SEARCH RESULT

Recently, new generation, promising functional alloys for different applications, developed via high entropy (HE) alloying method, have gained attention both from academia and industry. This technique is mainly alloying of at least five major elements in equiatomic or near equiatomic ratios and positioning all the elements in the same lattice using the high entropy of mixing of the system. These unique HE alloys can be obtained using the suitable combinations of almost all the metallic elements present on the periodic table. The main question is, “what is the most important property for a stainless steel?” Clearly, the answer is corrosion resistance. In addition, it is well known that protective surface films play a key role in corrosion resistance of the stainless steels. HE alloys are innovative and promising materials due to their excellent corrosion properties. Key documents on the corrosion behaviour of the high entropy stainless steels have been reviewed under this study.

International Iron & Steel Symposium
UDCS

Burak Dikici Hakan YILMAZER

Niobium (Nb) and Chromium (Cr), being crucial alloying elements in the high value alloys such as the High Strength Low Alloys (HSLA) and Stainless Steels, especially Austenitic Stainless Steels (AUST.SS), have been identified and classified as critical raw materials (CRM). The potential of not producing these high value alloys has an adverse effect on the EU and Turkish economy due to the fact that Nb and Cr. Therefore, it is necessary to develop a new generation of structural alloys that will be free from CRM elements and exhibiting superior performance. However, it is difficult to develop such proposed high performance alloys by conventional alloying, which are formed around a dominant element like iron in the steel. The High Entropy Alloying, an innovative approach introduced in the last decade, is the alloying using the alloying elements at equiatomic or near equiatomic percentage, consequently the presence of the high mixing enthalpy positioned the alloying elements within the same phase crystal lattice system. As alternatives to HSLA and AUST.SS alloys, the novel structural alloys can be designed and developed by means of HEA approach and gain to industries. The purpose of the study is the designing and developing novel structural alloys as an HSLA and AUST.SS) using innovative High Entropy Alloying (HEA) approach. The proposed High Entropy Structural Alloys (HESA) in this project will be manufactured through the conventional melting and thermomechanical processing. The HESA alloy groups, which will have key roles in many important industrial applications, are aimed at exhibiting superior mechanical properties and corrosion values and meeting the industrial and economic conditions of production.

International Iron & Steel Symposium
UDCS

Hakan YILMAZER Burak Dikici

Severe plastic deformation (SPD) has gained attention to ultrafine grained (<500 nm) and nano-grained (<100 nm) bulk materials producing. Equal channel angular pressing (ECAP) is the most common SPD process. ECAP has three critical disadvantages such as industrially discontinuity, limited small products, and non-uniform deformation such as gross distortions at the front and back of every billet. In this study, we systematically studied on an alternative approach which ECAP combined with the Conform process, developed for continuous extrusion-forming of metal wires (ECAPConform).The as-casted dilute copper alloys have been subjected to ECAP-Conform. The microstructural evaluation and hardness distribution have been investigated before and after ECAP-Conform.

International Iron & Steel Symposium
UDCS

Aslıhan GÖKDUMAN Hakan YILMAZER Ceren GÖDE Burak Dikici Jiri Dvorak Vaclav SKLENICKA Aslı GÜNAY BULUTSUZ Adem BAKKALOĞLU Halil GÖKER

High-performance Cu alloys are required for the female and male terminal conductors in the power transmission of automobiles. A good longevity-conductivity relation and consequently high mechanical strength and good conductivity are being sought. Recently, severe plastic deformation (SPD) has provided new opportunities in investigations of the unusual mechanical, physical and electrochemical properties by permitting grain refinement to ultrafine-grained (UFG) and/or nano grained (NG) level, especially under (<100 nm). In this study, the some dilute Cu-Sn alloys subjected to high pressure torsion (HPT) processing at various rotation numbers have been studıed systematically.

International Iron & Steel Symposium
UDCS

Hasan Köklü Hakan YILMAZER Ceren GÖDE Burak Dikici Yoshikazu Todaka Halil GÖKER

Abstract Metals and their alloys used in the biomedical industry due to their high mechanical and good fatigue properties [1]. It is well known that titanium (Ti) and its alloys are the most popular metallic materials used as implant [2]. Ti alloys are classified into 3 main groups as microstructure. This are α type (e.g. pure Ti), α+β type (e.g. Ti6Al4V) and β type (e.g. Ti–29Nb–13Ta–4.6Zr, described as TNTZ) alloys [3-4]. The major properties for a metallic biomaterial are no doubt biocompatibility and corrosion resistance [5]. Farnoush et al. [6] found that bioglass which composed in HA/bioglass coatings behaves as aide for sintering process as well as responsible for transformation of HA to β-TCP which is thought to be more bioactive material due to ion exchange capability. Other findings of the study were that with addition of bioglass both bonding strength [7] and corrosion resistance were increased. Also with bioglass coating higher oxide film stability obtained in simulated body fluid. Another study was revealed that with bioglass addition and increased sintering temperatures up to 700°C is more protective than pristine Ti6Al4V substrates in terms of corrosion resistance [8]. In this study, bioglass (45S5) doped hydroxyapatite (Ca10(PO4)6(OH)2) coatings has been successfully synthesized by sol-gel technique on different Ti alloys. The corrosion resistances of the coatings have been measured under in-vitro conditions by a potentiostat/galvanostat. Potentiodynamic polarization scanning (PDS) tests were performed on the samples in the Ringer’s solution (simulated body fluid, SBF) [9]. The surface morphologies of the coated sample on the different Ti alloys are presented in Fig. 1 The PDS results of CP Ti, Ti6Al4V and TNTZ alloys in Ringer's solutions at 37°C were shown in Fig. 2a–c. In addition, some important parameters calculated from the curves have been collected in Table

International Symposium on Light Alloys and Composite Materials
UHAKS

Mehmet Topuz Burak Dikici Serap Koç Mitsuo Niinomi Masaaki Nakai

Ti–29Nb–13Ta–4.6Zr (TNTZ) composed of non-toxic and non-allergenic Nb, Ta, and Zr alloying elements, has been extensively investigated [1] as an alternative to the conventional metal based biomaterials. TNTZ must combine both excellent mechanical biocompatibility, corrosion resistance, good cell-implant interactions and healing. Microstructural features such as the grain diameter, secondary phases, residual stress, nature of the surface oxide film, and lattice defects can play a major role in determining the physical response of the material that influence the biocompatibility of TNTZ [1,2]. Severe plastic deformation (SPD) has been a proven technique for controlling the grain size in ultrafine-grained (UFG) (<1000 nm) and/or nanograined (NG) (<100 nm) scale [3]. Furthermore, the influence of ultrafine graining and nanograining on corrosion resistance differs among metallic materials [4,5]. Thorpe et al. [4] reported that there is no differences in corrosion resistance in Ni-based metallic materials and pure Cu. On the other hand, Rofagha et al.[5] reported lower corrosion resistance in nanocrystalline Ni-P compared to the conventional polycrystalline Ni. Clearly, there is a strong connection between corrosion resistance and the microstructural features of metallic materials. Moreover, UFG/NS materials exhibits higher cell attachments compared to their course grained (CG) counterparts [6]. It is well known that high pressure torsion (HPT) is an effective processing for producing NG TNTZ [7]. In this study, the microstructural evolution and its effect on electrochemical behaviour of solution treated TNTZ (TNTZST) and aging treated TNTZ (TNTZAT) subjected to HPT processing were evaluated by electrochemical impedance spectroscopy (EIS) measurements in simulated body fluid (SBF). While TNTZST exhibited a single β body centred cubic (BCC) grain structure having a diameter of 40 µm, the microstructure of TNTZAT consisted of randomly distributed needle-like α (HCP) precipitates in the equiaxed β grains having a diameter of 40 µm. The microstructure of TNTZAHPT consists of NG elongated β grains with a 50 nm having subgrains of non-uniform morphologies resulting from distortion by severe torsional deformation.

International Symposium on Light Alloys and Composite Materials
UHAKS

Hakan Yilmazer Burak Dikici Mitsuo Niinomi Masaaki Nakai