Formation of Intermetallic Ni-Al Coatings by Mechanical Alloying with Different Intensities
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INTRODUCTION
IT is well known that intermetallic Ni-Al compounds offer a combination of good resistance to oxidation and enhanced mechanical properties at high temperatures.[1– 4] That is why they are widely used as protective coating materials for industrial alloys. One of the methods that can be effectively applied for fabricating aluminide coatings, as well as coatings with other materials, is mechanical alloying (MA).[5–13] Among possible MA methods of coatings fabrication, there are two conventional types, realized in vibratory[5–8] and planetary[9–13] activators. The vibratory activator has relatively low intensity (energy), whereas the planetary activator is well known as one of the most powerful methods. To form the desired phases in the coating materials, annealing is necessary after the vibratory activator process.[5–8] For the planetary activator process, the desired intermetallic phases can form directly in the coating layer during the MA process, and the consequent annealing leads to further phase transformations.[9–13] Though phase transformations and formation of intermetallic phases may occur directly during the MA process, the question about sequences of phase transformations remains open. For instance, formation of NiAl3 can be achieved in experiments by MA Ni and Al,[14] even though it is unfavorable in thermodynamics.[15] To improve the quality of intermetallic coatings, an understanding of the exact role of the parameters of MA and subsequent heat treatment is required. This article continues the study of phase transformations in MA NiAl coatings started in Reference 16; the particularities of formation such intermetallic coatings in vibratory and planetary types of activators are presented. V.YU. ZADOROZHNYY, Researchers, S.D. KALOSHKIN, Director of the College of New Materials and Nanotechnologies and Professor, M.N. CHURYUKANOVA, Researchers, and YU.V. BORISOVA, Engineer, are with the National University of Science and Technology, MISIS, Moscow 119049, Russia. Contact e-mail: [email protected] Manuscript submitted May 12, 2012. Article published online December 5, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
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EXPERIMENTAL DETAILS
Nickel plates of 10 9 7 9 2 mm and 20 9 20 9 2 mm dimensions were used as substrates for coating in vibratory and planetary activators, respectively. The hardness of the substrates was 350 HV. Ni (99.9 pct,
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