Mechanochemical Behavior of NiO-Al-Fe Powder Mixtures to Produce (Ni, Fe) 3 Al-Al 2 O 3 Nanocomposite Powder Z. ADABAVAZEH, F. KARIMZADEH, and M.H. ENAYATI (Ni, Fe) 3 Al-30 vol pct Al 2 O 3 nanocomposite powder was synthesized by mechanochemical reaction of Fe-NiO-Al powder mixtures. Structural evolution during mechanical alloying was studied by employing X-ray diffractometry (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM). After 78 minutes of milling, the (Ni, Fe) 3 Al-30 vol pct Al 2 O 3 nanocomposite can be synthesized by reaction 3Fe + 7Al + 6NiO with a combustion mode. DTA results revealed that milling for 60 minutes decreases the temperature of reaction from 1040 K to 898 K (767 °C to 625 °C). TEM images corroborate a homogenous dispersion of reinforcements in the matrix of the nanocomposite proving that the reduction in the crys- tallite size of both reinforcements and matrix is within the nanometer range. DOI: 10.1007/s11661-012-1138-0 Ó The Minerals, Metals & Materials Society and ASM International 2012 I. INTRODUCTION THE Ni 3 Al intermetallic compound exhibits advan- tageous properties including high melting temperature, high tensile strength and yield point, low density, high hardness, good thermal stability, high creep resistance, good corrosion, and oxidation resistance at elevated temperatures. [1,2] This is why the intermetallic compound is particularly ideal for many special applications such as cutting tools, coating blades in gas turbines, jet engines, corrosion resistant materials, and heat treatment fix- tures. The major barriers for the use of Ni 3 Al as structural materials are their low toughness and ductility at ambient temperature. [3,4] One practical processing route for direct synthesis of compounds and nanocom- posites is mechanical alloying (MA). [5–7] In recent years, there has been increased activity in research on the addition of a third alloying element to different inter- metallic compounds. It leads to the improvement of ductility and toughness at ambient temperature. [8–10] Mechanochemical synthesis, in which chemical reactions are induced by mechanical treatment, can raise the mechanical properties. [11–14] Several mechanochemically synthesized nanocomposites such as NiAl-Al 2 O 3 , [15] NiTi-Al 2 O 3 , [16] Fe 3 Al-Al 2 O 3 , [17] and (Fe, Ti) 3 Al- Al 2 O 3 [18] were previously reported. Rafiei et al. [18] stud- ied the formation of (Fe, Ti) 3 Al-Al 2 O 3 nanocomposites by mechanical alloying of Fe, Al, and TiO 2 powder mixture. Consolidation of the ball-milled powders into bulk, full density compacts while retaining nanoscale grain size is a major challenge. Many sintering tech- niques, e.g., hot pressing, hot extrusion, sintering forg- ing, and HIPing, were employed to consolidate the mechanically alloyed powders. Tavoosi et al. [19] investi- gated the fabrication of bulk Al-Zn/Al 2 O 3 metal matrix nanocomposites prepared by mechanical alloying and hot pressing. In this work, the aluminum and zinc oxide powder mixture was milled by a planetary ball mill and then hot pressed in a uniaxial die. However, there are few reports in the literature on the MA of ternary Ni-Fe-Al powders. Liu et al. studied the effects of Fe substitution for Al in NiAl alloy. Investigations were performed on the mechanical alloying of Ni 50 Al 50–x Fe x (x = 5, 10, 15, 20, 25, 30) powders mixture. [20] In our previous work, [21] the formation of (Ni, Fe) 3 Al intermetallic compound was investigated. In this study, the formation mechanism of the (Ni, Fe) 3 Al-30 vol pct Al 2 O 3 nanocomposite synthesized by mechanochemical reaction between Al, Fe, and NiO is reported. Finally, the formation mechanism and thermal stability in the milled powder at elevated temperatures was studied by employing X-ray diffractometry (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM). II. MATERIALS AND METHODS The powders of Fe (99.8 pct purity, particle size of ~100 lm, Merck, Darmstadt, Germany), Al (99.5 pct purity, particle size of 50 to 100 lm, Iran Powder Metallurgy Co., Mashhad, Iran), and NiO (99.9 pct purity, particle size of < 40 lm, Merck, Darmstadt, Germany) were mixed in the appropriate proportion to give the (Ni, Fe) 3 Al-Al 2 O 3 nanocomposite. Mechanical alloying was carried out in a planetary ball mill, nominally at room temperature and under Ar atmo- sphere. Al, Fe, and NiO with starting composition NiO- 23 wt pct Al-21 wt pct Fe were mixed according to Reaction [1] to produce a (Ni, Fe) 3 Al based nanocom- posite containing 30 vol pct Al 2 O 3 : 3Fe þ 7Al þ 6NiO ! 3 Ni; Fe ð Þ 3 Al ð70 vol pctÞ þ 2Al 2 O 3 ð30 vol pctÞ ½1 Z. ADABAVAZEH, MSc Graduate Student, and F. KARIMZADEH and M.H. ENAYATI, Associate Professors and Supervisors, are with the Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran. Contact e-mail: z.adabavazeh@ma.iut.ac.ir Manuscript submitted August 3, 2011. Article published online June 9, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A VOLUME 43A, SEPTEMBER 2012—3359