R. Caram

Surface engineered surgical tools and medical devices

Surface engineered surgical tools and medical devices / , Surface engineered surgical tools and medical devices / , کتابخانه دیجیتال جندی شاپور اهواز

Influence of the growth rate on the microstructure of a Nb–Al–Ni ternary eutectic

Abstract Solidification of a eutectic alloy from the melt produces composite materials, composed of two or more solid phases. Processing by directional solidification presents interesting and different properties when compared to the properties of its constituent phases. One of the ternary systems that has been little studied and exhibits eutectic reaction resulting in three intermetallic phases is the Nb–Al–Ni ternary system, which involves the NbAl3, Nb2Al and AlNbNi phases. Eutectic alloys from this system were processed in an arc melting furnace and in a Bridgman equipment for directional growth. The objective of the experiments was to determine the influence of growth parameters on the eutectic microstructure. The mechanical behavior of the composite was studied through microhardness testing and fracture toughness using Vickers indentation technique. Microstructural characterization and chemical compositions of the samples were investigated by using optical and scanning electron microscopy with energy dispersive spectroscopy.

Directional solidification processing of eutectic alloys in the Ni–Al–V system

Abstract Intermetallic matrix composites (IMCs) offer attractive properties, such as high toughness of the metal coupled with low density, high modulus and high strength of the intermetallics. Among a large number of the intermetallics, a particular interest has been shown in the NiAl intermetallic compound, since it exhibits several advantages over the currently used nickel-based superalloys. Recently, there has been a renewed interest in directional solidification of the eutectic alloys as a concept of reinforcing intermetallics with in situ refractory metals. The present study is related to the study of the eutectic alloys in the ternary NiAl–V system. The eutectic composition and temperature were accurately determined. It was concluded that the solidification behaviour of the Ni–Al–V eutectic is strongly dependent on the growth conditions, namely growth rate and orientation, and that it can be easily modified. Also, it was observed that the orientation of the grain, i.e., the direction of growth is the determining factor in the lamellar/rod transition as well as in the morphology of the degenerated structure.

PREPARATION AND CHARACTERIZATION OF Ti-Al-Nb ALLOYS FOR ORTHOPEDIC IMPLANTS

Pure titanium shows very interesting characteristics such as high strength-to-weight ratio, very good corrosion resistance and excellent biocompatibility, which make this material appropriate for use in orthopedic and dental implants. Due to the mechanical properties of pure titanium, its use in implants is restricted to applications which involve moderate mechanical stress, such as dental implants. In applications where high mechanical strength is necessary, like orthopedic implants, it is appropriate to employ titanium-based alloys, which have better properties than pure titanium. The present work is related to the microstructure and corrosion resistance characterization of the Ti-6Al-7Nb alloy, designed to be used in orthopedic prostheses.

Directional solidification of Pb-Sn eutectic with vibration

Abstract Pb—Sn eutectic alloy was directionally solidified at 1.4 to 3.2 cm/h with forced convection induced by axial vibration of the growth ampoule with a frequency of 10 to 40 Hz and an amplitude of 0.5 to 1.0 mm. To determine the exact growth rate, an interface demarcation technique was applied. The lamellar spacing was increased 10% to 40% in ingots solidified with vibration compared to those solidified without vibration. The number of grain boundaries was increased by vibration. The average intensity of convection in the melt under axial vibration of the ampoule was estimated by comparing the experimental results with a theoretical model.

Ti-Mo alloys employed as biomaterials: Effects of composition and aging heat treatment on microstructure and mechanical behavior

The correlation between the composition, aging heat treatments, microstructural features and mechanical properties of β Ti alloys is of primary significance because it is the foundation for developing and improving new Ti alloys for orthopedic biomaterials. However, in the case of Ti-Mo alloys, this correlation is not fully described in the literature. Therefore, the purpose of this study was to experimentally investigate the effect of composition and aging heat treatments on the microstructure, Vickers hardness and elastic modulus of Ti-Mo alloys. These alloys were solution heat-treated and water-quenched, after which their response to aging heat treatments was investigated. Their microstructure, Vickers hardness and elastic modulus were evaluated, and the results allow us to conclude that stabilization of the β phase is achieved with nearly 10% Mo when a very high cooling rate is applied. Youngs modulus was found to be more sensitive to phase variations than hardness. In all of the compositions, the highest hardness values were achieved by aging at 723K, which was attributed to the precipitation of α and ω phases. All of the compositions aged at 573K, 623K and 723K showed overaging within 80h.

Growth morphology of the NiAl–V in situ composites

Abstract Intermetallic matrix composites (IMCs) are considered candidate materials for high-temperature applications provided that the proper combination of properties can be developed. Among a large number of intermetallics, a particular interest has been shown in the NiAl-based composites. Attractive properties of this compound include higher melting temperature, better oxidation resistance, and lower density when compared to conventional superalloys. However, insufficient low-temperature fracture resistance is a major drawback. Stringent requirements for chemical and mechanical compatibility between the matrix and the reinforcing phase have recently renewed interest in directional solidification of the eutectic alloys. Microcomposite structures generated by directional solidification of eutectics offer many unique microstructural advantages, including thermodynamic stability up to the melting temperature, directional alignment and fine dispersion of component phases. Although a large number of directionally solidified eutectic systems have been investigated so far, little information on the eutectics in NiAl–V system has been reported. The present paper is concerned with the growth morphology of the NiAl–V in situ composites. Samples prepared by arc melting were processed in a directional solidification furnace with induction heating. The main objective was to analyze the solidification microstructure and morphology regarding the growth conditions and composition. Sample characterization, beside the optical and scanning electron microscopy (SEM), included the use of differential thermal analysis (DTA), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) technique.

Primary dendrite spacing as a function of directional solidification parameters in an AlSiCu alloy

Abstract Dendritic growth is of considerable importance, since this phenomenon controls solute segregation and hence, the material mechanical properties. The main objective of this investigation is to present a directional solidification study of the Al-8.5 wt% Si-2.5 wt% Cu alloy with dendritic growth. Such an alloy was processed at several growth rates and thermal gradients and an investigation of the dendritic growth was carried out. The solidification microstructure was studied by comparing experimental dendrite spacings with results furnished by theoretical models. Such a comparison allows one to calculate primary dendrite spacing as a function of growth rate, thermal gradient and alloy thermophysical parameters.

Microstructure of the microalloyed NiAl–V eutectics

Abstract Directional solidification (DS) of the eutectic alloys is an interesting concept of reinforcing intermetallics with in situ refractory metals. Considering that the morphology of eutectic microstructure governs the mechanical behavior of the material, the addition of a quaternary element to the NiAl–V system could, principally, modify the solidification microstructure, and consequently, alter its properties. The main goal of this work is to determine the influence of a quaternary element addition on the eutectic morphology of the as-cast and directionally solidified NiAl–V eutectic alloys. Samples with various compositions were arc-melted under inert atmosphere and processed in a Bridgman type solidification facility. The results obtained indicated that eutectic morphology may be effectively modified by microalloying. The conditions for the lamellar/fibrous transition were determined and a tentative explanation of the phenomenon observed was given.

Directional growth of Al-Nb-X eutectic alloys

Abstract Composite materials show attractive properties resulting from the combination of properties of their constituent phases. Special interest has been devoted to the intermetallic matrix composites, since they have been recognized as potential substitutes for the superalloys. An interesting and efficient means of preparation of the composite materials is the directional solidification of eutectic alloys. The eutectic microstructure of many systems possesses inherent thermal stability and may result in a composite material, with an aligned, finely dispersed microstructure. The goal of this study was to evaluate the influence of a ternary element addition (Cu, Si, Ni, Ti and Cr) on the microstructure of the Al–Nb eutectic system. Microstructural characterization of the as-cast and directionally solidified samples, revealed changes in the eutectic morphology from cellular to dendritic and from lamellar to rod or globular structure. Also, it was confirmed that the alloy containing 57.18% Al–40.40% Nb–2.42% Ni in atomic% exhibits a ternary eutectic reaction. The directional solidification of this alloy resulted in a regular three-phase eutectic microstructure.