Onur Tazegul

Conventional sintering of diamond cutting tool used in natural stone cutting

Diamond Tools, used in natural stone cutting, is produced commonly by powder metallurgy with Spark Plasma Sintering (SPS) and/or Conventional Sintering (CS). Co is generally used as metal matrices because of their bonding strength and optimum wear rate. However, because of cobalt’s high prices, other alloying elements are also used to decrease the cost of diamond tools. Aim of this study is to compare mechanical, physical, microstructural properties of diamond cutting tools made of Co-Ni-Cu-Sn matrix, produced by Spark Plasma Sintering and Conventional Sintering. Spark Plasma Sintering performed at 850 °C and Conventional Sintering performed at various temperatures (between 950 and 1150 °C) and times (1 to 4 hours). Then various properties (density, hardness, compression strength) of Conventional Sintered and Spark Plasma Sintered tools were investigated and compared. The experimental results showed that SPS tools have much better properties than CS tools.

A novel fabrication method for a TiO2 layer over CoCr alloy

ABSTRACT This study has been initiated to form a TiO2 layer having enhanced biological properties on the surface of a CoCr alloy, which is mostly used in manufacturing of orthopaedic implants. As a novel approach, CoCr alloy samples were first coated with titanium and then oxidised in air at 600°C for 60 h. Surface characterisation of the samples were made by structural surveys (scanning electron microscopic examinations, X-ray diffraction analyses), roughness and hardness measurements, bioactivity and wear tests. Results of the experiments have showed that fabrication of TiO2 as the outermost surface layer caused remarkable increment in the wear resistance and the bioactivity of the CoCr alloy.

Wear and corrosion characteristics of copper-based composite coatings

Purpose The purpose of this paper is to investigate the effects of reinforcing particles (B4C, TiB2 and TiC) on the physical, corrosion and wear behaviour of copper matrix composite coatings. Design/methodology/approach Coatings were produced by cold gas dynamic spraying process, and the contribution of reinforcements (B4C, TiB2 and TiC) to the coating characteristics was detected through microstructural examinations (scanning electron microscope examinations and X-ray diffraction analyses), hardness and electrical conductivity measurements, corrosion tests in Cl− environment with potentiostat/galvonostat apparatus and wear tests which were performed under dry conditions by reciprocating wear tester. Findings Coatings with high density, good bonding at the coating and substrate interface were obtained by cold gas dynamic spray process. The electrochemical polarisation test in a Cl− environment clearly indicated that the type of reinforcing particles did not significantly affect the corrosion performances of pure copper coating. In terms of the wear performances of the coatings, the best wear performance has been obtained for pure copper coating. Wear performance reduction of the composite coatings was related to the inhibition of continuous oxide layer formation on the worn surfaces due to third-body abrasion mechanism and delamination of oxide layer during wear tests. Originality/value Contrary to expectations, wear tests results of the study revealed the inverse effect of ceramic particle addition to the copper matrix in cold spray coating applications due to poor bonding between matrix and reinforcing particles.

The effect of SiC reinforcement on tribological behaviour of cold sprayed coatings in water

Abstract In this study, structural characteristics and tribological performance of the coatings deposited on a 1050 quality aluminium substrate by cold spraying of the feedstock consisting of 100% Al–12Si and 25 vol.% SiC + 75 vol.% Al–12Si powders were examined. Wear tests were conducted in air and in water against alumina ball under loads of 1 and 5 N by a reciprocating wear tester at room temperature. Presence of SiC particles in the structure enhanced the wear resistance of the Al–12Si coating both in air and water. As compared to the air testing condition, water containing media provided better tribological performance especially at the wear test load of 1 N. The findings of this study revealed potentiality of water to be used as a lubricant for SiC-reinforced Al–12Si matrix cold spray composite coatings at relatively low wear test loads.

Investigation and Application of Fe–Co−Cu Based Diamond Cutting Tools with Different Bronze Content Used in Marble Production

Marble is an industrial material with a very high commercial potential in the whole world. The diamond cutting tools find vast applications in the natural stone cutting industries. The main factor judging the performance of the diamond cutting tools is their wear resistance which is primarily affected by materials/process variables and unpredictable working conditions. For a successful cutting operation, wear rates of the matrix and the diamond must be comparable. Otherwise, detachment of diamond from the matrix or embedding of diamond into the matrix may occur. In order to optimize the performance of the tool during cutting, several additives may be incorporated into the matrix. Type and amount of the additions are firstly determined by the hardness of natural stone to be cut. In this study, performances of Fe-Co-Cu based commercial powders were used to evaluate their performance as a diamond bead matrix and the effect of bronze additions on the structural and mechanical properties of matrix was investigated. All materials in the form of powders were cold pressed first and then the pellets were sintered at 960 °C for 1 h in hydrogen atmosphere of a tunnel furnace. Microstructural and mechanical characterizations were performed by Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD), X-ray fluorescence (XRF), hardness, compression tests and wear test. Results showed that bronze additives had no negative effect on density of the samples. The mechanical properties and wear resistance of the samples decreased with increasing bronze content and they may become eligible for stones of different hardness.

Characterization of thermally oxidized titanium based coating

Purpose: Aim of the study is to improve the bioactivity of CoCr alloy upon covering the surface with titanium based coating. Design/methodology/approach: CoCr alloy was coated by cold spraying of powder mixture having a composition of 92 wt.%Ti + 8 wt.%Al. Coated samples were thermally oxidized at 600°C for 60 hours. Characterization of the coating was made by X-Ray diffraction analyses, microstructural surveys, cross-section and surface SEM elemental mapping analyses, roughness and hardness measurements. Findings: Results showed that sequential application of cold spray and thermal oxidation processes provided the multi-layered coating consisting of an inner titanium based layer and an outer oxide layer consisted of TiO2 and Al2O3. Thermal oxidation also caused the remarkable increasing in the surface hardness as compared to the as-cold sprayed state. Practical implications: Modifying the surface of CoCr metallic implants for long term success. Originality/value: Producing a multilayer coating on the surface of the CoCr alloy for biomedical application by sequential application of cold spray and thermal oxidation processes is the orginality of the study.