Beder, Murat

In this study, the effects of 0 wt% (C0), 10 wt% (C1), 20 wt% (C2) and 40 wt% (C3) B4C content on the microstructure, mechanical properties and dry wear properties of Al2024/B4C composites were investigated. In order to prepare Al2024 matrix composites with different B4C particle contents, mechanical milling (MM) and hot pressing (HP) were employed as powder metallurgy methods. It was found that the θ (CuAl2) phase content in the microstructure of Al2024/B4C compact materials increased with increasing B4C particle reinforcement, reaching its highest value at 40 wt% B4C (C3) reinforcement ratio. As the B4C particle reinforcement content increased, the hardness values of the composite samples increased. Flexural strength values were 445.30 MPa, 495.20 MPa, 277.59 MPa, and 129.37 MPa for samples coded C0, C1, C2, and C3, respectively. It was found that the C0 sample without particle reinforcement exhibited more than 10 times the volume loss of the C3 sample with the highest particle reinforcement at 450 m sliding distance. The SEM examination of the friction surfaces of the Al2024/B4C composite samples showed that the worn surfaces were composed of delamination, adhesion and smearing layers.

Beder, Murat; Varol, Temel; Akçay, Serhatcan Berk

Metal matrix composites are increasingly being recognized as new wear-resistant materials. The main purpose of this study is to investigate the microstructure, mechanical properties, and wear resistance of Al–Cu–Mg alloy matrix composites reinforced with high contents of Al2O3 particles. Moreover, the effects of 10, 20, and 40 wt% Al2O3 contents on the microstructure, mechanical properties, and dry wear resistance of the Al–Cu–Mg matrix composites are studied. The results show that the θ (CuAl2) phase ratio increases with increasing Al2O3 contents. The hardness values of the samples also increase with increasing Al2O3 contents. The highest tensile and flexural strengths are measured as 284 and 562.9 MPa, respectively, and these values are obtained for the composite material reinforced with 10 wt% Al2O3 particles. The continuous increase in the hardness of the samples with increasing Al2O3 content may cause the lowest volume loss for the 40 wt% Al2O3-reinforced composite. The friction surfaces show that the wear surfaces comprise adhesion, delamination, and smear layers. Overall, compared to the Al2O3-reinforced composite samples, pure Al–Cu–Mg alloy samples show approximately 2 times more mass gain.

Gul, Fatih

A titanium dioxide (TiO2) based memristor device having an active layer thickness of 10 nm was fabricated using radio frequency (RF) reactive sputtering and its resistive switching characteristics and carrier transport mechanisms were investigated. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to confirm the structural properties of the device. Measurement of the time-dependent current-voltage (I-V-t) was used to characterize resistive switching and memristive behavior. The characteristic pinched hysteresis I-V loops of the memristor were apparent. Bipolar and homogeneous resistive switching characteristics and a forming voltage of 2 V were detected in the device. The retention time exceeded 103 s and the endurance test was reasonably acceptable. In addition, the carrier transport mechanism of the device was revealed. The linear region of the low electric field demonstrated ohmic behavior, whereas the non-linear high electric field region was dominated by a Schottky emission carrier transport mechanism. A Poole-Frenkel emission mechanism acted as a secondary conduction mechanism. It was proposed that the Poole-Frenkel and Schottky emission mechanisms were associated with oxygen vacancies in the TiO2.

Gul, Fatih; Efeoglu, Hasan

In this study, direct-current reactive sputtered ZnO and ZnO1−x based thin film (30 nm and 300 nm in thickness) memristor devices were produced and the effects of oxygen vacancies and thickness on the memristive characteristics were investigated. The oxygen deficiency of the ZnO1−x structure was confirmed by SIMS analyses. The memristive characteristics of both the ZnO and ZnO1−x devices were determined by time dependent current–voltage (I-V-t) measurements. The distinctive pinched hysteresis I-V loops of memristors were observed in all the fabricated devices. The typical homogeneous interface and filamentary types of memristive behaviors were compared. In addition, conduction mechanisms, on/off ratios and the compliance current were analyzed. The 30 nm ZnO based devices with native oxygen vacancies showed the best on/off ratio. All of the devices exhibited dominant Schottky emissions and weaker Poole-Frenkel conduction mechanisms. Results suggested that the oxygen deficiency was responsible for the Schottky emission mechanism. Moreover, the compliance currents of the devices were related to the decreasing power consumption as the oxygen vacancies increased.

Çelik, İlhan

Magnesium and its alloys are the engineering materials which have the potential ability to be able to used widely particularly in the automotive, aerospace and in the biomedical sectors, especially thanks to their features such as lightness, specific strength that they have and biocompatibility. However, due to their poor wear resistance and corrosion resistance, the areas of usage are being restricted. This situation prevents Mg alloys to be used without any surface protection despite their good mechanical properties such as high strength/weight ratio. In this study, plasma spraying method is used to improve the poor corrosion resistance of AZ31 Mg alloy. Al2O3–13 wt% TiO2 (AT13) and Al2O3–40 wt% TiO2 (AT40) composite ceramic coatings were coated successfully on the surfaces of AZ31 Mg samples. The wear properties of the AT13 and AT40 coated samples were investigated for tribological applications. Surface morphology and microstructure of the duplex treated samples were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microhardness value of the uncoated AZ31 Mg alloy is 40±3 HV0.1, while the microhardness values of the AT40 and AT13 coatings are enhanced to 800±39 HV0.1 and 1500±35 HV0.1, respectively.