Graphite is commonly used in brake pads. The use of graphite powder has the main goal of solid state lubrication and friction coefficient stabilization. In this article results on resin bonded brake pads with focus on noise performance and heat dissipation are presented. Experimental tests are based on model friction materials with a known formulation and a reduced number of components for a better identification of the role of the graphite type. Results clearly indicate that both noise performance and thermal conductivity are strongly affected by the type of graphite. Guidelines for the selection of graphite types for optimized friction materials are given.

Modern water-atomised steel powder grades are characterised by the presence of two types of surface oxides: a thin iron oxide layer, covering more than 90% of the powder surface, and more thermodynamically stable particulate oxides. The development of inter-particle necks and carbon dissolution in the iron matrix both require efficient removal of the iron oxide layer. Hence, carbon reactivity strongly affects the surface oxide reduction that determines inter-particle neck development and carbon dissolution, and so microstructure development. An analysis is presented of the effect of three carbon sourcessynthetic graphite, natural graphite and carbon black -on microstructure and inter-particle neck development in Cralloyed PM steels. Metallographic and fractographic studies indicate that the most significant property of the carbon sources affecting reactivity is the carbon powder size. Carbon black shows the highest reactivity at elevated temperatures but is fully inert at temperatures below 900uC.

A B S T R A C T A detailed qualitative fatigue crack path study is made on Ni-Cu alloyed powder metallurgy (PM) steel with Mo prealloyed base powder. The microstructure is characterized by upper bainitic cores of the base powder particles surrounded by a Cu-rich martensite with islands of Ni-rich austenite. Earlier observations have shown that the visible surface cracks do not pass through the Ni-rich areas. The aim of the present study is to find the crack path in relation to the Cu-rich martensite and the Ni-rich austenite also below the surface. Successive grinding in steps of about 20 µm is made, and the surface crack in each level is recorded by light optical microscope (LOM). The main part of the crack path is found through high temperature bainite or along the interface between martensite and high temperature bainite. Ni-rich austenite is surrounded by martensite that hinders the crack from entering into austenite. The result indicates that austenite as such is not a strong crack stopper.

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Carbon is a key element for powder metallurgy. For example, carbon is the basic alloying element in PM sintered steel, and carbon powders are used as a carbon source for the production of hard metals. However, there are only a few studies about the mechanisms of carbon dissolution and reactivity in dependence on the carbon sources with solid metals/oxides. This work presents the effect of the carbon source (different graphite and carbon black types) on the reactivity and efficiency of oxides reduction during the sintering of PM steels and on the synthesis of nanocrystalline WC powders.This experimental work sets the basis for optimizing the production of PM steel parts and nano-WC powders based on raw material selection and process conditions.