Ahmet Türk

Characterization of Plasma Nitrided X32CrMoV33 Die Steel

In this study, nitriding behavior of plasma nitrided X32CrMoV33 die steel was investigated. Nitriding process was carried out at temperatures of 450, 500, and 550°C for treatment time in the range of 2–32 h. Depending on nitriding temperature and time, the thickness of compound layer ranged from 2 µm to 15 µm. The presence of γ′-Fe4N, ϵ-Fe2-3N, α-Fe, and Cr2N phases formed in the compound layer was confirmed by XRD analysis. Using cross-sectional samples and a microhardness indenter, hardness depth profiles were also obtained; it was found that the hardness of compound layer was over 1000 HV. Kinetic studies revealed that the effective diffusion coefficients for plasma nitrided X32CrMoV33 are approximately 40.3 × 10−14, 99.2 × 10−14, and 427 × 10−14 m2s−1 for 450, 500, and 550°C process temperatures, respectively. The activation energy for plasma nitrided X32CrMoV33 steel is 118.77 kJ mol−1.

Comparison of Oxidation and Thermal Shock Performance of Thermal Barrier Coatings

Operating temperatures in gas turbine engines have reached to 1200°C with the latest developments in coating technology. Thermal shock and furnace oxidation tests are widely used to determine thermal barrier coating (TBC) performance and its durability in aircraft applications. This paper presents the results of thermal shock and furnace oxidation tests, carried out with regard to the microstructure and TGO (thermally grown oxide) growth behavior of TBC systems. Isothermal oxidation behavior of TBCs was evaluated through examination of microstructure, formation, and growth behavior of TGO layers at 1200°C for different time periods in furnace oxidation tests. On the other hand, thermal shock behavior of TBC was evaluated through examination of its durability at 1200°C with thermal shock test, which was carried out until the coating failure became visible. The relationship between the TGO growth and oxidation behavior was discussed using furnace oxidation test results.

The effect of Cu and Al on the mechanical properties of gravity-cast hyper-eutectic Zn–Al-based alloys

A series of Zn – Al-based alloys, one group with 1 % Cu and the other without Cu, was produced by using gravity casting. The effect of Al content on hardness, ultimate tensile strength (UTS), impact strength, and tensile creep behaviour at 120 °C and an applied stress of 40 MPa has been investigated. It has been found that the hardness and UTS of the alloys considerably increased with increasing Al content, but the creep strength decreased. The impact strength of the alloys improved with increasing Al content up to 7.5 % and then reduced gradually with further increase in Al content. In addition, the effect of 1 % Cu addition on the mentioned properties has been determined. While the addition of 1 % Cu had a profound effect on increasing the hardness, UTS, and creep strength, it did not have a significant effect on the impact strength of the alloys. Metallographic examinations showed that an increasing Al content of the alloys increased the volume fraction of the Al-rich b dendrites in expense of a decreased volume fraction of the eutectic, which is in principle responsible for the change in mechanical properties of the alloys depending on the Al content

The effect of Ti alloying on the mechanical properties and microstructure of a Zn–Al–Cu–Mg alloy

Abstract The effect of Ti additions (0.01–0.20 wt.%) on the hardness, ultimate tensile strength, impact strength and creep properties of the gravity-cast Zn–Al–Cu–Mg alloy ZA-8 has been investigated. The Ti additions have no significant effect on the hardness. The ultimate tensile strength of the standard ZA-8 alloy has not been changed significantly with Ti additions up to 0.15 wt.% and then decreased with further increase in Ti content. The impact strength shows a maximum around 0.05–0.15 wt.% Ti. The lowest creep resistance is obtained at 0.01 wt.% Ti, and the highest value of creep resistance is reached for 0.20 wt.% Ti. Metallographic studies indicated that the addition of Ti has a profound effect on the microstructure. Also, Ti forms a complex-shaped intermetallic compound which was identified as TiZn15 by X-ray diffraction. It is suggested that the TiZn15 particles cause the increase in creep resistance and decrease in tensile strength.

Investigation of wear behaviour of HVOF sprayed WC-Co coatings for automotive parts in different working conditions

Reinforced metal matrix composite (MMC) hard coatings which are produced by thermal spray processes are used for various automotive parts such as piston rings and cylinder liners. Generally, WC-CoCr coatings are deposited by HVOF process for improving surface resistance of low alloyed steels. In this study, we examined the wear characteristics of WC-CoCr coatings on low alloyed steel substrate under different test conditions, using a sliding wear test unit with abrasive ball. Experimental studies discussed the effects of test load, temperature, work medium and sliding distance on the wear characteristics of coatings. Weight loss, wear track depth and width were observed. It was found that the weight loss of coatings increased in dry medium conditions. Wear weight loss was significantly reduced in lubricated condition due to decreasing friction. The wear track surface profile changed with lubrication and increasing temperature in test conditions. Under the base oil lubricated conditions the WC-CoCr coating performed well.

Comparison of Corrosion Performance of Zn and Zn/Al 85/15 Coatings Produced by TWEA

Zn and Zn/Al 85/15 coatings are produced at optimum conditions by twin wire electric arc (TWEA) spraying technique and are used in various industrial applications to improve corrosion protection. As an alternative for Zn coating, Zn/Al 85/15 alloys coating show very good corrosion resistances and can protect substrate materials against harsh corrosive environments. The weight ratio of 85 Zn and 15 Al is regarded as optimum value. The forms of coating material are wires with different diameters. The aim of this study is comparison of anticorrosion performance of Zn and Zn/Al 85/15 coatings on ductile iron pipe surfaces as protective coatings against corrosion. Test samples were prepared from Zn and Zn/Al 85/15 coated ductile iron pipes. Coatings were investigated by optical microscopy, scanning electron microscopy (SEM) and have been analyzed by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). They were compared according to protection performance against corrosion in salt spraying test according to ASTM B117. As a result of this study, Zn/Al 85/15 coating showed clear anticorrosion protection capacity against Zn coatings.