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Multiphase diffusion carbide coatings of the types: M 7 C 3 ± VC, M 7 C 3 ±TiC and M 7 C 3 ±VC±TiC have been produced by pack cementation method on three tool steels at 1000 C during 6 h using 15 powder mixtures. Thickness of diffusion coatings varied in the range of 14±32 lm while hardness was in the range 2012±5150 HV0,05. Phase composition of coatings depended on type of powder mixture and a steel. Hardness of coatings increased with FeV and/or FeTi concentration in the mixture while metallic luster and surface finishing increased with FeCr content. The maximum wear resistance was achieved for M 7 C 3 ±VC±TiC coating formed in the mixture containing Ti, V, Cr in the mass proportion 4:4:2. Coatings of lower hardness, formed in Cr-rich mixtures worn mainly by microcutting and grooving while harder coatings formed in V-rich mixtures worn mainly by oxidation. Appearance of brown turnish on the surface of the latter coatings lowered the wear intensity. No difference in wear mechanism and intensity was found for the same type of coating formed on different steel matrix.The goal of diffusion metallizing (chromizing, vanadizing, titanizing) consists on producing strongly adherent corrosion and wear resistant coatings characterized generally by a high hardness. [1±3] Despite of an important progress in developing new methods and techniques of surface modification there are still demands for simple and cheap technologies. Diffusion pack cementation belongs to such methods, its modification brings quickly economical advantages. [4±6] The great advantage of this method is that ferroalloys, the main component of powders, are relatively cheap and easily accessible. Moreover a powder mixture can be used several times because ferroalloy grains of average size 60 lm are exploited only in several microns per process. The exploited layer of grains is then eliminated by barreling before next application.Mechanism of formation of monolayer carbide coatings on ferritic alloys is well known. It was found [5] that M 7 C 3 coating grew inward a steel due to external Cr diffusion while TiC or VC coating grew outward from the original surface due to carbon diffusion from a steel through the forming coating. [7,8] There is a lack of information in the literature on the formation of carbide layers by simultaneous diffusion of several carbide forming metals into Fe±C-rich alloys. Codiffusion of Cr and V into a low-C steel described in [9] leads to formation of solid solution coatings. Chromizing applied after vanadizing enabled to produce a two-layers coating: VC M 7 C 3.[10] Earlier investigations [11±12] proved that the chemical and phase composition as well as hardness of an individual layer could be varied in a relatively broad range by changing composition of powder mixture. It was shown [12] using FeV±FeCr± FeTi mixtures that both single phase and multiphase diffusion carbide coatings could be formed on steels. Multiphase coatings consist of carbide layers of different composition, Table 1. Compositon of tool steels used as matrix...

In this paper, we examine the problem of optimising the process of topping up lubricating oil in medium-speed marine engines. This process is one of the methods that can be applied to improve the properties of lubricating oil. The amount of fresh oil added to lubricating oil system always balances its consumption, but the method used to top up depends on the marine engineer. Small amounts of fresh oil can be added at short intervals, or large ones at long intervals, and the element of randomness often plays a significant role here. It would therefore be valuable to find a method that can help the mechanical engineer to choose the right strategy. We apply a multi-criteria optimisation method for this purpose, and assume that the criterion functions depend on the concentration of solid impurities and the alkalinity, which are among the most important aspects of the quality and properties of lubricating oil. These criterion functions form the basis for multi-objective optimisation carried out with the use of the MATLAB computer program.