https://hdl.handle.net/20.500.12619/940 2026-04-13T16:06:20Z 2026-04-13T16:06:20Z Bindal, Cuma https://hdl.handle.net/20.500.12619/70256 2020-10-16T12:20:49Z 1995-01-01T00:00:00Z

Characterization of transfer layers on steel surfaces sliding against diamond-like hydrocarbon films in dry nitrogen Bindal, Cuma Carbon-rich transfer layers on sliding contact surfaces play important roles in the tribological performance of diamond-like hydrocarbon (DLHC) films. In this study, we investigated the nature of these layers formed on M50 balls during sliding against DLHC films (1.5 mu m thick) prepared by ion-beam deposition. Long-duration sliding tests were performed with steel balls sliding against the DLHC coatings in dry nitrogen at room temperature, approximately 22 +/- 1 degrees C. Results indicated that the friction coefficients of test pairs were initially about 0.12 but decreased steadily with sliding distance to 0.02-0.03 and remained constant throughout the tests, which lasted for more than 250000 sliding cycles (approximately 30 km). This low-friction regime appeared to coincide with the formation of a carbon-rich transfer layer on the sliding surfaces of M50 balls. Micro-laser Raman spectroscopy and electron microscopy were used to elucidate the structure and chemistry of these transfer layers and to reveal their possible role in the wear and friction behavior of DLHC-coated surfaces.

1995-01-01T00:00:00Z Bindal, Cuma https://hdl.handle.net/20.500.12619/70255 2020-10-16T12:20:49Z 1995-01-01T00:00:00Z

Formation and self-lubricating mechanisms of boric acid on borided steel surfaces Bindal, Cuma In this study, we investigated the formation and self-lubricating mechanisms of thin boron oxide and boric acid films on the surfaces of borided steel substrates. Specifically, we developed an annealing procedure which resulted in the formation of a glasslike boron oxide layer on borided steel surfaces. Annealing was performed at 750 degrees C for 5 min. During cooling, the boron oxide layer reacted with moisture in the surrounding atmosphere to form a thin boric acid film. The measured friction coefficients of sapphire and 440C steel balls against the unborided and borided sides ranged from 0.4 to 0.6. However, after short-duration annealing at 750 degrees C, the friction coefficients of borided steel surfaces were about 0.05 at steady state. Crystal chemical knowledge and Raman spectroscopy evidence were used to determine the formation and self-lubricating mechanisms of the thin boron oxide and boric acid films on borided surfaces.

1995-01-01T00:00:00Z Bindal, Cuma https://hdl.handle.net/20.500.12619/70252 2020-10-16T12:18:09Z 1996-01-01T00:00:00Z

Tribological properties of hard carbon films on zirconia ceramics Bindal, Cuma In this study, the authors investigated the tribological properties of hard diamondlike carbon (DLC) films on magnesia-partially stabilized zirconia (MgO-PSZ) substrates over a wide range of loads, speeds, temperatures, and counterface materials. The films were 2 mu m thick and produced by ion-beam deposition at room temperature. Tribological tests were conducted on a ball-on-disk machine with MgO-PSZ balk;, in open air of 30 to 50% relative humidity under contact loads of 1 to 50 N, at sliding velocities of 0.1 to 6 m/s, and at temperatures of 400 degrees C. Al2O3 and Si3N4 balls were also rubbed against the DLC-coated MgO-PSZ disks, primarily to assess their friction and wear performance and to compare it with that of MgO-PSZ balls. A series of long-duration lifetime tests was run at speeds of 1, 2, and 6 m/s under a 5 N load to assess the durability of these DLC films. Results showed that the friction coefficients of MgO-PSZ balls sliding against MgO-PSZ disks were 0.5-0.8 and the average specific wear rates of MgO-PSZ balls ranged from 1 x 10(-5) to 5 x 10(-4) mm(3)/N . m, depending on sliding: velocity, contact load, and ambient temperature. The friction coefficients of MgO-PSZ balls sliding against the DLC-coated MgO-PSZ disks ranged from 0.03 to 0.1. The average specific wear rates of MgO-PSZ balls were reduced by three to four orders of magnitude when rubbed against the DLC-coated disks. These DLC films could last 1.5 to 4 million cycles, depending an sliding velocity. Scanning electron microscopy and micro-laser Raman spectroscopy were used to elucidate the microstructural and chemical nature of the DLC films and worn surfaces.

1996-01-01T00:00:00Z Mimaroğlu, Abdullah Özel, Ahmet Sevinç, Vahdettin https://hdl.handle.net/20.500.12619/70253 2020-10-16T12:18:09Z 1996-01-01T00:00:00Z

A numerical study of geometric and material instability in uniaxial drawn polymers Mimaroğlu, Abdullah; Özel, Ahmet; Sevinç, Vahdettin In this study, the general purpose Finite Element Code, ABAQUS, with a non-linear solution has been employed to study the neck profile in drawn polymers. Attempts are made to obtain the relationship between the neck profile, neck propagation and uniaxial stress-strain behaviour of the polymers. Finite element analyses are carried out for destabilised polyvinyl chloride (uPVC), high-density polyethylene (HDPE), polypropylene (grades GSE108 and GSE16 ICI) and model uniaxial stress-strain behaviour. The results show a close relationship between the neck profile and the draw ratio and strain rate in the neck, that are related to the material, test speed and specimen geometry. Finally, the capability of the finite element technique in the prediction of the polymer stress-strain-strain-rate surface is discussed. Copyright (C) 1996 Elsevier Science Ltd

1996-01-01T00:00:00Z