Farshad Akhlaghi - School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran P. O. Box ۱۱۱۵۵-۴۵۶۳, Tehran, Iran
Fatemeh Abedini - School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran P. O. Box ۱۱۱۵۵-۴۵۶۳, Tehran, Iran

Al-Al۳Ni composites due to their high strength, creep resistance, fatigue resistance, good ductility, adequate toughness, high corrosion resistance and hardness have gained considerable attention in recent years. In the present investigation, for the first time, powder metallurgy (PM) method was used to in-situ produce Al-Al۳Ni composites. Commercially pure aluminum powders (۶۳-۱۲۵ μm) and the same sized pure nickel powders used as starting materials. The Al and Ni powders were initially soaked in NaOH and acetone respectively to remove their surface impurities. The Al/Ni powder mixtures with different Ni contents subjected to cold pressing and sintering at different temperatures for various times. Samples of Al powders without Ni addition were also prepared using identical procedures as for Al/Ni composites to serve as the reference samples. The results of XRD, optical microscopy and SEM studies as well as Brinell hardness measurements performed on the sintered compacts revealed that even after ۷۵ minutes sintering of an Al/Ni compact at ۶۴۰ ˚C, the unreacted Ni particles could be detected in the sample. The increased sintering temperature to ۶۵۵˚C resulted in more effective interaction between Al and Ni during sintering at ۱۵ minutes. However, sintering at this temperature for longer periods of time resulted in partial melting and deformation of the samples. Therefore, Ni powders subjected to high-energy ball milling to increase their activity. The XRD results confirmed that sintering at ۶۵۵˚C of the Al/Ni powder compact containing ۱۵wt.% of ball-milled Ni resulted in complete reaction and Al-Al۳Ni eutectic formed without any unreacted Ni. The porosity level of the samples increased with increasing percentage of Al۳Ni phase in the matrix. Brinell hardness values of all the composite samples were higher than that of their reference counterpart. The Al-۲۰wt.% Ni sample prepared by milled Ni exhibited the maximum hardness value being almost three times of that of the reference sample. However, the increased content of milled Ni to ۲۵wt.% resulted in some unreacted Ni particles in the matrix as was confirmed by XRD studies.

Al-Al۳Ni Composites, In-situ method, Powder metallurgy, Ball milling, Sintering, Hardness, XRD, OM, SEM