Browsing by Author "Ayvaz, SI"

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    Determination of diffusion kinetics, wear and corrosion behaviour of boro-sintered powder metal AISI 316 stainless steel alloy
    Ayvaz, SI; Zalaoglu, D; Özer, E; Bahçepinar, AI; Aydin, IB
    The study aimed to improve the hardness, wear, and corrosion resistance of powder metal AISI 316 stainless steel alloy using boro-sintering to form FeB and Fe2B compounds on the sample surface at different temperatures and durations utilizing Ekabor II boriding powder. The boride layer thickness was measured, and boron diffusion kinetics were determined. The boron diffusion activation energy was computed at 190.29 kJ & sdot;mol-1 during borosintering. The microhardness test revealed 12.5 times increase in the hardness of the AISI 316 stainless steel substrate. Adhesion tests using Daimler-Benz Rockwell C confirmed adequate substrate-coating adhesion of the formed boride layers. The ball-on-disc method results indicated that the wear resistance of boro-sintered samples exceeded that of unboronized AISI 316 stainless steel by a ratio ranging from 8.32 to 14.17. Corrosion tests of boronized powder metal AISI 316 stainless steel alloy samples were conducted in 3.5 % NaCl solution, demonstrating a 50 % reduction in corrosion rate with the boro-sintering process.
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    Comparative Study of Conventional and Microwave-Assisted Boriding of AISI 1040 and AISI 4140 Steels
    Ayvaz, SI; Özer, E
    In this study, AISI 1040 and AISI 4140 steels were boriding using Ekabor-II commercial boriding powder with powder-pack boriding method using microwave and conventional heating methods. The samples were borided at 950 & DEG;C for 2 and 6 hours in an Ar atmosphere in a microwave oven of Enerzi-Mh2912-V8. Biphasic structure (FeB/Fe2B) was formed in all borided AISI 4140 samples and AISI 1040 samples borided for 6 hours. A single-phase structure was observed in AISI 1040 steel borided for 2 hours. Compared to the conventional method, a 1.5-1.6 times thicker boride layer was obtained in AISI 4140 and AISI 1040 steels with microwave-assisted powder-pack boriding. The highest hardness was measured as 1561.8 HV0.05 for boriding AISI 4140 steel and 1499.7 HV0.05 for boriding AISI 1040 steel. The Vickers indentation fracture toughness of borided steels with microwave energy varied between 2.31 and 3.46 MPa & BULL;m1/2. It was determined that in all samples borided by the microwave-assisted and conventional powder-pack boriding method, the adhesion strength between the boride layers and the substrate obtained was sufficient.
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    Investigation of mechanical and tribological behavior of SiC and B4C reinforced Al-Zn-Mg-Si-Cu alloy matrix surface composites fabricated via friction stir processing
    Ayvaz, SI; Arslan, D; Ayvaz, M
    In this study, SiC and B4C reinforced Al-Zn-Mg-Si-Cu alloy matrix surface composites (SCs) were produced by friction stir processing (FSP) technique. Microstructural, mechanical, and tribological properties of produced SCs, and those of non-reinforced samples were examined. In B4C and SiC reinforced SCs fabricated by friction stir processing, approximately a 20% increase in hardness was achieved as compared to the base metal. The maximum microhardness values of B4C and SiC reinforced surface composites were determined as 88.1 and 89.7 HV, respectively. The tensile strengths of these samples were measured as 166.42 and 174.74 N.mm(-2), respectively. As a result of the tests performed under 3, 5, and 10 N applied loads, it was observed that the friction coefficient decreased in general with the applied load. A higher coefficient of friction was obtained in SiC reinforced SCs than those of B4C reinforced SCs and non-reinforced samples. It was determined that the wear rate of B4C reinforced SCs decreased by similar to 30-40% and SiC reinforced SCs by similar to 50-55% compared to non-reinforced samples. In the examinations, it was revealed that mechanically mixed layer formation effectively reduced wear rate in these samples compared to non-reinforced samples.
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    Effect of Shot Blasting on the Boriding Kinetics of AISI 316L Stainless Steel
    Ayvaz, SI; Aydin, I; Bahcepinar, AI
    In this study, the effect of shot blasting on boriding kinetics of AISI 316L stainless steel alloy was investigated. For this purpose, AISI 316L samples were shot blasted at 6 bar pressure using 300-500 mu m glass beads. Shot blasted samples were borided with powder pack boriding technique, using Ekabor 2 boriding powder, with 2, 4 and 6 boriding times at 850, 900 and 950 degrees C boriding temperatures. As a result of boriding, boride layers consisting of FeB and Fe2B phases with a microhardness of similar to 1497-2135 HV0.1 and an average thickness of similar to 9.6-49.27 mu m were obtained on the surface of AISI 316L stainless steel alloy samples. These boride layers on the AISI 316L stainless steel alloy surface were formed in flat morphology due to the high amount of alloying elements. In the kinetic studies, the activation energy of boron diffusion in AISI 316L stainless steel alloy was calculated as 204.68 kJ mol(-1). The obtained results showed that shot blasting decreased the boron diffusion kinetics compared to the results in the literature.
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    Enhancing the wear performance of Ti-6Al-4V against Al2O3 and WC-6Co via TiBn layer produced by boriding
    Ayvaz, SI
    In this study, mechanical and tribological properties of the borided dual-phase alpha + beta type Ti6Al4V titanium alloy were examined. For this purpose, Ti6Al4V alloy samples were borided for 6 h at a temperature of 1100 ? by the powder-pack boriding process. As a result of boriding, a boride layer consisting of TiB2 with a thickness of max similar to 25 mu m and TiB phases with a thickness of max similar to 10 mu m was obtained on the Ti6Al4V sample surfaces. As a result of the boride layer's nanoindentation tests carried out using the Berkovich indenter, it was found to have an elastic modulus of 534.255 GPa and a hardness of 36.537 GPa. Wear tests were carried out using the pin-on-disc method under a load of 10 N and with a sliding distance of 1000 m. Whereas the dominant type of wear in non-borided samples was abrasive wear, oxidative mild wear was generally observed in borided samples. In borided samples, as a result of becoming of surface smoother by hard asperities breaking and increasing the actual contact area, the friction coefficients increased. It was determined that with boriding, the wear performance of Ti6Al4V alloy improved similar to 46.8 times against the Al2O3 counterpart and similar to 4.57 times against WC-6Co counterpart.
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    Growth Kinetics and Microstructure of Iron Boride Layers on AISI 1050 Steel
    Ayvaz, SI
    Diffusion kinetics of boron in AISI 1050 steel is investigated. AISI 1050 steel samples are borided for 2, 4 and 6 h at 850, 900 and 950 degrees C by the powder-pack boriding method using Ekabor-II boriding powder. After the powder-pack boriding, about 25.4 - 118.9 mu m thick FeB/Fe2B boride layers are obtained on the surfaces of the samples. The boride layers have a typical tooth morphology and their hardness is 1071 - 1460 HV0.1. The growth rate constants for the boriding temperatures of 850, 900 and 950 degrees C for the AISI 1050 steel are determined to be 1.522 x 10 (-12), 2.964 x 10 (-13) and 6.354 x10 (-12) m(2) sec (-1), respectively. The boron diffusion activation energy in the AISI 1050 steel is 162.93 kJ mol (-1).
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    Tribological and adhesion properties of microwave-assisted borided AISI 316L steel
    Ayvaz, SI; Aydin, I
    In this study, AISI 316L stainless steel alloy samples were borided with powder-pack boriding method using Ekabor II powder with the support of a microwave furnace with a power of 2.9 KW and a frequency of 2.45 GHz. Boriding was carried out at 850, 900 and 950 degrees C temperatures for 2, 4 and 6 h of operation. A distinct diffusion barrier consisting of Fe-Ni-Si elements was detected in borided samples at 950 degrees C for 4 and 6 h. As a result of the Daimler Benz Rockwell-C adhesion tests, regions with insufficient adhesion strength were detected in these samples. In other samples, adhesion qualities between boride layers and substrate were in the range of HF1-HF3. The lowest specific wear rates were determined as 5.208 (mm(3) Nm(-1)) x 10(-6) and 5.210 (mm(3) Nm(-1)) x 10(-6) for the samples borided for 6 h at 850 degrees C and 4 h at 900 degrees C, respectively. It was determined that the increase in thickness of the brittle FeB compound increased the wear with the three-body abrasive wear mechanism.
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    Characterization of a Duplex Coating (Boriding plus Hydroxyapatite) on Austenitic Steel
    Bahçepinar, AI; Ayvaz, SI; Aydina, I
    In this study, duplex coating process (Boriding + Hydroxyapatite) was applied to 316L stainless steel alloys. Before coating, the substrate materials were shotblasted with 300-500 mu m glass beads in a vacuum type shot blast machine. Tribological properties of the alloy with boriding process, its bioactivity and biocompatibility was increased with the hydroxyapatite (HA) coating process. Powder pack boriding technique was used in boriding process and Electrophoretic deposition method (EPD) was used in HA coating process. At the end of the study, the microstructures (SEM), elemental analyzes of the coating surfaces (EDS), Ca/P ratios, coating thicknesses were determined. In addition, the hardness and adhesion qualities of the boride layer were determined. When the results obtained are evaluated, duplex layers were successfully formed for all parameters.
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    A novel method for determining effects of fire damage on the safety of the Type I pressure hydrogen storage tanks
    Ayvaz, M; Ayvaz, SI; Aydin, I
    Consumption of the fossil fuels causes greenhouse gas effect and environmental pollution, which are two basic problems of our age. As a result of this problem, clean and renewable alternative energy sources are beginning to replace fossil fuels. Nowadays, the use of hydrogen energy, which is one of the clean energy, is increasing in transportation and industrial areas. Increasing of hydrogen energy usage, scientists are attempting to solve the many safety problems (such as fire, burst, impact and hydrogen embrittlement) that can occur during the storage and consumption of hydrogen energy. In this study, during the event of fire, the safety of metallic Type I pressure hydrogen storage tanks is investigated by using a novel approach. In this new approach, the mechanical strength drops of the tank materials that is related with temperature rising are added to the safety calculations. In the study, 6061 T6 aluminum and SS 316L stainless steel alloys were used as hydrogen tank material. The safety of hydrogen tanks modelled using these alloys was investigated under different temperature conditions (22, 100, 200 and 300 degrees C) and internal pressure (15, 20 and 25 MPa). (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Effect of the Microwave Heating on Diffusion Kinetics and Mechanical Properties of Borides in AISI 316L
    Ayvaz, SI; Aydin, I
    In this study, the effect of microwave heating on boride formation and diffusion kinetics in 316L stainless steel alloys was investigated. Boriding was carried out in microwave furnace with 2.9 kW power and 2.45 GHz frequency. Four different boriding temperatures (800, 850, 900 and 950 degrees C) were used. Boriding was performed for 2, 4 and 6 h for each temperature. Boron layer thicknesses of boride layers were determined by optical microscope. SEM images were taken from the cross sections of the borided samples. Boron activation energy was determined as 244.15 kJ/mol in microwave environment. Two times thicker boride layer was obtained by microwave boriding process compared to the conventional heating process. The mechanical properties of the boride layers formed by microwave boriding (Young's modulus, hardness, yield strength, residual thermal stress) were determined by nanoindentation tests.