Narrow Results

The work functions of (001) and (00-1) surfaces of B₄C are investigated with density functional theory and symmetry slab model. These two surfaces are found to be almost nonpolarized and their work functions are 5.15 eV and 5.46 eV, respectively.

Surface composites are developed on Mg RZ 5 alloy by friction stir processing. During FSP, hard reinforcements are introduced into the matrix of RZ 5 alloy and dispersed uniformly by mechanical stirring action. The reinforcements dispersed were boron carbide, carbon nanotubes (multi-walled) and an 80:20 mixture of zirconia and alumina particles. Dynamic recrystallization and grain boundary pinning action by reinforcement particles resulted in the generation of fine-grained surface composites. Corrosion characteristics of the base material and the surface composites are studied by potentiodynamic polarization technique. The corrosion rates estimated for the surface composites are found to be far lesser than the base material while their polarization resistances were higher than the base material. Among all surface composites, B₄C particle reinforced surface composites exhibited the lowest corrosion rate of $\sim$15 mpy. Reduction in the corrosion rate of the surface composites is influenced by fine-grained microstructure and presence of harder reinforcement particles.

Based on the background of automotive mold surface strengthening, the effects of three different enhancements on the microstructure evolution, micro-hardness and wear resistance of laser cladding cobalt-based coatings were studied. The three reinforcing materials were Co45 alloy powder, Co45/8% B₄C mixed powder and Co45/8% B₄C/5% Cr₃C₂ mixed powder. They were respectively used to conduct laser cladding on the surface of die steel with preset powder method, with laser power of 2000W and scanning speed of 4mm/s. According to the test results, the hardness and wear resistance of the cladding coating were the best when Co45/8% B₄C powder was added. In addition, the study also found that B₄C reacted with Cr₃C₂ during laser cladding to eventually generate Cr₂B. The CrB₂ generated for the first time during the reaction was transformed into the most stable Cr₂B with an orthorhombic Fddd symmetry due to its poor stability. Therefore, the sample with Co45/8% B₄C/5% Cr₃C₂ mixed powder was affected with a slight decrease in microhardness and wear resistance.

Friction stir processing (FSP), which was the advancement in the friction stir welding technique, is thought to be an economic approach to alloying in the solid state that can be used to make composites. In this study, FSP was carried out to produce AA7075 (B₄$\mathrm{\text{C}}+\mathrm{\text{T}}$iN) composite by varying the composition of the reinforcement particles. Microstructural analysis was carried out and the homogenous distribution of the reinforced particles on the surface of AA7075 alloy was ensured. X-ray diffraction studies were carried out to analyze the phases present after fabricating the hybrid surface composites. Microhardness test was performed on the specimens before and after the fabrication process. Grain refinement in the friction stir processed zones was evidently seen in the optical microstructures. The combined effect of the ceramic powders and grain refinement led to increase in the microhardness in the hybrid surface composites compared with the base AA7075 plate. A 33.87% increase in microhardness was observed in the sample AA7075 reinforced with 75% B₄C and 25% TiN. Wear testing was carried out at various loads (5, 10, 15 and 20 N) and at different sliding velocities (300, 350, 400 and 450 rpm) and the track distance was maintained at 1000 m. It was observed that the highest wear rate is $3.2\times 10^{-7}$ cm³/Nm for the base plate AA7075 and the sample AA7075 reinforced with 50% B₄C and 50% TiN shows the lowest wear rate of $0.56\times 10^{-7}$ cm³/Nm. It is observed that the addition of B₄C and TiN has resulted in a significant improvement in the wear resistance of the AA7075 alloy.

The corrosion behavior of 316 stainless steel with 10wt.% B₄C composites has been investigated using electrochemical measurements and electron backscattered diffraction (EBSD) and scanning electron microscopy (SEM) analyzes are performed. Spark plasma sintering (SPS) is used to achieve various heat treatments, which are performed at the temperatures of 800^∘C, 900^∘C, and 1000^∘C. It significantly affects the materials’ ability to resist corrosion. The increase in grain size improves corrosion resistance, except at 900^∘C when recrystallization is imperfect. However, grain homogeneity should be taken into consideration. The corrosion behavior of the composites is assessed using Tafel plots. The corrosion rate of the sample at 900^∘C (0.2945mm/yr) is significantly lower than the rates of the samples at 800^∘C and 1000^∘C, respectively, as per the corrosion process of composites of 3.5wt.% NaCl solution. The B₄C contents have a significant impact on the particle size reduction, low-density average crystallite size, mechanical, hardness, corrosion resistance, and thermal stability of composite powder. It is primarily utilized in nuclear applications as a neutron radiation absorbent. The research has revealed that the sample at 900^∘C has fewer grain boundaries and the finest passivation film quality and superior corrosion resistance are found in intermediate grain size.