Brakes are a crucial element for a vehicle from safety point of view. A faulty brake is one of the major causes of road accidents. Hence constant efforts are going towards the development of brake systems as well as brake materials. Gray cast iron is the dominant materials for drum/disc rotor, while phenolic polymer matrix composites are used as brake pad/shoe materials. As a new disc/drum materials, aluminimum metal matrix composites (Al MMCs) are attractive for their lightweight (three times lighter than cast iron) properties, higher thermal conductivity, specific heat, superior mechanical properties and higher wear resistance over cast iron.

The study of the tribological behaviour of a brake is important because a good control of braking of a vehicle needs a consistent and steady friction property. Substantial information is available in literature on the tribology of Al MMC-metal system. The Al MMCs used in this study are mainly based on Al-SiC. Since phenolic based materials are being used as brake pad nowadays, tribology of Al MMC-phenolic brake pad system would be more relevant from a practical point of view. Very little information is available in literature on the Al MMC-phenolic brake pad system, although some of the leading car manufacturers are reporting to have introduced recently Al MMC in their new car models.

In this work boron carbide (B₄C)which is a material that is harder and lighter than SiC, is investigated as a way to improve the wear performance of Al MMC. A tribological study on SiC as well as B₄C Al MMC, and a understanding of wear and frictional mechanism of SiC and B₄C reinforced Al MMC running against brake pad material under varying operational and environmental condition, are of considerable importance both from a scientific and practical point of view.

Pure Al/SiC, B₄C MMCs are being made by stir casting. The cast MMCs are then hot extruded. Microstructural characterization is to be carried out by optical microscopy (OM) and scanning electron microscopy (SEM). The reaction layer at the matrix/particle interface, is investigated by EDX, XRD, Nano-indentation, TEM, etc.

Uni-directional sliding wear tests are carried out at different loads and speeds in a Pin-on-disc apparatus. The evolution of the coefficient of friction and the bulk temperature during wear tests is measured on-line. To identify the wear mechanisms involved in the sliding contacts, Al/MMC-Pad system worn surfaces and subsurface structure of the wear samples are studied using optical microscopy (OM), scanning electron microscopy (SEM). Surface films formed on the worn surfaces during wear test can be characterised using EDX, auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), etc.

This research is in the initial stage, and results will be presented in the coming months.

Part of this work is funded by the Belgian Office for Support to Developing Countries (ABOS). The research work is done partly at MTM-KU.Leuven (Belgium) and at the Bangladesh University of Engineering and Technology (BUET-Dhaka).