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Title: Validation of crystallographic correlation for faceted morphology in laser surface engineered alumina ceramic

Abstract

Surface modification of alumina ceramic using a high energy density continuous wave laser beam is associated with the formation of highly faceted pyramidal surface grains. Recently, we developed a phenomenological model explaining the faceted morphology by a fiber texture with a strong (1-210) component. Based on high resolution electron back-scattered diffraction, the present work proposes a more precise model showing that faceting of surface grains is closely linked with the evolution of a strong (2-310) fiber texture.

Authors:
 [1];  [1];  [2];  [2];  [2];  [1]
  1. ORNL
  2. Saarland University, Saarbrucken, Germany
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program; ORNL other overhead
OSTI Identifier:
931506
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Scripta Materialia; Journal Volume: 57; Journal Issue: 5
Country of Publication:
United States
Language:
English

Citation Formats

Harimkar, Sandip P, Daniel, Claus, Holzapfel, Christian, Leibenguth, Peter, M�cklich, Frank, and Dahotre, Narendra B. Validation of crystallographic correlation for faceted morphology in laser surface engineered alumina ceramic. United States: N. p., 2007. Web. doi:10.1016/j.scriptamat.2007.05.008.
Harimkar, Sandip P, Daniel, Claus, Holzapfel, Christian, Leibenguth, Peter, M�cklich, Frank, & Dahotre, Narendra B. Validation of crystallographic correlation for faceted morphology in laser surface engineered alumina ceramic. United States. doi:10.1016/j.scriptamat.2007.05.008.
Harimkar, Sandip P, Daniel, Claus, Holzapfel, Christian, Leibenguth, Peter, M�cklich, Frank, and Dahotre, Narendra B. Mon . "Validation of crystallographic correlation for faceted morphology in laser surface engineered alumina ceramic". United States. doi:10.1016/j.scriptamat.2007.05.008.
@article{osti_931506,
title = {Validation of crystallographic correlation for faceted morphology in laser surface engineered alumina ceramic},
author = {Harimkar, Sandip P and Daniel, Claus and Holzapfel, Christian and Leibenguth, Peter and M�cklich, Frank and Dahotre, Narendra B},
abstractNote = {Surface modification of alumina ceramic using a high energy density continuous wave laser beam is associated with the formation of highly faceted pyramidal surface grains. Recently, we developed a phenomenological model explaining the faceted morphology by a fiber texture with a strong (1-210) component. Based on high resolution electron back-scattered diffraction, the present work proposes a more precise model showing that faceting of surface grains is closely linked with the evolution of a strong (2-310) fiber texture.},
doi = {10.1016/j.scriptamat.2007.05.008},
journal = {Scripta Materialia},
number = 5,
volume = 57,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • This communication reports on the characterization of novel surface microstructure formed in rapidly solidified porous alumina ceramic. Advanced characterization techniques such as Orientation Imaging Microscopy (OIM) and Atomic Force Microscopy (AFM) are used to understand the crystallographic and morphological aspects of the resultant microstructure. Potential applications of laser surface modified alumina ceramics are presented.
  • Laser surface modification of porous alumina ceramic with a high power laser is associated with a series of physical processes such as heating, melting, and evaporation of material. Above certain threshold laser intensity ({approx}10{sup 10} W/m{sup 2}), rapid evaporation at melt surface generates strong recoil pressures. These laser-induced evaporation recoil pressures tend to drive the flow of molten material into the porous substrate thus contributing to the overall observed depth of melting. This paper presents a three-dimensional thermal model to calculate the temporal evolution of temperature during laser surface modifications of alumina ceramic. This is followed by the determination ofmore » recoil pressures at the evaporating surface based on experimentally verified physical model of melt hydrodynamics and laser-induced evaporation proposed by Anisimov [Sov. Phys. JETP 27, 182 (1968)]. Finally, Carman-Kozeny equations were employed to analyze the effect of recoil pressure on the depth of infiltration which is subsequently integrated with the calculated depth of melting from thermal model. Such an integrative approach results in better agreement of the predicted values of depths of melting with the experimental values.« less
  • Surfaces of alumina ceramic compacts were modified by irradiating with a high-power continuous wave laser to form a rapidly solidified continuous surface layer. A detailed characterization of the laser surface modified alumina using X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed a development of (110) crystallographic texture and a systematic evolution of surface microstructure in terms of surface grain size, porosity and roughness with laser processing fluence. Also, due to complexity of surface microstructures, a fractal based approach is suggested to completely describe the surface state of laser surface modified alumina. The results indicated that fractal dimensions of themore » surface microstructures can be effectively correlated with the surface features of laser surface modified alumina.« less
  • In order to study the early stages of nanofuzz growth in fusion-plasma-facing tungsten, mirror-polished high-purity tungsten was exposed to 80 eV helium at 1130 C to a fluence of 4 1024 He/m2. The previously smooth surface shows morphology changes, and grains form one of four qualitatively different morphologies: smooth, wavy, pyramidal, or terraced/wide waves. Combining high-resolution scanning electron microscopy (SEM) observations to determine the morphology of each grain with quantitative measurement of the grain's orientation via electron backscatter diffraction (EBSD) in SEM shows that the normal-direction crystallographic orientation of the underlying grain controls the growth morphology. Specifically, near-<001> || normalmore » direction (ND) grains formed pyramids, near-<114> to <112> || ND grains formed wavy and stepped structures, and near-<103> || ND grains remained smooth. Comparisons to control specimens indicate no changes to underlying bulk crystallographic texture, and the effects are attributed to surface energy anisotropy, although, surprisingly, the expected {101} low-energy planes were not the most stable. Future developments to control tungsten texture via thermomechanical processing, ideally obtaining a sharp near- <103> || ND processing texture, may delay the formation of nanofuzz.« less
  • The effect of laser beam operation mode on transition of grain morphology was studied during surface modification of alumina ceramic. A 4 kW HL 4006D continuous wave Nd:yttrium-aluminum-garnet (YAG) laser and a JK 701 pulsed Nd:YAG laser were employed to conduct surface modification of alumina. The laser beam operated in continuous wave mode generated faceted grain structure on the surface of the ceramic while the beam operated in pulsed mode produced nonfaceted grain structure. Such transition in grain morphology is mainly attributed to different levels of undercooling which is a function of cooling rates encountered in two different modes ofmore » laser operation.« less