Cast aluminum alloys containing dispersions of zircon particles
- PDF / 3,305,490 Bytes
- 11 Pages / 603 x 783 pts Page_size
- 40 Downloads / 218 Views
I.
INTRODUCTION
METAL'particulate c e r a m i c composites (cermets) were initially developed with a view to combine the mechanical properties of metals, especially the ductility, with the high temperature stability of brittle ceramics. Cermets have been generally made by consolidation of powders or infiltration o f powder compacts by liquid metals. During later years, considerable attention was given to the development o f metal-ceramic composites by other routes, especially casting techniques, since they offered greater flexibility in fabricating components particularly o f large size and/or intricate shapes. The basic problems encountered in these processes were (i) rejection o f the ceramic phase by the liquid metal due to their incompatibility and (ii) inhomogeneous distributions of the second phase due to the difference in densities of the constituents. Attempts were made to improve wettability o f the ceramic phase by liquid metals with various innovations such as metal coatings of ceramics, alloy additions in liquid metals to lower surface tension and/or promote interaction o f the melt with the second phase, use o f ultrasonics, processing under high vacuum or inert gas atmosphere, etc. Unfortunately, however, successful cast composites have been few and far between. Moreover, the amounts o f the second phase in the cast composites were generally low. At the onset o f liquid metallurgy techniques, a process was developed for the dispersion o f nickel coated graphite particles in aluminum alloy castings through injection o f a gas in the melt with a view to improve gall resistance of aluminum alloys.~Shortly, this process was followed by the advent of a new method2 termed "Vortex" which involved mechanical stirring o f liquid aluminum with an impeller *Percentage (pct) of A1 or alloying elements referst o weight percentage.
A. BANERJI is a Research Student, Technische Universit~it Berlin, Fachbereich 17-Werkstoss Wissenschaften, Institut fiir Metallforschung Metallkunde, Germany; M . K. SURAPPAis with the Department of Materials Engineering, Drexel University, Philadelphia, P A 19104; and P.K. ROHATGI is Director, Regional Research Laboratory, Library Building (G. E), Bhopal University, Bhopal-462026, India. Manuscript submittedJanuary 18, 1982. METALLURGICAL TRANSACTIONS B
for entraining graphite particles. Vortex method was subsequently used for developing various metal-matrix particulate ceramic composites.3-7 Of late, development o f compocasting techniques 8'9 made it possible to fabricate cast composites containing high volume fractions o f the ceramic phase. However, it was strongly felt that a simple approach is also necessary to suit the conventional foundry practice for the successful development o f cast metal matrix composites containing high volume fractions of the particulate ceramic phase. Therefore, a programme was initiated at CSIR, Trivandrum to develop aluminum based composite materials utilizing the large resources o f particulate ceramic oxides, available on the west coast of India,
Data Loading...
