Ti-Nb alloys are excellent candidates for biomedical applications such as implantology and joint replacement because of their very low elastic modulus, their excellent biocompatibility and their high strength. A low elastic modulus, close to that of the cortical bone minimizes the stress shielding effect that appears subsequent to the insertion of an implant. The objective of this study is to investigate the microstructural and mechanical properties of a Ti-Nb alloy elaborated by selective laser melting on powder bed of a mixture of Ti and Nb elemental powders (26 at.%). The influence of operating parameters on porosity of manufactured samples and on efficacy of dissolving Nb particles in Ti was studied. The results obtained by optical microscopy, SEM analysis and X-ray microtomography show that the laser energy has a significant effect on the compactness and homogeneity of the manufactured parts. Homogeneous and compact samples were obtained for high energy levels. Microstructure of these samples has been further characterized. Their mechanical properties were assessed by ultrasonic measures and the Young's modulus found is close to that of classically elaborated Ti-26 Nbingot.
To cite this version:A. Ramarolahy, Philippe Castany, F. Prima, P. Laheurte, Isabelle Péron, et al.. Microstructure and mechanical behavior of superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N biomedical alloys.Journal
AbstractIn this study, the microstructure and the mechanical properties of two new biocompatible superelastic alloys, Ti-24Nb-0.5O and Ti-24Nb-0.5N (at.%), were investigated. Special attention was focused on the role of O and N addition on α ″ formation, supereleastic recovery and mechanical strength by comparison with the Ti-24Nb and Ti-26Nb (at.%) alloy compositions taken as references. Microstructures were characterized by optical microscopy, X-ray diffraction and transmission electron microscopy before and after deformation. The mechanical properties and the superelastic behavior were evaluated by conventional and cyclic tensile tests. High tensile strength, low Young's modulus, rather high superelastic recovery and excellent ductility were observed for both superelastic Ti-24Nb-0.5O and Ti24Nb-0.5N alloys. Deformation twinning was shown to accommodate the plastic deformation in these alloys and only the {332} 113 twinning system was observed to be activated by electron backscattered diffraction analyses.
Although mechanical stress is known as being a significant factor in bone remodeling, most implants are still made using materials that have a higher elastic stiffness than that of bones.Load transfer between the implant and the surrounding bones is much detrimental, and osteoporosis is often a consequence of such mechanical mismatch. The concept of mechanical biocompatibility has now been considered for more than a decade. However, it is limited by the choice of materials, mainly Ti-based alloys whose elastic properties are still too far from cortical bone. We have suggested using a bulk material in relation with the development of a new beta titanium-based alloy. Titanium is a much suitable biocompatible metal, and betatitanium alloys such as metastable TiNb exhibit a very low apparent elastic modulus related to the presence of an orthorhombic martensite. The purpose of the present work has been to investigate the interaction that occurs between the dental implants and the cortical bone. 3D finite element models have been adopted to analyze the behaviour of the bone-implant system depending on the elastic properties of the implant, different types of implant geometry, friction force, and loading condition. The geometry of the bone has been adopted from a mandibular incisor and the surrounding bone. Occlusal static forces have been applied to the implants, and their effects on the bone-metal implant interface region have been assessed and 2 compared with a cortical bone/ bone implant configuration. This work has shown that the low modulus implant induces a stress distribution closer to the actual physiological phenomenon, together with a better stress jump along the bone implant interface, regardless of the implant design.Keywords: Dental biomechanics, Beta titanium alloy, Low modulus implant, Numerical modelling, Bone-implant interface
IntroductionOver the last few decades, considerable progress in dental implantology has been made, with success rates exceeding 95% [1]. Implant stability is commonly considered as playing a major role in a successful osseointegration. Obtaining post-operative osseointegration is necessary in order to establish a solid and durable connection between the implant and the osseous structure. In agreement with the Wolff law, a process of osseous remodelling adapted to the stress level occurs after implantation [2][3][4]. This process is controlled by mechanical loads.When the occlusal forces induced on the bone exceed a physiological level, bone resorption can occur, with possible failure [5]. More importantly, the long-term performance of an implant is known to be strongly dependent on the bone tissue interaction [6]. The strain state which takes place at the interface between the bone and implant controls the bone tissue remodelling mechanisms [7]. Bone resorption is associated with a low strain state, and bone necrosis occurs when strain exceeds the maximum level.Evaluation of the risk requires a comprehension of the load transfer along the bone-dental implant interface. T...
In this study, the potential of microporous 3D metal-organic framework (MOF) for curing epoxy resin has been discussed. First, MIL-101 (Cr), a chromium based MOF, was synthesized under hydrothermal condition and then characterized by using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric (TGA) measurements. Epoxy nanocomposites containing 0.1, 0.3 and 0.5 wt.% of MOF nanocrystals were subsequently prepared and their curability was studied in terms of the universal dimensionless Cure Index (CI) criterion under nonisothermal differential scanning calorimetry (DSC). Based on calculations made on the basis of the CI, epoxy nanocomposites containing 0.1, 0.3, and 0.5 wt.% of MOF were labeled Good and Excellent thanks to an enhanced chemical interaction between MOF and epoxy matrix, where the heat of cure in the system was surprisingly even higher than that of the neat epoxy. It was demonstrated that introduction of MOF into epoxy significantly improved the heat release during crosslinking process of epoxy, as indicated by a 63% rise in the enthalpy of cure at MOF loading of 0.1 wt.%. Addition of thermally stable MOF nanomaterials to the epoxy resin improved thermal decomposition resistance of epoxy. Up to 0.3 wt.% loading, the system revealed acceptable thermal stability at elevated temperature featured by more residue remained at the end of test, while sample containing 0.5 wt.% MOF resisted against decomposition at early stages of degradation due to higher thermal stability of MOF with respect to epoxy resin.
Mechanisms of superelasticity were investigated by in situ cyclic tensile tests performed under synchrotron X-ray radiation on Ti-24Nb-0.5N and Ti-24Nb-0.5O compositions of metastable b titanium alloys. Analyses of diffraction patterns acquired under load and after unloading for each cycle were used to determine the characteristics of the potential mechanisms of deformation in both alloys. The Ti-24Nb-0.5N alloy exhibits the conventional behavior of superelastic b titanium alloys. Synchrotron X-ray diffraction (SXRD) experiments proved that superelasticity is exclusively due to the occurrence of a stress-induced martensitic (SIM) transformation from the b phase to the a 00 phase. The evolution of volume fraction of a 00 martensite corresponds exactly to the variation of the recovery strain of the cyclic tensile curve. Conversely, the Ti-24Nb-0.5O alloy displays a nonconventional behavior. SXRD experiments showed a huge ability of the b phase to deform elastically until 2.1%. Surprisingly, a reversible SIM transformation also occurs in this alloy but starts after 1% of applied strain that corresponds to the yield point of the stress-strain curve. Although the SIM transformation occurs, the b phase simultaneously continues to deform elastically. The superelasticity of this alloy is unexpectedly due to a combination of a high elastic deformability of the b phase and a reversible SIM transformation. In both alloys, the lattice parameters of the a 00 martensite evolve similarly in accordance with the initial texture of the b phase and the crystallography of the transformation.
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