Journal of Alloys and Compounds 478 (2009) 193–196 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Effect of Ni–Al atomic ratio on glass formation in La–Al–Cu–Ni bulk metallic glasses Peiyou Li a , Shandong Li a,∗ , Zongjun Tian b , Zhigao Huang a , Fengming Zhang c , Youwei Du c a Department of Physics, Fujian Normal University, Fuzhou 350007, China b College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China c National Laboratory of Solid State Microstructure, and Department of Physics, Nanjing University, Nanjing 210093, China article info Article history: Received 1 September 2008 Received in revised form 24 November 2008 Accepted 25 November 2008 Available online 3 December 2008 Keywords: Bulk metallic glass Glass forming ability Atomic ratio abstract Glass forming ability (GFA) and thermal properties were investigated for La 62 Al 14 (Cu 1-x Ni x ) 24 (x = 0.2, 0.4, 0.6 and 0.8) bulk metallic glasses (BMGs). The experimental results show that in the La-based La–Al–(Cu–Ni) pseudo-ternary system, optimum glass formation actually occurs at the Ni:Al ratio of 1:1. It has been found that the GFA is much better in the range of unstable intermetallic compound (AlNi) than that of adjacent stable intermetallic compound (AlNi 3 ). The asymmetry of negative heat of mixing between the atomic pairs of La–Cu and La–Ni, Al–Cu and Al–Ni is also considered as another influencing factor of GFA. It might be an effective way to develop and design BMGs by adjusting the Ni–Al atomic ratio in Al–Ni-contained alloy systems. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Over several decades, the investigation of glass forming abil- ity (GFA) is important for the design and development of new bulk metallic glasses (BMGs) [1–7]. Turnbull’s early work [1] sug- gested that reduced glass transition temperature T rg (=T g /T l , T g is glass transition temperature, and T l is liquidus temperature) is a key indicator in determining GFA. As eutectic is always associated with the minimum liquidus temperature, the glass formation is generally related to deep-eutectic and eutectic composition [1,8,9]. Some empirical rules have been proposed to achieve BMGs with high GFA in multicomponent systems, which are described as fol- lows [10]: the multicomponent system should consist of more than three elements, and the main constituent elements should differ significantly in atomic size (by more than 12%) and should have negative heats of mixing with other constituent elements. Li and co-workers [5] found that the optimum composition for glass for- mation in the La–Al–(Cu,Ni) pseudo-ternary system is actual at an off-eutectic composition. Recently, Zhang and co-workers [6] discussed that a new method of “row substitution” with similar atomic sizes but different valence electronic structures to the sub- stituted element can improve GFA significantly. Thus, the selected optimum compositions including deep-eutectic, eutectic or off- eutectic composition and “row substitution” are recognized as the ∗ Corresponding author. Tel.: +86 591 28198956; fax: +86 591 83486160. E-mail address: dylsd007@yahoo.com.cn (S. Li). most effective ways to improve the GFA in multicomponent alloy systems. In this paper, the glass forming asymmetry of the pseudo- ternary La 62 Al 14 (Cu 1-x Ni x ) 24 alloys was investigated by the symmetric substitution of Ni for Cu. It is found that the Ni–Al atomic ratio and the asymmetry of negative heats of mixing with the main constituent elements play important roles of glass forming asym- metry in the present La-based BMGs. The optimum GFA actually occurs at the Ni:Al ratio of 1:1 or in the range of unstable com- pounds. 2. Experimental procedure The ingots with nominal compositions of La62Al14(Cu1-xNix)24 (x = 0.2, 0.4, 0.6 and 0.8) were prepared by arc melting a mixture of pure La (99.5 at.%), Al (99.9 at.%), Cu (99.999 at.%) and Ni (99.9 at.%) in a high-purity argon atmosphere. Each ingot was remelted at least four times to achieve chemical homogeneity. Cylindrical alloy rods with the diameter of 10 mm were prepared by copper mold suction casting. The glassy structure of these samples were characterised by X-ray diffraction (XRD) with Cu K radiation at 30 kV. The thermal stability of the glassy samples was evaluated using a differential scanning calorimeter (DSC) and differential thermal analyzer (DTA) under a continuous argon flow at a heating rate of 0.33 K s -1 . 3. Results and discussion Fig. 1 shows XRD patterns for the transverse sections of the La 62 Al 14 (Cu 1-x Ni x ) 24 alloy rods with 10mm in diameter. There are crystalline peaks superimposed on a wide diffused amorphous peak for the La 62 Al 14 (Cu 0.2 Ni 0.8 ) 24 alloy. This indicates that the rod sample is a mixture of amorphous and crystalline phases. 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.11.117