Papers by Author: Carlos Roberto Grandini

Abstract: This paper deals with the study of the development, structural and microstructural characterization and, selected mechanical properties of Ti-25Ta-50Zr alloy for biomedical applications. The alloy was melted in an arc furnace and various solution heat treatments were performed to analyze the influence of the temperature and time on the structure, microstructure, microhardness and elastic modulus of the samples. The structural and microstructural results, obtained by X-ray diffraction and microscopy techniques, showed that the solution heat treatment performed at high temperatures induces the formation of the β phase, while solution heat treatment performed at low temperatures induces the formation of the α” and ω metastable phases. Regarding the effect of time, samples subjected to heat treatment for 6 hours have only the β phase, indicating that lengthy treatments suppress the α” phase. Regarding the hardness and elastic modulus, the alloy with the α” and ω phases, after treatment performed at a temperature of 500 °C, has a high hardness value and elastic modulus due to the presence of the ω phase that hardens and weakens alloys. The titanium alloys developed in this study have excellent mechanical properties results for use in the orthopedic area, better than many commercial materials such as cp-Ti, stainless steel and Co-Cr alloys.

Abstract: Zirconium alloys have many applications in industry in services too harsh for stainless steels, nickel alloys or where a noteworthy improvement in service life may be achieved, by choosing zirconium alloys instead of other metals, such as high permeability to thermal neutrons and excellent corrosion resistance in nuclear reactor environments. Mixing alloying elements, such as niobium, molybdenum, tin, titanium and tantalum, with zirconium changes its physical and chemical properties, especially its resistance to corrosion. In this study, specimens of Zr-1.0Nb alloy were obtained by melting in a furnace with non-consumable electrodes in argon atmosphere. Different samples were prepared to ensure good homogeneity of the specimens. The melting procedure was tested several times to determine the parameters that ensure proper alloy handling. These parameters include the melting point of the alloys under pressure and the current in the furnace. Using the derived melting parameters and processing parameters, it has been obtained Zr-1.0Nb alloy specimens with appropriate homogeneity, as confirmed by auxiliary characterization techniques, such as optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. For these methods, the requirements for physicochemical properties in the nuclear sector were incorporated into the analyses.

Abstract: Titanium is used in the biomedical field due to its mechanical strength/density, corrosion resistance, and biocompatibility. In this paper, the preparation, and the structural, microstructural, and mechanical characterization of Ti-20Zr-2.5Mo and Ti-20Zr-7.5Mo alloys are presented. The elements were melted into an arc furnace with an argon controlled atmosphere. To determine the amount of impurities present in each alloy, an analysis of the chemical composition was conducted using EDS. The samples were characterized by measurements of density, X-ray diffraction (with the diffractograms refined by the Rietveld method), and optical and scanning electron microscopy. The mechanical properties were evaluated using Vickers microhardness test and modulus of elasticity. The results showed that that α’/α’’ and α’'/β phases coexisted in both of the prepared alloys, respectively. The alloys have higher hardness than cp-Ti and their modulus of elasticity values are very close to the modulus values of cp-Ti.

Abstract: Titanium alloys are constantly being studied for possible applications as biomaterials. However, studies suggest that aluminum and vanadium, when used in the human body over long period of time, are associated with adverse reactions and allergies. So there is a need to develop alloys that are both free of these elements and have mechanical properties that are good as or better than the Ti-6Al-4V alloy. In this paper, alloys were prepared from the Ti-10Mo-xZr system (x = 5, 10, 15, 20 wt%). These were characterized by their chemical composition via energy dispersive spectroscopy (EDS), density, x-ray diffraction, optical microscopy, and microhardness. The results showed that the alloys have the desired stoichiometry and a good homogeneity structure. Microstructure analyses indicated the predominance of the β phase with a body-centered cubic crystal structure and that the addition of substitutional elements caused the solid solution to harden.

Abstract: Ti and Ti-based alloys have favorable properties for biomedical applications, such as high specific strength, low Young’s modulus, excellent corrosion and wear resistance, and good biocompatibility. The addition of alloying elements and heat treatments can result in a good combination of properties. Mo and Zr are β-stabilizer elements that decrease the Young’s modulus and increase the mechanical strength and corrosion resistance. Oxygen is an interstitial element that can improve mechanical strength and prevent ω phase formation. In this study, we analyzed the influence of substitutional and interstitial elements, and some heat treatments in the crystalline structure, microstructure and selected mechanical properties (Vickers microhardness, Young’s modulus and internal friction) of Ti-15Zr-xMo (5, 10, 15 and 20 wt%) alloys. The alloys exhibited dependence on the alloying elements and heat treatments, which resulted in different structural and microstructural changes. The mechanical properties were dependent on phase transformations induced by the compositions and heat treatments.

Abstract: Titanium alloys present favorable properties to industry applications that depend on their composition and microstructure. Adding alloy elements and thermomechanical treatments can change the microstructure of titanium alloys. In this paper, Ti-15Zr alloys with different molybdenum quantities were prepared and hot-rolled, having been previously subjected to homogenizing heat treatment. The results showed that the microstructure of the alloys was sensible to heat treatment, in accordance with the theoretical prediction from the molecular orbital method.

Abstract: Ti and its alloys are widely used as biomaterials. Their main properties are excellent corrosion resistance, relatively low elastic modulus, high specific strength, and good biocompatibility. The development of new Ti alloys with properties favorable for use in the human body is desired. To this end, Ti alloys with Mo, Nb, Zr, and Ta are being developed, because these elements do not cause cytotoxicity. The presence of interstitial elements (such as oxygen and nitrogen) induces strong changes in the elastic properties of the material, which leads to hardening or softening of the alloy. By means of anelastic spectroscopy, we are able to obtain information on the diffusion of these interstitial elements present in the crystalline lattice. In this paper, the effect of oxygen on the anelastic properties of some binary Ti-based alloys was analyzed with anelastic spectroscopy. The diffusion coefficients, pre-exponential factors, and activation energies were calculated for oxygen and nitrogen in these alloys.

Abstract: Because of their low elasticity modulus, titanium alloys have excellent biocompatibility, and are largely used in orthopedic prostheses. Among the properties that are beneficial for use in orthopedic implants is the elasticity modulus, which is closely connected to the crystal structure of the material. Interstitial elements, such as oxygen, change the mechanical properties of the material. Anelastic spectroscopy measurements are a powerful tool for the study of the interaction of these elements with the metallic matrix and substitutional solutes, providing information on the diffusion and concentration of interstitial elements. In this study, the effect of oxygen on the anelastic properties of alloys in the Ti-15Mo-Zr system was analyzed using anelastic spectroscopy measurements. The diffusion coefficients, pre-exponential factors, and activation energies of these alloys were calculated for oxygen.

Abstract: The Ti-15Mo-xNb system integrates a new class of titanium alloys without the presence of aluminum and vanadium, which exhibit cytotoxicity, and that have low elasticity modulus values (below 100 GPa). This occurs because these alloys have a beta structure, which is very attractive for use as biomaterials. In addition, Brazil has about 90% of the world’s resources of niobium, which is very important economically. It strategically invests in research on the development and processing of alloys containing this element. In this paper, a study of the influence of heat treatments on the structure and microstructure of the alloys of a Ti-15Mo-xNb system is presented. The results showed grain grown with heat treatment and elongated and irregular grains after lamination due to this processing. After quenching, there were no changes in the microstructure in relation to heat-treated and laminated conditions. These results corroborate the x-ray diffraction results, which showed the predominance of the β phase.

Abstract: The interaction among heavy interstitial atoms present in metals with bcc structure is studied using anelastic spectroscopy. This technique makes it possible to obtain information on interstitial concentration, precipitation, solubility limit, and diffusion. The diffusion coefficients of nitrogen in niobium were obtained using the relaxation parameters obtained from anelastic spectroscopy measurements for different oscillation frequencies of the system. The results showed the interstitial diffusion of nitrogen present in solid solution in niobium when submitted to different charges of nitrogen at a temperature of 1373 K and a partial pressure in the order of 10^-4 Torr. The exponential variation of the pressure experimentally in function of the time was thus obtained.