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Focused Ion Beam Study of Ni5Al Single Splat Microstructure

Published online by Cambridge University Press:  26 February 2011

Yuhong Wu ,
Meng Qu ,
Lucille A Giannuzzi ,
Sanjay Sampath  and
Andrew Gouldstone
Yuhong Wu
Affiliation:
yuhwu@notes.cc.sunysb.eduSUNY Stony BrookMaterials Science and Engineering130 Heavy EngineeringSUNY Stony BrookStony Brook NY 11794-2275United States
Meng Qu
Affiliation:
mqu@gmail.com, SUNY Stony Brook, Materials Science and Engineering, 130 Heavy Engineering, SUNY Stony Brook, Stony Brook, NY, 11794-2275, United States
Lucille A Giannuzzi
Affiliation:
Lucille.Giannuzzi@fei.com, FEI Corp, HIllsboro, OR, 97124, United States
Sanjay Sampath
Affiliation:
ssampath@ms.cc.sunysb.edu, SUNY Stony Brook, Materials Science and Engineering, 130 Heavy Engineering, SUNY Stony Brook, Stony Brook, NY, 11794-2275, United States
Andrew Gouldstone
Affiliation:
bubbleraft@gmail.com, SUNY Stony Brook, Materials Science and Engineering, 130 Heavy Engineering, SUNY Stony Brook, Stony Brook, NY, 11794-2275, United States
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Abstract

Thermally sprayed (TS) coatings are widely used for surface engineering across a range of industries, including aerospace, infrastructure and biomedical. TS materials are formed via the successive impingement, rapid quenching and build-up of molten powder particles on a substrate. The impacted ‘splats’ are thus the fundamental microstructural constituents of the coatings, and their intrinsic properties, as well as intersplat bonding and morphology, dictate coating behavior. Beyond the obvious practical considerations, from a scientific standpoint, splats represent a fascinating template for study, due to the highly non-equilibrium processing conditions (rapid deceleration from sub-sonic velocities, million-degree/sec cooling rates). In the literature, many studies of isolated splats on substrates have been carried out, but these have focused on overall morphology (disc-shape vs fragmented). Direct observations of microstructure, in particular cross-section, are limited in the specimen preparation stage due to splat size (tens of microns in diameter, 1-2 microns in thickness). However, Focused Ion Beam (FIB) techniques have allowed this problem to be addressed in a robust manner; in this paper we will discuss such approaches to observe Ni5Al splats on stainless steel substrates. Cross-sections through the splat and the substrate were created by recourse to ion milling and the ion beam itself provided good channeling contrast for grain imaging. The typical splat microstructure with sub-micron Ni(Al) columnar grains, a chill zone at the bottom and a lift off area is observed in high detail. In addition, an amorphous aluminum oxide top layer of 100-200 nm is partially present on top of the Ni(Al) columnar grains. At the splat/substrate interface, defects such as micro- and nano-scale pores were characterized for the first time and will be discussed. These observations provide insights into splat and interface formation during the deposition process and may drastically improve our current understanding of Ni5Al splat properties.

Keywords

scanning electron microscopy (SEM)thin filmmicrostructure
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 983: Symposium LL – Focused Ion Beams for Analysis and Processing , 2006 , 0983-LL04-04-KK04-04
Copyright
Copyright © Materials Research Society 2007

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