Crystallization behaviour and mechanical properties of rapidly solidified Al 87.5 Ni 7 Mm 5 Fe 0.5 amorphous alloy K. L. Sahoo Æ P. Poddar Æ Goutam Das Æ B. Ravi Kumar Received: 13 June 2006 / Accepted: 16 January 2007 / Published online: 1 May 2007 Ó Springer Science+Business Media, LLC 2007 Abstract The crystallization behaviour and the mechan- ical properties of rapidly solidified Al 87.5 Ni 7 Mm 5 Fe 0.5 alloy ribbons have been examined in both as-melt-spun and heat-treated condition using differential scanning calorim- etry, X-ray diffractometry (XRD), transmission electron microscopy (TEM), tensile testing and Vicker’s microh- ardness machine. XRD and TEM studies revealed that the as-melt-spun ribbons are fully amorphous. The amorphous ribbon undergoes three-stage crystallization process upon heating. Primary crystallization resulted in the formation of fine nanocrystalline fcc-Al particles embedded in the amorphous matrix. The second and third crystallization stages correspond to the precipitation of Al 11 (La,Ce) 3 and Al 3 Ni phases, respectively. Microhardness and tensile strength of the ribbons were examined with the variation of temperature and subsequently correlated with the evolved structure. Initially, the microhardness of the ribbon increases with temperature followed by a sharp drop in hardness owing to the decomposition of amorphous matrix that leads to formation of intermetallic compounds Introduction Al-rich (>80 at.%) nanophase composites such as rapidly solidified Al–TM–RE (TM = transition metal, RE = rare earth) alloys have received considerable research interest because of their scientific and technological importance [1–4]. These alloys can be quenched from the melt to a completely amorphous structure [3, 5] or to a mixed structure having uniform distribution of Al nanocrystals in an amorphous matrix [2, 4, 6, 7]. It is well established that the amorphous structure provides higher strength compared to conventional crystalline materials [6]. It has been reported that Al–Ni–Ln (Ln = Y, La or Ce) amor- phous alloys exhibit tensile strength above 1000 MPa with good bending ductility, even in Al-rich compositions of 84–86 at.% [3]. On partial crystallization, the nano- scale fcc-Al particles are uniformly dispersed in the amorphous matrix and a higher tensile strength coupled with good ductility is obtained when the volume fraction of the nanoscale Al particles is around 20–30% [3]. It has been reported [3, 8] that the tensile strength is further improved on addition of extra TM e.g., Fe in Al–Ni–RE systems. The ultrafine dislocation-free Al particles are responsible for such a high strength [9, 10]. During the crystallization process the amorphous matrix become enriched in solute elements resulting in an increase of strength [11, 12]. The resulting strength can be described by a simple rule of mixtures involving the strengthened amorphous matrix and the Al nanocrystals of ideal strength [12]. The crystalline particles, smaller than a critical size, become defect-free and its deformation resistance is higher than the amorphous matrix [3]. The mechanical properties and structural evolution of Al–Ni– Ce [8], Al–Ni–Y [4], and Al–Ni–La [3, 7] amorphous alloys have been extensively investigated. Replacement of pure rare earth elements by cost effective rare earth ele- ments such as misch metal (Mm) is potentially attractive and reduces the cost of materials. Some studies [13–17] have been undertaken to investigate the kinetics of the primary crystallization, and mechanical behaviour of amorphous and partially devitrified Al–Ni–Mm alloys. K. L. Sahoo (&)  P. Poddar  G. Das  B. R. Kumar National Metallurgical Laboratory, Jamshedpur 831007, India e-mail: klsah@nmlindia.org 123 J Mater Sci (2007) 42:6665–6671 DOI 10.1007/s10853-007-1530-0