Solidification Processing of Magnesium Based In-Situ Metal Matrix Composites by Precursor Approach

In-situ magnesium based metal matrix composites (MMCs) belong to the category of advanced light weight metallic composites by which ceramic dispersoids are produced by a chemical reaction within the metal matrix itself. In-situ MMCs comprised uniform distribution of thermodynamically stable ceramic dispersoids, clean and unoxidized ceramic-metal interfaces having high interfacial strength. In last two decades, investigators have been collaborating to explore the possibility of enhancing the high temperature creep resistance performance in polymer-derived metal matrix composites (P-MMCs) by utilizing polymer precursor approach. A unique feature of the P-MMC process is that since all constituents of the ceramic phase are built into the polymer molecules itself, there is no need for a separate chemical reaction between the host metal and polymer precursor in order to form in-situ ceramic particles within the molten metal. Among the different polymer precursors commercially available in the market, the silicon-based polymers convert into the ceramic phase in the temperature range of 800–1000°C. Therefore, these Si-based polymers can be infused into molten Mg or Mg-alloys easily by simple stir-casting method. This chapter mainly focuses on understanding the structure–property correlation in both the Mg-based and Mg-alloy based in-situ P-MMCs fabricated by solidification processing via polymer precursor approach

Processing of ultrafine-size particulate metal matrix composites by advanced shear technology

Copyright @ 2009 ASM International. This paper was published in Metallurgical & Materials Transactions A 40A(3) and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.Lack of efficient mixing technology to achieve a uniform distribution of fine-size reinforcement within the matrix and the high cost of producing components have hindered the widespread adaptation of particulate metal matrix composites (PMMCs) for engineering applications. A new rheo-processing method, the melt-conditioning high-pressure die-cast (MC-HPDC) process, has been developed for manufacturing near-net-shape components of high integrity. The MC-HPDC process adapts the well-established high shear dispersive mixing action of a twin-screw mechanism to the task of overcoming the cohesive force of the agglomerates under a high shear rate and high intensity of turbulence. This is followed by direct shaping of the slurry into near-net-shape components using an existing cold-chamber die-casting process. The results indicate that the MC-HPDC samples have a uniform distribution of ultrafine-sized SiC particles throughout the entire sample in the as-cast condition. Compared to those produced by conventional high-pressure die casting (HPDC), MC-HPDC samples have a much improved tensile strength and ductility.EP-SR

Effect of increase in heterogeneous nucleation sites on the aging behavior of 6061/SiC metal matrix composites

Materials Research Bulletin3081023-1030MRBU

Processing-microstructure-mechanical properties of Al based metal matrix composites synthesized using casting route

Key Engineering Materials104-107Pt 1259-274KEMA

Fluidity of aluminum-silicon-alumina composite.

Fluidity of Al-11.8 pet Si alloy containing up to 5.5 wt pet dispersed ν-A12O3 particles has been studied. Spiral fluidity of Al-11.8 pet Si alloy decreases with an increase in the amount of dispersed alumina particles (for a given size) and decrease in the particle size (for a given weight percent). The spiral fluidity(F) of Al-11.8 pet Si-Al2O3 composite correlates well with the total surface area of dispersed A12O3 particles and it can be expressed by the equation of the typeF = a − bx wherex represents the total surface area of alumina particles present in unit weight of the composite and, a and b are constants. Part of the observed decreases in fluidity could be attributed to expected increases in the effective viscosity of composite melts due to the presence of dispersed A12O3 particles. However, the fluidity of Al-11.8 pct Si-5.5 pet A12O3 (60µm) composite poured at 740 °C is at the same level as of Al-11.8 pet Si alloy poured at 700 °C. Hence, the fluidity of Al-11.8 pet Si alloy containing up to 5.5 wt pet A12O3 particles is adequate to make variety of castings at 740 °C

Effect of interfacial characteristics on the failure-mechanism mode of a SiC reinforced Al based metal-matrix composite

Journal of Materials Processing Technology671-394-99JMPT

Correlation between microstructure and wear behavior of AZX915 Mg-alloy reinforced with 12 wt% TiC particles by stir-casting process

The present work concerns with correlation between microstructure and wear behavior of AZX915 Mg-alloy reinforced with 12 wt% of TiC particles by stir-casting process. Dry sliding tests were performed under ambient environment by using a pin-on-disc (EN8 steel) configuration with a normal load of 50 N at a constant sliding speed of 2.50 ms−1. While as-cast composite experienced delamination wear, heat treated composite suffered from delamination and oxidation wear during dry sliding contact. Moreover, the heat treated composite exhibited lower friction and higher wear rate as compared to the as-cast composite. Friction and wear behavior were correlated with microstructures based on the concept of oxidation tendency and crack nucleation/propagation. Further, a schematic model has been proposed illustrating wear mechanisms from the point of view of subsurface microstructural evolution of the AZX915-TiCp composite

The UPAL process: a direct method of preparing cast aluminium alloy-graphite particle composites.

A direct method of preparing cast aluminium alloy-graphite particle composites using uncoated graphite particles is reported. The method consists of introducing and dispersing uncoated but suitably pretreated graphite particles in aluminium alloy melts, and casting the resulting composite melts in suitable permanent moulds. The optical pretreatment required for the dispersion of the uncoated graphite particles in aluminium alloy melts consists of heating the graphite particles to 400° C in air for 1 h just prior to their dispersion in the melts. The effects of alloying elements such as Si, Cu and Mg on the dispersability of pretreated graphite in molten aluminium have also been reported. It was found that additions of about 0.5% Mg or 5% Si significantly improve the dispersability of graphite particles in aluminium alloy melts as indicated by the high recoveries of graphite in the castings of these composites. It was also possible to disperse upto 3% graphite in LM 13 alloy melts and retain the graphite particles in a well distributed fashion in the castings using the pre-heat-treated graphite particles. The observations in this study have been related to the information presently available on wetting between graphite and molten aluminium in the presence of different elements and our own thermogravimetric analysis studies on graphite particles. Physical and mechanical properties of LM 13-3% graphite composite made using pre-heat-treated graphite powder, were found to be adequate for many applications, including pistons which have been successfully used in internal combustion engines

Regarding the effect of aging heat treatment on the failure behaviour of a SiC reinforced Al based metal matrix composite

Indian Journal of Engineering and Materials Sciences511-