Erdem Atar

Residual stress estimation of ceramic thin films by X-ray diffraction and indentation techniques

Abstract The residual stresses in ceramic thin films obtained by the indentation method have been found to be three times higher than those of the X-ray diffraction method. This discrepancy can be eliminated by setting the geometrical factor for the Vickers pyramid indenter to 1 in the relevant equation of the indentation method.

Hardness characterisation of thin Zr(Hf, N) coatings

Abstract In this study, depth-sensing Vickers indentation tests were conducted on Zr(Hf,N) coatings, containing different amounts of Hf (0–21 wt.%). The coatings were deposited on hardened AISI D2 cold-work tool steel with a physical vapour deposition technique. Hardness characteristics of the coatings were analysed under six different indentation loads (0.01–0.1 N) according to load and energy methods. The same Vickers hardness numbers were obtained from the conventional load method under indentation loads that create indents having depths lower than 10% of the coating thickness. An energy method, which was derived from the work of indentation, gave similar Vickers hardness numbers over a wide range of indentation depths (up to 25% of the coating thickness). The hardness numbers of Zr(Hf,N) coatings calculated by these two methods, which are independent of the indentation depth, did not change with increasing Hf content of the coatings. The average Vickers hardness number obtained from the energy method is approximately half that from the load method. After correcting the conventional-load-method HV numbers according to the Oliver and Pharr procedure, the difference between HV numbers calculated by load and energy methods significantly decreased.

Raman spectroscopy characterization of hypo-eutectic CoCrWC alloy tribolayers

Purpose This paper aims to study microstructure and high temperature tribological performance of hypo-eutectic CoCrWC hardfacing alloy (Stellite 12) deposited on steel substrate by plasma-transferred arc (PTA) welding technique. Design/methodology/approach Microstructural characterization of the deposited coating was made using electron probe microanalysis, X-ray diffraction and microhardness tester. Dry sliding wear tests were carried out with a ball-on-disc type tribometer at room and elevated temperature. Worn surfaces of the samples were examined by the EDX equipped SEM and Raman spectroscopy. Findings Results revealed that at room temperature and 300°C plasticity dominated wear mechanism was operative. Under oxidation dominated wear conditions (400, 500, 600 and 700°C), testing temperature plays a crucial role on the characteristics of the oxide tribolayers formed on worn surfaces. Development of Cr2O3 in the tribolayer at 600 and 700°C was beneficial in increasing wear resistance of examined coating. Originality/value While the sliding wear performance of Stellite alloys at room temperature has been investigated in details, published studies on tribological behavior of Stellite alloys with varying temperature are scarce. Therefore, the present work was undertaken to study the wear mechanisms and the type of tribolayers formed during sliding wear of PTA welding deposited hypo-eutectic Stellite 12 coating with increasing temperature up to 700°C.

Tribological Properties of CrN Coated H13 Grade Tool Steel

The characteristics of CrN coated martensitic H13 grade tool steels were studied. CrN coatings were deposited by the arc physical vapor deposition (PVD) before and after the pulse plasma nitriding of the samples. The PVD and plasma nitriding techniques were applied in relevant workshops by folowing the commercial practice parameters. Experimental results showed that CrN coating deposited on the nitrided surfaces exhibited superior scratch and wear resistances as compared to that deposited on the original martensitic surface.

An Overview on Surface Hardening of Titanium Alloys by Diffusion of Interstitial Atoms

In this paper, diffusional surface hardening processes utilized to overcome the poor tribological performance of titanium and its alloys is briefly introduced. More specifically, surface treatments known as thermal oxidation, nitriding and boriding offering the advantage of producing graded surfaces comprising hard compound layer and diffusion zone by diffusion of interstitial atoms (oxygen, nitrogen and boron) are overviewed.

Friction and Wear Behaviour of Borided Ti6Al4v Alloy Sliding Against Al2O3 and Si3N4 Balls in Water

This study focuses on tribological performance of as-received and borided Ti6Al4V alloys against ceramic counterfaces (Al2O3 and Si3N4 balls) in water. The wear mode of the alloy changed from ploughing to polishing by achieving a remarkable reduction in wear loss upon boriding. On the borided surface, the destructive action of the Si3N4 ball was very limited, when compared to that of the Al2O3 ball.

Effect of Oxidation on the Wear Behavior of a ZrN Coating

In the present study tribological performance of ZrN coatings deposited on hardened AISI D2 quality cold work tool steel by arc-Physical Vapor Deposition technique has been examined in as-deposited and oxidized conditions. ZrN coatings were oxidized at 400 oC for various times up to 12 h. Reciprocating wear tests carried out by rubbing Al2O3 balls on the coatings, revealed significant improvement in wear resistance of ZrN coating upon oxidation. Oxidation treatment at 400 oC for 12 h yielded seven times higher wear resistance than as-deposited ZrN coating, beside significant reduction in the wear of counterface (Al2O3 ball).

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.

Enhanced wear resistance of Stellite 12 by Mo addition and LSM

ABSTRACT Aiming at additional improvements in the properties of Stellite 12 PTA hardfacing alloy deposited on 4140 steel substrate, the authors have adopted a dual approach. During PTA deposition Stellite 12 hardfacing powder was alloyed with 10 wt-% Mo, followed by laser surface melting (LSM). Addition of 10 wt-% Mo, led to an increase in the volume fraction of Co and W-rich complex carbides. Later on LSM executed on the PTA led to the development of unique microstructure near the surface, characterised by the segregation of hard Cr-rich carbides. The resultant layers were subjected to mechanical characterisation, at room temperature, e.g. hardness and wear resistance. It was concluded that combining both approaches i.e. addition of Mo during the hardfacing process followed by LSM of deposited layer gave additional improvements in mechanical properties owing to evolution of a unique carbide structure.

Structural Changes on the Surface of Alloy Ti6Al7Nb Under Gas Nitriding

The structure of titanium alloy Ti6Al7Nb (the surface nitride layer, the intermediate layer and the diffusion layer) is studied after nitriding at 950, 1120 and 1250°C for 12 h at atmospheric nitrogen pressure. The thickness of the nitride and diffusion layers is shown to increase with increase in the nitriding temperature. The growth of the nitride layer is accompanied by segregation of aluminum in the intermediate layer.