Papers by Author: Ali Göksenli

Abstract: Erosive wear is defined as material loss from surface due to impact of liquid and solid particles. This mechanism can be seen widely in the industry such in mining, valves, pipe and pump systems. Characteristics and wear amount of erosive wear is affected by different parameters like geometry, impact speed, impingement angle of the hard particles, solid-liquid rate, material hardness and toughness. To determine the effect of these parameters on erosive wear, a wear slurry tank is designed. Before the prototype design of the test tank, different geometrical parameters of the tank are analyzed using simulation software. By computational investigations, the 3-D flow in a liquid/solid (slurry) tank is established and analyzed. Aim of the mathematical analysis was to detect the effect of the tank design parameters on liquid impact velocity and distribution on the test specimen surface. According to the results, geometrical parameters of the tank such as; baffle width, propeller length, assembly position of the specimens in the slurry tank, the distance between the propeller and specimens are defined.

Abstract: The present work deals with the formation of NiP/NiB 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, NiP and NiB coatings are amorphous in their as-plated condition and after applying heat-treatment at 450 °C for 1 h, both NiP and NiB 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.

Abstract: 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.

Abstract: In this study failure analysis of a mini van diesel engine intake valve is analyzed in detail. Failure occurred at the groove of the valve. First mechanical and chemical properties of the valve are determined. After visual investigation of the fracture surface it is concluded that fracture occurred due to fatigue. Damaged valve, valve seat, cylinder block and piston surface is investigated and construed. Failure constituted 300 kilometers after the rectification of the engine. Therefore rectification and assembly steps of valve and engine parts are analyzed in detail. Considering assembly, design and working conditions of the engine, stresses occurring at the failure surface are calculated. Endurance limit and fatigue safety factor is determined. Because of high fatigue safety factor, reasons for failure are investigated and effects causing stress increase at groove of the valve are established. These effects are faulty assembly of the valve and valve seat causing a high impact effect. In conclusion effect of impact ratio on stress increase is explained.

Abstract: In this paper corrosion-fatigue failure of a roller in a cardboard production plant has been analyzed. The failure occurred at the bearing neck of the roller. Mechanical and chemical properties of the roller are determined and the fracture surface is investigated. Forces applied on the roller is examined, stress calculations are carried out and fatigue safety factor is calculated. Stress analysis is also applied to roller and bearing neck by using Finite Element Method (FEM) and the results are compared with the calculated values. Because of very high safety factor, reasons for failure are investigated and effects of fatigue failure are determined. These effects are corrosion-fatigue, working conditions and notch effect. In conclusion precautions which have to be taken to prevent a similar failure is explained by using FEM.