Structure, Microstructure, and Some Selected Mechanical Properties of Ti-Ni Alloys

Titanium nickel (Ti-Ni) alloys with low nickel (Ni) content can be used as biomaterials because they improve the mechanical properties, corrosion, and wear resistance of commercially pure titanium (Cp-Ti). Among the mechanical properties of a biomaterial, elastic modulus and microhardness are very important, and each varies according to the microstructure and interstitial elements such as oxygen and nitrogen as well as the amount of substitutional element and thermomechanical processing. Heat treatments are used to obtain a homogeneous microstructure, free of internal stresses structural, microstructural, also to retain or change the size of the phases. In this chapter, the preparation, chemical, structural, and microstructural, and mechanical characterization of Ti-Ni alloys are presented. The structural and microstructural characterization showed the predominant presence of α and Ti2Ni phases. There is no clear variation of the microhardness due to the amount of nickel. The dynamic elastic modulus was slightly above the Cp-Ti due to the addition of a new intermetallic phase (Ti2Ni) but did not vary significantly with the amount of Ni

Stress-induced ordering due heavy interstitial atoms in Nb-0.3 wt.% Ti alloys

Abstract The mechanical properties of metals with bcc structure, such as niobium and their alloys, are changed of a significant way by the introduction of heavy interstitial elements. These interstitial elements (oxygen, for example) present in the metallic matrix occupy octahedral sites and constitute an elastic dipole of tetragonal symmetry and might produce anelastic relaxation. Polycrystalline samples of Nb-0.3 wt.% Ti (Nb-Ti) alloy with oxygen in solid solution were analysed. The anelastic spectroscopy measurements had been made in a torsion pendulum, with frequencies in the Hz range, in a temperature range between 300 and 700 K. The results showed thermally activated relaxation structures were identified four relaxation process attributed to stress-induced ordering of single oxygen, nitrogen and carbon atoms around niobium and stress-induced ordering of single oxygen atoms around titanium atoms

Minimization of polymerization shrinkage effects on composite resins by the control of irradiance during the photoactivation process

High levels of shrinkage stress caused by volumetric variations during the activation process are one of the main problems in the practical application of composite resins. Objective The aim of this study is to reduce the shrinkage stress and minimize the effects caused by composite resin volumetric variation due to the photopolymerization. In this way, this work proposes a systematic study to determine the optimal dimming function to be applied to light curing processes. Material and Methods: The study was performed by applying mathematical techniques to the optimization of nonlinear objective functions. The effectiveness of the dimming function was evaluated by monitoring the polymerization shrinkage stress during the curing process of five brands/models of composites. This monitoring was performed on a universal testing machine using two steel bases coupled in the arms of the machine where the resin was inserted and polymerized. The quality of the composites cured by the proposed method was analyzed and compared with the conventional photoactivation method by experiments to determine their degree of conversion (DC). Absorbance measurements were performed using Fourier-transform infrared spectroscopy (FT-IR). A T-test was performed on DC results to compare the photoactivation techniques. We also used scanning electron microscopy (SEM) to analyze in-vitro the adhesion interface of the resin in human teeth. Results: Our results showed that the use of the optimal dimming function, named as exponential, resulted in the significant reduction of the shrinkage stress (~36.88% ±6.56 when compared with the conventional method) without affecting the DC (t=0.86, p-value=0.44). The SEM analyses show that the proposed process can minimize or even eliminate adhesion failures between the tooth and the resin in dental restorations. Conclusion: The results from this study can promote the improvement of the composite resin light curing process by the minimization of polymerization shrinkage effects, given an operational standardization of the photoactivation process

Preparação e caracterização de uma liga de titânio com a adição de tântalo e zircônio para aplicações biomédicas

Ligas de titânio são amplamente utilizadas na área biomédica devido à sua excelente resistência à corrosão em fluídos corpóreos, elevada razão resistência mecânica/densidade, baixo módulo de elasticidade e comprovada biocompatibilidade. As ligas mais promissoras para serem utilizadas na área biomédica possuem elementos em solução sólida que diminuem a temperatura de transformação de fase do titânio. Tais elementos são denominados beta-estabilizadores e obtêm-se como resultado a diminuição do módulo de elasticidade e uma excelente resistência à corrosão. Os elementos tântalo e zircônio, quando acrescentados ao titânio, melhoram a resistência à corrosão e diminuem o módulo de elasticidade, pois o tântalo é considerado um elemento β-estabilizador e o zircônio atua como elemento estabilizador desta fase, na presença de outro elemento β-estabilizador. Neste trabalho, a liga Ti-25Ta-5Zr foi preparada por fusão à arco, visando aplicações biomédicas. As caracterizações química, estrutural, microestrutural e mecânica foram realizadas por intermédio de medidas da composição química, análise de gases, espectrometria por dispersão de energia (EDS), difração de raios X, microscopias óptica e eletrônica de varredura, microdureza Vickers e módulo de elasticidade.  Os resultados obtidos mostraram uma boa estequiometria e homogeneidade da liga. As análises estrutural e microestrutural corroboraram entre si e indicaram que a liga possui a coexistência de duas fases, α‖ (com estrutura cristalina ortorrômbica) e β (com estrutura cristalina cúbica de corpo centrado). A microdureza elevou-se com a adição de tais elementos e o módulo de elasticidade possui valores abaixo das ligas utilizadas comercialmente, satisfatório para aplicação como implante ortopédico. Palavras-chave: Biomateriais, Ligas de titânio, Microestrutura

Effect of the substitutional elements on the microstructure of the Ti-15Mo-Zr and Ti-15Zr-Mo systems alloys

AbstractTitanium alloys have excellent biocompatibility, and combined with their low elastic modulus, become more efficient when applied in orthopedic prostheses. Samples of Ti-15Mo-Zr and Ti-15Zr-Mo system alloys were prepared using an arc-melting furnace with argon atmosphere. The chemical quantitative analysis was performed using an optical emission spectrometer with inductively coupled plasma and thermal conductivity difference. The X-ray diffractograms, allied with optical microscopy, revealed the structure and microstructure of the samples. The mechanical analysis was evaluated by Vickers microhardness measurements. The structure and microstructure of alloys were sensitive to molybdenum and zirconium concentration, presenting α′, α″ and β phases. Molybdenum proved to have greater β-stabilizer action than zirconium. Microhardness was changed with addition of molybdenum and zirconium, having Ti-15Zr-10Mo (436±2HV) and Ti-15Mo-10Zr (378±4HV) the highest values in each system

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

Experimental assessment of low-temperature martensite transformations in Ni-rich polycrystalline Ni-Ti alloys

Ultrasonic velocity and attenuation measurements of a commercially available Ni-rich polycrystalline NieTi alloy were simultaneously obtained upon cooling from room temperature (RT) down to 130 K. The anelastic spectra show multiple anomalies in both velocity and attenuation curves, which evidence a complex nature of structural rearrangements exhibited by NieTi alloy, associated with relaxations and phase transformations. In particular, some evident anomalies at 285 and 180 K, not previously exploited using ultrasonic measurements on Ni-rich polycrystalline NieTi alloy, were associated with austenite to pre-martensitic (B2 / R) and pre-martensitic to martensitic (R/ B19’) phase transitions, respectively. The peculiar temperature separation between these transformations was interpreted based on chemical composition and the NieTi alloy microstructure evolution. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were also used to add complementary results about phase transformations and thermal events exhibited by NieTi alloy at low temperatures

Os objetivos do laboratório didático na visão dos alunos do curso de Licenciatura em Física da UNESP-Bauru

Há mais de cinqüenta anos, existe a preocupação em se definir os objetivos para o laboratório didático, revisando currículos e buscando ações mais localizadas e orientadas de acordo com o avanço crescente de conhecimentos das concepções alternativas de vários tópicos da Física por parte dos alunos, levando-se em conta as dificuldades específicas enfrentadas por eles no processo ensino-aprendizagem. Podem-se identificar duas linhas filosóficas que norteiam o processo ensino-aprendizagem com relação aos objetivos do laboratório didático. Uma linha defende que para sedimentar os conceitos expostos em aulas teóricas é necessária a prática em laboratório. A outra linha defende que o alvo da prática em laboratório deveria ser a obtenção e análise de dados, levando-se em conta a teoria aprendida. Atualmente, se percebe um crescimento por parte de profissionais que entendem haver uma necessidade de planejar, definir e hierarquizar objetivos detalhados, além de propiciar atividades que favoreçam de acordo com cada classe dentro da linha filosófica a que se identifica o profissional, não se esquecendo que ainda existem profissionais que não aceitam essa postura. Dentro desta perspectiva, foi aplicado um questionário a trinta alunos do curso de Licenciatura em Física da UNESP-Bauru, que já cursaram as cinco disciplinas práticas básicas do curso. Os alunos pontuaram de acordo com a sua visão dos objetivos reais frente aos objetivos ideais do laboratório didático. Os resultados mostraram que o laboratório didático vem cumprindo seu papel na opinião dos alunos do curso de Licenciatura em Física.In the last fifty years, there have been the worry in defining the objectives for the didactic laboratory, revising curricula and looking for more specific and guided actions in agreement with the growing progress of knowledge in the alternative conceptions of several topics of the Physics on the part of the students, taking into account their difficulties in the teaching-learning process. We can identify two philosophical lines that guide the teaching learning process with relationship to the objectives of the didactic laboratory. One line defends that it is necessary to practice in laboratory the concepts exposed in theoretical classes in order to settle them. The other line defends that the objective of the practice in laboratory should be the acquisition and analysis of data, accounting for the learned theory. Nowadays, it is notable the growing number of professionals that understand the needs of planning, defining and organizing each of the aims. Besides, it is necessary to keep activities that propitiate different and unlike insights, considering that these are professionals that do not share this philosophical concept. In this perspective, a questionnaire was applied to thirty students attending the Physics Course at UNESP-Bauru, which have studied the five basic practices disciplines of the course. The students punctuated according to its vision of the real objectives facing the ideal objectives of the didactic laboratory. The results showed that the didactic laboratory has been paying its role in a suitable way