Effect of Tool Shoulder Diameter on the Surface Hardness of Aluminum-Molybdenum Surface Composites Developed by Single a
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ALUMINUM (Al) alloys are used in transportation, defense, and aerospace applications owing to its light weight and high specific strength. However, low surface hardness is a limiting factor in the use of these alloys for various strategic applications. Microstructural modification by surface alloying or surface composite formation can overcome this limitation.[1] The surface alloy or composite formation can be achieved through either liquid- or solid-state processing route. Almeida and Vilar[2] have explained that laser surface alloying (LSA) forms of alloy in the liquid phase by melting, and leads V.P. MAHESH and AMIT ARORA are with the Advanced Materials Processing Research Group, Materials Science and Engineering, Indian Institute of Technology Gandhinagar, Gandhinagar, Gujarat 382355, India. Contact e-mail: [email protected] Manuscript submitted March 25, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
to the formation of intermetallic phases which may lead to poor mechanical performance. In metal matrix composites, ceramic reinforcement particles may react with the matrix at the interface, leading to the formation of carbides or other products. This results in lower mechanical properties of the surface composites.[3] Ralph et al.[4] presented a detailed review on processing of metal matrix composites (MMCs) by ceramic reinforcements such as Al2O3, SiC, and B4C in particulate, whiskers, and fiber forms. They showed shrinkage mismatch between the matrix and reinforcement during solidification leading to reduced mechanical properties. Yang et al. analyzed the distribution of Al2O3 nanoparticles in AA6061 matrix during the FSP and macrohardness variation.[5] The depth of the surface composite is extended upto the tool pin height and no specific interface is observed in the prepared sample. Sharma et al. studied the strategies for the uniform distribution of SiC reinforcement particles in AA5083SiC surface composites fabricated by FSP.[6] The change in the process parameters such as rotational speed and
overlapping processing passes varied the reinforcement distribution in the surface composites. Friction stir processing (FSP) is a solid-state processing method used to develop surface composites.[7] During FSP, the base material does not melt and the formation of intermetallic phases can be avoided along with reduced thermal effects on the surface. The fine grained microstructure developed during FSP due to severe plastic deformation also leads to superior surface properties.[8] The hardness improvement in FSPed Al surface composites is attributed to the finer grain size and Orowan strengthening mechanism due to the incorporated reinforcement particles.[9] Sahraeinejad et al.[10] observed the breakdown of reinforcement particles in the stir zone during the FSP due to severe plastic deformation. Friction stir processing is used to fabricate AZ31MWCNTs (multi-walled carbon nanotubes) surface composites with improved surface hardness.[11] The combined effect of grain refinement and the presence of MWCNTs introd
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