Solidification of Mg–Zn–Zr Alloys: Grain Growth Restriction, Dendrite Coherency and Grain Size

AbstractThe quality and the stability of devices prepared from polycrystalline layers of organic–inorganic perovskites highly depend on the grain sizes prevailing. Tuning of the grain size is either done during layer preparation or in a post-processing step. Our investigation refers to thermal imprint as the post-processing step to induce grain growth in perovskite layers, offering the additional benefit of providing a flat surface for multi-layer devices. The material studied is MAPbBr3; we investigate grain growth at a pressure of 100 bar and temperatures of up to 150 °C, a temperature range where the pressurized stamp is beneficial to avoid thermal degradation. Grain coarsening develops in a self-similar way, featuring a log-normal grain size distribution; categories like ‘normal’ or ‘secondary’ growth are less applicable as the layers feature a preferential orientation already before imprint-induced grain growth. The experiments are simulated with a capillary-based growth law; the respective parameters are determined experimentally, with an activation energy of Q ≈ 0.3 eV. It turns out that with imprint as well the main parameter relevant to grain growth is temperature; to induce grain growth in MAPbBr3 within a reasonable processing time a temperature of 120 °C and beyond is advised. An analysis of the mechanical situation during imprint indicates a dominance of thermal stress. The minimization of elastic energy and surface energy together favours the development of grains with (100)-orientation in MaPbBr3 layers. Furthermore, the experiments indicate that the purity of the materials used for layer preparation is a major factor to achieve large grains; however, a diligent and always similar preparation of the layer is equally important as it defines the pureness of the resulting perovskite layer, intimately connected with its capability to grow. The results are not only of interest to assess the potential of a layer with respect to grain growth when specific temperatures and times are chosen; they also help to rate the long-term stability of a layer under temperature loading, e.g. during the operation of a device.

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Mean Field Analysis of Orientation Selective Grain Growth Driven By Interface-Energy Anisotropy

MRS Proceedings ◽

10.1557/proc-343-65 ◽

1994 ◽

Vol 343 ◽

Cited By ~ 2

Author(s):

J. A. Floro ◽

C. V. Thompson

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Growth ◽

Texture Evolution ◽

Mean Field ◽

Orientation Distribution ◽

Interface Energy ◽

Abnormal Grain Growth ◽

Field Analysis ◽

Energy Anisotropy

ABSTRACTAbnormal grain growth is characterized by the lack of a steady state grain size distribution. In extreme cases the size distribution becomes transiently bimodal, with a few grains growing much larger than the average size. This is known as secondary grain growth. In polycrystalline thin films, the surface energy γs and film/substrate interfacial energy γi vary with grain orientation, providing an orientation-selective driving force that can lead to abnormal grain growth. We employ a mean field analysis that incorporates the effect of interface energy anisotropy to predict the evolution of the grain size/orientation distribution. While abnormal grain growth and texture evolution always result when interface energy anisotropy is present, whether secondary grain growth occurs will depend sensitively on the details of the orientation dependence of γi.

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The Effect of Grain Size on Superplastic Deformation of Ti-6Al-4V Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.551-552.387 ◽

2007 ◽

Vol 551-552 ◽

pp. 387-392 ◽

Cited By ~ 4

Author(s):

Wen Juan Zhao ◽

Hua Ding ◽

D. Song ◽

F.R. Cao ◽

Hong Liang Hou

Keyword(s):

Grain Size ◽

Grain Growth ◽

Superplastic Deformation ◽

Initial Strain Rate ◽

Deformation Mode ◽

Tensile Tests ◽

Optical Microscope ◽

Coarse Grained ◽

Transmission Electron ◽

Grain Growth Model

In this study, superplastic tensile tests were carried out for Ti-6Al-4V alloy using different initial grain sizes (2.6 μm, 6.5μm and 16.2 μm) at a temperature of 920°C with an initial strain rate of 1×10-3 s-1. To get an insight into the effect of grain size on the superplastic deformation mechanisms, the microstructures of deformed alloy were investigated by using an optical microscope and transmission electron microscope (TEM). The results indicate that there is dramatic difference in the superplastic deformation mode of fine and coarse grained Ti-6Al-4V alloy. Meanwhile, grain growth induced by superplastic deformation has also been clearly observed during deformation process, and the grain growth model including the static and strain induced part during superplastic deformation was utilized to analyze the data of Ti-6Al-4V alloy.

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Change in Grain Size Distribution during Grain Growth

Materials Science Forum ◽

10.4028/www.scientific.net/msf.94-96.325 ◽

1992 ◽

Vol 94-96 ◽

pp. 325-330 ◽

Cited By ~ 3

Author(s):

Y. Takayama ◽

T. Tozawa ◽

H. Kato ◽

Norio Furushiro ◽

S. Hori

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Growth ◽

Grain Size Distribution

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A Study on The Phase Transformation and Exchange-Coupling of (Nd0 95La0 05)9 5FebalCo5Nb2B10.5 Nanocomposites

MRS Proceedings ◽

10.1557/proc-577-209 ◽

1999 ◽

Vol 577 ◽

Author(s):

Q. Chen ◽

B. M. Ma ◽

B. Lu ◽

M. Q. Huang ◽

D. E. Laughlin

Keyword(s):

Grain Size ◽

Magnetic Properties ◽

Phase Transformation ◽

Thermal Treatment ◽

Grain Growth ◽

Exchange Coupling ◽

Phase Distribution ◽

Maximum Energy ◽

Treatment Temperature ◽

Phase Identification

ABSTRACTThe phase transformation and the exchange coupling in (Ndo095Lao005)9.5FebaICOsNb 2BI05 have been investigated. Nanocomposites were obtained by treating amorphous precursors at temperatures ranging from 650TC to 9500C for 10 minutes. The magnetic properties were characterized via the vibrating sample magnetometer (VSM). X-ray diffraction (XRD), thermomagnetic analysis (TMA), and transmission electron microscopy (TEM) were used to perform phase identification, measure grain size, and analyze phase distribution. The strength of the exchange coupling between the magnetically hard and soft phases in the corresponding nanocomposite was analyzed via the AM-versus-H plot. It was found that the remanence (Br), coercivity (Hci), and maximum energy product (BHmax) obtained were affected by the magnetic phases present as well as the grain size of constituent phases and their distribution. The optimal magnetic performance, BHm, occurred between 700°C to 750°C, where the crystallization has completed without excessive grain growth. TMA and TEM indicated that the system was composed of three phases at this point, Nd2(Fe Co) 14B, ca-Fe, and Fe3B. The exchange coupling interaction among these phases was consistently described via the AM-versus-H plot up to 750°C. The Br, Hci, and BHmax degraded severely when the thermal treatment temperature increased from 750°C. This degradation may be attributed to the grain growth of the main phases, from 45 to 68nm, and the development of precipitates, which grew from 5nm at 750°C to 12nm at 850°C. Moreover, the amount of the precipitates was found to increase with the thermal treatment temperatures. The precipitates, presumably borides, may cause a decrease in the amount of the a-Fe and Fe 3B and result in a redistribution of the Co in the nanocomposites. The increase of the Co content in the Nd 2(Fe Co) 14B may explain the increase of its Curie temperature with the thermal treatment temperatures. In this paper, we examine the impacts of these factors on the magnetic properties of (Ndo 95Lao 05)9 5FebaICosNb2B10.5 nanocomposite.

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Grain Growth in Nanocrystalline Nickel

MRS Proceedings ◽

10.1557/proc-580-183 ◽

1999 ◽

Vol 580 ◽

Cited By ~ 9

Author(s):

G.D. Hibbard ◽

U. Erb ◽

K.T. Aust ◽

G. Palumbo

Keyword(s):

Thermal Stability ◽

Grain Size ◽

Grain Growth ◽

Size Distributions ◽

Nanocrystalline Nickel ◽

Scanning Calorimetry ◽

Solute Content ◽

Grain Size Distributions ◽

Thermal Stability Of ◽

Total Solute Content

AbstractIn this study, the effect of grain size distribution on the thermal stability of electrodeposited nanocrystalline nickel was investigated by pre-annealing material such that a limited amount of abnormal grain growth was introduced. This work was done in an effort to understand the previously reported, unexpected effect, of increasing thermal stability with decreasing grain size seen in some nanocrystalline systems. Pre-annealing produced a range of grain size distributions in materials with relatively unchanged crystallographic texture and total solute content. Subsequent thermal analysis of the pre-annealed samples by differential scanning calorimetry showed that the activation energy of further grain growth was unchanged from the as-deposited nanocrystalline nickel.

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Recrystallization and Grain Growth during Alloy 718 Processing

Materials Science Forum ◽

10.4028/www.scientific.net/msf.539-543.3094 ◽

2007 ◽

Vol 539-543 ◽

pp. 3094-3099

Author(s):

Nho Kwang Park ◽

Jeoung Han Kim ◽

Jong Taek Yeom

Keyword(s):

Grain Size ◽

Grain Growth ◽

Heat Treatments ◽

Grain Structure ◽

Alloy 718 ◽

Compression Tests ◽

Δ Phase ◽

Grain Boundary Characteristics ◽

The Difference ◽

Boundary Characteristics

In Alloy 718 ingot cogging process, dynamic and metadynamic recrystallizations, and static grain growth occur, and also the presence of δ phase plays a key role in controlling the grain size. In this study, the evolution of grain structure in VIM/VAR-processed Alloy 718 ingots during post-cogging heat treatments is dealt with. Compression tests were made on VIM/VAR-processed Alloy 718 ingot at temperatures between 900oC ~ 1150oC. Heat treatments were made on the compression-tested specimens, and the variation of grain size was evaluated. Constitutive equations for the grain growth are established to represent the evolution of microstructures. Special attention is paid to the evolution of grain structure under the condition of dynamic and metadynamic recrystallizations, and grain growth. The grain growth rate depends mainly on the presence of δ-phase below the δ-solvus temperature, and on the difference in the grain boundary characteristics above it.

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