JOURNAL OF NEW MATERIALS
Year:2010 | Volume:1 | Issue:1|Papers Count:8

Titania porous bioceramic coating covered by hydroxyapatite causes the substrate to be more corrosion resistant and biocompatible. In this study, Ca and P contained titania was coated on Ti-6Al-4V alloy substrate by applying plasma electrolytic oxidation (PEO) with changing parameters such as time and voltages. After obtaining optimized sample, then it was treated hydrothermally at different time intervals until hydroxyapatite crystals were nucleated on titania porosities. Morphology and cross section, chemical composition, topography and hardness of the coating were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), Atomic force microscope (AFM) and nano indentation test, respectively. Also, the corrosion behaviors of the coating were studied by polarization and electrochemical impedance spectroscopy. According to the obtained results, hydrothermal treatment on optimized sample causes the formation of hydroxyapatite crystals in Titania porosities. These crystals are in nanometric dimensions and lumped shape. In addition, the coating on the substrate caused an increase in corrosion resistance of the sample in simulated body environment considerably.

Centrifugal casting as a high capable technique has been frequently used for production of high performance castings. In two decades its capabilities has been progressed towards the production of cast components with functionally graded microstructures. A controlled attribution of the centrifugal force in this technique can cause a desirable grading of the microstructures hence properties in different sections of the castings. In this research, functionally graded Al-11wt.%Mg2Si hypoeutectic alloy with graded distribution of a-Al phase was cast as a cylindrical specimen using the centrifugal casting. During the solidification, the initially formed α-Al grains due to the higher density in compared with the remained melt, were segregated in the centrifugal force direction. The microstructural observations reveal two distinguished layers in radial direction of the cast cylinder: the outer layer with a higher volume fraction of a-Al grains and the inner one with the eutectic structure. To modify the cast structure hence mechanical properties, the cast sample was subjected under solution and ageing heat treatments. The microstructural observations of the heat treated sample shows no noticeable change in the cast graded microstructure; however the eutectic structure was distorted from laminar to a fine dot-like structure. This minor microstructural evolution is accompanied with an increase in hardness of different sections of the sample.

In this investigation different series of Fe-Cr-C hardfacing alloys with the constant ratio of Cr/C=6 were fabricated by GTAW on AISI 1010 mild steel substrates. OES method was used for determining chemical composition of surface layers while OM, SEM, XRD were used for studying the microstructure and phases characteristics, hardness test (Vickers macro hardness method) was also used to determine hardness of surface layers. The metallographic examination and XRD results indicated that all specimens microstructure consisted of austenite and chromium-iron carbides, (Cr,Fe)7C3, moreover by increasing of carbon and chromium content in hardface layers, the volume fraction of (Cr,Fe)7C3 increased while it caused to decreasing the austenite volume fraction and increasing hardness of the top surface layers. In addition wear Test result Shows that with increasing the chromium and carbon content in hypoeutectic alloys, the wear resistance increase, study of SEM of worn surface determined that wear mechanism of hypo eutectic alloys was micro ploughing, and in eutectic and hyper eutectic were microcutting and micro cracking.

In this study Ni50Al50 and Ni25Cr25Al50 were undergone mechanical alloying and heat treatment. The structural changes of powder particles during processes were studied by X-ray diffraction (XRD). It appeared that there are different phase transformations after both treatments: Ni50Al50 formed a nanocrystalline, orderly NiAl intermetallic compound; on the other hand (NiCr) Al intermetallic which itself was produced from Ni50Cr25Al25. The morphology and cross sectional area of the powder particles were characterized by scanning electron microscopy (SEM). The conclusion was that during initial stages of milling the layers of Cr, Ni, and Al are produced which subsequently are transformed into the final product upon further treatments.