Department of Metallurgical and Materials Engineering
Permanent URI for this collection
Browse
Browsing Department of Metallurgical and Materials Engineering by Author "Davut, Kemal"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item COATING OF TITANIUM (TiAl6V4) ALLOY BY ELECTROSPUN POLY (ε CAPROLACTONE) (PCL)(2022-01-24) Algelal, Hasan Mohammed Ali Abdullah; Şaşmazel, Hilal; Davut, KemalThe goal of this study is to fabricate a biomaterial implant composed of Titanium alloy TiAl6V4 coated with poly (ε caprolactone) (PCL) using electrospinning mechanism. Moreover, the effect of surface-treatment for the titanium alloy on the coating is also studied, whereas coating thickness is determined using a micrometer. Characterization of specimens’ morphology is executed using Scanning Electron Microscopy (SEM). The wettability of the surface is performed using the contact angle (CA) and the optical micrographs of the Titanium alloy microstructure are carried out using optical microscopy. The detection of composition and elements in the substrates Energy dispersive spectroscopy (EDS) is also performed. For more quantitative analysis of surface morphology and to evaluate the roughness at the surface of implants, AFM and roughness measurements are used. To determine the adhesion of the PCL to the TiAl6V4 , adhesion test is conducted. EDS shows that the obtained specimens are free from any other elements after being treated. The optical microscopy is used to observe the changes in the microstructure through optical micrographs, after pre-treating the alloys. Through SEM, the change in the surface morphology after grinding, polishing, and etching is also recorded. The roughness measurements indicate the mean values of roughness quantitatively, which are gradients from 0.005 micron in 3 micron polishing TiAl6V4 sample to 0.56 micron in the 120 grinding TiAl6V4 sample. After measurement, the thickness of the coating is determined as 0.01 mm. The contact angle measurement shows that the best sample in hydrophilicity is the etched alloy after coating it with PCL, which is 58.63 °. The adhesion test also proves that the best two samples for coating adhesion are the etched and 1200 grinding: more than 99% of the coating do not stick out of the coating after the removal of the tape.Item MATERIAL CHARACTERIZATION STUDIES FOR CARBURIZED QUENCHING PROCESS DESIGN AND QUALITY ASSESSMENT(2022-02-25) Yıldız, Seçil; Davut, Kemal; Şimşir, CanerCarburized quenching is a surface hardening process applied to low and medium carbon steel parts to improve fatigue and wear resistance. Distortion, cracking, inadequate case depth and surface/core hardness are the most frequently encountered problems during this process. During the last two decades, computer simulations became popular to predict and avoid those problems instead of conventional analytical and trial-and-error approaches. Aside from troubleshooting, heat treatment simulations enable determination of optimal process parameters yielding the desired microstructure and residual stress distribution to improve the performance of the part. Primary aim of this study is to complement computational materials engineering methods to develop a material data set for the carburized quenching simulation of DIN 22NiCrMo2-2 (SAE 8620H) steel. For that purpose, first, the raw material is characterized chemically and microstructurally to provide necessary input to computational techniques. Then, the kinetics of austenite growth, which has strong impact on phase transformations during succeeding quenching step, is investigated. Finally, critical temperatures and transformation kinetics are determined and presented in the form of TTT and CCT diagrams. Raw material characterization results indicate that the billets are qualified for the process and the validation study as the billets are free of macro-segregation and exhibit a homogeneous and mildly banded equiaxed ferritic/pearlitic grain structure. Moreover, austenite grain growth study revealed that the grain growth in 22NiCrMo2- 2 can be expressed by an ideal grain growth law. Finally, computationally and experimentally determined CCT diagrams are in a good agreement. The largest differences between computationally and experimentally determined TTT diagrams are observed in the bainitic transformation range which is more sensitive to hard to control factors such as local chemical composition and local prior austenite grain size. Secondary aim of this study is to conduct microstructural investigations for the quality assessment and validation of computer simulations conducted in complementary studies within the scope of the same project. In one of those complementary studies, an experimental Design of Experiments (DoE) using the Taguchi method is conducted on steel shafts made of DIN 22NiCrMo2-2 and 16MnCr5 steels to minimize the variability of the industrial process. In the other study, the same DoE is investigated using computer simulations. This thesis complements those studies with determination of microstructure and hardness distributions. The experimental results indicate an agreement with the simulations results and the agreement can be improved with better characterization of bainite transformation kinetics including its dependence on stress, local grain size and chemical composition.Item NONDESTRUCTIVE CHARACTERIZATION OF BEARING STEELS BY MAGNETIC BARKHAUSEN NOISE TECHNIQUE(2017-06-02) Arslan, Ebru; Davut, Kemal; Şimşir, CanerOne of the most popular type of bearing steels is 100Cr6. The strength, toughness, hardness, fatigue life, wear resistance of it can be improved by heat treatment applications which also changes the microstructure. For controlling the microstructure, traditional metallographic and XRD- based methods, that involve taking representative specimens from lots, are used. Magnetic Barkhausen noise (MBN) technique may provide an alternative nondestructive, fast and practical measurement method to those traditional techniques. This study aims at investigating the possibility of nondestructive characterization of microstructure of heat treated 100Cr6 bearing steels by using the MBN technique. For that purpose, 100Cr6 steel specimens were heat treated in a quenching dilatometer under different austenitization conditions and then quenched to room temperature and to -130°C, in order to generate variations in their microstructures. After heat treatment applications, microstructural properties of the specimens including the fraction and distribution of carbides, amount of retained austenite and also hardness were determined by metallographic and XRD analysis. Moreover, MBN measurements were performed and then the results were correlated to the microstructural parameters. MBN signals correlate with the microstructure variations in the 100Cr6 steel samples via simple linear relations; however, the prediction bands were quite wide and the MBN technique was not sufficiently sensitive, for direct characterization of hardness, retained austenite and carbide fraction of the specimens that were quenched to room temperature. In order to characterize these interdependent microstructural parameters via MBN technique, non-linear relations based on carbide dissolution kinetics are needed. On the other hand, the MBN measurement results of the sub-zero treated specimens showed that; elimination of retained austenite significantly improved the goodness of fit of on those linear relations. Although coefficient of determinations of both carbide fractions and hardness were acceptable, it can be improved by developing a newer non-linear model. Nevertheless, all of the results were promising for the future applications of MBN technique on nondestructive characterization of microstructure variations in 100Cr6 steels.