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The hardened steel materials have great demand for the manufacturing of automotive, aircraft and machine tool components due to their better strength, wear resistance and high thermal stability. The hard machining offers many potential benefits compared to grinding, which remains the standard finishing process for critical hardened surfaces. To enhance the implementation of this technology, questions about the ability of this process to produce surfaces that meet the surface finish and integrity requirements must be answered and it must be justified economically. With the development of harder work materials, the tool material technology is advancing at a faster rate so as to enable machining of these materials by higher material removal rate with reliability of performance. This review article presents an overview of the previous research on machining of hard steel materials. It mainly focuses on the influence of extrinsic factors on machinability of hardened steels, such as variation of cutting forces, chip morphology, tool wear and resulting surface integrity in the machined surface.

We report the fabrication of alumina (Al2O3) and silicon carbide (SiC) particulates reinforced Al metal matrix composites (Al MMCs) by stir casting method. The effect of reinforcement and heat treatment on the corrosion properties of Al matrix and r-Al MMCs were investigated by polarization, impedance and weight loss methods. Taguchi's experimental design method was employed to set the process parameters. In order to find the optimal process parameter levels, orthogonal arrays of Taguchi, the signal-to-noise (S/N) ratio, the analysis of variance (ANOVA), and regression analyses were employed. The analysis on the effect of these parameters on the corrosion rates has also been discussed. The results revealed that the rate of corrosion decrease with increase in the content of Al2O3 and SiC particulates in the r-Al MMCs. A significant enhancement in the corrosion resistance was observed with heat treated of Al alloy and its composites. The morphological analysis by SEM micrographs revealed the lesser formation of cavities due to corrosion upon the increase in Al2O3 content which would be beneficial for corrosive application.

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The current research aims to develop a hybrid metal matrix composition that focuses on the nickel alloy and its thermal properties. The different temperature ranges are used to analyze the function of MMCs such as thermal conductivity and coefficient of thermal expansion. This paper addresses the thermal properties obtained from a series of Al2O3 and TiO2 reinforced nickel alloy (ASTM A494 M), with dispersed particle sizes ranging from 40-45 microns of Al2O3 and 1-5 microns of TiO2. The quantity of the Al2O3 addition varies from 3-12 weight % and 9 weight % of TiO2 unvarying in the stages of three weight percentages. The microstructural investigation states that, because of the stir casting on the vortex, the distribution of reinforcements is uniform with a strong bond. With the increase in Al2O3 and TiO2 content in HMMCs, a thermal property is found to diminish significantly. The results indicate that the reinforcements have a major effect on the thermal expansion coefficient as well as on the thermal conductivity of the hybrid composites being produced. Various types of microstructural have been performed using electron microscopy scanning and EDAX. The limited examination of the exhaust valve of the I C engine shows that the nickel combination composites can be utilized as a substitute for the present valve material (Ni-Cr alloy steel). All tests acted in this investigation meet ASTM specifications.

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