Hindawi Publishing Corporation Journal of Nanomaterials Volume 2013, Article ID 101508, 6 pages http://dx.doi.org/10.1155/2013/101508 Research Article Applied Pressure on Altering the Nano-Crystallization Behavior of Al 86 Ni 6 Y 4.5 Co 2 La 1.5 Metallic Glass Powder during Spark Plasma Sintering and Its Effect on Powder Consolidation X. P. Li, 1 M. Yan, 1 G. Ji, 2 and M. Qian 1 1 Te University of Queensland, School of Mechanical and Mining Engineering, ARC Centre of Excellence for Design in Light Metals, Brisbane, QLD 4072, Australia 2 Unit´ e Mat´ eriaux et Transformations, UMR CNRS 8207, Universit´ e Lille 1, Bˆ atiment C6, 59655 Villeneuve d’Ascq, France Correspondence should be addressed to M. Yan; m.yan2@uq.edu.au Received 19 December 2012; Accepted 25 January 2013 Academic Editor: Jianxin Zou Copyright © 2013 X. P. Li et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Metallic glass powder of the composition Al 86 Ni 6 Y 4.5 Co 2 La 1.5 was consolidated into 10 mm diameter samples by spark plasma sintering (SPS) at diferent temperatures under an applied pressure of 200 MPa or 600 MPa. Te heating rate and isothermal holding time were fxed at 40 ∘ C/min and 2min, respectively. Fully dense bulk metallic glasses (BMGs) free of particle-particle interface oxides and nano-crystallization were fabricated under 600MPa. In contrast, residual oxides were detected at particle-particle interfaces (enriched in both Al and O) when fabricated under a pressure of 200 MPa, indicating the incomplete removal of the oxide surface layers during SPS at a low pressure. Transmission electron microscopy (TEM) revealed noticeable nano-crystallization of face-centered cubic (fcc) Al close to such interfaces. Applying a high pressure played a key role in facilitating the removal of the oxide surface layers and therefore full densifcation of the Al 86 Ni 6 Y 4.5 Co 2 La 1.5 metallic glass powder without nano-crystallization. It is proposed that applied high pressure, as an external force, assisted in the breakdown of surface oxide layers that enveloped the powder particles in the early stage of sintering. Tis, together with the electrical discharge during SPS, may have beneftted the viscous fow of metallic glasses during sintering. 1. Introduction Metallic glasses (MGs) have been investigated for decades due to their intrinsically unique physical and chemical properties [1]. Al-based MGs are promising advanced materials which have attracted increasing attention for their ultrahigh specifc strength and relatively low cost compared with most other MGs [2]. However, due to their low glass forming ability (GFA), fabrication of Al-based BMGs through a conventional cooling process from liquid has proved to be challenging [3– 5]. Te frst conceptual Al-based BMG with 1 mm diameter was fabricated using a copper mold casting approach in 2009 [6] since the Al-based MG was frst reported in 1988 [7] and the alloy reported [6] remains to be the best glass forming Al- based BMG to date. Te slow development of Al-based BMGs in terms of their GFA impedes the potential application of these materials. Since MG powder can be readily prepared by gas- atomization [8], powder metallurgy (PM), especially the spark plasma sintering (SPS) technique, ofers an alternative to the fabrication of BMGs. Fully dense Ti-, Ni-, Cu-, and Fe-based BMGs with >10 mm diameters have been fabricated using SPS [9–12]. Tese MGs have much higher glass tran- sition temperatures (  ) [1, 3] compared to Al-based MGs and therefore can be readily consolidated at high sintering temperatures without nano-crystallization. As for Al-based BMGs, because their   temperatures are generally <300 ∘ C, nano-crystallization is easy to occur during SPS. Hence, few studies have succeeded in fabricating fully dense Al-based BMGs without crystallization [13–15]. On the other hand, a previous study [16] has revealed that MG powder is enveloped by an oxide layer which would inhibit viscous fow of the amorphous material for full densifcation. As a result, it is essential to remove this surface oxide layer to enable viscous