Jiyun Zheng,Guogang Shu,Wei Wang,Qiulin Li,Wei Liu
Surface quality improvement by Cu activation and oxidation roughening process was studied during electroless coating Cu on boron carbide (B 4 C) particles. The surface morphology was characterized by scanning electron microscope (SEM) and the phase identification was determined by X-ray diffraction (XRD) analysis. Two aspects concluding surface activation and surface roughening were investigated to understand the effect of each on Cu coating. Cu activation process increased surface activity of B 4 C by pre-deposition Cu nano-crystals, which was effective and cost-saving when compared with conventional Pd activation method. The influence of activation pH on electroless Cu coating was discussed and a moderate pH 12 is suitable for Cu deposition. Surface roughening process availably promoted wettability of B 4 C particles with aqueous solution. Etched pits were formed on B 4 C surface and resulted in fresh surface exposed after oxidization roughening process, which was beneficial for Cu bonding and coating on B 4 C surface.
Chuandong Wu,Kaka Ma,Jialu Wu,Pan Fang,Guoqiang Luo,Fei Chen,Qiang Shen,Lianmeng Zhang,Julie M. Schoenung,Enrique J. Lavernia
We report on an investigation of the influence of reinforcement particle size on the microstructure and mechanical behavior of Al metal matrix composites . In our work, Al 7075/B 4 C composites containing three types of B 4 C particle sizes (56.9 µm, 4.2 µm and 2.0 µm) were synthesized and studied. For a constant value of volume fraction of B 4 C, the composite with coarse reinforcement particles exhibited a relatively homogeneous and discrete distribution of the B 4 C particles while the composites with fine reinforcement exhibited agglomeration of the B 4 C particles. The composite with the smallest B 4 C particles possessed the highest yield strength and fracture strength. Quantitative analysis of the strengthening mechanisms revealed that smaller B 4 C particles lead to larger values in strain gradient strengthening as well as CTE mismatch strengthening, which are significantly correlated to the geometrically necessary dislocations caused by the presence of B 4 C. In addition, the different spatial distributions of the B 4 C particles contributed to different fracture mechanisms in the composites.
Zhitao Yu,Minghui Chen,Xuan Kong,Wenyao Sun,Fuhui Wang
Copper matrix self-lubricating composites have the advantage of low friction coefficient, but usually suffer from the low mechanical strength , ductility and wear resistance. Ceramic particles reinforcing has been demonstrated an effective way in strengthening metal matrix composites . However, the poor wettability was always a critical issue. In this study, B 4 C particles were introduced into a copper matrix self-lubricating composite. Before spark plasma sintering , the B 4 C particles were pre-metallized with Ni to form a core-shell microstructure (Ni@B 4 C), which improves wettability and bonding strength with the copper alloy , builds up a coherent/semi-coherent interface, and notably enhances mechanical properties. After the incorporation of pre-metallized Ni@B 4 C particles, the compressive strength , hardness and engineering strain are increased by 62, 113 and 76%, respectively. What is more, the composite exhibits improved tribological performances . Owing to the successful transfer of lubricant WS 2 to the wear surface during sliding as well as the greatly enhanced hardness, its friction coefficient is decreased to 0.16, while the wear rate is reduced to 7.53 × 10 −6 mm 3 /N·m, which is 81% lower than that of CW . The composite achieves well-balanced mechanical and tribological properties after pre-metallized B 4 C particles incorporation.
With the advantage of micro-size and nano-size B 4 C particles, micro-/nano-bimodal size B 4 C particles have been widely used to fabricate excellent composites with high strength and ductility. In this study, micro-/nano-bimodal size B 4 C particles reinforced aluminum matrix composites with three different volume fractions (3%, 5% and 7%) were fabricated by spark plasma sintering (SPS) followed by hot extrusion and rolling (HER). The microstructure evolution and mechanical properties of as-SPSed, as-extruded and as-rolled composites were investigated. Results show that the microscopic electrical discharge between the particles in SPS promotes the densification of composites. The maximum relative density of as-SPSed composites increases from 99.21% to 99.65% after HER. Nano-size B 4 C particles distribute mainly at the gap of 6061Al particles in as-SPSed composites, while the microstructure presents more homogeneous after HER. Pin effect of nano-size B 4 C particles stimulates dynamic recrystallization (DRX) and grain refining. Texture orientation of the 6061Al grain exists in the as-extruded and as-rolled B 4 C/6061Al NCs. No new phases are detected in composites in all deformation stages. The tensile strength of as-SPSed composites increases when compared with 6061Al matrix, and the tensile strength of as-rolled composites after hot extrusion is enhanced to 305 MPa. Fracture mechanisms of as-extruded and as-rolled composites mainly include 6061Al matrix tear, particle/matrix interfacial tear and micro-size B 4 C particle fracture.
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