Mansour Mhaede

Influence of shot peening on corrosion properties of biocompatible magnesium alloy AZ31 coated by dicalcium phosphate dihydrate (DCPD)

Magnesium alloys are promising materials for biomedical applications because of many outstanding properties like biodegradation, bioactivity and their specific density and Youngs modulus are closer to bone than the commonly used metallic implant materials. Unfortunately their fatigue properties and low corrosion resistance negatively influenced their application possibilities in the field of biomedicine. These problems could be diminished through appropriate surface treatments. This study evaluates the influence of a surface pre-treatment by shot peening and shot peening+coating on the corrosion properties of magnesium alloy AZ31. The dicalcium phosphate dihydrate coating (DCPD) was electrochemically deposited in a solution containing 0.1M Ca(NO3)2, 0.06M NH4H2PO4 and 10mL/L of H2O2. The effect of shot peening on the surface properties of magnesium alloy was evaluated by microhardness and surface roughness measurements. The influence of the shot peening and dicalcium phosphate dihydrate layer on the electrochemical characteristics of AZ31 magnesium alloy was evaluated by potentiodynamic measurements and electrochemical impedance spectroscopy in 0.9% NaCl solution at a temperature of 22±1°C. The obtained results were analyzed by the Tafel-extrapolation method and equivalent circuit method. The results showed that the application of shot peening process followed by DCPD coating improves the properties of the AZ31 surface from corrosion and mechanical point of view.

Innovative surface modification of Ti–6Al–4V alloy with a positive effect on osteoblast proliferation and fatigue performance

A novel approach of surface treatment of orthopaedic implants combining electric discharge machining (EDM), chemical milling (etching) and shot peening is presented in this study. Each of the three techniques have been used or proposed to be used as a favourable surface treatment of biomedical titanium alloys. But to our knowledge, the three techniques have not yet been used in combination. Surface morphology and chemistry were studied by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Fatigue life of the material was determined and finally several in-vitro biocompatibility tests have been performed. EDM and subsequent chemical milling leads to a significant improvement of osteoblast proliferation and viability thanks to favourable surface morphology and increased oxygen content on the surface. Subsequent shot-peening significantly improves the fatigue endurance of the material. Material after proposed combined surface treatment possesses favourable mechanical properties and enhanced osteoblast proliferation. EDM treatment and EDM with shot peening also supported early osteogenic cell differentiation, manifested by a higher expression of collagen type I. The combined surface treatment is therefore promising for a range of applications in orthopaedics.

Fatigue behaviour of commercially pure aluminium processed by rotary swaging

Fatigue strength of ultrafine-grained commercially pure aluminium (Al 1050) produced by severe plastic deformation (rotary swaging) was investigated. Fatigue tests were carried out on smooth and notched specimens. Results show improved static and fatigue strength of the rotary swaging processed material. However, the processed material was highly notch sensitive due to low work hardening capability, low ductility as well as low uniform strain. It was found that post-deformation annealing above recrystallization temperature can additionally enhance the work hardening capability and the ductility of the swaged material, which led to marked reduction in fatigue notch sensitivity. At the same time, this reduction is accompanied with pronounced loss in strength. Fatigue notch sensitivity of commercially pure aluminium can be good correlated to the work hardening capability and ductility. This behaviour was discussed in details based on microstructure and mechanical properties study.

Evaluating the effects of hydroxyapatite coating on the corrosion behavior of severely deformed 316Ti SS for surgical implants

The present work investigates the effects of severe plastic deformation by cold rolling on the microstructure, the mechanical properties and the corrosion behavior of austenitic stainless steel (SS) 316Ti. Hydroxyapatite coating (HA) was applied on the deformed material to improve their corrosion resistance. The martensitic transformation due to cold rolling was recorded by X-ray diffraction spectra. The effects of cold rolling on the corrosion behavior were studied using potentiodynamic polarization. The electrochemical tests were carried out in Ringers solution at 37±1 °C. Cold rolling markedly enhanced the mechanical properties while the electrochemical tests referred to a lower corrosion resistance of the deformed material. The best combination of both high strength and good corrosion resistance was achieved after applying hydroxyapatite coating.

Microstructural Effects on Corrosion Behavior of Investment Cast Ti-6.5Al-3.4Mo-1.7Zr Alloy

Abstract Ti–6.5Al–3.4Mo–1.7Zr was cast as rods in a graphite mold using vacuum induction furnace. The cast rods were hot swaged then heat treated by using two regimes which resulted in fine and coarse lamella structures. The influence of these different structures on the corrosion behavior of α+β Ti-alloy samples was investigated. Potentiodynamic polarization in 3.5%NaCl solution showed that the swaged condition exhibited the highest corrosion resistance compared to the others. After isothermal oxidation for different times (2, 4, 8 and 16h), maximum weight gain was obtained after 8 h and the corrosion resistance of the swaged material was significantly higher than the other conditions. Thereby, isothermal oxidation enhanced markedly the corrosion resistance of the studied Ti-alloy. Among various conditions of the isothermally oxidized samples, the as-cast condition showed the highest value of pitting potential.