Nucleation and Concurrent Anomalous Grain Growth of alpha-Al2O3 During gamma - alpha Phase Transformation

1991 ◽  
Vol 74 (9) ◽  
pp. 2270-2279 ◽  
Author(s):  
Ting C. Chou ◽  
Tai G. Nieh
Keyword(s):  
Phase Transformation ◽  
Grain Growth ◽  
Alpha Phase

Microstructural Development of Electrical Steels under Si and Al Diffusion

2006 ◽  
Vol 258-260 ◽  
pp. 39-45
Author(s):  
José Barros ◽  
Yvan Houbaert
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Grain Growth ◽  
Alpha Phase ◽  
Microstructural Development ◽  
Diffusion Annealing ◽  
Electrical Steels ◽  
Common Features ◽  
Columnar Grain ◽  
Size And Morphology

The effect of Si and Al diffusion from a coating in the microstructure of electrical steels have been investigated for three different processing routes. In general the final texture is not affected by the diffusion of Si or Al from the coating whereas the grain size and mor- phology can be affected if the silicon content of the substrate is low enough to allow phase transformation. The gamma to alpha phase transformation caused by the diffusion of Si and Al determines the grain size and morphology resulting in columnar grain growth. The evolu- tion of the microstructures during the diffusion annealing for the production of high Si steels shows some common features with the microstructure evolution during the grain growth in conventional low silicon (Si < 3 wt.%) electrical steels.

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

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.

scholarly journals In-situ Experiments to Capture the Evolution of Microstructure During Phase Transformation of Titanium Under Dynamic Loading

2018 ◽  
Vol 183 ◽  
pp. 03020
Author(s):  
Benjamin M. Morrow ◽  
David R. Jones ◽  
Paulo A. Rigg ◽  
George T. Gray ◽  
Ellen K. Cerreta
Keyword(s):  
Phase Transformation ◽  
Dynamic Loading ◽  
Microstructural Analysis ◽  
Alpha Phase ◽  
Material Behavior ◽  
High Rate ◽  
Omega Phase ◽  
In Situ Experiments ◽  
Consistent Picture ◽  
Underlying Mechanisms

Under sufficient stresses, such as during dynamic loading, titanium experiences a phase transformation from hcp alpha phase to hexagonal omega phase. Omega phase is often retained in the microstructure after unloading, and has a strong influence on subsequent mechanical properties. Simulations suggest there are multiple pathways and underlying mechanisms for this transformation. Due to the incredibly short timescales involved, experimental measurements for model validation have been difficult. However, new capabilities at the Advanced Photon Source have enabled diffraction measurements during plate impact experiments to study the evolution of titanium during transformation. These high-rate data allow us to probe the mechanism and kinetics of phase transformations in new ways. Recent results will be presented and compared to post-mortem characterization of soft-recovered shocked specimens. Comparisons are made with previous tests where material was shock-loaded and soft recovered for microstructural analysis. Together these techniques create a consistent picture of material behavior during the shock-induced ff–! phase transformation in titanium.

Effect of Deposition Conditions on Intrinsic Stress, Phase Transformation and Stress Relaxation in Tantalum Thin Films

1991 ◽  
Vol 239 ◽  
Author(s):  
A. Mutscheller ◽  
L. A. Clevenger ◽  
J.M.E. Harper ◽  
C. Cabrai ◽  
K. Barmakt
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Phase Transformation ◽  
Stress Relaxation ◽  
Compressive Stress ◽  
Stress Relief ◽  
Beta Phase ◽  
Alpha Phase ◽  
Intrinsic Stress

AbstractWe demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes complete stress relaxation and a large decrease in the resistance of tantalum thin films. 100 nm beta tantalum thin films were deposited onto thermally oxidized <100> silicon wafers by dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured during temperature-ramped annealing in purified He. Upon heating, films that were initially compressively stressed showed increasing compressive stress due to thermo-elastic deformation from 25 to 550°C, slight stress relief due to plastic deformation from 550 to 700°C and complete stress relief due to the beta to alpha phase transformation at approximately 700–800°C. Incomplete compressive stress relaxation was observed at high temperatures if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800°C. This incomplete beta to alpha phase transition was most commonly observed on samples that had radio frequency substrate bias greater than -100 V. We conclude that the main stress relief mechanism for tantalum thin films is the beta to alpha phase transformation that occurs at 700 to 800°C.

Crystal grain growth during phase transformation in cerium metal at high pressure

1995 ◽  
Vol 52 (13) ◽  
pp. 9107-9110 ◽  
Author(s):  
Guoliang Gu ◽  
Yogesh K. Vohra ◽  
Keith E. Brister
Keyword(s):  
High Pressure ◽  
Phase Transformation ◽  
Grain Growth

Beta-alpha phase transformation in Ti and TiO alloys

1974 ◽  
Vol 34 (2) ◽  
pp. 181-189 ◽  
Author(s):  
M. Cormier ◽  
F. Claisse
Keyword(s):  
Phase Transformation ◽  
Alpha Phase
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