Less-rigid coating in Ti obtained by laser surface alloying with Nb

[EN] The fabrication of parts with stiffness gradation specifically designed to attain higher mechanical and/or biomedical performance is receiving increasing scientific and technological interest. This work reports the use of laser surface alloying to introduce Nb into the surface layer of Ti pieces and thus obtain continuous coatings composed of Ti-Nb alloys. By controlling the laser processing parameters, coatings with lower Young's modulus and higher hardness compared to the substrate, practically free of cracks and with very low porosity were obtained, using energy densities in the range of 24 to 65 J/mm(2). However, compositional heterogeneity mainly due to microsegregation during the solidification process was observed. Increasing the energy density resulted in deeper fusion zones, which increased the substrate fusion and thus decreased the Nb content and produced a coating with a microstructure predominantly composed of alpha/alpha' acicular phase. On the other hand, the Nb content of the coatings produced with lower energy densities was high enough (similar to 20-30%(in) (mass)) to (meta) stabilize the less-rigid alpha" and beta phases, which promoted the highest reductions in the Young's modulus of the investigated coatings. Besides the lower stiffness, all coatings presented at least twice the hardness of the substrate. Maps of the properties constructed from the nanoindentation results showed that, despite the compositional heterogeneity, homogenous values of Young's modulus and hardness were attained and the change in the interface region was gradual, in agreement with the concept of functionally graded materials.The authors gratefully acknowledge the Sao Paulo State Research Foundation (FAPESP, Brazil) (Grant 2011/19982-2) for its financial support.Azevedo De Carvalho, LR.; Sallica-Leva, E.; Rayón Encinas, E.; Fogagnolo, JB. (2018). Less-rigid coating in Ti obtained by laser surface alloying with Nb. Surface and Coatings Technology. 346:19-28. https://doi.org/10.1016/j.surfcoat.2018.04.038S192834

Correlation between magnetic interactions and domain structure in A1 FePt ferromagnetic thin films

We have investigated the relationship between the domain structure and the magnetic interactions in a series of FePt ferromagnetic thin films of varying thickness. As-made films grow in the magnetically soft and chemically disordered A1 phase that may have two distinct domain structures. Above a critical thickness $d_{cr}\sim 30$ nm the presence of an out of plane anisotropy induces the formation of stripes, while for $d<d_{cr}$ planar domains occur. Magnetic interactions have been characterized using the well known DCD-IRM remanence protocols, $\delta M$ plots, and magnetic viscosity measurements. We have observed a strong correlation between the domain configuration and the sign of the magnetic interactions. Planar domains are associated with positive exchange-like interactions, while stripe domains have a strong negative dipolar-like contribution. In this last case we have found a close correlation between the interaction parameter and the surface dipolar energy of the stripe domain structure. Using time dependent magnetic viscosity measurements, we have also estimated an average activation volume for magnetic reversal, $\langle V_{ac}\rangle \sim 1.37\times 10^{4}$ nm$^{3},$ which is approximately independent of the film thickness or the stripe period.Comment: 25 pages, 11 figure

Ti-6Al-4V triply periodic minimal surface structures for bone implants fabricated via selective laser melting

PublishedJournal ArticleResearch Support, Non-U.S. Gov'tTriply periodic minimal surface (TPMS) structures have already been shown to be a versatile source of biomorphic scaffold designs. Therefore, in this work, Ti-6Al-4V Gyroid and Diamond TPMS lattices having an interconnected high porosity of 80-95% and pore sizes in the range of 560-1600 μm and 480-1450 μm respectively were manufactured by selective laser melting (SLM) for bone implants. The manufacturability, microstructure and mechanical properties of the Ti-6Al-4V TPMS lattices were evaluated. Comparison between 3D micro-CT reconstructed models and original CAD models of the Ti-6Al-4V TPMS lattices shows excellent reproduction of the designs. The as-built Ti-6Al-4V struts exhibit the microstructure of columnar grains filled with very fine and orthogonally oriented α' martensitic laths with the width of 100-300 nm and have the microhardness of 4.01 ± 0.34 GPa. After heat treatment at 680°C for 4h, the α' martensite was converted to a mixture of α and β, in which the α phase being the dominant fraction is present as fine laths with the width of 500-800 nm and separated by a small amount of narrow, interphase regions of dark β phase. Also, the microhardness is decreased to 3.71 ± 0.35 GPa due to the coarsening of the microstructure. The 80-95% porosity TPMS lattices exhibit a comparable porosity with trabecular bone, and the modulus is in the range of 0.12-1.25 GPa and thus can be adjusted to the modulus of trabecular bone. At the same range of porosity of 5-10%, the moduli of cortical bone and of the Ti-6Al-4V TPMS lattices are in a similar range. Therefore, the modulus and porosity of Ti-6Al-4V TPMS lattices can be tailored to the levels of human bones and thus reduce or avoid "stress shielding" and increase longevity of implants. Due to the biomorphic designs, and high interconnected porosity and stiffness comparable to human bones, SLM-made Ti-6Al-4V TPMS lattices can be a promising material for load bearing bone implants.This work is supported by the UK Technology Strategy Board (TSB) funded project(TP14/BA036D) entitled “SAVING – Sustainable product development via design optimisation and AdditiVe manufacturing”, National Natural Science Foundation of China (Grant no. 51375188 and 51375189) and the Guangdong Innovative and Entrepreneurial Research Team Program (No. 2013C071)

A finite element model for the thermo-elastic analysis of functionally graded porous nanobeams

In this study, for the first time, a nonlocal finite element model is proposed to analyse thermo-elastic behaviour of imperfect functionally graded porous nanobeams (P-FG) on the basis of nonlocal elasticity theory and employing a double-parameter elastic foundation. Temperature-dependent material properties are considered for the P-FG nanobeam, which are assumed to change continuously through the thickness based on the power-law form. The size effects are incorporated in the framework of the nonlocal elasticity theory of Eringen. The equations of motion are achieved based on first-order shear deformation beam theory through Hamilton's principle. Based on the obtained numerical results, it is observed that the proposed beam element can provide accurate buckling and frequency results for the P-FG nanobeams as compared with some benchmark results in the literature. The detailed variational and finite element procedure are presented and numerical examinations are performed. A parametric study is performed to investigate the influence of several parameters such as porosity volume fraction, porosity distribution, thermal loading, material graduation, nonlocal parameter, slenderness ratio and elastic foundation stiffness on the critical buckling temperature and the nondimensional fundamental frequencies of the P-FG nanobeams. Based on the results of this study, a porous FG nanobeam has a higher thermal buckling resistance and natural frequency compared to a perfect FG nanobeam. Also, uniform distributions of porosity result in greater critical buckling temperatures and vibration frequencies, in comparison with functional distributions of porosities

Additive manufacturing: unlocking the evolution of energy materials

The global energy infrastructure is undergoing a drastic transformation towards renewable energy, posing huge challenges on the energy materials research, development and manufacturing. Additive manufacturing has shown its promise to change the way how future energy system can be designed and delivered. It offers capability in manufacturing complex 3D structures, with near-complete design freedom and high sustainability due to minimal use of materials and toxic chemicals. Recent literatures have reported that additive manufacturing could unlock the evolution of energy materials and chemistries with unprecedented performance in the way that could never be achieved by conventional manufacturing techniques. This comprehensive review will fill the gap in communicating on recent breakthroughs in additive manufacturing for energy material and device applications. It will underpin the discoveries on what 3D functional energy structures can be created without design constraints, which bespoke energy materials could be additively manufactured with customised solutions, and how the additively manufactured devices could be integrated into energy systems. This review will also highlight emerging and important applications in energy additive manufacturing, including fuel cells, batteries, hydrogen, solar cell as well as carbon capture and storage

Open Celled Porous Titanium

Among the porous metals, those made of titanium attract particular attention due to the interesting properties of this element. This review examines the state of research understanding and technological development of these materials, in terms of processing capability, resultant structure and properties, and the most advanced applications under development. The impact of the rise of additive manufacturing techniques on these materials is discussed, along with the likely future directions required for these materials to find practical applications on a large scale

The use of laser surface modification to obtain hardness and stiffness gradients in titanium parts

Orientador: João Batista FogagnoloTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: O titânio e suas ligas apresentam propriedades interessantes do ponto de vista tecnológico, tais como alta razão resistência/peso, alta resistência à corrosão, baixo módulo de elasticidade e boa biocompatibilidade, motivos pelos quais são muito empregados na fabricação de implantes ortopédicos, cujas falhas são frequentemente devidas à ação conjunta de fenômenos de fadiga, corrosão e desgaste. Assim, visando aumentar o desempenho em relação a tais fenômenos, modificações superficiais são realizadas em componentes de titânio e suas ligas. Muitos dos esforços realizados nessa área relatam modificações superficiais em titânio e suas ligas que visam aumentar a resistência ao desgaste e à corrosão, enquanto que outros se focam em metodologias para aumento da resistência à fadiga. No entanto, a grande maioria das alternativas disponíveis para aumentar a resistência ao desgaste e à corrosão são contraproducentes em relação à resistência à fadiga. A obtenção de revestimentos em componentes de titânio com menor módulo de elasticidade e maior dureza pode vir a atender à necessidade de aumento da resistência à fadiga conjuntamente com aumento da resistência ao desgaste ou à corrosão. Neste contexto, este trabalho tem por objetivo o estudo do processo de obtenção de ligas na superfície a laser com camada de pó pré-depositada, viabilizando a adição de elementos biocompatíveis e estabilizadores de fases de menor módulo de elasticidade. Por meio do controle dos parâmetros de processo, objetiva-se introduzir elementos de liga betagênicos, em quantidade suficiente para estabilizar as fases ? e/ou ?¿¿ do titânio. Inicialmente, estudou-se alternativas de processamento sob condições de maior controle da atmosfera de processamento, visando diminuir a contaminação do revestimento por oxigênio e nitrogênio. Foram obtidos cordões individuais da liga Ti-Nb sobre substrato de titânio comercialmente puro, nos quais, dependendo das condições de processo, foram obtidas fases com menor módulo de elasticidade, com significativo aumento de dureza em relação ao substrato, e isentos de fases formadas devido a contaminação por oxigênio e nitrogênio. Em um equipamento especialmente construído para esse fim, fez-se um estudo mais detalhado da influência dos parâmetros de processo, como potência do laser, composição e espessura da camada de pó pré-depositada, sobre as características morfológicas, estruturais e microestruturais e a consequente alteração do módulo de elasticidade e dureza do revestimento. Observou-se as diferentes relações entre os parâmetros de processo com características como o teor do elemento de liga introduzido na zona de fusão, necessário para a estabilização das fases com menor módulo de elasticidade. Foi possível a obtenção de revestimentos com módulo de elasticidade cerca de 30% menores que o do substrato e aumentos de dureza em torno a 100%, comprovando a capacidade da técnica de produzir componentes com gradientes de módulo de elasticidade e durezaAbstract: Titanium and its alloys have interesting properties from a technological point of view, such as high strength-to-weight ratio, high corrosion resistance, low Young¿s modulus and good biocompatibility, what make them useful in the manufacturing of orthopedic implants, whose failures are often due to jointed action of fatigue, corrosion and wear phenomena. Thus, to increase their performance in these phenomena, surface modifications are realized in titanium components and their alloys. Many of the efforts in the surface modification area of titanium and its alloys are aimed to increase wear and corrosion resistance, whereas others focus on methods to increase the fatigue strength. However, most of the alternatives available to increase to wear and corrosion resistance are counterproductive with respect to the fatigue strength. Surface coating of titanium components with higher hardness and lower Young¿s modulus may come to meet higher fatigue strength with increased wear and corrosion resistance. In this context, this work aims to study the laser surface alloying with preplaced powder technique, enabling the addition of biocompatible elements, which should be stabilizers of lower Young¿s modulus phases. By controlling the process parameters, a suitable amount of betagenic alloying element, enough to stabilize the ? and / or ?'' phases, was introduced. Initially, the use of alternatives for greater control of the processing atmosphere were tried in order to reduce contamination of the modified layer by oxygen and nitrogen. Depending on the process parameters, less-rigid phases relative to the substrate were obtained, free of phases formed due to contamination of oxygen and nitrogen. In an especially equipment constructed for this purpose, a more detailed study of the influence of process parameters was made, such as laser power, composition and thickness of the pre-deposited layer of powder on morphological, structural and microstructural characteristics and the consequent changing in Young¿s modulus and hardness of the modified layer. It was observed different relationships between process parameters and features such as the alloy content introduced into the fusion zone. It was obtained a coating with Young¿s modulus about 30% lower and hardness about 100% higher than that of the substrate, demonstrating the ability of laser surface alloying to produce components with gradients of Young¿s modulus and hardnessDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânica33003017CAPE