In recent times, aluminum matrix syntactic foams (AMSFs) have become considerably attractive for many industries such as automotive, aviation, aerospace and composite sector due to their features of low density, good compression strength, perfect energy absorption capacity and good ductility. Since the AMSF includes filler materials providing high porosity, it can be also named as composite foam and can be placed between traditional metal foams and particle reinforced composites. Glass and ceramic hollow spheres, fly ash cenospheres and ceramic porous materials are usually used in the AMSFs, but, lately, different types of fillers being cheaper and stronger have also being investigated. Although many scientific efforts have been made for the last decade to understand mechanical and physical properties of these advanced materials, studies have mainly been performed on relatively small size samples and remained in laboratory. Therefore, there is still room for improvement in terms of fabrication techniques. In this paper, our aims are to scrutinize newest studies about ASMFs, to create new viewpoints and to introduce an alternative bright perspective for probable real applications.

Formation of nickel–boron–molybdenum ( Ni – B – Mo ) coating on steel by electroless plating and evaluation of their morphology, hardness and tribological properties post heat treatment at different temperatures for 1 h is investigated. The 25 μm thick coating is uniform and adhesion between the substrate and coating is good. Ni – B – Mo coating was amorphous-like structure in their as-plated condition and by 400°C heat-treated coating, nickel fully crystallized and nickel borides and molybdenum carbide were formed. All coatings exhibited higher hardness than the substrate steel. Hardness values of all coatings up to 400°C did not change distinctively but decreased partly beyond 400°C. Friction coefficient reached lowest value post heat treatment at 300°C but later increased with increasing tempering temperature. Wear resistance was lowest in as-plated coating; however it reached the highest value at 300°C. Worn surface of the coatings showed the abrasive wear as the dominant wear mechanism. An additional adhesive wear mechanism was detected in coating tempered at 550°C. Moreover, our results confirmed that the molybdenum addition improved the thermal stability of the resulting coating. Therefore, Ni – B – Mo coating has potential for application in precision mould, optical parts mould or bipolar plates, where thermal stability is essential.

The Ni-B-Mo coating on steel by electroless plating and the evaluation of the morphology and corrosion performance after applying heat treatments at different temperatures for 1 h were investigated in this study. The 25-lm-thick coating was uniform and adhesion between the substrate and the coating was good. The coating consisted of an amorphous-like structure in their as-plated condition, and after annealing at 400°C for 1 h, crystallized nickel, nickel borides, and molybdenum carbide were formed. Immersion tests in 10% HCl solution and potentiodynamic polarization measurements in 3.5% NaCl aqueous solution were applied to investigate corrosion resistance. The corrosion performance of heat-treated coatings was compared with steel and the as-plated coating. By increasing the annealing temperature, corrosion potential shifted toward a noble direction, corrosion current density decreased and the weight loss of specimens decreased, demonstrating an increase in corrosion resistance. Best corrosion performance was achieved by the coating heat treated at 550°C .

The present work deals with the formation of Ni-B-W coating on steel by electroless plating process and evaluation of their corrosion resistance after applying heat treatments at different temperatures for 1 h. The Ni-B-W coating was prepared using alkaline borohydride- reduced electroless nickel bath. Scanning electron microscopy of the surface cross-sectional view of the electroless Ni-B-W coating was analyzed and layer characteristics was investigated. Coating structure was investigated using XRD. The study reveals that the Ni-B-W coating is amorphous in their as-plated condition and upon heat treatment at 400 0C for 1 h, Ni-B-W coating crystallize and produce nickel and nickel borides in the coatings. Annealing temperature dependence of the corrosion resistance of the coating was investigated by potentiodynamic polarisation measurements. These results show that the Ni–B-W coating annealed at 650 0C exhibit better corrosion resistance than those of coatings with other annealing temperature. The corrosion resistance increased after the crystallisation of the coating, due to factors like; decrease of porosity and internal stress and the formation of tungsten oxide on the surface acting as a protective layer.

No abstract