S. Zeytin

The characterization of borided 99.5% purity nickel

Abstract A series of experiments were performed to evaluate some properties of borided 99.5% purity nickel. Boronizing was carried out in a solid media consisting of Ekabor powders at 950°C for 2, 4, and 8 h, respectively. Data on intermetallic silicides and borides (Ni 5 Si 2 , Ni 2 B) that formed on the surface of nickel substrate during boronizing were confirmed by a classical metallographic technique and X-ray diffraction (XRD) analysis. It was observed that the predominant phase in the coating layer was a silicide. It is probable that the formation of the nickel silicide layer was due to silicon in the boronizing powder. The hardness of silicides was measured by using a Vickers indenter with a load of 0.5 N. The microhardness of silicides formed on the surface of the nickel substrate reached up to 805 HV. Metallographic studies revealed that the silicide layer has an equiaxed granular morphology, whereas the boride layer formed had a needle-shaped structure. Depending on process temperature and boronizing time the thickness of coating layers ranged from 123 to 281 μm. The thickness of silicide and boride layers depended strongly on the processing time at 950°C. The longer boronizing time resulted in the thicker surface layer. The distribution of alloying elements from the surface to the interior was determined using energy dispersive X-ray spectroscopy (EDS).

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.

Rapid Synthesis of Metallic Reinforced in Situ Intermetallic Composites in Ti-Al-Nb System via Resistive Sintering

Abstract Intermetallics are known as a group of materials that draws attention with their features such as ordered structure, high temperature resistance, high hardness and low density. In this paper, it is aimed to obtain intermetallic matrix composites and also to maintain some ductile Nb and Ti metallic phase by using 99.5% purity, 35-44 μm particle size titanium, niobium and aluminium powders in one step via recently developed powder metallurgy processing technique - Electric current activated/assisted sintering system (ECAS). In this way, metallic reinforced intermetallic matrix composites were produced. Dominant phases of TiAl3 and NbAl3 which were the first compounds formed between peritectic reaction of solid titanium, niobium and molten aluminum in Ti-Al-Nb system during 10, 30 and 90 s for 2000 A current and 1.5-2.0 voltage were detected by XRD and SEM-EDS analysis. Hardness values of the test samples were measured by Vickers indentation technique and it was detected that the hardnesses of intermetallic phases as 411 HVN whereas ductile metallic phase as 120 HVN.