Abstract.
Current processing methods for metal matrix composites (MMC) often produces agglomerated reinforced particles in the ductile matrix and also form unwanted brittle secondary phases due to chemical reaction between matrix and the reinforcement. As a result they exhibit extremely low ductility. In addition to the low ductility, the current processing methods are not economical for producing engineering components.
In this paper we demonstrate that these problems can be solved to a certain extent by a novel rheo-process. The key step in this process is application of sufficient shear stress on particulate clusters embedded in liquid metal to overcome the average cohesive force of the clusters. Very high shear stress can be achieved by using the specially designed twin-screw machine, developed at Brunel University, in which the liquid undergoes high shear stress and high intensity of turbulence. Experiments with Al alloys and SiC reinforcement reveal that, under high shear stress and turbulence conditions Al liquid penetrates into the clusters and disperse the individual particle within the cluster, thus leading to a uniform microstructure.
Introduction Demands set by the automotive and aerospace industries have led to the development of innovative combinations of composite materials. A large majority of these materials are metal matrix
composites (MMC) in which metallic matrices are reinforced with high strength and high modulus
phases, such as carbides, nitrides, and oxides.
Particulate MMCs have been shown to offer improvements in strength, wear resistance, structural efficiency, reliability and control of physical properties such as density and coefficient of thermal expansion, thereby providing improved engineering performance in comparison to the un-reinforced matrix [1-8]. Several authors [1,3,4] reviewed the applications for MMCs and major markets of ground transportation, thermal management, aerospace, industrial, recreational and infrastructures.
In all these applications, the principal advantage of MMCs is that their physical and mechanical properties can be enhanced to desired level by tailoring their microstructures for specific engineering applications. MMCs are generally processed with liquid metal routes such as stir casting and infiltration.
Powder metallurgy route is also used for specific applications. However, infiltration route is most commonly used method by the industries and accounts for largest volume in primary production
(~60%) [7]. In this method, a ceramic preform of the desired shape is infiltrated with the liquid
metal by the application of a pressure or by pressure-less techniques.
It was first widely used in the automotive industry but is now also a preferred process in the thermal management industry as a result of the ability to produce high quality near net shape or net shape components. Due to the high volume fraction of ceramic reinforcements, liquid metal infiltration is not appropriate for components that require thermo-mechanical deformation or for fracture sensitive applications. Additional process called insertion casting method has to be employed to dilute the reinforcement content to the required level.
Mau donasi lewat mana?
Donate with PaypalGopay-