Copper infiltrated high speed steel skeletons

Purpose: This article is a monographic summary of the most important research results from the last 10 years regarding HSS based materials. This materias were produced with powder metallurgy technology using spontaneous infiltration. The presented results answer the question of how iron, tungsten carbide and copper additives influence the final properties of these materials and present additional microstructural phenomena revealed during their manufacture. Design/methodology/approach: Materials were produced by spontaneous infiltration. Porous skeletons for infiltration were produced by pressing and pressing and sintering of mixed powders. Copper was used as the infiltrant. Findings: The molten copper was drawn into the porous skeletons, through a capillary action, and filled virtually the entire pore volume to get the final densities exceeding 97% of the theoretical value. Research limitations/implications: As part of further research, microstructures of M30WC composites obtained by direct infiltration of copper into as-sintered porous skeletons using TEM are planned. Practical implications: Efficiant mechanical strength, high hardness, adequate heat resistance and good wear resistance of M3 type 2 HSS powder produced by woter atomisation make it an attractive material for manufacture of valve train components, for example valve seat inserts. Originality/value: The novelty in the article are the results of research on the microstructure made using TEM, the results of testing materials after heat treatment, untypical for high- speed steels. The article attempts to explain the influence of iron addition on properties - such a slight loss of mass as a result of its addition. The second aim of this work is to analyse the microstructural changes during sintering porous skeletons made from HSS with WC additions.

Surface texturing to promote formation of protective tribofilms on combustion engine valves

In a combustion engine, the valve system controls the flow of gases in to and out of the combustion chamber. The contacting surfaces experience a harsh tribological situation with high temperatures, high speed impacts, corrosive environment and high closing forces causing micro sliding in the interface. The components have to endure in the range of hundreds of millions to a billion operational cycles, resulting in extreme demands on low wear rate. Such low wear rates can be accomplished by the protective action from tribofilms forming from oil residues, avoiding a pure metal-to-metal contact. Such tribofilms are found on well-functioning engine valves from a variety of engines, but some stationary gas engines experience problems with wear occurring seemingly randomly at normal running conditions. For some reason, the tribofilm has not protected the surfaces sufficiently, causing wear. One way to combat the random behaviour could be to promote robust function of the protective tribofilms by texturing the valve sealing surfaces to improve the capture and storage of oil residues. By stabilising the supply in this way, the damage from periods with low access to tribofilm forming material could be reduced. The present work demonstrates that turning of the valve seat inserts, creating valleys perpendicular to the sliding motion, can be developed into a useful solution. The amount and localisation of tribofilms became more predictable and stable than without the texture, leading to reduced component wear. The valleys should not be too wide, since this increased the amount of exposed metal if the tribofilm flaked off. When having the same width, the deeper valleys showed less flaking off of the tribofilm.