Ihsan Efeoglu

Multi-pass sub-critical load testing of titanium nitride coatings

TiN coatings deposited by closed field unbalanced magnetron sputter ion plating (CFUBMS) have been scratch tested in two modes. An initial conventional scratch test has been carried out to determine the critical load, and multiple scratches have been made over single tracks at different fractions of the critical load. It is shown that, even at very high fractions of the critical load, the coatings do not fail adhesively or cohesively; rather, they simply become progressively thinner with successive passes of the diamond. Scanning electron microscopy of the worn surfaces has revealed a previously unobserved wear mechanism that shows that the coating adhesion can be truly described as perfect.

The structural and tribological properties of MoS2-Ti composite solid lubricants

MoS 2 -Ti composite solid lubricant films were deposited on an AISI D2 tool steel and silicon wafer by CFUBMS (closed field unbalanced magnetron sputtering). The deposition process was performed for nine different test conditions at various levels of target current, working pressure, and substrate voltage using the Taguchi L 9 (3 4 ) experimental method. It was observed that the chemical composition of MoS 2 -Ti composite films was significantly affected by sputtering parameters. It was determined that the microstructure of composite films is neither crystalline nor amorphous; in other words, it is quasi-amorphous, and (002) and (100) planes characteristic of MoS 2 occurred. The friction coefficients of the films were determined over 1800 s and at a loading of 10 N by means of a pin-on-disk tribotester. The changes in friction coefficient were related to structural changes based on Ti addition and the different levels of deposition parameters.

Microstructure and structural behavior of ion-nitrided AISI 8620 steel

Abstract The ion nitriding behavior of AISI 8620 alloy steel has been examined under varying process conditions. The process variables included time (1–8 h), temperature (450–600°C) and a 70% H2–30% N2 gas mixture. The structure of the compound layer was studied by X-ray diffraction (XRD) and light optical microscopy. These studies showed that the thickness of the compound layer increased with increasing time at 500°C and 550°C; however, at 600°C, the thickness of the compound layer decreased with increasing time. Phase changes during ion nitriding at 600°C have been investigated using XRD, scanning electron microscope (SEM) and energy dispersive spectrometry (EDS). The maximum surface hardness was obtained at 500°C for 8 h and a larger diffusion layer was obtained at 600°C for 8 h. A braunite layer formed at 600°C.

Mechanical and structural properties of AISI 8620 steel TiN coated, nitrided and TiN coated+nitrided

Abstract The mechanical and structural properties of TiN-coated, plasma-nitrided and TiN coated–nitrided AISI 8620 steel were investigated. The plasma nitriding process was carried out under various conditions of temperature (500°C), time (1, 4, 10 h), and gas mixture (70% N2+30% H2) at 10-mbar working pressure. The titanium nitride coatings were deposited using a closed-field unbalanced magnetron sputtering system (CFUBMS). Nitrided, TiN-coated and TiN+nitrided sample surface were characterized using microhardness tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The highest microhardness (10 gf) was obtained at 500°C for 4 h nitriding time. The alloy nitrides produced (CrN, Mn4N) showed a stable condition at all nitriding times. The adhesion of nitrided+TiN coated sample was obtained at 4 h using a plasma-nitrided process.

Tribological properties of composite multilayer coating

Abstract The use of surface coatings is emerging as one of the most important approaches in reducing friction and wear in various tribological applications. Even though single layer coatings have a wide range of applications, the performance of the single layer alone may not always be adequate to meet the desired tribological property requirements. Hence, coatings consisting of multilayers to meet different property requirements in demanding applications are required. In this study, the tribological properties of a graded composite multilayer coating, with a specific layer sequence of MoS2/Ti–MoS2/TiBN–TiBN–TiB2–Ti deposited on tool steel substrate, have been investigated at temperatures of 40 and 400°C respectively. The experimental results from the tests at 40°C have shown that the friction coefficient value ranges between 0·02 and 0·034. It was found that the deposition parameters influenced the friction and durability of the coatings. Higher substrate bias was found to result in higher friction, and the coating deposited at high substrate bias and low N2 flow showed the lowest durability. The friction coefficient and durability of the coatings were found to be highly dependent on temperature. At high temperature, the friction coefficient increases almost threefold, and the durability decreases significantly.

Deposition and Adhesion Characterization of Ti(BN:MoS2) Based Composite Thin Films Prepared by Closed-Field Unbalanced Magnetron Sputtering

Composite structured solid thin films were deposited on 52100 tool steel by co-sputtering from BN, TiB2, MoS2 and Ti targets using a closed-field unbalanced magnetron sputtering process (CFUBMS). The structural and mechanical properties of the composite structured coatings were investigated. The composition and morphology of the films were investigated using X-ray diffraction and scanning electron microscopy (SEM). The adhesion properties of the films were characterized by the use of a Revetest-scratch tester. The adhesion test results indicated that bias voltage was the most effective coating parameter related to the critical load.

CHARACTERIZATION OF TiB2 COATING ADHERENCE BY A MULTI-PASS SCRATCH TESTING

TiB2 films deposited using various deposition techniques are used to increase the wear lifetime of industrial components. The performance of TiB2 films is dependent on the coating–substrate adhesion. In this study, the fatigue behavior of TiB2 films was investigated using the multi-mode scratch method. Films of TiB2 were deposited on silicon wafers and AISI M2 steel substrates at different frequencies by pulsed-dc closed field unbalanced magnetron sputtering (CFUBMS). The microstructures of the films were investigated using SEM techniques, and the hardness was measured using a microhardness tester. A multi-mode operation was used for sliding-fatigue, like multi-pass scratching in the same track at different fractions of critical load (bidirectional sliding) and a standard mode using progressive load operation. It was observed that the films deposited at low frequencies had higher adhesion strength and microhardness, and a denser microstructure.

Adhesion and tribological properties of TiTaBN coatings with a graded interlayer deposited by pulsed DC biased and continuous dc biased magnetron sputtering

The properties of TiBN-based coatings are significantly affected by adding alloying elements and coating parameters. Therefore, in this study, TiTaBN coatings with graded interlayer (CWGIL) were deposited on D2 steel substrates by pulsed DC biased (PDCB) and continuously DC biased (CDCB) closed field unbalanced magnetron sputtering (CFUBMS). The structural, mechanical, adhesion and tribological properties of the coatings were analysed with EDS, SEM, XRD, microhardness, scratch testing and a pin-on-disc tribo-tester (under various atmospheric conditions). TiTaBN CWGIL deposited by PDCB magnetron sputtering (MS) had a very dense microstructure, high hardness and a high critical load value. TiTaBN CWGIL deposited by PDCB MS had a lower friction coefficient, the wear rate and the penetration depth in all atmospheric conditions. In conclusion, the application of a PDCB substrate instead of a CDCB one dramatically increases the performance of CFUBMS-deposited TiTaBN coatings.

Tribological degradation of MoS2–Ti sputtered coating when exposed to elevated temperatures

Abstract The use of solid lubricants is an effective way to control friction and wear in applications where traditional lubricants such as oils and greases cannot be used. MoS2 is a popular solid lubricant which has been widely used in many applications, especially space applications in view of its good performance in vacuum. Recent developments in physical vapour deposition technology have led to the development of sputtered MoS2 films doped with different metals to improve their durability and reduce the detrimental effects of oxidation and humidity on their tribological performance. In this work, a MoS2–Ti coating deposited on a hot forming tool steel substrate has been studied at ambient and elevated temperatures. The objective was to investigate how the friction and durability of the MoS2–Ti coating are affected after exposure to elevated temperatures. The results have shown that low friction values of ∼0·02 were obtained at room temperature and low relative humidity of 25%. An increase in relative humidity to 40% led to an increase in friction by almost 100%. There was a very significant degradation in frictional characteristics as well as durability after the MoS2–Ti coating was exposed to 400°C. The wear of the counter surface also increased when sliding against the MoS2–Ti coating exposed to elevated temperatures. This has been attributed to interaction of the counterbody with hard abrasive molybdenum oxides formed on the MoS2–Ti coating due to exposure to elevated temperatures.

An investigation of the relationship between heat treatment and microstructure in (TiAlV)N and (TiAl)N ceramic films

(TiAl)N and (TiAlV)N films coated on M2 high-speed tool steel were heat-treated in an argon atmosphere at temperatures of 700°C, 800°C and 900°C for 3 h. The structural and mechanical properties of the ceramic films were examined by microindentation hardness testing, X-ray diffraction (XRD) and scanning electron microscopy. Annealing at elevated temperatures led to a decrease in the hardness of the ceramic films. The magnitude of this hardness change became larger with increasing annealing temperature. Elevated temperature anneals also modified the distribution of elements in the ceramic films. XRD data show that phase transformations take place in the structure. These transformations resulted in a decrease in the hardness, residual stress and spacing between the planes of the film. The surface topography was not affected by the heat treatment.