A.H. Ucisik

Fracture toughness of boride formed on low-alloy steels

Abstract In this study, we investigated the fracture toughness of boride layers formed on steel surfaces. The samples used for this study were prepared from low-alloy and low-carbon steels essentially containing Cr and/or Mn as the major elements. Boronizing was done in a salt bath consisting of borax, boric acid, and ferro-silicon. The temperature of the bath was 940 °C and the boronizing was conducted at an atmospheric pressure for 5–7 h. The presence of borides, e.g. Fe 2 B, was revealed by X-ray h diffractometry, SEM, and optical microscopy. The fracture toughness of borided surfaces was measured via Vickers indenters with a load of 2 N. It was found that the fracture toughness of the borides ranged from 4 to 6 MPa 1/2. The fracture toughness of the borides depends strongly on chemical composition of substrate and boronizing time. Mn as an alloying element has a beneficial effect on fracture toughness, and the longer boronizing time results in higher fracture toughness.

A tribological comparison of pure and boronized chromium

Boronized metals are potential candidate materials for various industrial applications as well as for joint arthroplasty. This is due to their high hardness and corrosion resistance. In the present research, we investigated the tribological performance of boronized chromium when worn against bearing steel E52100. Pure chromium was used as a control material and tested under similar conditions. Three test conditions were used-dry sliding, with water, and with simulated body fluid (SBF). The highest coefficient of friction obtained was for chromium boride under dry sliding conditions. Water and SBF acted as lubricants and lowered the coefficient of friction. The friction coefficient for Cr and chromium boride was lowest under SBF conditions. SEM analysis showed that the wear modes were different under different test conditions. TEM analysis showed a layered-like structure of debris that could have acted as a lubricant and caused a very low friction coeffi.

An evaluation of human articular cartilage on femoral head

In this study, we investigated stress relaxation behavior of the human articular cartilage on femoral head. Articular cartilage is a white dense connective tissue that covers the bone ends within diarthrodial joints and works as a weight-transmitting and energy-absorbing material. Human articular cartilage on femoral head was used as test material. Relaxation tests were carried out by using the indentation technique via Instron Universal Testing Machine. Test materials were investigated in an isotonic salt solution at 37 °C. To keep the temperature constant, two vessels being in each other were utilized. Thus, hot water was circulated in the outer vessel and isotonic salt solution was kept in the inner vessel. Experimental results showed that there is a remarkable difference between normal and degenerated cartilage for the same age and sex. It was observed that the relaxation percent of normal cartilage as a function of relaxation time is much higher than that of degenerated cartilage.

Wear Behavior of Niobium Boride Coatings

Boride coatings on corrosion resistant refractory metals are potentially used as implanting materials. In this research, we investigated wear mechanisms of boride coatings on pure niobium using a pin-on-disk tribometer. Surface morphology studied using scanning electron microscope shows the compressed boride layer with indistinguishable regions such as coating intermediate transition layer and the substrate. The surface analysis after wear tests was conducted using an atomic force microscope (AFM). It was found that the boride coating underwent deformation wear, and debris formed and accumulated at both ends of the track due to adhesion.

The effect of high flux hemodialysis on polymeric hollow fibers used in dialyzers

High flux dialysis the first choice of therapy for hemodialysis patients within the last decade due to its clinical outcome. In this study the effect of dialysis environment on the mechanical and structural stability of high flux dialyzers containing polysulfone membranes were investigated. Dialysis sessions were performed on a certain group of patients with dialysis ages less than two years and without any other accompanying disease. Mechanical data and XRD results revealed the differences in material characteristics between virgin and used membranes obtained from polysulfone membranes. With the help of tensile tests it was shown that the mechanical properties used membranes were reduced in terms of ultimate tensile strength. XRD experiments revealed that the degree of crystallinity of the polysulfone dialysis membranes were raised. It was concluded that high flux dialyzer membranes are becoming more brittle and having more crystallinity after dialysis session. By this way the membranes are more prone to mechanical defects during dialysis. The degree of crytallinity increases under cyclic loading which resembles the changing of the pump speed or transmembrane pressure during dialysis in case of clinical situations like hypotension during dialysis. This issue is very important for dialysis centers performing reuse procedures for dialysis centers, because any damage to dialysis membranes would cause very serious clinical complications.

The Influences of Reuse Solution and the Hemodialysis Environment on the High Flux Polyamide Hollow Fiber Membranes

In order to reveal the effect of reuse solution and the hemodialysis environment on the stability of high flux polyamide hollow fiber membranes, mechanical tests, surface and X-ray diffraction studies were performed on both virgin 17S high flux polyamide hollow fiber and used-processed 17S high flux polyamide hollow fiber membranes. Used fibers were left in 4% formaldehyde solution for 14 hours and then in 5% sodium hypochloride (bleach) solution for 6 hours in order to disinfect the membrane for the reuse idea. Tensile tests performed on both virgin and used-processed fibers reveal that toughness and ductility of the used-processed fibers are lower than the virgin ones. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies performed on virgin and used-processed fiber visualized the morphological changes. Rough surface with defects and cracks was seen in used-processed fiber, whereas a smoother surface morphology was seen in virgin fibers. Alterations in pore morphology and the size of the pores became greater in used processed fibers. Cracks, merging of pores and also more defects were visualized in used-processed fibers. Thus, easy crack initiations and easy propagations were expected in used-processed fibers which were also confirmed by tensile test experiments. In addition to these mechanical and surface studies experiments, X-ray diffractometry studies also revealed the changes in the structure of the used-processed fibers. New or growth of the existing phases and orientations were observed in usedprocessed fibers. This study showed that dialysis environment caused structural changes on membranes which may cause clinical complications.

The Effects of Different Antiembolic Agents on the Crystallinity of Fractured Bones during the Healing Period

In order to decrease the potential clinical problems that could be caused by embolism Antiembolic agents are routinely used in orthopaedics&traumatology clinics, especially after arthroplastic operations or in case of having tumor and major trauma in order. This study was designed to evaluate the side effects of different antiembolic agents on the bone fracture healing. After experiments on animals, where “enoxaparin”, “fondaparinux” and “heparin” are used as antiembolic agents given after bone fracture, fractured and healed bones are studied by using X-Ray Diffraction technique. To reach this idea, initially, rat which was used as experimental animal was injected by different antiembolic agents. After sacrificing(with the permission of ethical committee) of animal XRD studies were performed on the bones in Material Laboratories of GYTE(Gebze Yuksek Technology Enstitusu) in order to reveal changes in the crystallinity of the bone samples.

Stability of Polymeric Hollow Fibers Used in Hemodialysis

High flux dialysis the first choice of therapy for hemodialysis patients within the last decade due to its clinical outcome. In this study the effect of dialysis environment on the mechanical and structural stability of high flux dialyzers containing polysulfone membranes were investigated. Dialysis sessions were performed on a certain group of patients with dialysis ages less than two years and without any other accompanying disease. Mechanical data and XRD results revealed the differences in material characteristics between virgin and used membranes obtained from polysulfone membranes. With the help of tensile tests it was shown that the mechanical properties used membranes were reduced in terms of ultimate tensile strength. XRD experiments revealed that the degree of crystallinity of the polysulfone dialysis membranes were raised. It was concluded that high flux dialyzer membranes are becoming more brittle and having more crystallinity after dialysis session. By this way the membranes are more prone to mechanical defects during dialysis. The degree of crytallinity increases under cyclic loading which resembles the changing of the pump speed or transmembrane pressure during dialysis in case of clinical situations like hypotension during dialysis. This issue is very important for dialysis centers performing reuse procedures for dialysis centers, because any damage to dialysis membranes would cause very serious clinical complications.

On the structural changes and mechanical stability of polymeric hollow fibers used in hemodialysis

In this study, the effect of hemodialysis on the mechanical behavior of cellulosic hemophan, polysulfone and cellulose acetate type polymeric hollow fibers was investigated. Simple tensile tests were performed on virgin and used fibers. It was observed that mechanical parameters, ultimate tensile strength, ductility and toughness values were dropped after dialysis session.

Tribological Properties of Boronized Chromium for Biological Applications

Biomaterials being natural or man-made are crucially important for comprising whole or part of living structures. In order to prolong the service life of biomaterials is of vital importance. In this research, the tribological properties of boronized chromium were investigated. Boronizing heat treatment was performed in a solid medium by using Ekabor powders at 940°C for 2, 4, 6 and 8h. Pin-on-disc tribometer was used to conduct the wear and friction tests under a load of 5N. Experiments were conducted in dry conditions as well as in simulated body liquid (SBF). Fundamental aspects of wear mode and lubrication behaviour were studied using surface characterization technique such as TEM, and X-ray diffraction. Results revealed evidence of tribo-chemical interactions between SBF and work piece materials.