Influence of interstitial elements on internal friction measurements in Nb and Nb-Zr alloys

Internal friction and frequency measurements as a function of temperature have been carried out in Nb and Nb-Zr policrystalline samples, using a torsion pendulum in the temperature range between 300K and 700K the heating rate was 1K/min and the pressure was kept better than 5x10(-3) mbar. Metals with bce lattice containing solute atoms dissolved interstitially often show anelastic behaviour due to a process know as stress-induced ordering responsible for the appearance of Snoek peaks. In the Nb sample it has been identified two constituent peaks corresponding to the interstitial-matrix interactions (Nb-O and Nb-N), but for the Nb-Zr samples with interstitial solute concentrations very close to those measured for the unalloyed Nb, it was not observed any mechanical relaxation peaks due to the presence of oxygen and nitrogen in solid solution.

Effect of heavy interstitials on anelastic properties of Nb-1.0 wt% Zr alloys

The mechanical properties of metals with bcc structure, such as niobium and its alloys, have changed significantly with the introduction of heavy interstitial elements. These interstitial elements (nitrogen, for example), present in the alloy, occupy octahedral sites and constitute an elastic dipole of tetragonal symmetry and might produce anelastic relaxation. This article presents the effect of nitrogen on the anelastic properties of Nb-1.0 wt% Zr alloys, measured by means of mechanical spectroscopy using a torsion pendulum. The results showed complex anelastic relaxation structures, which were resolved into their constituent peaks, representing each relaxation process. These processes are due to stress-induced ordering of the interstitial elements around the niobium and zirconium of the alloy.

Nitrogen diffusion in the Nb-1.0wt%Zr measured by mechanical spectroscopy

The scientific and technological development in the area of new materials contributed to several applications of niobium and its alloys in nuclear power plants as well as in aerospace, aeronautics, automobile and naval industries. This paper presents the interstitial diffusion coefficients of nitrogen in solid solution in the Nb-1.0wt%Zr alloy using internal friction measurements obtained by mechanical spectroscopy, which uses a torsion pendulum operating at an oscillation frequency between 1.0 Hz and 10.0 Hz. The temperature range varies from 300K to 700K, at a heating rate of 1 K/min and vacuum better than 2 x 10(-6) Torr. The results showed an increase of the interstitial diffusion coefficient of nitrogen that was correlated with configurational considerations for the octahedral interstitials.

Anelastic relaxation due to interstitial solutes diffusion in Nb and Nb-1 wt% Zr

Metals and alloys containing solute atoms dissolved interstitially often show anelastic behavior due to a process know as stress-induced ordering. The application of mechanical spectroscopy measurements to diffusion studies in body-centered cubic metals has been extensively used in the last decades. However the kind of preferential occupation of interstitial solutes in body-centered cubic metals is still controversial. The anelastic properties of the Nb and Nb-1 wt% Zr polycrystalline alloys were determined by internal friction and oscillation frequency measurements using a torsion pendulum inverted performed between 300K and 650K, operating in a frequency oscillation in the hertz bandwidth. The interstitial diffusion coefficients of oxygen and nitrogen in Nb and Nb-1 wt% Zr samples were determined at two distinct conditions: (a) for low concentration of oxygen and (b) for high concentration of oxygen.

Characteristic zirconium-rich coring structures in Mg-Zr alloys

The most characteristic feature of the microstructure of a magnesium alloy that contains more than a few tenths per cent soluble zirconium is the zirconium-rich cores that exist in most grains. The morphology, distribution and composition of cores observed in a Mg-0.56%Zr alloy and the small particles present in them were investigated. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Influence of the Substitutional Solute on the Mechanical Properties of Ti-Nb Binary Alloys for Biomedical Use

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparation of Ni-Ti-Mo and Ni-Ti-Mo-Zr Alloys by High-Energy Ball Milling and Subsequent Hot Pressing

This work discusses on the preparation of Ni-45Ti-5Mo, Ni-40Ti-10Mo and Ni-46Ti-2Mo-2Zr (at-%) alloys by high-energy ball milling and hot pressing, which are potentially attractive for dental and medical applications. The milling process was performed in stainless steel balls (19mm diameter) and vials (225 mL) using a rotary speed of 300rpm and a ball-to-powder weight ratio of 10:1. Hot pressing under vacuum was performed in a BN-coated graphite crucible at 900 degrees C for 1 h using a load of 20 MPa. The milled and hot-pressed materials were characterized by X-ray diffraction, electron scanning microscopy, and electron dispersive spectrometry. Peaks of B2-NiTi and Ni4Ti3 were identified in XRD patterns of Ni-45Ti-5Mo, Ni-40Ti-10Mo and Ni-46Ti-2Mo-2Zr powders milled for 1h. The NiTi compound dissolved small Mo amounts lower than 4 at%, which were measured by EDS analysis. Moreover, it was identified the existence of an unknown Mo-rich phase in microstructures of the hot-pressed Ni-Ti-Mo alloys.

The Influence of Small Quantities of Oxygen in the Structure, Microstructure, Hardness, Elasticity Modulus and Cytocompatibility of Ti-Zr Alloys for Dental Applications

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influence of the substitutional solute on the mechanical properties of Ti-Nb binary alloys for biomedical use

Titanium alloys are widely used in the manufacture of biomedical implants because they possess an excellent combination of physical properties and outstanding biocompatibility. Today, the most widely used alloy is Ti-6Al-4V, but some studies have reported adverse effects with the long-term presence of Al and V in the body, without mentioning that the elasticity modulus value of this alloy is far superior to the bone. Thus, there is a need to develop new Ti-based alloys without Al and V that have a lower modulus, greater biocompatibility, and similar mechanical strength. In this paper, we investigated the effect of Nb as a substitutional solute on the mechanical properties of Ti-Nb alloys, prepared in an arc-melting furnace and characterized by density, X-ray diffraction, optical microscopy, hardness and elasticity modulus measurements. The X-ray and microscopy measurements show a predominance of the α phase. The microhardness values showed a tendency to increase with the concentration of niobium in the alloy. Regarding the elasticity modulus, it was observed a nonlinear behavior with respect to the concentration of niobium. This behavior is associated with the presence of the α phase.

Synthesis of M2AC (M = Ti, V, Cr, Nb, Zr, A = Al, Sn, S) (MAX) carbide phases and study of their physical behavior under extreme conditions

Materials known as Mn+1AXn phases, where n is 1, 2, or 3, and M represents an early transition metal, A an A-group element, and X is either Carbon and/or Nitrogen [1], are fast becoming technologically important materials due to the interesting combination of unique properties. However, a lot of important information about the high temperature and high pressure behavior of many of these compounds is still missing, which needs to be determined systematically. ^ In this dissertation the synthesis of M2AC (M = Ti, V, Cr, Nb, Zr) and A = (Al, Sn, S) compounds by arc melting, vacuum sintering and piston cylinder synthesis is presented along with the synthesis of Zr 2SC, which has been synthesized for first time in bulk form, by piston cylinder technique. The microstructural analysis by electron microscopy and phase analysis by x-ray diffraction is presented next. Finally, a critical analysis of the behavior of these compounds under the application of extreme pressure (as high as 50 GPa) and temperature (≈ 1000°C) is presented. ^ The high pressure studies, up to 50 GPa, showed that these compounds were structurally intact and their bulk moduli ranged from 140 to 190 GPa. The high temperature studies in the inert atmosphere showed that the M 2SnC compounds were unstable above 650°C and the expansion along the a-axis was higher than that along the c-axis, unlike the other phases. M2SC compounds on the other hand showed negligible difference in the thermal expansion along the two axes. The oxidation study revealed that Ti2AC (Al, S) compounds had highest resistance to oxidation while the M2SnC compounds had the least. Furthermore, from the oxidation study of these compounds, which were short time oxidation experiments, it was found that all of these compounds oxidized to their respective binary oxides. ^

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.

Production, microstructural characterization and mechanical properties of as-cast Ti-10Mo-xNb alloys

Beta titanium (Ti) alloys are one of the most promising groups of Ti alloys for biomedical applications. This work presents the production, microstructural characterization, and mechanical properties of as-cast Ti-10Mo-xNb (x = 0, 3, 6, 9, 20, and 30) alloys. They were produced via arc melting and characterized by scanning electron microscopy and X-ray diffraction. The density of each alloy was measured by the Archimedes method and the mechanical characterization was carried out by using the Vickers microhardness test and Young`s modulus measurements. The results show a near beta microstructure for niobium (Nb) contents lower or equal to 9 wt% while beta single-phase microstructure was obtained for higher Nb additions. The microhardness values decreased with the increase of Nb content in the alloys. The elastic modulus values of Ti-10Mo-3Nb and Ti-10Mo-20Nb alloys were lower than those of cp Ti and Ti-6Al-4V.

Corrosion behavior of Ti-xNb-13Zr alloys in Ringer`s solution

Ti-6Al-4V alloy has been widely used in restorative surgery due to its high corrosion resistance and biocompatibility. Nevertheless, some studies showed that V and Al release in the organism might induce cytotoxic effects and neurological disorders, which led to the development of V-free alloys and both V- and Al-free alloys containing Nb, Zr, Ta, or Mo. Among these alloys, Ti-13Nb-13Zr alloy is promising due to its better biomechanical compatibility than Ti-6Al-4V. In this work, the corrosion behavior of Ti, Ti-6Al-4V, and Ti-xNb-13Zr alloys (x=5, 13, and 20) was evaluated in Ringer`s solution (pH 7.5) at 37 degrees C through open-circuit potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Spontaneous passivity was observed for all materials in this medium. Low corrosion current densities (in the order of 10(-7) A/cm(2)) and high impedance values (in the order of 10(5) Omega cm(2) at low frequencies) indicated their high corrosion resistance. EIS results showed that the passivating films were constituted of an outer porous layer (very low resistance) and an inner compact layer (high resistance), the latter providing the corrosion resistance of the materials. There was evidence that the Ti-xNb-13Zr alloys were more corrosion resistant than both Ti and Ti-6Al-4V in Ringer`s solution.

Effect of the Oxygen on the Mechanical Properties of Ti-Mo Systems Alloys

Titanium alloys normally contain oxygen, nitrogen, or carbon as impurities, and although this concentration is low, these impurities cause changes in the mechanical properties of Ti alloys. Oxygen is a strong alpha-phase stabilizer and its addition causes solid-solution strengthening, shape memory effect, and superelasticity. The most promising alloys are those with Nb, Zr, Ta, and Mo as alloying elements. In this paper, the preparation, processing, and characterization of Ti-Mo alloys (5 and 10 wt%) used as biomaterials are presented, along with the influence of oxygen on their mechanical properties. The addition of oxygen causes an increase in the elasticity modulus of the Ti-5Mo alloy due to an increase in the alpha' phase volume fraction, which possesses a higher modulus than the alpha '' phase. Ti-10Mo possesses a mixture between alpha '' and beta phases, oxygen enters these two structures and causes a dominating effect.

Diffusion of Interstitial Solutes in Nb-46wt% Ti Alloys Measured by Mechanical Spectroscopy

The mechanical properties of metals with a body-centered cubic (bcc) structure, such as Nb, Ta, V, and their alloys, are modified with the introduction of interstitial impurities, such as O, N, C, or H. These metals can dissolve great amounts of O and N, for example, to form solid solutions. The interstitial solute atoms (ISA) in metals with a bcc structure occupy octahedral sites and cause local distortion with tetragonal symmetry. So ISA in these metals forms an elastic dipole that can align along one of the three cubic axis of the crystal. In the present paper, the torsion pendulum technique was employed for the investigation of various interactions among the metallic matrix and different interstitial solutes in the Nb-46wt%Ti alloy. From the relaxation spectra, we obtained the diffusion coefficients, pre-exponential factors, and activation energies for nitrogen in the Nb-46wt%Ti alloy.