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Yildiz R.A.,University of Zagreb | Goksenli A.,University of Zagreb | Yuksel B.,Istanbul Aydin University | Muhaffel F.,TU Istanbul | Aydeniz A.,University of Zagreb
Advanced Materials Research | Year: 2013

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 borohydridereduced 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°C 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°C 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. © (2013) Trans Tech Publications, Switzerland. Source


Aydeniz A.I.,TU Istanbul | Goksenli A.,TU Istanbul | Dil G.,TU Istanbul | Muhaffel F.,TU Istanbul | And 2 more authors.
Materiali in Tehnologije | Year: 2013

In this study the formation of a Ni-B-W coating on steel using an electroless plating process and evaluation of the hardness, wear and corrosion resistance was analyzed. The Ni-B-W coating was prepared using an alkaline borohydride-reduced electroless nickel bath. Scanning electron microscopy (SEM) of the cross-sectional view of the Ni-B-W coating was analyzed and the layer characteristics were investigated. The Ni-B-W coating was characterized using XRD. The study reveals that the Ni-B-W coating is amorphous in the as-plated condition and after heat treatment at 450 °C for 1 h the Ni-B-W coatings crystallize and produce nickel and nickel borides. The hardness of the as-plated and heat-treated Ni-B-W coatings were compared with Ni-B coatings. In both coatings the hardness increased with heat treatment. The wear resistance of Ni-B-W coatings annealed at different temperatures was analyzed using a ball-on-flat test. The wear resistance of the coating increased with heat treatment and reached a maximum value at 400 °C. An optical microscope and EDS analysis were applied on the wear tracks to determine the wear mechanism. Ductile failure and an abrasive wear mechanism were dominant for the coating heat treated up to 400 °C. Network cracks and shearing marks were detected for the coatings annealed at 450 °C and above, indicating brittle failure. For investigating the corrosion characteristics of the coatings, immersion tests in 5 % H2SO4 and 10 % HCl acidic solutions for seven days were applied. According to the corrosion test results, the Ni-B-W coatings showed good corrosion resistance in the H2SO4 solutions. Source


Dil G.,TU Istanbul | Goksenli A.,TU Istanbul | Calli C.,TU Istanbul | Muhaffel F.,TU Istanbul | And 3 more authors.
Advanced Materials Research | Year: 2014

The present work deals with the formation of Ni-P/Ni-B duplex coatings by electroless plating and evaluation of their hardness and wear resistance. The duplex coatings were prepared with Ni-P as the inner layer. To analyze the structure of the coatings, XRD analysis was carried out. According to the results, Ni-P and Ni-B coatings are amorphous in their as-plated condition and after applying heat-treatment at 450 °C for 1 h, both Ni-P and Ni-B coatings crystallize and produce nickel, nickel phosphide and nickel borides in the coatings. To determine the surface morphology and cross-section characteristics of the coatings, SEM observations were carried out and concluded that duplex coatings are uniform and good coherent exists between the duplex layers and the coatings are also connected closely to the substrate. The hardness of electroless nickel duplex coatings increased with applying heat treatment and reached maximum value at coatings annealed at 400 °C. To analyze the tribological properties, pin-on-disc tests were carried out. The wear track patterns on the coatings and on Al2O3 balls were then examined by optical microscopy and EDS. The friction coefficient and wear rate of the coatings were lower than the substrate steel. Friction coefficient decreased from 0.43 to 0.36 and wear resistance decreased from 11.3 to 6.4 by applying heat treatment at 450 °C for 1 h to duplex coatings. © (2014) Trans Tech Publications, Switzerland. Source

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