Influence of cooling rate on microstructure of Ti-Nb alloy for orthopedic implants

Beta titanium alloys form one of the most versatile group of materials with respect to processing, microstructure and mechanical properties, mainly in applications as biomaterials. Development of new Ti-based alloys for implant application involves more biocompatible metallic alloying elements, such as Nb, Ta, Zr and Mo. Heat treatment of Ti alloys plays an important role in determining microstructure. The aim of this work is the analysis of microstructure and phases formed during water quenching of beta Ti-20Nb alloy through different cooling rates. Ti-20Nb alloy was swaged at 780-860 degrees C and then machined as a cylinder. Cylindrical sample was treated within the beta field and then water quenched from the bottom imposing different cooling rates through the sample. Samples from different regions (cooling rates) were characterized by using X-ray diffractometry (XRD), scanning (SEM) and transmission electron microscopy (TEM), and Vickers microhardness. XRD results showed the increase of beta/alpha phases peak intensity ratio increase with decreasing of cooling rate. As the distance from the bottom (water source) of Ti-20Nb sample decreases, the imposed cooling rate increases, the volume of a martensite acicular phase increases and the size decreases with diminishing of a phase quantity. The lowest elastic modulus E=74 GPa was found for water quenched sample under a cooling rate of 160 K/s. (C) 2006 Elsevier B.V. All rights reserved.27490891

High resolution transmission electron microscopy study of the hardening mechanism through phase separation in a beta-Ti-35Nb-7Zr-5Ta alloy for implant applications

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)beta-Ti alloys are highly attractive metallic materials for biomedical applications due to their high specific strength, high corrosion resistance and excellent biocompatibility, including low elastic modulus. This work aims to clarify the hardening mechanism of a beta-Ti-Nb-Zr-Ta alloy using different characterization techniques. Ingots (50 g) of Ti-35Nb-7Zr-5Ta (wt.%) alloy were arc furnace melted in an Ar((g)) atmosphere, homogenized, hot rolled, solubilized and finally aged at several temperatures from 200 to 700 degrees C for 4 h. Microstructure characterization was performed using X-ray diffraction, optical microscopy, scanning and high resolution transmission electron microscopy (HR-TEM). The 4 h aging showed that the highest hardness values were found when aged at 400 degrees C and the HR-TEM images confirmed splitting of spots on the Fourier space map, which indicated the presence of a coherent interface between separated phases (beta and beta') and explains the hardening mechanism of the alloy. Through geometric phase analysis analysis, using the HR-TEM image, the localized strain map showed 5-10 nm domains of the beta and beta' phases. The combination of suitable values of yield strength, hardness and low Young's modulus makes Ti-35Nb-7Zr-5Ta alloy suitable for medical applications as a metallic orthopedic implant. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.6416251629Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Effects of double aging heat treatment on the microstructure, Vickers hardness and elastic modulus of Ti-Nb alloys

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Aging heat treatment can be a good way to optimize mechanical properties, changing the microstructure, and hence, the mechanical behavior of Ti alloys. The effects of aging heat treatments on beta-type Ti-30Nb alloy were investigated to evaluate the kinetics of alpha '' -> alpha + beta transformation. The results obtained from differential scanning calorimetry and high-temperature X-ray diffraction experiments indicated the complete decomposition of orthorhombic alpha '' phase at close to 300 degrees C, followed by a phase precipitation at 470 degrees C. The aging heat treatments also enabled us to observe a transformation sequence alpha '' -> beta + omega -> beta + omega + alpha, indicating martensite decomposition and omega phase precipitation at 260 degrees C after 2 h, followed by a phase nucleation after heating at 400 degrees C for 1 h. The elastic modulus and Vickers hardness of Ti-30Nb alloy were found to be very sensitive to the microstructural changes caused by heat treatment. (C) 2011 Elsevier Inc. All rights reserved.627673680Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Effect of cooling rate on Ti-Cu eutectoid alloy microstructure

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Titanium alloys present a combination of properties that makes them suitable materials for various medical applications, and there is special interest in Ti-Cu alloys for the fabrication of dental prostheses. The addition of Cu to Ti lowers the melting point of the alloy, as well as leading to the development of desirable mechanical properties. In this study a eutectoid alloy was prepared and heat treated, then cooled at various cooling rates. The eutectoid structure (alpha + Ti(2)Cu) was observed for all cooling rates used, and evidence of alpha' martensite was found for cooling rate higher than 9 degrees C s(-1). Lower cooling rates resulted in higher modulus values. This was attributed to the volume fraction of the alpha and Ti(2)Cu phases. Higher cooling rates produced structures with lower modulus values and greater hardness, a result attributed mainly to the development of a martensitic structure. (C) 2008 Elsevier B.V. All rights reserved.29310231028Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Brazilian Synchrotron Light Laboratory (LNLS)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Electrochemical corrosion behavior of gas atomized Al-Ni alloy powders

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This is a study describing the effects of microstructure features of spray-formed Al-Ni alloy powders on the electrochemical corrosion resistance. Two different spray-formed powders were produced using nitrogen (N-2) gas flow (4 and 8 bar were used). Electrochemical impedance spectroscopy (EIS), potentiodynamic anodic polarization techniques and an equivalent circuit analysis were used to evaluate the electrochemical behavior in a dilute 0.05 M NaCl solution at room temperature. It was found that a N-2 gas pressure of 8 bar resulted in a microstructure characterized by a high fraction of small powders and fine cell spacings, having improved pitting potential but higher corrosion current density when compared with the corresponding results of a coarser microstructure array obtained under a lower pressure. A favorable effect in terms of current density and oxide protective film formation was shown to be associated with the coarser microstructure, however, its pitting potential was found to be lower than that of the finer microstructure. (C) 2012 Elsevier Ltd. All rights reserved.69371378FAEPEX-UNICAMPConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Microstructure evolution and mechanical properties of Al-Zn-Mg-Cu alloy reprocessed by spray-forming and heat treated at peak aged condition

Machining chips of the alloy AA7050 were reprocessed by spray forming followed by hot-extrusion and heat treatment. The spray-formed deposit presented a microstructure with hardening η' precipitates within the matrix and equilibrium η precipitates at the grain boundaries, refined grains and low segregation of the main elements Zn, Cu and Mg. The final microstructure at peak aged condition is mainly composed by Guinier-Preston (GP) zones, η' metastable, η equilibrium , Al3Zr dispersoids and the coarse Al7Cu2Fe intermetallic. A well-defined precipitation free zone along grain boundaries was not observed. Good mechanical properties were achieved. © 2013 Elsevier B.V. All rights reserved