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In this research, the effects of friction stir processing (FSP) and nano TiO2 particles on the microstructure, mechanical and tribologic properties of A356 Al alloy were investigated. The starting dendritic structure transformed into the Al matrix with a uniform distribution of Si-rich particles due to FSP. The results showed that FSP improves the nano-hardness and elastic modulus by 11% and 6%, respectively. The combined effects of FSP and nano TiO2 could raise the hardness and elastic modulus of the composite by 87% and 16% with respect to those of the base metal. The law of mixture rule was modified to relate the hardness and elastic modulus of the composite to those of the constituents. The results of wear tests showed that the mechanism of wear changes from adhesive in the base metal to abrasive in the fabricated composite. [ABSTRACT FROM AUTHOR]

In this research, composites of A356- nano SiC (0.5 and 1.5 wt%) and A356-5 wt% of micro SiC were produced by stir casting technique. After applying T6 heat treatment on a part of cast ingots, all samples were studied by optical and SEM microscopy and mechanical testing techniques. It was found that adding SiC particles decreases dendrite lengths because the particles act as the preferential nucleation sites for the solidification of matrix. The best modifying effect was observed in the composite containing micro SiC particles. The T6 heat treatment on A356 resulted in the dissociation and globularization of Si platelikes and formation of complex AlMg SiFe intermetallics and nano-sized Mg 2 Si particles. The mechanical strength of A356 increased considerably by combining T6 heat treatment and adding micro/nano SiC particles. The highest strength was obtained in the composite containing 1.5 wt% nano SiC. The SEM observations showed that fracture in cast A356 occurs along the dendrite boundaries. However, the T6 treated alloy showed a combined interdendritic and cleavage fracture. The same combined mode of fracture was observed for the alloy with 0.5 wt% nano SiC. The brittle fracture in the composites was attributed to the existence of SiC and/or intermetallic compounds in the matrix. The fracture mode for other composites was fully cleavage. [ABSTRACT FROM AUTHOR]

In this study, hot compression tests were performed at temperatures in range of 850–1150 °C and strain rates of 0.001–100 s −1 to study the hot deformation behavior of 26NiCrMoV 14-5 steel. The relationship between flow stress, temperature and strain rate was established using a power-law equation and the activation energy was determined in range of 200–600 kJ/mol. Some irregularities were observed in the activation energy and peak strain at temperatures below 1000 °C and low strain rates (<1 s −1 ). Optical microscopy observations confirmed the absence of dynamic recrystallization (DRX) at the mentioned condition. Stress relaxation tests and TEM observations showed that dynamic precipitation (DP) of carbide particles would be responsible for partial dynamic recrystallization in low temperature-low strain rate regime. Unlikely, at high temperatures DP was absent and complete DRX was obtained. The results showed that the power dissipation and instability maps are nearly insensitive to DP. The complete processing-microstructure map showed a possible instability region at 850 °C and strain rate of 100 s −1 ; and other deformation regimes would lead to the safe deformation. The region of interaction between DP and DRX was introduced at temperatures below 1000 °C and strain rates below and 1 s −1 . [ABSTRACT FROM AUTHOR]

• Microstructure in SZ and TMAZ is controlled by temperature and strain. • Dynamic globularization refines the austenite islands in SZ. • Microstructure was more refined at low traverse and high rotation speeds. • A linear equation connected the hardness to the ratio of rotation to traverse speed. • The pair of 1000 RPM rotation speed and 12 mm/Min. traverse speed were the best choice. The effects of rotational speed in range of 800–1600 rpm and traverse speed in range of 12–40 mm/min on the mechanical and microstructural properties of 2205 duplex stainless steel were studied. The temperature and strain were crucial to the microstructural evolutions in the stir and thermomechanical affected zones. The major microstructural evolution is the breaking of austenite islands and morphological change into spherical volumes named as "dynamic globularization". The hardness was maximum in the stir zone and decreased by passing through the thermomechanical and heat affected zones. A linear equation was developed between hardness and the ratio of ω/S. The highest hardness was obtained at 1000 RPM and 12 mm/Min. The results of tensile test showed that the ultimate tensile strength (UTS) and fracture strain are improved by FSP. UTS and fracture strain increased with increase in the rotation speed and decrease in the traverse speed. [ABSTRACT FROM AUTHOR]