The increasing need for materials with light weight, high resistance to corrosion and wear, toughness and strength, machinability, high thermal capacity etc. for various applications is unending. This demand has continued to stretch the exploitation and manipulation of various functionally graded materials (FGMs) and their production methods. This study explores one of the FGM production processes called the centrifugal casting technique (CCT). The centrifugal casting process has several potential advantages over traditional casting methods. This study provides information regarding the basic functionally graded production methods and their applications and also discusses categories of CCT, evolution and process parameters.

This paper discusses the main Functionally Graded Materials (FGMs) and their bulk fabrication techniques, their development, principles and applications. The fabrication processes considered include powder metallurgy (PM), sintering, squeeze casting, infiltration process, compocasting, centrifugal casting, stir casting, material prototyping. The paper provides an overview of the FGM processing parameters including reinforcement particles size and volume %, temperature, pressure (for PM), and stirrer and mould rotational speeds (for stir and centrifugal casting processes respectively). The paper notes that the FGMs are widely used in the following sectors: automotive, medical, aerospace, aviation, nuclear energy, renewable energy, chemical, engineering, optics electronics etc.

Enhanced tribological and location-specific properties achieved in functionally graded metallic composites make them potential materials for futuristic engineering components. The present investigation aims on the processing of homogenous and functionally graded Al matrix composites reinforced with SiC particles of 23 µm average particle size by gravity and centrifugal casting techniques. The sizes of the primary aluminium and eutectic silicon phases are finer towards the outer periphery due to the higher solidification rate. Functionally graded Al–SiCp composite rings produced by centrifugal casting show higher concentration of SiCp towards outer periphery, followed by a gradient transition region and the particle depleted zone. Particle agglomerates formed due to partially wetted particles associated with voids and gas porosities segregate towards the inner periphery. The higher concentration of reinforcement particles near the outer periphery in FGM enhances the hardness and wear resistance in rotary and reciprocating wear studies. Centrifugal cast alloys show enhanced wear resistance than the gravity cast specimen due to fine grains of primary aluminium and eutectic silicon. The rotary and reciprocating wear test shows the adhesive and abrasive type wear mechanisms.

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The study investigates the application of centrifugal casting process in the production of a complex shape component, Pelton turbine bucket. The bucket materials examined were functionally graded aluminium A356 alloy and A356-10%SiCp composite. A permanent mould for the casting of the bucket was designed with a Solidworks software and fabricated by the combination of CNC machining and welding. Oil hardening non-shrinking die steel (OHNS) was chosen for the mould material. The OHNS was heat treated and a hardness of 432 BHN was obtained. The mould was put into use, the buckets of A356 Alloy and A356-10%SiCp composite were cast, cut and machined into specimens. Some of the specimens were given T6 heat treatment and the specimens were prepared according to the designed investigations. The micrographs of A356-10%SiCp composite shows more concentration of SiCp particles at the inner periphery of the bucket. The maximum hardness of As-Cast A356 and A356-10%SiCp composite were 60 BRN and 95BRN respectively, recorded at the inner periphery of the bucket. And these values appreciated to 98BRN and 122BRN for A356 alloy and A356-10%SiCp composite respectively after heat treatment. The prediction curves of the ultimate tensile stress and yield tensile stress show the same trend as the hardness curves.

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This study examines the possibility of fabricating a complex, non-cylindrical, Pelton turbine bucket by centrifugal casting technique. Oil hardening non-shrinking die steel material was selected for the permanent mould production, machined with computer numerical control and heat treated to a hardness of 432 BHN. Aluminium alloys, A390 and A390-5%Mg, were considered as the Pelton turbine bucket materials, cast and characterised. The effects of centrifugal casting technique and thermal treatment on the mechanical properties and corrosion resistance of A390 and A390-5%Mg alloys were studied. A hardness of 150 BHN (maximum) was recorded near the inner surface of the bucket and 157 BHN (maximum) was recorded at the outer periphery of the cylindrical cast. It was observed that A390-5%Mg by gravity casting shows higher corrosion resistance than the A390 alloy. Furthermore, the specimen from the outer zone of the circular cast shows a higher corrosion resistance than the specimen from the inner periphery.