Enver Oktay

Characterization of 17-4 PH stainless steel foam for biomedical applications in simulated body fluid and artificial saliva environments

Highly porous 17-4 PH stainless steel foam for biomedical applications was produced by space holder technique. Metal release and weight loss from 17-4 PH stainless steel foams was investigated in simulated body fluid and artificial saliva environments by static immersion tests. Inductively coupled plasma-mass spectrometer was employed to measure the concentrations of various metal ions released from the 17-4 PH stainless steel foams into simulated body fluids and artificial saliva. Effect of immersion time and pH value on metal release and weight loss in simulated body fluid and artificial saliva were determined. Pore morphology, pore size and mechanical properties of the 17-4 PH stainless steel foams were close to human cancellous bone.

Physical properties of thorium oxalate powders and their influence on the thermal decomposition

Thorium oxalate dihydrate powders were obtained by precipitation from thorium nitrate solution using oxalic acid in the presence of ultrasound and mechanical agitation. Properties measured included particle morphology, particle size and particle size distribution, and specific surface area. The thermal decompositions of the powders were investigated by using thermogravimetry and differential thermal analysis techniques. The result showed that the thermal decomposition stages of the thorium oxalate dihydrate obtained by mechanical and ultrasonic agitation are same. The decomposition reactions of the oxalates precipitated in the presence of ultrasound proceed in a narrower temperature interval, within a shorter period of time. The kinetic parameters for each stage were calculated.

Grain growth in MnO-added ZnO—6 wt% Bi2O3 ceramic system

Abstract The grain growth kinetics in the 0–5 wt% MnO-added ZnO—6 wt% Bi2O3 system was studied using the simplified phenomenological grain growth kinetics equation G n = K 0 .t. exp (− Q RT ) together with the physical properties of the sintered samples. The grain growth exponent value (n) and the apparent activation energy for the ZnO—6wt% Bi2O3 system was found to be 5 and 200 kJ mol−1, respectively. These values support the published data for the grain growth mechanism of the ion diffusion model in liquid phase sintering. The addition of MnO lowered the grain growth exponent value to 4 and the apparent activation energy for the grain growth process was increased systematically from 200 kJ mol−1 to 250 kJ mol−1 for the additions of MnO from 0 to 5wt%. This was attributed to the reduction of the equilibrium solubility of ZnO in liquid Bi2O3 phase present between the ZnO grains during sintering.

Corrosion behaviour and microstructure evolution of 17-4 PH stainless steel foam

Abstract This study describes corrosion behaviour and microstructure evolution of 17-4 PH stainless steel foam, which was produced for biomedical implant applications. 17-4 PH stainless steel foam was produced by the space holder-sintering technique. The effect of boron addition, aging, sintering temperature and sintering time on the corrosion behaviour and microstructure of the 17-4 PH stainless steel foam was investigated. Microstructure of the 17-4 PH stainless steel foams was examined by using scanning electron microscope (SEM) and optical microscope. The corrosion behaviour of the 17-4 PH stainless steel foam was investigated by using neutral salt spray (fog) and accelerated aging tests. The 17-4 PH stainless steel foams were exposed to salt spray solution, which consisted of 5% NaCl with pH of 6.68, in a closed cabin at 35°C. The surface of the foams after the corrosion test was observed by optical microscope and the digital photographs were analysed by an image analyser. The corrosion resistance of boron-added foams was higher than boron-free 17-4 PH stainless steel foams. Aging heat treatment slightly decreased the corrosion resistance of the 17-4 PH stainless steel foams. Increasing sintering temperature and sintering time increased the corrosion resistance of the stainless steel foams.

Production and Precipitation Hardening of Beta-Type Ti-35Nb-10Cu Alloy Foam for Implant Applications

In this study, beta-type Ti-35Nb-10Cu alloy foams were produced by powder metallurgy method for dental implant applications. 35% Nb was added to stabilize the beta-Ti phase with low Young’s modulus. Cu addition enhanced sinterability and gave precipitation hardening capacity to the alloy. Sintered specimens were precipitation hardened in order to enhance the mechanical properties. Electrochemical corrosion behavior of the specimens was examined by electrochemical impedance spectroscopy in artificial saliva. Electrochemical impedance spectroscopy results indicated that the oxide film on the surface of foam is a bi-layer structure consisting of outer porous layer and inner barrier layer. Impedance values of barrier layer were higher than porous layer. Corrosion resistance of specimens decreased at high fluoride concentrations and at low pH of artificial saliva. Corrosion resistance of alloys was slightly decreased with aging. Mechanical properties, microstructure, and surface roughness of the specimens were also examined.

Characterization of microstructure of H13 tool steel using ultrasonic measurements

This study presents nondestructive characterization of microstructure of AISI H13 hot work tool steel. Heat treatments were carried out in order to obtain different microstructural phases in the tool steel specimens. The microstructural phases were characterized by metallographic examinations and hardness measurements. Velocities of ultrasonic longitudinal and transverse waves were measured by means of pulse-echo method using contact type normal beam probes. Ultrasonic apparent attenuation also determined in the steel specimens having different microstructural phases. A lower value of ultrasonic velocity was observed for the martensite compared to the other microstructures, while the opposite was observed in ultrasonic attenuation. Results show that the use of ultrasonic measurements in order to correlate them with the microstructures is fast and reliable, permitting nondestructive characterization of microstructure in steels.

Localised corrosion behaviour of biomedical implant materials using electrochemical potentiokinetic reactivation and critical pitting potential methods

Abstract In this study, localised corrosion properties of the biomedical grade Ti–Nb–Cu alloy and AISI 316 austenitic stainless steel specimens were investigated. Ti–Nb–Cu alloy specimens were produced by powder metallurgy method. Nb was used for beta-phase Ti stabiliser. Beta-Ti phase has low Young’s modulus close to bone, higher wear resistance and biocompatibility. Cu was added to enhance sinterability of the Ti–Nb–Cu alloy; in addition, Cu is antibacterial. The AISI 316 austenitic stainless steel alloy was investigated as wrought (fully dense) specimens. Localised corrosion properties of the Ti–Nb–Cu and AISI 316 stainless steel alloys were examined by electrochemical potentiokinetic reactivation, critical pitting potential and Tsujikawa–Hisamatsu electrochemical tests in Hank’s simulated body fluid solution. Effect of the Cu content of the Ti–Nb–Cu alloys and pH level of the simulated body fluid on the corrosion behaviour of the specimens was studied.

Characterization of Heat Treated Titanium-Based Implants by Nondestructive Eddy Current and Ultrasonic Tests

This study presents nondestructive characterization of microstructure and mechanical properties of heat treated Ti, Ti-Cu, and Ti-6Al-4V titanium-based alloys and 17-4 PH stainless steel alloy for biomedical implant applications. Ti, Ti-Cu, and 17-4 PH stainless steel based implants were produced by powder metallurgy. Ti-6Al-4V alloy was investigated as bulk wrought specimens. Effects of sintering temperature, aging, and grain size on mechanical properties were investigated by nondestructive and destructive tests comparatively. Ultrasonic velocity in specimens was measured by using pulse-echo and transmission methods. Electrical conductivity of specimens was determined by eddy current tests. Determination of Young’s modulus and strength is important in biomedical implants. Young’s modulus of specimens was calculated by using ultrasonic velocities. Calculated Young’s modulus values were compared and correlated with experimental values.

Effect of grain size on the ultrasonic parameters in stainless steels

In this study, the influence of grain size on the velocity of ultrasonic waves and ultrasonic attenuation in stainless steels was investigated. The aim of this study is to demonstrate the capability of ultrasonic techniques in the assessment of the grain size of steels. Heat treatment processes were carried out in order to obtain different grain sizes for AISI 304 stainless steel specimens. AISI 316 stainless steel specimens were produced by casting and tested in as-cast condition. Velocities of ultrasonic longitudinal and transverse waves were measured by means of pulse-echo method using contact type normal beam probes with 1 and 4 MHz frequencies. Apparent attenuation coefficient of longitudinal waves was determined at 4 MHz. Youngs modulus of the specimens was also determined. The results showed that ultrasonic longitudinal and transverse wave velocities and Youngs modulus were decreased with increasing grain size of the specimens. The apparent attenuation coefficient of longitudinal waves was increased with increasing grain size.

Effect of CaCl2 on the desulphurization by CaO of a carbon-saturated Fe-Si-S alloy

Abstract The desulphurization of a carbon-saturated Fe-Si-S alloy by CaO and CaO-7.5% CaCl2 slags at 1300 °C, and by CaO-10% CaF2 and CaO-7.5% CaCl2 slags at 1450 °C were investigated. The results indicated that the addition of 7.5% CaCl2 to CaO improved the desulphurization of the carbon-saturated Fe-Si-S alloy at 1300 °C by forming a liquid reaction surface. X-ray diffraction studies on the reaction surface of CaO showed that solid CaS formed on the lime surface. This solid reaction product reduces the transfer of sulfur to the CaO surface. At 1450 °C, CaO-10% CaF2 and CaO-7.5% CaCl2 slags contain both liquid and solid phases. X-ray diffraction studies showed that a smaller amount of solid CaS formed on the reaction surface of the CaO-7.5% CaCl2 slag than on the CaO-10% CaF2 slag. The formation of a smaller amount of solid CaS and the presence of a liquid phase at the metal-slag interface enhanced the desulphurization with CaO-7.5% CaCl2 at 1450 °C.