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The grain size of materials is significantly reduced by dynamic recrystallization (DRX), which improves the properties and performance of the materials, and it helps to extend the applications further. DRX behavior of the composite materials is greatly affected by the addition of reinforcement to the matrix due to the heterogeneous temperature of the composite. Therefore, the present investigation aims to study the DRX behavior of hot upset sintered Al-B4C composite with various percentages of B4C content (2, 4 and 6 wt.% of B4C) with 90% of initial relative density. Hot upset tests were performed for various temperatures (300-500 °C) and strain rates (0.1-0.3 s−1). The DRX grain size was significantly altered not only with deformation conditions but also with the addition of reinforcement in the matrix. The fracture surface of the sintered composite was analyzed for various compositions. Ductile fracture is observed in the 2 and 4 wt.%B4C content, and ductile and brittle fractures were observed in the 6 wt.%B4C composites. DRX models were established between grain size and deformation conditions for various compositions to predict the grain size, and the developed models were validated. The measured and calculated DRX grain size absolute error and mean absolute error were not exceeding 8.9 and 7.7%, respectively. [ABSTRACT FROM AUTHOR]

The paper reports wear and friction performance of Al-12Si aluminum alloy reinforced with 1.5 wt% submicron boron carbide (B4C) particles. Composite material is fabricated by ultrasonic stir casting process. Microstructural examination is carried out using optical microscopy and field emission scanning electron microscopy (FESEM). Incorporation and agglomeration-free dispersion of B4C particles is detected in the aluminum matrix. Pin-on-disc tribotester is used to evaluate tribological performance of fabricated composite and base alloy under room temperature dry conditions. Nominal contact pressure of 0.707 MPa is applied against EN31 steel counterface, and sliding speeds are varied between 0.25 and 1.25 m/s. Influence of sliding distance is investigated by varying sliding durations from 10 to 40 min at two fixed load-speed (PV) factors of 10 and 25 Nm/s. Worn pin surfaces and collected wear debris are analyzed using FESEM and energy-dispersive spectroscopy to reveal undergoing wear mechanisms. After initial decrease, wear rate increased almost linearly with speed and became twofold at the top speed. Wear rate transition is seen at 0.5 m/s with sliding distance for the applied pressure. Friction coefficient is not influenced significantly with sliding distance for the fixed PV condition. Adhesion and delamination governed the wear mechanism of base alloy while mechanically mixed layer played key role in the wear performance of composite matrix. Improved wear resistance of aluminum matrix is observed due to incorporation of small amount of B4C particulates making the composite better suited for wear-resistant applications than base alloy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The trend of spontaneous progress of different interfacial reactions was analyzed. • Based on the first principles, the Gibbs free energies of different interfacial reactions were calculated. • The influence mechanism of Ti element on the interfacial reaction of Al-B 4 C composites was analyzed. • The formation mechanisms of the interfacial reaction layer in Al–B 4 C and Al–Ti–B 4 C systems were discussed. The effect of titanium (Ti) on the interfacial reactions and micro-structures of the Al-B 4 C composites were studied using theoretical calculations based on the first-principles approach of density functional theory in combination with experimental analysis. The experimental results showed that the addition of Ti caused a more uniform distribution of B 4 C particles and the disappearance of interfacial micro-cracks. Three interfacial reaction layers were formed on the surface of B 4 C particles, the inner layer was composed of Al 3 BC, the middle layer constituted fine-grained TiB 2 , and the outer layer consisted of coarse-grained TiB 2. The thermodynamic analysis showed that the most favorable reaction paths in the Al-B 4 C and Al-Ti-B 4 C systems were 9Al + 2B 4 C → 2Al 3 BC + 3AlB 2 and 6Al + 3Ti + 2B 4 C → 2Al 3 BC + 3TiB 2 , respectively. Finally, the formation mechanism of the interface reaction layers in Al–B 4 C and Al–Ti–B 4 C systems were discussed. The results indicated the inter-diffusion of interfacial atoms in the melt, atomic diffusion rate, atomic concentration, atomic size and lattice mismatch were the factors influencing the formation and growth of the B 4 C-Al 3 BC-TiB 2 interface reaction layer. [ABSTRACT FROM AUTHOR]

In the present investigation, Al/B 4 C composite samples were prepared by hot press method. Thermal properties of the samples containing different reinforcement contents were evaluated. XRD characterization did not reveal the presence of any detrimental phase. Density and microhardness measurements confirmed proper compaction and high hardness of the samples, respectively. SEM observations showed no evidence of cracks at the matrix/reinforcement interface and it was seen that B 4 C particles had high wettability with Al matrix. Dilatometry tests demonstrated that by improving the reinforcement content, the coefficient of thermal expansion declined in a way that Al/25% B 4 C sample had the lowest thermal expansion coefficient (8 ppm/C), which makes it suitable for heat sink applications. Moreover, the experimental results were in good agreement with thermoelastic models in specific temperature ranges. • Hot press method resulted in near theoretical density Al/B 4 C composites. • Hardness of the samples improved with enhancing the reinforcement volume fraction. • CTE of the composite samples non-linearly varied with temperature elevation. • Al/25%B 4 C had the lowest CTE, which is recommended for thermal applications. • Thermoelastic models well-predicted the thermal behavior of the experimental data. [ABSTRACT FROM AUTHOR]