Browsing by Author "Ustel, F"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    CUTTING-TOOL RECYCLING PROCESS WITH THE ZINC-MELT METHOD FOR OBTAINING THERMAL-SPRAY FEEDSTOCK POWDER (WC-Co)
    Altuncu, E; Ustel, F; Turk, A; Ozturk, S; Erdogan, G
    Various recycling processes for WC-Co cermets from cutting tools, such as chemical modification, thermal modification, the cold-stream method and the electrochemical method have been investigated and some of them are actually employed in industry. However, these conventional methods have many problems to be solved and they are not always established technologies. Therefore, a more economical and high-efficiency recycling procedure needs to be developed. In this study we investigated the applicability of the zinc-melt method (ZMM) for recycling WC-Co as a powder from cutting-tool scraps. It was proven that ZMM is an available technique for recovering the WC powder from the cutting tools. WC-Co powders are recovered and then spray dried, sintered and obtained as a feedstock material for thermal-spray coating processes.
  • No Thumbnail Available
    Item
    Investigation of Bond Strength of Spray Dried Hydroxyapatite-Wollastonite Composite Powder After Plasma Spray
    Bastan, FE; Karaarslan, O; Erdogan, G; Ustel, F
    Hydroxyapatite (HA) is one of the most significant calcium phosphate bio-ceramic which is used commercially in biomedical application due to its similar structure with natural bone, bioactivity, and stability in body fluid. HA has excellent biological properties, while plasma sprayed HA coatings have poor bond strength which makes it difficult to use HA coated implants under mechanical stress. Wollastonite (CS) is a calcium silicate based bioactive ceramic which is used in thermal spraying due to its higher bond strength than HA coatings, however it dissolves quicker than HA in simulated body fluid (SBF). The aim of this work is to produce HA-CS composite powder in order to increase bond strength of the coating. In this study, commercial CS and precipitated HA mixture suspension which involved wt. 20% CS was prepared for spray drying (SD) application. HA-CS composite microspheres were granulated by spray drying to supply homogeneity of coating and carry powders to the plasma easily. Afterwards, HA and HA-CS composite microspheres were coated by plasma spraying on carbon steel. Results showed that HA-CS composite coatings have higher adhesion strength, while it decomposes easier to other calcium phosphates than pure HA coating. Additionally, HA-CS coating has higher rate of porosity and un-melted particles.
  • No Thumbnail Available
    Item
    Spray drying of hydroxyapatite powders: The effect of spray drying parameters and heat treatment on the particle size and morphology
    Bastan, FE; Erdogan, G; Moskalewicz, T; Ustel, F
    The physical and chemical properties of spray dried hydroxyapatite (SD-HA) are significantly depended on precipitation and spray drying (SD) process parameters. This study presents the effects of precipitation pH, solid content, slurry feed rate, atomization pressure, hot air temperature and hot air flow rate on the particle size distribution of SD-HA. Moreover, the physical and chemical properties of SD-HAs and heat treated micro-granules depending on the precipitation pH were investigated. Taguchi Experimental Design (DoE) was employed to optimize the parameters and to determine the significant factors. The physical properties of SD-HA and heat treated micro-granules were analyzed via particle size analyzer, SEM and TEM. RAMAN and FTIR were carried out to examine the chemical properties. Increasing of the precipitation pH led to slightly increase of the median particle size and the high temperature stability of the SD-HA. DoE results demonstrated the most significant SD parameters as atomization pressure and slurry feed rate. The increases in heat treatment temperature decreased the specific surface area, pore volume and particle size of SD-HA, while increased the crystallinity and powder density. SD-HA were stable up to 1250 degrees C and decomposed at approximately 1450 degrees C. (C) 2017 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Wear Behavior of Plasma-Sprayed Al-12Si/SiC Composite Coatings under Dry and Water-Lubricated Sliding
    Akgun, S; Sahin, S; Ustel, F
    Powders of Al-12Si with 25 and 50wt% SiC particles were ball-milled in a conventional rotating ball mill with alumina balls for 2h. The milled powders were plasma-sprayed onto aluminum and stainless steel substrates to obtain Al matrix composites with high SiC weight fraction. The microstructure characteristics of the sprayed composites were investigated by metal microscopy. Surface roughness, coating thickness and microhardness were measured. Microhardness values increased when the amount of SiC particles in Al-12Si coatings increased. The wear behavior of the coatings under dry-sliding and water-lubricated sliding with stainless steel counter material was studied using ball on disc for 10kN. Wear surfaces were investigated with scanning electron microscopy (SEM). Increasing SiC content of coatings increased the wear resistance. The highest wear resistance in coatings was observed in the coating having 50% SiC.
  • No Thumbnail Available
    Item
    Influence of long time post annealing on thermal stability and thermophysical properties of plasma sprayed La2Zr2O7 coatings
    Erdogan, G; Ustel, F; Bobzin, K; Öte, M; Linke, TF; Zhao, LD
    Thermal barrier coatings (TBCs) were applied to gas turbines to function at higher gas temperatures. Extensive effort has been invested in identifying new materials with even better performance compared to yttria-stabilized zirconia (YSZ) being the industry standard up-to-date. La2Zr2O7 (LZ) with the pyrochlore structure has received attention and been identified as a new candidate material for TBCs. In this study, two different coatings produced with commercial and high-energy ball milled LZ powders were investigated. Coatings were annealed for 50 h, 100 h, 200 h and 500 h at 1150 degrees C. Microstructures of the coatings were examined with Scanning Electron Microscopy and thermal conductivities were investigated with laser flash measurements. Mercury porosimetry was used as well to identify pore size changes that might occur with annealing process. X-Ray diffraction analysis was used to determine any possible phase changes. The results showed a sintering effect leading to an increase in thermal conductivity, and after 500 h heat treatment time, phase decomposition occurred on LZ based coatings. (C) 2016 Elsevier B.V. All rights reserved.