Solidification of nitrogen-atomized Al 86 Ni 6 Y 4.5 Co 2 La 1.5 metallic glass
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J.Q. Wanga) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
G.B. Schaffer The University of Queensland, School of Mechanical and Mining Engineering, ARC Centre of Excellence for Design in Light Metals, Brisbane, QLD 4072, Australia
M. Qianb) The University of Queensland, School of Mechanical and Mining Engineering, ARC Centre of Excellence for Design in Light Metals, Brisbane, QLD 4072, Australia (Received 16 November 2010; accepted 10 January 2011)
A comprehensive investigation has been made of the solidification of nitrogen-atomized Al86Ni6Y4.5Co2La1.5, using focused ion beam, transmission electron microscopy, and other analytical means. Face-centered cubic Al2Y was identified to be the leading crystalline phase rather than crystalline Al. A new orthorhombic-structured phase was identified in partially or fully crystallized powder particles. Apart from oxygen, nitrogen was also found to be associated with the leading crystalline phase Al2Y in which nitrogen exists as substitutional Nx. These findings facilitate the basis for understanding the unique aspects of the Al86Ni6Y4.5Co2La1.5 bulk metallic glass, including its powder preparation by gas atomization.
I. INTRODUCTION
Bulk metallic glass (BMG) was first realized in a Pdbased system1 and subsequently in many other systems such as Fe-based,2,3 Cu-based,4,5 Ti-based,6,7 Mgbased,8,9 and Zr-based systems.10–12 The unique microstructural features and properties of BMGs have drawn significant attention from the scientific community.13,14 Al-based BMGs, however, are only a very recent development; the first Al-based BMG with a composition of Al86Ni6Y4.5Co2La1.5 (all in at.%) was fabricated in 2009.15 All other Al-based amorphous alloys known to date are of limited glass forming ability (GFA), being amorphous only to a thickness of a few ten or hundred micrometers.15,16 Given the challenges encountered in developing Albased BMGs, it is necessary to understand the solidification of Al-based BMGs for future development of superior materials. In this regard, powder particles with different diameters offer an attractive start point as they represent a wide range of cooling rates, enabling one to pursue a detailed microstructural study from fully amorphous to fully crystallized states.17–20 In addition, powder
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2011.13 944
J. Mater. Res., Vol. 26, No. 7, Apr 14, 2011
http://journals.cambridge.org
Downloaded: 18 Mar 2015
metallurgy (PM) provides a potential solution to the fabrication of Al-based BMGs from amorphous powder,21,22 particularly when consolidated with the assistance of high pressure such as by spark plasma sintering. It is, therefore, also of necessity to understand the microstructural characteristics of gas-atomized Al86Ni6Y4.5Co2La1.5 powder particles for BMG fabrication from powder. Using focused ion beam (FIB), transmission electron microscopy (TEM), and oth
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