Eder S.N. Lopes

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.

Effects of Cooling Rate and Sn Addition on the Microstructure of Ti-Nb-Sn Alloys

Ti-based alloys present unique properties and hence, are employed in several industrial segments. Among Ti alloys, β type alloys form one of the most versatile classes of materials in relation to processing, microstructure and mechanical properties. It is well known that heat treatment of Ti alloys plays an important role in determining their microstructure and mechanical behavior. The aim of this work is to analyze microstructure and phases formed during cooling of β Ti-Nb-Sn alloy through different cooling rates. Initially, samples of Ti-Nb-Sn system were prepared through arc melting furnace. After, they were subjected to continuous cooling experiments to evaluate conditions for obtaining metastable phases. Microstructure analysis, differential scanning calorimetry and X-ray diffraction were performed in order to evaluate phase transformations. Depending on the cooling rate and composition, α” martensite, ω phase and β phase were obtained. Elastic modulus has been found to decrease as the amount of Sn was increased.

Effects of Aging Heat Treatment on the Microstructure of Ti-Nb and Ti-Nb-Sn Alloys Employed as Biomaterials

The mechanical behavior of β titanium alloys applied as orthopedic biomaterials depends directly on their microstructural features, and can be improved by tailoring the microstructure through the control of their phase transformations. The aim of this investigation is to discuss phase transformations during the aging heat treatment of β Ti-30Nb and β Ti-30Nb-2Sn alloys and to correlate microstructure and mechanical behavior. The results of high temperature XRD experiments showed decomposition of orthorhombic α” phase, followed by the precipitation of ω and α phases. The mechanical behavior of Ti-Nb and Ti-Nb-Sn alloys was found to be highly sensitive to the microstructural changes caused by the addition of Sn and by heat treatments.

Paired evaluation of calvarial reconstruction with prototyped titanium implants with and without ceramic coating

PURPOSE To investigate the osseointegration properties of prototyped implants with tridimensionally interconnected pores made of the Ti6Al4V alloy and the influence of a thin calcium phosphate coating. METHODS Bilateral critical size calvarial defects were created in thirty Wistar rats and filled with coated and uncoated implants in a randomized fashion. The animals were kept for 15, 45 and 90 days. Implant mechanical integration was evaluated with a push-out test. Bone-implant interface was analyzed using scanning electron microscopy. RESULTS The maximum force to produce initial displacement of the implants increased during the study period, reaching values around 100N for both types of implants. Intimate contact between bone and implant was present, with progressive bone growth into the pores. No significant differences were seen between coated and uncoated implants. CONCLUSION Adequate osseointegration can be achieved in calvarial reconstructions using prototyped Ti6Al4V Implants with the described characteristics of surface and porosity.

Microstructure evolution of Ti-30Nb-(4Sn) alloys during classical and step-quench aging heat treatments

Recent studies involving step-quench (SQ) heat treatments have shown that, unlike classical quench-and-aging (QA) heat treatments, SQ route can favour precipitation mechanisms that are strongly dependent on decomposition of the parent β-phase. In this work, Ti–30Nb and Ti–30Nb–4Sn (wt-%) alloys were subjected to cold-working, recrystallisation and then to either classical or SQ heat treatments at 400°C. Among QA samples, ω-phase is formed in both alloys during the heating ramp. By the SQ route, we found extensive isothermal ω-phase precipitation in Ti–30Nb during aging. On the other hand, a complete suppression of ω-phase in Ti–30Nb–4Sn was observed, thus, α-phase precipitation could take place improving hardness while still preserving a low elastic modulus.

Solute lean Ti-Nb-Fe alloys: An exploratory study

In this study, we explored the Ti-Nb-Fe system to find an optimal cost-effective composition with the lowest elastic modulus and the lowest added Nb content. Six Ti-(31-4x)Nb-(1+0.5x)Fe ingots were prepared and Nb was substituted with Fe, starting at Ti-31Nb-1.0Fe and going up to Ti-11Nb-3.5Fe (wt%). The ingots were subjected to cold rolling, recrystallization and solution treatment, followed by water-quenching (WQ), furnace cooling (FC) or step-quenching to 350°C, which caused massive formation of isothermal ω phase. All the water-quenched alloys displayed athermal ω phase, which is apparently the result of fully collapsed β phase. The Fe content improved the compressive strength of the alloys. In the FC alloys, substitution with Fe favored the formation of α phase instead of ω phase, giving rise to a solute-rich β phase with a lattice parameter of 0.3249nm. Among the FC alloys, the lowest modulus of 83±4GPa was obtained in the Ti-19Nb-2.5Fe alloy, which exhibited fine and well dispersed α precipitation and absence of ω phase. DSC experiments indicated that the experimental alloys showed varying phase stability during heating.

Mechanical and microstructural properties of fixation systems used in oral and maxillofacial surgery

ObjectivesThis paper aims to evaluate in vitro the mechanical and microstructural properties of internal fixation systems used in oral and maxillofacial surgeries.Materials and methodsFour brands of internal fixation systems (screws and 4-hole straight plates) were selected and assigned to four groups: G1 Leibinger®, G2 Tóride®, G3 Engimplan®, and G4 Medartis®. The systems were submitted to Vickers hardness testing, metallographic and interstitial elements chemical composition analyses. Data were submitted to ANOVA and Tukey’s test for statistical analysis.ResultsPlates in groups 1, 2, and 3 showed similar microstructure and mechanical properties, different from those in G4 revealing larger grains. In all groups, the screws showed similar microstructure, with uniform arrangement and size of grains; the screws showed higher hardness values than those observed for the plates.ConclusionsThe results indicate that all materials tested are adequate for use in oral maxillofacial surgeries.