Fatih Erdemir

Microstructural characterization and mechanical properties of functionally graded Al2024/SiC composites prepared by powder metallurgy techniques

Abstract Al2024/SiC functionally graded materials (FGMs) with different numbers of graded layers and different amounts of SiC were fabricated successfully by powder metallurgy method and hot pressing process. The effects of increasing SiC content and number of layers of Al2024/SiC FGMs on the microstructure and mechanical properties of the composite were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) analyses indicated that Al and SiC were dominant components as well as others such as Al4C3, CuAl2, and CuMgAl2. A maximum bending strength of 1400 MPa was obtained for two-layered FGMs which contained 40% SiC (mass fraction) on top layer. A decrease in microhardness and changes in porosity were discussed in relation to the SiC content and the intermetallics formation. The results show that the increase in microhardness values and intermetallic formation play a major role on the improvement of mechanical properties of the composites.

New Coating Technique for Al–B4C Composite Coatings by Mechanical Milling and Composite Coating

Mechanical milling (MM) process as a novel technique for producing Al–B4C composite coatings on the surface of low carbon steel was investigated. The coating thickness, morphology, and cross-section microstructure of the composite coatings were analyzed with scanning electron microscopy (SEM). Also, Vickers microhardness and surface roughness of the coating layer were measured. It was found that a dense Al–B4C composite coating could deposit on the surface, particularly, if longer milling periods. The microstructure of Al–B4C composite coatings revealed that the distribution of B4C particles in the Al matrix was homogenous. Increasing milling time from 6 to 30 h resulted in increase of the microhardness values from 220 to 280 HV for the pre-interface layer (5 μm).

Microstructure and Abrasive Wear Behavior of CuSn10–Graphite Composites Produced by Powder Metallurgy

In this study, CuSn10 metal-matrix composites (MMCs) reinforced with 0, 1, 3, and 5 vol.% graphite particulates were fabricated by powder metallurgy. The microstructure, relative density, hardness, and abrasive wear behavior of the composites were investigated. The abrasive wear tests were conducted on unreinforced matrix and CuSn10–graphite composites using a pin-on-disk-type machine. The effects of sliding distance, applied load, graphite particle content, and abrasive grit sizes on the abrasive wear properties of the composites have been evaluated. The microstructure evolution of composites and the main wear mechanisms were identified using a scanning electron microscope and an energy-dispersive X-ray spectrometer (EDS). The density and hardness of the sintered CuSn10–graphite composites decreased with increasing graphite content. The abrasive wear resistance increased with increasing graphite content, but the abrasive wear resistance decreased with increasing sliding distance, applied load, and abrasive grit size. Moreover, the wear resistance of the composite was found to be considerably higher than that of the CuSn10 matrix alloy and increased with increasing graphite particle content.

Development and characterization of bronze-Cr-Ni composites produced by powder metallurgy

Abstract In this study, the bronze-Cr-Ni composites were prepared by means of the powder metallurgical method. The influence of the composition and compact pressure on microstructure, density, hardness and electrical conductivity was examined. Scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX) were used to analyze the microstructure of the contact materials. The results showed that density of the bronze-Cr-Ni composites decreased with increasing Ni content. Increasing compact pressure led to lower porosity and consequently improved the density of bronze-Cr-Ni composites. The relative green density increased from 78% to 95% with the increase in the compact pressure from 200 MPa to 800 MPa. The hardness values showed a decrease from 95.1 BHN to 71.6 BHN by the addition of Ni from 1 wt% to 5 wt% at 800 MPa. It was found that addition of Ni at 1 wt% was required to achieve increased hardness and sufficient conductivity for bronze-Cr-Ni composites. The electrical conductivities of contact materials containing 3 wt% Ni and 5 wt% Ni was lower than that of 1 wt% Ni.

Determining the effect of flake matrix size and Al2O3 content on microstructure and mechanical properties of Al2O3 nanoparticle reinforced Al matrix composites

ABSTRACT In this study, Al2024 matrix composites reinforced with Al2O3 nanoparticle contents ranging from 1 to 5 wt% were produced via a new method called as flake powder metallurgy (FPM). The effect of flake size and Al2O3 nanoparticle content on the reinforcement distribution, microstructure, physical, and mechanical properties of the composites were studied. SEM analysis was performed to investigate the microstructure of metal matrix and the distribution of nanoparticles. The hot-pressed density increased with decreasing the matrix size. The hardness of the Al2024–Al2O3 nanocomposites fabricated by using fine matrix powders increased as compared to the Al2024–Al2O3 nanocomposites produced by using coarse matrix powders. It has been found that the FPM method proposed in this study revealed to be an effective method for the production of nanoparticle reinforced metal matrix composites.

Artificial neural network-based prediction technique for coating thickness in Fe-Al coatings fabricated by mechanical milling

ABSTRACT The objective of this study was to evaluate the effect of milling time, milling speed and particle size of initial powders on the coating thickness of Fe-Al intermetallic coating by using artificial neural network (ANN). Coating morphology and cross-section microstructures were evaluated using a scanning electron microscope (SEM). It was found that an increase in the milling time provided an increase in the coating-layer thickness due to the cold welding process between particles and the steel substrate. The microstructure of the coating surface was refined by ball impacts in the milling process. As a result of this study, the ANN was found to be successful for predicting the coating thickness of Fe-Al intermetallic coatings. The correlation between the predicted values and the experimental data of the feed-forward back-propagation ANN was quite adequate. The mean absolute percentage error (MAPE) for the predicted values didn’t exceed 7.46%. The ANN model can be used for predicting the coating thickness of Fe-Al intermetallic coating produced for different milling time, milling speed and particle size.

Repair of aged bulk-fill composite with posterior composite: Effect of different surface treatments

OBJECTIVE In the present study, the ability of posterior resin composite to repair aged bulk-fill resin composite and vice versa were assessed by shear bond strength testing. MATERIALS AND METHODS Resin composite substrates were aged and surfaces were abraded with abrasive papers, then bulk-fill substrates were repaired with posterior resin composite and vice versa using different surface treatments (no surface treatment [control]; etching with 37% phosphoric acid [H3 PO4 ] for 20 seconds; etching with 10% hydrofluoric acid [HF] for 20 seconds; etching with 37% H3 PO4 for 20 seconds + adhesive application; etching with 10% HF for 20 seconds + adhesive application; adhesive application only). Shear bond strengths (SBS) were then measured and surface roughness values (Ra) were determined. Cohesive strengths of nonaged resin composites were measured and used as reference groups. Resin composite surfaces after acid etching were evaluated by SEM. Data were analyzed using ANOVA and Fishers LSD tests (P < .05). RESULTS ANOVA showed that resin composite repair type did not affect SBS significantly (P = .850), while it showed that surface treatments significantly affected the SBS (P = .000). Only a combination of etching with 10% HF for 20 seconds with resin adhesive application provided similar SBS values with those of the positive control. CONCLUSIONS It was concluded that the aged bulk-fill resin composite would be effectively repaired with conventional posterior resin composite or vice versa if proper repair protocol was deployed. CLINICAL SIGNIFICANCE The combination of 10% HF etching and adhesive application would provide efficient repair strength when the aged bulk fill resin composite is repaired with conventional posterior resin composite or vice versa.

Bonding performance of universal adhesives to er,cr:YSGG laser‐irradiated enamel

Universal adhesives have been recently introduced for use as self‐etch or etch‐and‐rinse adhesives depending on the dental substrate and clinical condition. However, their bonding effectiveness to laser‐irradiated enamel is still not well‐known. Thus, the aim of this study was to compare the shear bond strength (SBS) of universal adhesives (Single Bond Universal; Nova Compo‐B Plus) applied to Er,Cr:YSGG laser‐irradiated enamel with SBS of the same adhesives applied in self‐etch and acid‐etching modes, respectively. Crown segments of sixty bovine incisors were embedded into standardized acrylic blocks. Flattened enamel surfaces were prepared. Specimens were divided into six groups according to universal adhesives and application modes randomly (n = 10), as follows: Single Bond Universal/acid‐etching mode; Nova Compo‐B Plus/acid‐etching mode; Single Bond Universal/self‐etching mode; Nova Compo‐B Plus/self‐etching mode; and Single Bond Universal/Er,Cr:YSGG Laser‐etching mode; Nova Compo‐B Plus/Er,Cr:YSGG Laser‐etching mode. After surface treatments, universal adhesives were applied onto surfaces. SBS was determined after storage in water for 24 h using a universal testing machine with a crosshead speed of 0.5 mm min−1. Failure modes were evaluated using a stereomicroscope. Data was analyzed using two‐way of analyses of variances (ANOVA) (p = 0.05). Two‐way ANOVA revealed that adhesive had no effect on SBS (p = 0.88), but application mode significantly influenced SBS (p = 0.00). Acid‐etching significantly increased SBS, whereas there are no significant differences between self‐etch mode and laser‐etching for both adhesives. The bond strength of universal adhesives may depend on application mode. Acid etching may significantly increase bond strength, while laser etching may provide similar bond strength when compared to self‐etch mode.