallisation only occurs after soaking for 5 minutes at 545°C, which is characterised by formation of a lot of fine equiaxed grains. RAP is suitable for fabricating high-quality semisolid billet of 7050 aluminum alloy with an average grain size ranging from 47.4 um to 70.5 um and a roundness ranging from 1.3 to 1.7. Grain growth occurs as the samples were soaked at 610°C and 615°Cfor prolonged soaking time. When the isothermal temperatures were 610°C and 615°C, the coarsening rate constants were 359.5μm3s-1 and 470.5μm3s-1, respectively, indicating an increase of coarsening rate constant (K) with the increasing isothermal temperature. Coarsening tends to occur via Ostwald ripening and coalescence. Ostwald ripening plays an important role during the whole coarsening process, but the grain coalescence only contributes to coarsening after soaking for 12 minutes. 625°C is an optimal temperature to keep cylinder shape of the sample due to collapse of the sample above this temperature, leading to difficult clamping.

Microstructure Evolution and Coarsening Mechanism of 7075 Semi-Solid Aluminum Alloy Pre-Deformed by ECAP Method

2016 ◽  
Vol 256 ◽  
pp. 294-300 ◽  
Author(s):  
Jin Long Fu ◽  
Yu Wei Wang ◽  
Kai Kun Wang ◽  
Xiao Wei Li
Keyword(s):  
Aluminum Alloy ◽  
Solid State ◽  
Ostwald Ripening ◽  
Liquid Fraction ◽  
Isothermal Holding ◽  
Angular Pressing ◽  
Average Grain Size ◽  
Semi Solid ◽  
Equiaxed Grains ◽  
Kinetics Of

To investigate the influence of refined grains on the microstructure of 7075 aluminum alloy in semi-solid state, a new strain induced melting activation (SIMA) method was put forward containing two main stages: pre-deformation with equal channel angular pressing (ECAP) method and isothermally holding in the semi-solid temperature range. The breaking up and growth mechanisms of the grains and kinetics of equiaxed grains coarsening during the semi-solid holding were investigated. The results showed that the average grain size after ECAP extrusion decreased significantly, e.g., microstructure with average globular diameter less than 5μm was achieved after four-pass ECAP extrusion. Obvious grain coarsening had been found during isothermal holding in the semi-solid state and the roundness of the grains increased with the increasing holding time. The proper microstructure of 66.8μm in diameter and 1.22 in shape factor was obtained under proper soaking condition (at 590°C for 15 min). Two coarsening mechanisms, namely, coalescence in lower liquid fraction and Ostwald ripening in higher liquid fraction contributed to the grain growth process.

Analysis and characterization by electron backscatter diffraction of microstructural evolution in the adiabatic shear bands in Fe–Cr–Ni alloys

2009 ◽  
Vol 24 (8) ◽  
pp. 2617-2627 ◽  
Author(s):  
Huajie Yang ◽  
Yongbo Xu ◽  
Yasuaki Seki ◽  
Vitali F. Nesterenko ◽  
Marc André Meyers
Keyword(s):  
Microstructural Evolution ◽  
Electron Backscatter Diffraction ◽  
Shear Bands ◽  
Adiabatic Shear ◽  
Adiabatic Shear Bands ◽  
Localized Deformation ◽  
Ni Alloys ◽  
Electron Backscatter ◽  
Backscatter Diffraction ◽  
Equiaxed Grains

The microstructural evolution inside adiabatic shear bands in Fe–Cr–Ni alloys dynamically deformed (strain rates > 104 s−1) by the collapse of an explosively driven, thick-walled cylinder under prescribed strain conditions was examined by electron backscatter diffraction. The observed structure within the bands consisted of both equiaxed and elongated grains with a size of ∼200 nm. These fine microstructures can be attributed to recrystallization; it is proposed that the elongated grains may be developed simultaneously with localized deformation (dynamic recrystallization), and the equiaxed grains may be formed subsequently to deformation (static recrystallization). These recrystallized structures can be explained by a rotational recrystallization mechanism.

scholarly journals Novel cloaking lamellar structures for a screw dislocation dipole, a circular Eshelby inclusion and a concentrated couple

2020 ◽  
Vol 476 (2241) ◽  
pp. 20200095
Author(s):  
Xu Wang ◽  
Peter Schiavone
Keyword(s):  
Conformal Mapping ◽  
Screw Dislocation ◽  
Lamellar Structure ◽  
Stress Fields ◽  
Uniform Stress ◽  
Dislocation Dipole ◽  
Lamellar Structures ◽  
Eshelby Inclusion ◽  
Mapping Techniques ◽  
Concentrated Couple

Using conformal mapping techniques, we design novel lamellar structures which cloak the influence of any one of a screw dislocation dipole, a circular Eshelby inclusion or a concentrated couple. The lamellar structure is composed of two half-planes bonded through a middle coating with a variable thickness within which is located either the dislocation dipole, the circular Eshelby inclusion or the concentrated couple. The Eshelby inclusion undergoes either uniform anti-plane eigenstrains or uniform in-plane volumetric eigenstrains. As a result, the influence of any one of the dislocation dipole, the circular Eshelby inclusion or the concentrated couple is cloaked in that their presence will not disturb the prescribed uniform stress fields in both surrounding half-planes.

Additivity of Hardening by Nanolamellar Structure and Antiphase Domain in Ti-39at%Al Single Crystals

2008 ◽  
Vol 1086 ◽  
Author(s):  
Yuichiro Koizumi ◽  
Yoritoshi Minamino ◽  
Takayuki Tanaka ◽  
Kazuki Iwamoto
Keyword(s):  
Lamellar Structure ◽  
Antiphase Domain ◽  
Dislocation Motion ◽  
Additional Stress ◽  
Slip Direction ◽  
Prism Slip ◽  
Screw Dislocations ◽  
Lamellar Structures ◽  
Mixed Microstructure ◽  
Antiphase Domains

AbstractA mixed microstructure of antiphase domains (APD) and fine lamellar structure were introduced in a Ti-39at%Al single crystal and it was examined whether the APD hardening works even in nano-scaled lamellar structures. The hardness increases with decreasing APD size even where the L is smaller than 100 nm below which the hardening by lamellar refining saturates. The mechanism of the additivity of strengthening by APD and lamellar structure is discussed in the context of the geometries of slip direction, lamellar boundaries and APD boundaries (APDBs). For {1100}<1120> prism slip (the easiest slip system of α2-Ti3Al), the lamellar boundaries are parallel to the slip direction, and therefore they interrupt the motion of screw dislocations effectively. On the other hand, APDBs inclined from lamellar boundaries can effectively obstruct the dislocation motion regardless of the dislocation character because the shear of such APDBs results in the formation of step-like APDBs on the slip-plane and requires additional stress for dislocation motion whereas APDBs parallel to the slip direction can be sheared without forming such a step-like APDB. Accordingly, APDs and lamellar structure can contribute to the strengthening complementarily.

Evolution of Antiphase Domains and γ Lamellae in Ti-39at%Al Single Crystals

2006 ◽  
Vol 980 ◽  
Author(s):  
Yuichiro Koizumi ◽  
Kazuki Iwamoto ◽  
Takayuki Tanaka ◽  
Yoritoshi Minamino ◽  
Nobuhiro Tsuji
Keyword(s):  
Single Crystals ◽  
Structure Formation ◽  
Lamellar Structure ◽  
Lamellar Spacing ◽  
Antiphase Domain ◽  
Single Phase State ◽  
Preferential Nucleation ◽  
Phase Temperature ◽  
Antiphase Domains ◽  
The Moment

AbstractWe studied antiphase domain (APD) growth and lamellar structure formation during isothermal annealing of Ti-39at%Al single crystals at α2+γ dual phase temperature after quenching from α single phase state, intending to obtain a APD/lamellae mixed microstructure and to examine whether such a microstructure provides a strength higher than that obtained only by refining lamellar structure. The effect of plastic deformation prior to the annealing was also examined expecting a acceleration of γ lamellae formation through a preferential nucleation of γ-plates at dislocations. The lower was the annealing temperature, the smaller both the APD size and the lamellar spacing at the moment of a homogeneous lamellar structure formation tended to be, although naturally both the APD growth and the γ lamellae formation were slower. However, the APD size in the homogeneous lamellar structure was no smaller than 400 nm. A structure with finer APDs and finer lamellar structure was obtained by deforming the crystal before annealing since the lamellar structure formation was accelerated and the time for APD growth before the lamellar structure formation was shortened. For instance, a structure with an average lamellar spacing of 88 nm and an average APD size of 214 nm was obtained by deforming the crystals to 10 % plastic strain and subsequently annealing at 1073 K for 1×104 s, while no γ plate was obtained only by such an annealing without deformation.

Mechanism of Cementite Spheroidization from Different Initial Microstructures in Fe-0.65C-2.33Mn Alloy

2019 ◽  
Vol 815 ◽  
pp. 107-113
Author(s):  
Li Ma ◽  
Tao Jia ◽  
Xiu Hua Gao ◽  
Run Ni
Keyword(s):  
Electron Microscopy ◽  
Cooling Rate ◽  
Local Equilibrium ◽  
Lamellar Spacing ◽  
Initial Structure ◽  
Equilibrium Conditions ◽  
Transmission Electron ◽  
Spheroidizing Annealing ◽  
Carburizing Process ◽  
Scanning Electron

The spheroidization mechanism from different initial microstructures during spheroidizing heat treatment was studied in Fe-0.68C-2.33Mn alloy. Two types of initial microstructures, i.e. pearlite and martensite, were obtained by varying the cooling rate. The microstructure and property evolution during spheroidizing annealing was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The DICTRA software, assuming local equilibrium conditions, was used to simulate the carburizing process of different initial microstructures through different cooling rate. The results indicate that the spheroidization mechanism of cementite was related to the initial microstructures and the smaller lamellar spacing of pearlite inhibited the coarsening of cementite, resulting in the size of cementite smaller than that of martensite as the initial structure.

scholarly journals Influence of Plastic Deformation on Microstructural Evolution of 100Cr6 Bearing Ring in Hot Ring Rolling

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4355
Author(s):  
Guanghua Zhou ◽  
Wenting Wei ◽  
Qinglong Liu
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Microstructural Evolution ◽  
Vickers Hardness ◽  
Microstructural Characterization ◽  
Lamellar Spacing ◽  
Rolling Process ◽  
Rolling Reduction ◽  
Ring Rolling ◽  
Bearing Rings

The hot ring rolling technology as the crucial procedure for the manufacture of bearing rings plays an important role in determining the final microstructure of bearing rings. In this work, the influence of the hot ring rolling process on the microstructural evolution of 100Cr6 bearing rings was investigated using a three-dimensional (3D) numerical model and microstructural characterization. It was found that the significant microstructural refinement occurs at the different regions of the rings. However, owing to the non-uniform plastic deformation of hot rolling, the refinement rate of grain size and decrease of pearlite lamellar spacing (PLS) also showed uniformity at different regions of the rings. Furthermore, the degree of grain refinement had been limited with the increase of rolling reduction. Due to the refined grain size and decreased PLS, the Vickers hardness increased with the increase of rolling reduction. Moreover, the Vickers hardness from the outer surface to the inner surface of the ring is asymmetrical u-shaped, which had the law of lower hardness in the center area and higher hardness on the surface.

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