Abstract
The article provides analysis of operating conditions for the «valve – valve guide» heavy-loaded and heat-stressed friction unit of the gas distribution mechanism of powerful internal combustion engines and establishes requirements to materials for valve guides. It describes nanoc omposite materials based on copper powder with aluminum, carbon, iron and oxygen additives developed by the authors of the present article. The reactionary mechanical alloying method and powder metallurgy technologies in use made it possible to develop materials having a dispersion-strengthened structure with nano-disperse level sizes of structural components (dispersoids, subgrains). They have a recrystallization temperature of over 950оС, good therm-conductivity, a low linear thermal expansion coefficient and excellent tribotechnical properties. For example, a copper nanocomposite material containing 0.9 wt % aluminum, 0.3 wt % carbon, 0.4 wt % iron and 0.017 wt % oxygen, by its tribotechnical properties, greatly surpasses CuNi2Si (F65 DIN 17666) bronze widely used by many leading engine-making companies for production of valve guides. By their properties, the developed materials meet requirements that have to be imposed on modern and promising materials for valve guides of powerful internal combustion engines.
Highlights
In internal combustion engines a number of friction units («piston – cylinder liner», «plain bearing – shaft», «valve seat – valve», etc.) experience the impact of high loads and temperatures during engine operation [1, 2]
The valve guide can heat up to 90% of the heating temperature of the valve itself [6].It should be added to the above said that the given tribocoupling is under impact of an aggressive medium, which is explained by gases moving at the speed of 400...600 m/s
The above-mentioned dispersion-hardened copper alloys have good tribotechnical properties; all of them have an insufficiently high softening temperature. It is lower than the temperatures valve guides operate at. This is primarily explained by the fact that at high temperatures fine reinforcing phases being a part of the copper matrix dissolve in it and do not prevent material grain coarsening [10]
Summary
In internal combustion engines a number of friction units («piston – cylinder liner», «plain bearing – shaft», «valve seat – valve», etc.) experience the impact of high loads and temperatures during engine operation [1, 2]. This is primarily explained by the fact that at high temperatures fine reinforcing phases (dispersoids) being a part of the copper matrix dissolve in it and do not prevent material grain coarsening [10] These copper alloys have a low heat resistance and their application in powerful engines not always provides the required service life of the «valvevalve guide» tribocoupling. In connection with the above said, an attempt was made in the present work to develop anti-friction and heat-resistant nanocomposite materials based on copper powder for valve guides of powerful engines with the use of the mechanism of dispersion strengthening and minimization of sizes of structural components up to the nanodisperse level
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