Sandra G. Schneider

Study of the non-linear stress-strain behavior in Ti-Nb-Zr alloys

The aim of this work is to study the elastic behavior of some Ti-Nb-Zr alloys (Ti-8Nb-13Zr, Ti-13Nb-13Zr, Ti-18Nb-13Zr and Ti-41.1Nb-7.1Zr) developed to biomedical applications. These alloys were produced by arc melting under argon atmosphere. Uniaxial tensile tests, carried out in a MST servo-hydraulic machine, were employed in their mechanical characterization. The occurrence of non-linear stress-strain behavior in the conventional elastic region (total strain values up to 0.2%) lead to the Ramberg-Osgood relationship, modified by Hill, in order to analyze that portion of the obtained curves. The present study involves the following properties: initial elastic modulus, tangent modulus, secant modulus, proof stress and the Ramberg-Osgood parameter (n). The results demonstrate that these alloys are not similar with respect to the mechanical behavior. Furthermore, it is shown that the degree of non-linearity in the stress-strain behavior is quantified by the parameter (n).

Dynamical Elastic Moduli of the Ti-13Nb-13Zr biomaterial alloy by mechanical spectroscopy

Dynamical Elastic Moduli of the Ti-13Nb-13Zr biomaterial alloy were obtained using the mechanical spectroscopy technique. The sample with heat treatment at 1170K for 30 minutes and water quenched with subsequent aging treatment at 670 K for 3 hours (TNZ + WQ + 670 K/3 h), was characterized through decay of free oscillations of the sample in the flexural vibration mode. The spectra of anelastic relaxation (internal friction and frequency) in the temperature range from 300 K to 625 K not revealed the presence of relaxation process. As shown in the literature, the hcp structure usually does not exhibit any relaxation due to the symmetry of the sites in the crystalline lattice, but if there is some relaxation, this only occurs in special cases such as low concentration of zirconium or saturation of the stoichiometric ratio of oxygen for zirconium. Dynamical elastic modulus obtained for TNZ + WQ + 670 K/3 h alloy was 87 GPa at room temperature, which is higher than the value for Ti-13Nb-13Zr alloy (64 GPa) of the literature. This increment may be related to the change of the proportion of α and β phases. Besides that, the presence of precipitates in the alloy after aging treatment hardens the material and reduces its ductility.

Elastic Behavior of the Ti-13Nb-13Zr Alloy Obtained by Anelastic Spectroscopy

Measurements of anelastic relaxation (internal friction and frequency) as a function of temperature were carried out in samples of Ti-13Nb-13Zr using two experimental apparatus: Flexural Vibration of the first tone of samples in Acoustic Elastometer System (Vibran Technology®) operating in a kilohertz bandwidth, and Torsional Vibration of the samples in Kê-type Torsion Pendulum operating in a hertz bandwidth. Experimental spectra of anelastic relaxation were determined in the temperature range from 300 K to 450 K for a heating rate of 1K/min under pressure of 10-5 Torr, in both apparatus. The results show a relaxation structure strongly dependent on the microstructure of the material. The dynamical elastic modulus (E) of Ti-13Nb-13Zr alloy can be determined by flexural vibrations by frequency (f) measurements (f  E1/2). The anelastic relaxation spectrum of Ti-13Nb-13Zr alloy was a function of temperature obtained by torsional vibrations, not revealing the presence of interstitial solutes in solid solution in the temperature range of measurements.

Influência do tratamento térmico no comportamento mecânico não-linear elástico da liga Ti-13Nb-13Zr

Ti-13Nb-13Zr alloy was produced by arc melting, solution treated at 1000°C/1h followed by water quenching, cold forged and annealed at 1000°C/1h or 900°C/30min followed by water quenching. Mechanical properties of this alloy were evaluated by tension tests at room temperature. The elastic region of the stress-strain curve was analyses according to the modified equation of Ramberg-Osgood, which degree of non-linearity is associated to parameter n. It was observed that aging treatment at 400°C/3h, after the annealing, decreases the differences between mechanical properties; moreover, the linearity of elastic region improves.

AVALIAÇÃO DAS PROPRIEDADES MICROESTRUTURAIS E MECÂNICAS DAS LIGAS TI-35NB-7ZR E TI-41,1NB-7,1ZR PARA APLICAÇÃO BIOMÉDICA

The aim of this work was to achieve Ti-β alloys without considerable toxic elements (Al and V) with lower elastic moduli to improve the mechanical compatibility with the bone (17 GPa-35 GPa) [1,2]. Ti-35Nb-7Zr and Ti-41,1Nb-7,1Zr alloys were produced in fusion by arc melting under argon atmosphere. The ingots, with the initial diameter of 18 mm were submitted to solution heat treatment, cool rotary forging and recrystallization treatment until 6 mm of diameter. The microstructural analyses were performed using Optical Microscopy, X-ray diffraction and hardness. The mechanical characterization was evaluated through uniaxial tensile tests. The results showed that properties are dependent on the compositions studied. Microstructure results indicated that both alloys are Ti-β. Ti-35Nb-7Zr in β-solution treated condition posses the lowest value of hardness (157 HV). Vickers hardness values for alloys within 35Nb and 41,1Nb, in the recrystallization condition were very close 161 and 169 HV, respectively. The Ti-35Nb-7Zr alloy presented the lowest elastic modulus (54 GPa) and the highest ductility, based on reduction of area and elongation without change tensile strength

Growth of Calcium Phosphate Using Chemically Treated Titanium Oxide Nanotubes

Many materials with different surfaces have been developed for dental and orthopedics implants. Among the various materials for implants, titanium and bioactive ones such as calcium phosphates and hydroxyapatite, are widely used clinically. When these materials are inserted into bone several biological reactions occur. Thes processes can be associated with surface properties (topography, roughness and surface energy). In this work, ingots were obtained from titanium and molybdenum by using an arc-melting furnace. They were submitted to heat treatment at 1100°C for one hour, cooled in water and cold worked by swaging. Titanium nanotubes were fabricated on the surface of Ti-7,5Mo alloy by anodization, and then treated with NaOH solution to make them bioactive, to induce growth of calcium phosphate in a simulated body fluid. . It is shown that the presence of titanium nanotubes induces the growth of a sodium titanate nanolayer. During the subsequent in-vitro immersion in a simulated body fluid, the sodium titanate nanolayer induced the nucleation and growth of nano-dimensioned calcium phosphate. These titanium nanotubes can be useful as a well-adhered bioactive surface layer on Ti implant metals for orthopedic and dental implants.

Low-Frequency High-Temperature Internal Friction in Ti-13Nb-13Zr Alloy

Recent studies have been done to achieve biomedical alloys containing non-toxic elements and presenting low elastic moduli. It has been reported that Ti-Nb-Zr alloys rich in beta phase, especially Ti-13Nb-13Zr, have potential characteristics for substituting conventional materials such as Ti-6Al-4V, stainless steel and Co alloys. The aim of this work is to study the internal friction (IF) of Ti-13Nb-13Zr (TNZ) alloy due to the importance of the absorption impacts in orthopedic applications. The internal friction of this alloy produced by arc melting was measured using an inverted torsion pendulum with the free decay method. The measurements were performed from 77 to 700 K with heating rate of 1 K/min, in a vacuum better than 10-5 mBar. The results show a relaxation structure at high temperature strongly dependent on microstructure of the material. Qualitative discussions are presented for the experimental results, and the possibility of using the TNZ as a high damping material is briefly mentioned.