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Additive Manufacturing of Metals Using Powder Bed-Based Technologies
Published in Amit Bandyopadhyay, Susmita Bose, Additive Manufacturing, 2019
M. J. Mirzaali, F. S. L. Bobbert, Y. Li, A. A. Zadpoor
Post-AM heat-treatment processes could be used to modify the microstructure of SLM Ti-6Al-4V alloy [147]. Heat treatments at temperatures higher than the β transus temperature can result in a more homogeneous structure at the macro level. Full annealing at temperatures of >850°C has been recommended for SLM Ti-6Al-4V to increase its fracture strain and ductility [147]. In most cases, the mechanical properties of AM Ti-6Al-4V are higher than those of wrought titanium alloys while exhibiting lower ductility. Moreover, slight anisotropies in the yield and tensile strengths related to the build directions have been reported [141]. Adding other (biocompatible) elements (e.g., Ta, Nb, Zr, Mo) can result in lower values of the elastic modulus as compared to Ti-6Al-4V, as these elements are often β-stabilizing elements [122,148]. The examples of these Ti-based alloys with improved biocompatibility are Ti-6Al-7Nb [149] and Ti-24Nb-4Zr-8Sn [150].
Overview of Pulsed Electron Beam Treatment of Light Metals
Published in T. S. Srivatsan, T. S. Sudarshan, K. Manigandan, Manufacturing Techniques for Materials, 2018
Subramanian Jayalakshmi, Ramachandra Arvind Singh, Sergey Konovalov, Xizhang Chen, T. S. Srivatsan
Similar to the Ti–6Al–4V alloy, the Ti–6Al–7Nb alloy is a preferred choice as a bio-implant material for purpose of dental implants and orthopedic implants (Challa et al. 2013). In a study on the Ti–6Al–7Nb alloy, PEB treatment was conducted with the primary intent of improving the surface characteristics while concurrently understanding the corrosion behavior (Kim and Park 2015). For an energy density of 7 to 10 J/cm2 and an anode-target distance of 30 mm, the surfaces were irradiated with PEB treatment (Kim and Park 2015). The process parameters did play an important role in determining the surface characteristics as was evident from the depth of the resolidified layer following PEB treatment (Figure 11.34) (Kim and Park 2015). Potentio-dynamic polarization behavior in an aqueous solution of sodium chloride (NaCl) revealed the PEB-treated alloy to exhibit excellent corrosion resistance (a more noble corrosion potential, low corrosion current density and a high polarisation resistance) when compared to the untreated alloy (Figure 11.35) (Kim and Park 2015). The formation of re-passivation (protective) surface layer coupled with an increase in surface hydrophobicity (Figure 11.36), as determined by measurement of wettability (contact angle), were considered to be the key reasons for the improved corrosion resistance of the PEB-treated alloy (Kim and Park 2015).
Phenomena of tribocorrosion in medical and industrial sectors
Published in J.-P. Celis, P. Ponthiaux, Testing tribocorrosion of passivating materials supporting research and industrial innovation: Handbook, 2017
Titanium alloys: The excellent corrosion resistance of titanium alloys results from the formation of very stable, continuous, highly adherent, and protective oxide films on metal surfaces. Because titanium metal itself is highly reactive and has an extremely high affinity for oxygen, these beneficial surface oxide films form spontaneously and instantly when fresh metal surfaces are exposed to air and/or moisture. In fact, a damaged oxide film can generally form itself instantaneously if at least traces (that is, parts per million) of oxygen or water (moisture) are present in the environment. However, anhydrous conditions in the absence of a source of oxygen may result in titanium corrosion, because the protective film may not be regenerated if damaged. The nature, composition, and thickness of the protective surface oxides that form on titanium alloys depend on environmental conditions. In most aqueous environments, the oxide is typically TiO2, but may consist of mixtures of other titanium oxides including TiO2, Ti2O3, and TiO. Titanium (cp-Ti, ASTM F-67) and its alloys typically used in biomedical applications (Ti-6Al-4V, ASTM F-136-02a and Ti-6Al-7Nb, ASTM F-1295-05) can be considered as the most corrosion-resistant of the alloys described here. This is based on the very high stability of the TiO2 passive film that forms spontaneously on the alloy surface [21].
Review on effect of Ti-alloy processing techniques on surface-integrity for biomedical application
Published in Materials and Manufacturing Processes, 2020
Numerous research work established that V is more toxic when compared to alternate implant materials like Ni and Cr. Therefore, V was replaced with Nb in Ti-6Al-4 V, and a new Ti-6Al-7Nb alloy was formed. (Cui et al.[17]) performed a tensile test for Ti–6Al–7Nb alloy and its mechanical properties were identified by a detailed analysis of hot compression tests. When Ti–6Al–7Nb alloy was hot deformed in 750–850° C, dynamic recrystallization of phase occurred with a strain rate of less than 1 s−1.Ti–6Al–7Nb possesses excellent deformability and higher resistance to flow (Lee et al.[18]). However, recent findings show that Al pose potential neurological toxicity. With rising levels of Al in the lungs, severe damage is bound to occur (Luo et al.[19], Albrektsson et al.[20]). Currently, Ti alloy with different chemical compositions are being explored that have low toxicity, long-term stability, lower elastic modulus, and high strength that matches the human bone (Frosch et al.[21], Bomba et al.[22], Golosova et al.[23]). With the development of new Ti alloys, there is a need to test the mechanical and biological properties in order to prove their adaptability in the human body (Kalebo et al.[24]). A Bone Harvest Chamber model was developed to predict the rate of bone formation. It was found that the environment for regeneration of bone in an osseointegrated Ti implant is superlative.
Influence of cutting conditions on surface characteristics in micro-milling of Ti-6Al-7Nb alloy
Published in Materials and Manufacturing Processes, 2019
Ti-6Al-7Nb alloy used in this investigation is a specific alloy for medical implant fabrication. It possesses α/β structure and mechanical properties similar to Ti-6Al-4V. ‘V’ in Ti-6Al-4V is toxic and it is replaced with ‘Nb’ in Ti-6Al-7Nb alloy. Implants including knee, hip and dental are manufactured using Ti-Nb-based alloy. Table 1 shows the chemical composition. Workpiece of size 50 X 50 X 3 mm is used for experimentation.
A novel study on mechanically alloyed nanocrystalline Ti-6Al-4V alloy fabricated by spark plasma sintering
Published in Powder Metallurgy, 2021
Showkat Ali, R. Karunanithi, M. Prashanth, S. Sivasankaran
In the past decades and currently, Ti and Ti-based alloys are being used conventionally in various applications, namely, military, aerospace, high-temperature parts in space, automotive and structural industries. Titanium alloys are normally applied in biomedical parts due to outstanding properties (lower in density and thermal conductivity, higher in mechanical properties and more in corrosion resistance) [1]. Among several titanium alloys, Ti-6Al-7Nb is mainly used in biomedical implant parts [2]. Several manufacturing routes are available to fabricate the parts from Titanium alloys in which the conventional casting method followed thermomechanical methods (hot working like rolling, extrusion, forging) are common ones [3]. However, the formation of impurities, unwanted intermetallic phases, more processing time are the major shortfalls in these methods. Powder metallurgy (P/M) techniques can be the best choice to eliminate the drawback obtained from the conventional thermomechanical processing route [4]. Net shape via P/M route followed by isothermal forging in Ti-based alloys can be easily achieved due to superplastic characteristics at elevated temperature [4,5]. Nanocrystalline/ultrafine-crystalline nature of Ti-based alloys can give extensive mechanical properties compared to the coarse crystalline range [6]. Several studies have reported that nanocrystalline/ultrafine-crystalline nature in the materials can vary the mechanical, thermal and magnetic properties considerably [7]. Manufacturing of Ni, Al, Cu and Fe based nanostructured materials have been explored due to the attainment of several benefits [8]. In addition, some researchers have focused on synthesise nanostructured Ti-based alloys to enhance the mechanical properties [9,10]. Mechanical alloying (MA) is the best and cost-effective method (solid-state processing P/M route) to produce nanostructured powders [11] which is one of the high-energy ball milling (HEBM) techniques. Previously, the MA was used to synthesise dispersion hardened (i.e. reinforcement of ceramic powders over ductile matrix) matrix material [12], intermetallic compounds [13], quasicrystalline and amorphous materials [14,15]. Based on literature and the author’s best of knowledge, still more work is to be investigated on nanocrystalline Ti-6Al-4V alloy. The main objectives of the present research works are: to synthesise nanocrystalline Ti-6Al-4V alloy powders using MA with different milling times (0, 20, 40, 60, 80, 100 and 120 h (h)), to consolidate the powders by spark plasma sintering (SPS), to examine the various structural parameters such as crystalline size, lattice strain, dislocation density, lattice parameter and stacking fault probability using XRD, to study the structural properties developed Ti-6Al-4V nanocrystalline alloy using several models namely uniform deformation model (UDM) and uniform stress distribution (USDM) model, to examine the powders surface morphology using advanced electron microscopes (HRSEM, and HRTEM), physical and flow properties, and to investigate the mechanical performance of Ti-6Al-4V alloy (hardness, compressive strength and flexural strength).