Al based ultra-fine eutectic with high room temperature plasticity and elevated temperature strength C.S. Tiwary a,n , S. Kashyap a , D.H. Kim b , K. Chattopadhyay a a Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, Karnataka, India b Center for Non-Crystalline Materials, Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, South Korea article info Article history: Received 31 January 2015 Received in revised form 6 May 2015 Accepted 8 May 2015 Available online 16 May 2015 Keywords: Nano-eutectic alloy Strength Ductility Ternary alloy abstract Developments of aluminum alloys that can retain strength at and above 250 °C present a significant challenge. In this paper we report an ultrafine scale Al–Fe–Ni eutectic alloy with less than 3.5 at% transition metals that exhibits room temperature ultimate tensile strength of 400 MPa with a tensile ductility of 6–8%. The yield stress under compression at 300 °C was found to be 150 MPa. We attribute it to the refinement of the microstructure that is achieved by suction casting in copper mold. The char- acterization using scanning and transmission electron microscopy (SEM and TEM) reveals an unique composite structure that contains the Al–Al 3 Ni rod eutectic with spacing of 90 nm enveloped by a lamellar eutectic of Al–Al 9 FeNi ( 140 nm). Observation of subsurface deformation under Vickers indentation using bonded interface technique reveals the presence of extensive shear banding during deformation that is responsible for the origin of ductility. The dislocation configuration in Al–Al 3 Ni eutectic colony indicates accommodation of plasticity in α-Al with dislocation accumulation at the α-Al/Al 3 Ni interface boundaries. In contrast the dislocation activities in the intermetallic lamellae are limited and contain set of planner dislocations across the plates. We present a detailed analysis of the fracture surface to rationalize the origin of the high strength and ductility in this class of potentially promising cast alloy. & 2015 Elsevier B.V. All rights reserved. 1. Introduction The growth of metal intermetallic in-situ composite through eutectic solidification is an elegant method for producing com- posite materials for high temperature applications. In this kind of composite, the fibers of intermetallics are grown inside the metallic matrix during solidification of the alloy [1–8]. Although well known for decades, their applications for aluminum alloys are limited often due to poor room temperature ductility [1–8]. Recently, it has been shown that eutectics at nano-length scale with micron size primary phase can exhibit high strength and plasticity [9–12]. The high strength in these cases is mainly due to nano/ultrafine eutectic while plasticity was derived from soft dendrites, which enhance dislocation activity [13–17]. Therefore, the strength and plasticity of the composites are strongly related through volume fraction, morphology and length scale of the eutectic phase constituents. For improvement in strength the volume fraction of the hard intermetallic must be maximized [2]. But high intermetallic fraction drops the ductility. To overcome the relatively poor ductility that is often observed in binary eutectic alloys, several ternary alloying additions have been attempted [13,18–22]. The ternary addition refines eutectic and forms small size colonies [18–21]. Under suitable conditions increasing ternary additions can yield a combination of two kinds of eutectics with two different spacings [22,23]. Synergy of these two eutectics and two length scales represent opportunity for alloy development. There are several Al based eutectics with intermetallics (e.g. Al 2 Cu, Al 3 Ni and Al 3 Zr) [1,2]. Among these, Al matrix with Al 3 Ni fiber eutectic has widely been studied as model system for deformation and fracture behavior of fiber reinforced in-situ grown metal–matrix composites [2–8]. The eutectic micro- structure in this case possesses excellent thermal stability upto 500 °C and the hardness of Al 3 Ni fiber does not reduce sig- nificantly, notably up to 250 °C [2–8]. However, the eutectic alloy exhibits a low ductility and a yield strength of  140 MPa at room temperature [2–8]. We therefore, explored the possibility of syn- thesizing a composite of two eutectics by adding ternary alloying elements. We have chosen Fe which is a natural impurity element in aluminum alloys and hence in general less welcome in common alloys [1,2]. In Al rich corner, it forms Al rich solid solution which coexists with Al 3 Ni and Al 9 FeNi intermetallics (Fig. 1(a)). The alloy Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2015.05.024 0921-5093/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ91 8022932262; fax: þ91 8023600472. E-mail addresses: cst311@gmail.com, cst.iisc@gmail.com (C.S. Tiwary). Materials Science & Engineering A 639 (2015) 359–369