The present work is associated with research concentrating on the innovation and use of hybrid heat treatment for eutectoid steel powder (0.8 wt%) reinforced Al-Zn-Mg (Al 7075) alloy composites. Due to high hardness, wear resistance, tensile strength and flexibility modifying heat treatment, heat treatable aluminium metal matrix composites reinforced with heat treatable hard steel particles may be the choice to explore. In this work, an attempt is made to increase hardness and tensile properties to higher levels through hybrid heat treatment, comprising simultaneous treatment to matrix and reinforcement in 3 different routes (Pearlite, Bainite and Martensite) compared to conventional age hardening treatment. SEM images and microhardness distribution witnessed the phase transformation in both matrix and reinforcement. Aging kinetics in conventional age hardening and hybrid treatments is accelerated by the increase in the quantity of reinforcement and increase in aging temperature. The improvement in hardness and tensile strength obtained by conventional age hardening path is further improved by the hybridisation path. Hybridisation route with martensite reinforcement phase shows excellent result in hardness, strength followed by bainite and pearlite path respectively in the decreasing order. In all heat treatment cycles, lower aging temperature marks greater property enhancement compared to higher temperature. Al 7075 with 6 wt% steel powder reinforced (martensite form) composite showed excellent peak age hardness, tensile strength compared to lesser quantity reinforced composites.
The viscous heat generation in the lubricant film of a hydrodynamic journal bearing causes a rise in temperature of the fluid film. Considering the influence of the temperature variation along and across the film, the performance of a journal bearing is investigated under adiabatic conditions for different values of thermal conductivity of the lubricant. In this analysis, the temperature of the journal surface has been chosen to ensure that there is no net heat transfer from the lubricant The results show that the variation of temperature across the film affects bearing performance significantly and that an increase in lubricant thermal conductivity enhances bearing performance.
The solitary distinguished thermal treatment to aluminium alloy matrix of nonferrous group with uniformly dispersed reinforcement particles is precipitation or age hardening with or without mechanical working. Al7075 ternary alloy composites belongs to Al-Zn-Mg group and bulk properties can be enhanced by the formation of the immensely small consistently spread out precipitates of solute rich second phase within the matrix phase. The treatment comprises solutionising (550°C) supported by controlled aging (100 and 180°C) below the solvus temperature of the given alloy. Aging expedites the diffusion of solute atoms to form secondary particles (intermetallics) from the room temperature super saturated solid solution. This process is supported by deformation known as rolling as post activity, develops strain hardening in matrix and reinforcement. The present work shows the distinction in the aging phenomenon on alloy and alloy matrix composites (reinforced with 3 and 6 wt% of eutectoid steel powder, 10-30 micron size) upon undergoing cold rolling prior to aging i.e., after solution treatment. The variation in the hardness distribution with aging kinetics for both aging temperatures with and without cold deformation (10 and 20%) in between the consecutive stages like, solution treatment and aging were investigated and peak hardness values were noted in each aging temperatures and results were analysed. In every hardness test 10 trials were performed and the average of 6 consistent readings are taken as the outcome. 20 to 40% improvement in peak hardness is observed with intentional deformation over without deformation. The composite may be used for light duty cold working dies where bulk hardness and frictional characteristics are very important.
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