Journal of Alloys and Compounds 500 (2010) 30–33 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Production of a nanocrystalline Ni 3 Al-based alloy using mechanical alloying Masoud Nazarian Samani a,b,∗ , Ali Shokuhfar a , Ali Reza Kamali b , Morteza Hadi b a Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Tehran, Iran b Department of Materials Science and Engineering, Malek Ashtar University of Technology, Shahin Shahr, Iran article info Article history: Received 13 July 2008 Received in revised form 25 February 2009 Accepted 26 February 2009 Available online 13 March 2009 Keywords: Ni3Al-based alloy Mechanical alloying Nanostructured materials Hot pressing abstract A new Ni 3 Al-based alloy has been successfully made via densification of mechanically alloyed powders with nominal compositions of Ni–8.14Al–7.83Cr–1.45Mo–0.01B (wt%). Mechanical alloying (MA) was car- ried out in a planetary ball mill under different conditions. The effect of MA on the structure of elemental powders was investigated. A Ni-based solid solution was produced after 10 h of milling that transformed to a disordered Ni 3 Al intermetallic compound with nanocrystalline structure on further milling. The rate of this transformation depended on milling variables such as mill rotation speed and milling media. The yield strength of produced alloy increased with increasing temperature up to 600 ◦ C beyond which it decreased. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Ni 3 Al-based alloys are well known for their excellent high tem- perature properties such as good mechanical strength, positive temperature coefficient of flow stress, attractive oxidation, creep resistance and alloy design flexibility. The most attractive property of Ni 3 Al is that its yield strength increases with increasing tem- perature up to about 800 ◦ C [1–3]. Poly-crystalline Ni 3 Al is a brittle material at room temperature [1,4] and has poor strength and creep properties at high temperatures [5,6]. A number of Ni 3 Al-based alloys have been designed to overcome these limitations. In these alloys, the third element is used to enhance the mechanical proper- ties. Boron is added as the key trace addition since it improves the grain boundary cohesive strength and room temperature ductility. The other alloying additions include Cr for reducing environmen- tal embrittlement and oxidation at higher temperatures, Mo for increasing strength at ambient and elevated temperatures, and Zr for reducing solidification shrinkage and macroporosity through the formation of +Ni 5 Zr as a low melting point (1170 ◦ C) eutectic phase [3]. Ni 3 Al-based alloys, especially the well known alloy of IC-221M, are produced by melting and casting processes [6–12]. The major problem in production of these alloys via melting processes is the strong tendency of aluminum to oxidize at elevated temperatures and metal-ceramic interaction during the melting [6,10,12]. On the other hand, the presence of 1.7wt% Zr in the IC-221M alloy leads ∗ Corresponding author. Tel.: +98 912 7085285; fax: +98 312 5228530. E-mail address: Masoud.Nazarian@gmail.com (M. Nazarian Samani). to the formation of +Ni 5 Zr eutectic phase [9]. Ni 5 Zr segregates in grain boundaries and hardly dissolves in the alloy [13]. In addition, it limits the hot working of IC-221M. One approach to overcome these problems is to produce the Ni 3 Al-based alloys in their net shape by a powder metallurgy process as there is no melting step in these processes. Therefore, Zr can be removed from the chemical composition of the alloy. In this research, a new alloy with nominal compositions of Ni–8.14Al–7.83Cr–1.45Mo–0.01B (wt%) was produced by mechan- ical alloying and hot pressing processes. The effects of process variables such as milling media (wet or dry milling) and milling speed on the kinetics of the MA process were also investigated. 2. Experimental 2.1. Materials and procedures Elemental high purity Ni, B, Cr, Mo and Al powders with an average particle size of 10 m were mixed to give the nominal compositions of Ni–8.14Al–7.83Cr–1.45Mo–0.01B (wt%). MA was performed for different milling times at room temperature using a Fritsch P6 planetary ball mill under Ar atmo- sphere. The powder and the stainless steel milling balls were sealed in a stainless steel vial. The ball-to-powder weight ratio was 10:1. MA was carried out under three different milling conditions, series I–III in Table 1. Samples were taken at selected time intervals and characterized by X-ray diffraction (XRD) in a Seifert 3003TT diffractometer using filtered Cu K radiation ( = 0.15406 nm) at 40 kV and 30 mA. Energy-dispersive X-ray spectroscopy (EDX) coupled with the “Vega©Tescan” scan- ning electron microscope (SEM) was used for the semiquantitative examination of microstructure. The lattice parameters, the mean crystallite size and the mean lattice strain (the latter two determined by the Williamson–Hall method) were calculated from the XRD data taking into account Cu K radiation. A hot pressing machine (model ASTRO HP-20-4560) was used for densification of mechanically alloyed powders. Densification was carried out in a graphite mold under a pressure of 6MPa at a temperature of 1,000 ◦ C for 10 min. The compressive 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.02.140