Investigation of the Sintering Behavior of Ultrapure α-Alumina Containing Low Amounts of SiO2 or CaO

2006 ◽  
Vol 317-318 ◽  
pp. 1-6 ◽  
Author(s):  
Nicolas Louet ◽  
Thierry Epicier ◽  
Gilbert Fantozzi
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Oxygen Vacancies ◽  
Glassy Phase ◽  
Intermediate Stage ◽  
Abnormal Grain Growth ◽  
Sintering Behavior ◽  
Critical Temperatures ◽  
Heterogeneous Microstructures

The target of this work is to investigate the effect of small additions of SiO2 or CaO on the sintering behavior and the microstructure of an ultrapure α-alumina compound. The sintering behavior has been investigated through extensive dilatometric study. SiO2 additions lead to a significant decrease in shrinkage rate during the intermediate stage of sintering whereas CaO is beneficent to densification. It has been found that during this stage which corresponds to the maximum of densification rate, grain boundaries diffusion controls densification through oxygen vacancies. The study of the densification behavior under different atmospheres help us to explain the role of the additives in agreement with electroneutrality equations. S.E.M. investigations confirm the well know correlation between doping and heterogeneous microstructures. After doping with SiO2 or CaO, abnormal grain growth appears at temperatures corresponding to the lowest eutectics given by Al2O3-SiO2 or Al2O3-CaO phase diagrams. H.R.T.E.M. observations show that below the critical temperatures for abnormal grain growth, additives enrichment is observed near grain boundaries (GBs). Above these temperatures, glassy phase for SiO2-doping and calciumhexaluminate (CA6) for CaO-doping are present at grain boundaries.

Microstructure of Polycrystalline MgO Penetrated by a Silicate Liquid

1996 ◽  
Vol 2 (3) ◽  
pp. 113-128 ◽  
Author(s):  
Sundar Ramamurthy ◽  
Michael P. Mallamaci ◽  
Catherine M. Zimmerman ◽  
C. Barry Carter ◽  
Peter R. Duncombe ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Glassy Phase ◽  
Silicate Liquid ◽  
Two Phase ◽  
The Matrix ◽  
Devitrification Process ◽  
Phase Mixture

Dense, polycrystalline MgO was infiltrated with monticellite (CaMgSiO4) liquid to study the penetration of liquid along the grain boundaries of MgO. Grain growth was found to be restricted with increasing amounts of liquid. The inter-granular regions were generally found to be comprised of a two-phase mixture: crystalline monticellite and a glassy phase rich in the impurities present in the starting MgO material. MgO grains act as seeding agents for the crystallization of monticellite. The location and composition of the glassy phase with respect to the MgO grains emphasizes the role of intergranular liquid during the devitrification process in “snowplowing” impurities present in the matrix.

A Role of Low Energy Grain Boundaries in the Abnormal Grain Growth in Fe-3%Si Alloy

2011 ◽  
Vol 127 ◽  
pp. 89-94 ◽  
Author(s):  
Ye Chao Zhu ◽  
Jiong Hui Mao ◽  
Fa Tang Tan ◽  
Xue Liang Qiao
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Electron Backscatter Diffraction ◽  
Dominant Role ◽  
Coincidence Site Lattice ◽  
Diffraction Method ◽  
Abnormal Grain Growth ◽  
Low Energy ◽  
Backscatter Diffraction

Low energy grain boundaries were considered to be important in abnormal grain growth by theoretical deduction. The disorientation angles and coincidence site lattice grain boundaries distribution of more than 20 Goss grains and their neighboring matrix grains in primary recrystallized Fe-3%Si alloy were investigated using an electron backscatter diffraction method. It was found that the frequency of low energy grain boundaries of Goss grains which are more likely to abnormally grow are higher than their neighboring matrix grains, which indicated that low energy grain boundaries play a dominant role in the abnormal grain growth of Fe-3%Si alloy. The result meets well with the abnormal grain growth theory.

scholarly journals Role of β(FeAl) nanoparticles in abnormal grain growth in the annealing of cast Cu-Al-Mn-Fe shape memory alloys

2020 ◽  
Vol 30 (4) ◽  
pp. 510-516
Author(s):  
Shuiyuan Yang ◽  
Xinyu Qing ◽  
Jixun Zhang ◽  
Lipeng Guo ◽  
Shen Hong ◽  
...  
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Grain Growth ◽  
Abnormal Grain Growth

An Overview of Accomplishments and Challenges in Recrystallization and Grain Growth

2007 ◽  
Vol 558-559 ◽  
pp. 33-42 ◽  
Author(s):  
Anthony D. Rollett ◽  
Abhijit P. Brahme ◽  
C.G. Roberts
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Degrees Of Freedom ◽  
Driving Forces ◽  
Excess Free Energy ◽  
Abnormal Grain Growth ◽  
Process Models ◽  
Three Dimensions ◽  
Polycrystalline Materials ◽  
General Process

The study of microstructural evolution in polycrystalline materials has been active for many decades so it is interesting to illustrate the progress that has been made and to point out some remaining challenges. Grain boundaries are important because their long-range motion controls evolution in many cases. We have some understanding of the essential features of grain boundary properties over the five macroscopic degrees of freedom. Excess free energy, for example, is dominated by the two surfaces that comprise the boundary although the twist component also has a non-negligible influence. Mobility is less well defined although there are some clear trends for certain classes of materials such as fcc metals. Computer simulation has made a critical contribution by showing, for example, that mobility exhibits an intrinsic crystallographic anisotropy even in the absence of impurities. At the mesoscopic level, we now have rigorous relationships between geometry and growth rates for individual grains in three dimensions. We are in the process of validating computer models of grain growth against 3D non-destructive measurements. Quantitative modeling of recrystallization that includes texture development has been accomplished in several groups. Other properties such as corrosion resistance are being related quantitatively to microstructure. There remain, however, numerous challenges. Despite decades of study, we still do not have complete cause-and-effect descriptions of most cases of abnormal grain growth. The response of nanostructured materials to annealing can lead to either unexpected resistance to coarsening, or, coarsening at unexpectedly low temperatures. General process models for recrystallization that can be applied to industrial alloys remain elusive although significant progress has been made for the specific case of aluminum alloy processing. Thin films often exhibit stagnation of grain growth that we do not fully understand, as well as abnormal grain growth. Grain boundaries respond to driving forces in more complicated ways than we understood. Clearly many exciting challenges remain in grain growth and recrystallization.

scholarly journals On the Role of Grain Boundaries During Sintering

2021 ◽  
Author(s):  
Torsten Staab ◽  
Ricardo Helm ◽  
Andreas Diegeler
Keyword(s):  
Mass Transport ◽  
Grain Boundaries ◽  
Average Distance ◽  
Intermediate Stage ◽  
Sintering Process ◽  
Positron Annihilation Lifetime ◽  
Boundary Signal ◽  
Increasing Temperature ◽  
Good Agreement

We present new results in positron annihilation lifetime spectroscopy (PALS), thermo-optical dilatometry and microscopy, which are indicating a strong correlation between grain-boundaries and mass transport during the sintering process of carbonyl iron powder. In this particular system we were able to show that the change in particle shape and size with increasing temperature yields an anisotropy in shrinkage, which manifests itself in a higher shrinkage perpendicular to the compaction axis. In the intermediate stage of sintering, where the major mass transport occurs, the average distance between two grain boundaries could be determined to (3,73 ± 0,18) μm at T = 744°C. This is in good agreement with previous calculations of positron pathways in defect free particles. Furthermore, due to sintering temperatures far above the annealing temperature of dislocations in iron, the existence of dislocations in the bulk of the particles is very unlikely. These claims are reflected by the collected positron data, which exhibit a clear grain boundary signal of ∼ 250ps while no vacancy or dislocation signal (typically ∼ 160 ps) is evident in the intermediate stage of sintering.

Role of abnormal grain growth on the ferroelectric properties of SrBi2Ta2O9 thin films fabricated by R.F. Magnetron sputtering

1998 ◽  
Vol 21 (1-4) ◽  
pp. 419-428 ◽  
Author(s):  
Choelhwyi Bae ◽  
Jeon-Kook Lee ◽  
Si-Hyung Lee ◽  
Yoon Baek Park ◽  
Hyung-Jin Jung
Keyword(s):  
Thin Films ◽  
Magnetron Sputtering ◽  
Grain Growth ◽  
Ferroelectric Properties ◽  
Abnormal Grain Growth

Analysis of Oxygen Vacancy Trapping at [001] Symmetric Tilt Grain Boundaries in Barium Titanate by Atomistic Simulations

2010 ◽  
Vol 445 ◽  
pp. 39-42 ◽  
Author(s):  
Takashi Oyama ◽  
Nobuyuki Wada ◽  
Hiroshi Takagi
Keyword(s):  
Barium Titanate ◽  
Grain Boundaries ◽  
Atomistic Simulation ◽  
Oxygen Vacancies ◽  
Atomistic Simulations ◽  
Multilayer Ceramic Capacitors ◽  
Simulation Techniques ◽  
Electrical Degradation ◽  
Symmetric Tilt

The role of grain boundaries (GBs) in the diffusion of oxygen vacancies (VO••s) in barium titanate (BaTiO3) and its mechanism were investigated using atomistic simulation techniques. It was found that GBs trapped VO••s at specific sites in the course of the diffusion, and the excess energy reflecting structural distortion of the GB was closely related to the availability of the trapping. GBs therefore act as a resistance of the diffusion of VO••s, suggesting that electrical degradation of multilayer ceramic capacitors (MLCCs), which is derived from vacancy diffusion, enables to be additionally improved by controlling GB structures in BaTiO3-based dielectrics.

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