Content area
Full Text
Key words: Friction composite materials, friction coefficient, wear rate, powder metallurgy.
Abstract: The composites tested in this research contain mainly iron, then copper, nickel and graphite. The aim of the paper is to emphasize the influence of nickel content on the tribological properties of these composites. The initial powder mixtures were mechanically milled in a planetary ball mill in order to assure a good chemical homogeneity and a uniform distribution of components. As prepared mixtures were compacted by closed die pressing, and then sintered in a belt carrier furnace. The friction coefficient and wear rate were determined. The optimal value of nickel that assures the best tribological properties was established. Future research will study the influence of adding ceramic powders to the tested compositions on the resulting tribological properties.
1. INTRODUCTION
Friction materials belong to the class of complex materials containing metallic, non-metallic and/or organic components which function is to improve the friction coefficient and wear resistance. One of their main applications is vehicle's braking system (Figure 1). Brake disc, brake pads, wheel caliper are some parts of these systems. The materials employed to fabricate these components have to fulfill some requirements such as high friction coefficient, low wear rate, good corrosion resistance and thermal conductibility, long life in service etc. All the properties mentioned above have to be stable in time, at high temperatures and high charging loads [2].
Present day research is aimed towards explaining the phenomena that occur at the brake pad - brake disc interface. Chemical composition, material's properties, the quantity of lubricant, friction/lubricant ratio are some of the parameters with an important influence on these phenomena [3, 4, 5, 6].
Iron and copper are among the most used metallic components for fabricating brake friction materials. Iron-based friction materials are materials with a large number of components. Some of these components role is to assure friction properties to the materials, and the others, lubricants, have to assure a good wear resistance. Howbeit, some components are, at the same time, not only friction but also lubricating components.
Recent research showed that copper is such a component. It has a dual role in these materials: as reinforcing component of iron matrix, and as solid lubricant [7]. It also has an important...