Conventional Titanium Alloys Research Articles

Overcoming strength-ductility trade-off by hybridising different classes of titanium alloys

Two types of HYbrid Titanium Alloys (HYTAs) were created using laser powder bed fusion (LPBF): a ternary HYTA composed of α commercially pure (CP) Ti, α-β Ti-64, and β Ti-5553, and a binary HYTA made of α CP Ti and β Ti-5553. The resulting microstructures were highly heterogeneous, incorporating all possible phases and structures, which do not co-exist in traditional monolithic titanium alloys. Detailed characterisation of the intricate microstructures revealed the significant influences of several factors including the distribution of alloy particles, Marangoni convection and solute diffusion during melting, and solute microsegregation during solidification. Despite the different combinations of ingredient powders, the ternary and binary HYTAs exhibited nearly identical tensile properties, with a remarkable combination of high yield strength (1000 MPa) and enhanced ductility (uniform elongation of ∼15% and total elongation of ∼20%), surpassing various conventional titanium alloys. Both HYTAs exhibited highly heterogeneous microstructures and displayed effective coordination of major mechanisms enabling smooth transfer of deformation between regions with a wide range of hardness (4–6 GPa), leading to their exceptional performance. This outcome further demonstrates the potential of microstructure hybridisation as an innovative strategy for future alloy development.

A strategy for designing Ti-based in-situ bulk metallic glass composites with tailored structural metastability using conventional titanium alloys

The metastability of the dendritic phase is crucial in determining the mechanical properties and mechanisms of the Ti-based in-situ dendrite-reinforced bulk metallic glass composites (BMGCs). However, tailoring the metastability effectively remains challenging. In this study, we propose a straightforward and effective strategy to tailor the dendrites composition and metastability using conventional Titanium alloys. Initially, six common Titanium alloys with increasing content of β-stabilizing elements such as Ti, Ti–6Al–4V, Ti–13Nb–13Zr, Ti–15Mo, Ti–12Mo–6Zr–2Fe and Ti-4.5Fe-6.8Mo-1.5Al were selected. Subsequently, a series of in-situ dendrite-reinforced BMGCs denoted as T1-T6 were designed by alloying these Titanium alloys with a specific amorphous alloy. It was found that the microstructure, stability and mechanical behaviors of these composites change significantly as the content of β-stabilizing elements in the dendritic phase increases monotonically. Based on their microstructure and mechanical behaviors, these composites can be classified into three categories: T1, T2 and T3, T4-T6. The T1 alloy exhibits brittle deformation characteristics due to the significantly higher elastic modulus of the dendritic phase. In contrast, the T2 and T3 alloys demonstrate good tensile plasticity and remarkable work-hardening ability, attributed to the metastable β phase undergoing stress-induced phase transformation during deformation. On the other hand, the T4-T6 alloys, consisting of stable β phase, deform via dislocation slip, resulting in a higher yielding stress and compression plasticity. The composition design strategy presented in this study, along with the correlation between mechanical behaviors and dendrite stability, may offer a novel perspective for the development of Ti-based in-situ dendrite-reinforced BMGCs.

Additive manufacturing of a new titanium alloy with tunable microstructure and isotropic properties

Conventional titanium alloys have a high propensity in developing columnar grains with strong textures during additive manufacturing (AM), which causes pronounced anisotropy in mechanical properties and hampers their practical applications. In this study, a new metastable β titanium alloy with high Fe addition (Ti-3Al-6Fe-6V-2Zr, wt.%) was designed for AM, and the strategies and underlying mechanisms to eliminating the structural heterogeneity including grain morphology, Fe element segregation and phase constituent distribution were elaborately investigated. It was demonstrated that the alloy has an outstanding intrinsic capability of forming equiaxed grains during direct energy deposition (DED) due to the positive effect of Fe on constitutional supercooling. The final microstructure of bulk sample was determined by the directly deposited microstructure and subsequent microstructure coarsening caused by cyclic heating, and homogeneously equiaxed microstructure without texture could be achieved when the heat-affected zones can fully cover the formerly deposited layer. Despite of very high level of Fe addition, both microscale and macroscale Fe segregation were completely suppressed during DED, by taking the advantages of fast solidification rate and tailoring the heating effect between the adjacent layers. Moreover, the problem related to the heterogeneity in α phase distribution along the building direction was solved by mitigating the heat accumulation during DED. On the basis of these understandings, homogeneously equiaxed Ti3662 alloy with isotropic mechanical properties of high strength (~1200MPa) and decent ductility (~10%) was finally fabricated by DED, which stands a good chance for practical application. This study demonstrates that the special metallurgical process during AM largely expands the design space of titanium alloys on the aspects of composition and microstructure, which can be utilized to fabricate titanium alloys with desirable microstructure and excellent properties.

Porous titanium alloys for medical application: Progress in preparation process and surface modification research

Excellent mechanical properties and biocompatibility are the most sought-after attributes in biomedical materials for the regeneration of damaged tissues. However, conventional dense titanium alloys possess a modulus significantly higher than that of human tissues, leading to potential stress-shielding effects. Medical porous titanium alloys can reduce the elastic modulus of the material, promote tissue fixation and vascular regeneration, and improve the suitability for human tissue properties. With the continuous development of technology, the preparation process of porous titanium alloys has undergone a series of multifaceted transformations and improvements in the aspects of powder sintering, fiber preparation, and additive manufacturing processes, and its structural characteristics and mechanical properties are constantly evolving in a controllable direction. Alongside the enhancement of the material’s mechanical properties through porous design, optimization of the properties at the implant-tissue interface also leads to improved antimicrobial and osteogenic properties of porous titanium. Due to the complex internal structure of porous titanium alloys, surface modification is mainly carried out in fluid media, which is realized by morphological modification and the introduction of functional substances. Over time, the surface modification of porous titanium alloys for medical applications has progressed from morphological modification and introduction of chemical composition to the loading of bioactive substances. This evolution aims to enhance safety and efficiency in the use of these materials. This paper reviews the preparation and surface modification processes of porous titanium alloys for medical use and summarizes the advantages, disadvantages, and influencing factors among different processes, with a view to providing new ideas for the development of porous implants for medical use.

Effects of He-ion irradiation on microstructures of low activation Ti-Ta-V alloy from atomic simulations and irradiation experiments

Most conventional titanium alloys contain nuclides with long half-lives, which is not conductive to material recovery after decommissioning. To recover components from post-service reactors safely and effectively, it is necessary to use materials with low activation and rapid induction of radioactive decay. In this work, a low-activation α-titanium alloy Ti-5Ta-1.6 V was prepared and irradiated with 80 keV helium ions to 6.8 dpa at room temperature. The mechanical properties and irradiation swelling properties of Ti-5Ta-1.6 V alloy were mainly investigated. The results showed that compared with the commercially pure titanium alloy (CP-Ti), the mechanical properties of Ti-5Ta-1.6 V were substantially improved. After ion irradiation, the irradiation swelling rate of Ti-5Ta-1.6 V (in mass ratio) was found to be significantly lower than that of CP-Ti by atomic force microscopy (AFM) technology. Molecular dynamic (MD) simulations were used to study the irradiation behavior and cascade collisions process, and the Ti-5Ta-1.6 V produced a small number of stable defects with cluster size and number density, which is consistent with the results of irradiation experiments. The results indicate that Ti-5Ta-1.6 V is expected to be a promising new titanium alloy for nuclear applications, which provides a new idea for the selection and optimization of low-activation and radiation-resistant nuclear materials.

Designing ultra-strong and ductile hierarchical titanium alloys via interstitial solute-mediated multi-morphologic α-nanoprecipitates

In conventional duplex titanium (Ti) alloys, the soft primary α-precipitates (αp) are beneficial to ductility with the loss of high yield strength, while the continuous α-precipitates at grain boundaries (GBs, αGBs) often accompanied with α precipitate-free zones (α-PFZs) renders the strain incompatibility for limited ductility. Here, to overcome this longstanding issue, we utilize interstitial (O and N) atoms to notably strengthen the α-phase, and simultaneously architect the multi-morphologic secondary α-precipitates (αs) so as to improve the strain compatibility nearby GBs, thus develop a Ti-4.1Al-2.5Zr-2.5Cr-6.8Mo (wt.%) alloy with ultra-high yield strength of ∼1580 MPa and good ductility of ∼8.2%. The phase boundaries between the hard α-precipitates and the soft β-matrix not only act as dislocation barriers for strengthening, but also as sustainable dislocation sources for ductilizing to achieve a good combination of strength and ductility in our Ti alloys. This strategy not only sheds light on the understanding of the strength-ductility synergy of duplex Ti alloys, but also offers an available pathway to design ultra-strong and ductile alloys.

The corrosion behavior of TA1 and TC4 in Proton Exchange Membrane Water Electrolyzers

Titanium Bipolar Plates (BPPs) are frequently utilized in Proton Exchange Membrane Water Electrolyzers (PEMWE) nowadays since they could endure the challenging working environment. Notably, the extreme anodic potential and acidic environment of the PEMWE are extremely critical for BPPs’ performances. In this study, we explored the corrosion behaviors of conventional titanium alloys of TA1 and Ti-6Al-4V (TC4) at simulated operating conditions. To evaluate their corrosion behaviors, potentiodynamic polarization, electrochemical impedance spectroscopy, and potentiation, polarization experiments were executed. Additionally, scanning electron microscopy (SEM) was applied to detect the morphologies before and after the electrochemical measurements. Finally, the corrosion mechanisms of TA1 and TC4 were analyzed and discussed by X-ray photoelectron spectroscopy (XPS). After 7 days of potentiostatic polarization, the corrosion current density of TA1 remained at 3×10−8 A·cm−2, which was nearly one order of magnitude lower than that of TC4. These experimental data confirmed that the TA1 alloy had superior corrosion resistance to the TC4 alloy during long-term running in PEMWE operating conditions.

Insights into Phase Evolution and Mechanical Behavior of the Eutectoid Ti–6.4(wt%)Ni Alloy Modified with Fe and Cr

Titanium alloys gain increasing importance in industry due to the expansion of advanced manufacturing technologies such as additive manufacturing. Conventional titanium alloys processed by such technologies suffer from formation of large primary grains and anisotropy of mechanical properties. Therefore, novel alloys are required. Herein, the effect of ternary alloying elements Fe and Cr on the Ti–6.4(wt%)Ni eutectoid system is investigated. Both elements act as eutectoid formers. Fe and Cr show sluggish transformation behavior, whereas Ni is an active eutectoid‐forming element. Thereby, sluggish refers to slow and active to fast transformation kinetics. The focus of this work is on the combined addition of such elements studied under different heat‐treatment conditions. It is shown in the results that largely varying microstructures can be generated resulting in hardness values ranging from 239 to 556 HV0.1. Moreover, the formation of a substructure within the α phase of direct aged alloys is observed. The formation mechanism of this substructure is investigated in detail. The mechanical properties are discussed based on the microstructural characteristics. The presence of intermetallic Ti2Ni phase increases the Young's modulus, whereas the presence of ω phase results in embrittlement. The results shed light upon the complex phase formation and decomposition behavior of titanium alloys based on Ti–6.4Ni.

Micromechanics-Based Thermo-Mechanical Simulation of SCS-6 Fiber-Reinforced Ti-6Al-7Nb Matrix Nanocomposite

This paper uses a sequential micromechanical method to characterize the thermomechanical properties of a hybrid nanocomposite. It does this by using analytical models (such as the modified rule of mixtures, Tsai-Pagano model, and Schapery model) and numerical models (such as the Finite element model), which are modeled using the commercial software ABAQUS. Investigations are made to determine how the aspect ratio, waviness, and volume fractions of the reinforcement affect the thermo-mechanical performance of the hybrid nanocomposite. It has been shown that adding CNT ESFs to conventional SiC-reinforced titanium alloy composites (TMCs) improves the resulting HTMNC thermo-mechanical properties. It is found that the addition of CNT ESFs to TMCs improves the thermo-mechanical characteristics of the resulting hybrid nanocomposite (i.e., HTMNCs) more in the transverse direction than in the axial direction for all volume fractions of SiC fiber. For instance, it is observed that adding a 2.69% volume fraction of CNT ESFs to the TMCs with a 30% volume fraction of SiC fiber enhances the axial elastic modulus by 2.6% and 2.4% while increasing the transverse elastic modulus by 4.2% and 3.5%, based on the CNT ESFs are straight and wavy. On the other hand, for the same volume fraction of SiC fiber and the addition of 2.69% volume fraction of Straight CNT ESFs, the transverse and axial CTE of the HTMNCs are reduced by 5.33% and 2.53%, respectively. Moreover, when the SiC fiber aspect ratio increases, the axial elastic modulus increases while the transverse elastic modulus exhibits no change. In contrast to the elastic modulus, the CTE increases in the transverse direction while decreasing in the axial direction.

Microstructure, phase composition and hardness of Ti–Au cladding deposited on Ti–6Al–4V substrate by electron beam powder bed fusion method

In this study, a Ti–Au cladding was deposited on a substrate from the Ti–6Al–4V alloy by the electron beam powder bed fusion method in a vacuum. The main goal was to assess the possibility of using titanium powders and gold foils as a feedstock for additive manufacturing of such dental products. The microstructure, chemical element distributions, phase composition and hardness of the formed Ti–Au alloy were studied using optical microscopy, energy dispersive X-ray analysis, as well as X-ray diffraction and nanoindentation tests. Gold-containing intermetallic compounds were observed through the entire cladding thickness. The α-Ti, α-Au, AuTi and AuTi3 phases were found, in addition to the Ti3Au one, which provided hardness values greater than those of conventional titanium alloys. It was shown by results of the crystal-geometric and X-ray phase analysis that the AuTi3 phase possessed the most densely packed A15 structure. This fact correlated with the obtained data on the deviation of the atomic volume per ion from Zen's law and the high hardness levels. Metallurgical patterns of the microstructure formation that affected the functional properties of such claddings were discussed and a further research direction was proposed.

A strategy to design Ti-based in-situ bulk metallic glass composites containing controllable volume fraction and composition of the dendrite phase using conventional titanium alloy Ti–6Al–4V

Up to now, the composition design in the field of Ti-based in-situ dendrite reinforced bulk metallic glass composites (BMGCs) has been a great challenge. In this work, a simple but effective strategy is proposed to tailor the dendrite composition and volume fraction by using conventional Titanium alloy Ti–6Al–4V, and a series of in-situ dendrite reinforced BMGCs (Z1-Z4) are prepared based on it. The dendrite volume fraction can be adjusted by changing the proportion of the Titanium alloy Ti–6Al–4V, while the compositions of the dendrites are highly correlated with Ti–6Al–4V. In these alloys, with the increase of the mass percent of the added Titanium alloy Ti–6Al–4V, the volume fraction of the dendrite phase increases monotonically from Z1 to Z4 alloy. Z1 alloy behaves like a BMG with a high yield strength and limited plasticity due to its small dendrite size. Z2-Z4 alloys show excellent plasticity and significant work-hardening ability, because the dendrite size is appropriate and the dendrites undergo stress-induced martensite transformation during compression. From Z2 to Z4 alloy, with the increase of dendrite volume fraction from 56% to 78%, the yield strength does not decrease, which is due to the gradually enhanced stability of the dendrites. This composition design strategy is effective and universal, which can provide a new perspective for the composition design and development of TiZr-based in-situ dendrite reinforced BMGCs.

Metastable dual-phase Ti–Nb–Sn–Zr and Ti–Nb–Sn–Fe alloys with high strength-to-modulus ratio

Conventional dual-phase titanium (Ti) alloy exhibits high strength and toughness, but the high elastic modulus makes it unsuitable for biomedical implants. In this study, two novel metastable dual-phase (α"+β) Ti–Nb–Sn–(Zr/Fe) systems have been developed using [Mo]eq theory. The dual-phase α"+β structure contributed to the alloys’ characteristics of high strength and low elastic modulus. The bending strengths of Ti–(16−22)Nb–8Sn–(5−8)Zr and Ti–(17−19)Nb–8Sn–(0.5–1.5)Fe alloys (1023–1190 MPa and 960–1308 MPa, respectively) were obviously higher than that of Ti–25 Nb–8Sn (962 MPa). Among them, both Ti–18Nb–8Sn–7Zr and Ti–19Nb–8Sn–0.5Fe with dual phase had lower elastic moduli (50.4 and 50.5 GPa, respectively) than Ti–25Nb–8Sn (52 GPa), which can avoid the stress shielding effect after implantation. Ti–18Nb–8Sn–7Zr and Ti–19Nb–8Sn–0.5Fe alloys exhibited greater bending strength-to-modulus ratios (20.3 and 19.0, respectively) than those of c.p. Ti (7.1) and Ti–25Nb–8Sn (18.5). Both dual-phase Ti–18Nb–8Sn–7Zr and Ti–19Nb–8Sn–0.5Fe with low elastic moduli and high strength-to-modulus ratios are promising candidates for bio-implant applications.

Development of Titanium Matrix Composites for Aerospace applications

Titanium Matrix Composites are very interesting for aerospace applications. These materials typically present higher Young Modulus and resistance than conventional titanium alloys. The ceramic reinforcement can be continuous or discontinuous (fibers or particles). Main advantages of discontinuously reinforced TMCs are the isotropic mechanical properties and the lower production costs. This work presents the development of discontinuously reinforced TMCs with TiC as reinforced particles. The reinforcement was obtained by Combustion Synthesis and the final consolidation by Spark Plasma Sintering. Main advantage of this PM process is the short processing time. Regarding the thermos-mechanical characterization, the material presents higher stiffness and resistance with higher thermal conductivity than conventional Ti-6Al-4V. This work also presents the scale-up of the SPS process to obtain aerospace demonstrators. Machining and joining issues are also considered.

Comparison of the shear bond strength of composite resins with zirconia and titanium using different resin cements.

The shear bond strength of conventional zirconia (3Y-TZP), translucent zirconia (5Y-PSZ), and titanium alloy (Ti6Al4V) thermocycled using different phosphate monomer resin cements were investigated. In this study, 120 specimens of 3Y-TZP, 5Y-PSZ, and Ti6Al4V were cemented to nanocomposite resin cylinders using PANAVIA™ V5 and Rely X™ U200. The bond area and resin cement thickness were controlled as per ISO 29022:2013 and 4049:2009. Each resin cement group was used with/without the Clearfil ceramic primer plus. The shear bond strength of the 12 groups was statistically analyzed using two and one-way ANOVA to determine the properties of the different materials and resin cements (α = 0.05). The mode of failure was observed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The titanium alloy groups showed better shear bond strength than the zirconia groups (p < 0.05). PANAVIA™ V5 without primer showed significantly lower shear bond strength than other cements in zirconia and titanium alloy specimens (p < 0.05). Titanium alloy with Rely X™ U200 with a Clearfil ceramic primer plus showed the highest shear bond strength (6.37 ± 1.60 MPa). SEM images showed mixed failures in zirconia groups and cohesive failures in titanium alloy groups. The titanium alloy showed better shear bond strength than zirconia when the Clearfil ceramic primer plus was used. The primer solution containing MDP and resin cement with phosphoric methacrylate ester showed similar shear bond strength with 3Y-TZP and 5Y-PSZ. The resin cement without phosphate monomers demonstrated the least shear bond strength.

Biofunctional micro/nanostructured “volcano-like” layer-coated 3D porous Ti-10Ta-2Nb-2Zr scaffolds improve osteogenesis and osseointegration for dental implants in vitro and in vivo

Ti-10Ta-2Nb-2Zr (TTNZ) alloy has been previously suggested to be a promising alternate biomaterial for implant applications. However, its mismatch in elastic modulus with human bone and its lack of sufficient bioactivity are two concerns that need to be addressed further. In this study, for the first time, we attempted to use macroporous structures on TTNZ alloy scaffolds manufactured by selective laser melting (SLM) to reduce their modulus of elasticity and strengthen bone interlocking. Then, we modified scaffold surfaces with hydroxyapatite (HA) coating by microarc oxidation (MAO) to promote osseointegration. The microstructure, surface morphology, chemical composition, mechanical properties, biological activities and osteogenesis performance of this scaffold were systematically investigated in vitro and in vivo. The results revealed that scaffolds with this novel porous alloy possess a lower elastic modulus than solid structures. A micro/nanostructured layer with HA was successfully formed, which was verified by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). At the same time, this surface has increased hydrophilicity and roughness compared to unmodified surfaces and commercial pure titanium (CP-Ti). Furthermore, in vitro studies found that compared with MAOTTNZ samples with lower porosity, bare TTNZ samples, and CP-Ti samples, MAOTTNZ with adequate porosity could improve protein adsorption, cell proliferation, adhesion, alkaline phosphatase (ALP) activity and osteogenesis-related gene expression. In vivo studies, including those in which microcomputerized tomography, histological examination and biomechanical testing of macroporous MAOTTNZ scaffolds were performed, demonstrated that the formation of new bones was significantly boosted in rabbits after implantation. Consequently, this research presents an option for conventional titanium alloys with improved osteogenesis and osseointegration that could be used in further dental implant applications. • A 3D-printed porous implant with a novel nontoxic TTNZ alloy was developed. • A bioactive volcano-like HA coating was prepared on macroporous TTNZ scaffold. • The new micro/nanostructured surface showed high hydrophilicity and roughness. • The MAO-modified/porous TTNZ composite promotes osteogenesis and osseointegration.

Novel Experimentation for the Validation of Mechanistic Models to Describe Cold Dwell Sensitivity in Titanium Alloys

Previous mechanistic models, proposed to explain the process of damage accumulation and stress redistribution between strong and weak regions inherent within the microstructure of α/β and near α titanium alloys, are validated through a matrix of experiments employing a non-standard variant of the alloy Ti 685. The grain size of the model material was deliberately processed to offer grains up to 20 mm in diameter, to facilitate constitutive measurements within individual grains. A range of experiments were performed under static and cyclic loading, with the fatigue cycle conducted under either strain or load control. Data will be reported to demonstrate significant variations in elastic and plastic properties between grains and emphasise the role of time dependent strain accumulation. Implications for the “dwell sensitive fatigue” or “cold creep” response of conventional titanium alloys will be discussed.

Surface burn behavior in creep-feed deep grinding of gamma titanium aluminide intermetallics: characterization, mechanism, and effects

This article presents the surface burn behavior when creep-feed grinding gamma titanium aluminide (γ-TiAl) intermetallic. First, the main characteristics of burnt surface morphology were detected. Subsequently, surface burn mechanism was revealed by analyzing compositional changes in the surface layer via X-ray photoelectron spectroscopy. Lastly, the effects of grinding temperature on grinding force and surface integrity were discussed. Finding showed that a high grinding temperature would lead to a heavy color, from light brown to hyacinthine, on the burnt surface. The burning process was dominated by oxidation of Ti and Al. Ti was generally in the state of TiO2 on the ground surface, whereas lower valence oxide of Ti was found on the subsurface. This oxide layer could produce a reduced ratio of the tangential grinding force to the normal one. Elevated temperature would produce grinding and quenching cracks on a burnt surface, and tensile residual stress might be developed if the temperature is extremely high. Surface morphology and topography characteristics indicated that, unlike conventional titanium alloys (e.g., Ti-6Al-4V), a marginal physical reaction occurred on the workpiece surface during the burning process of γ-TiAl intermetallics due to poor material ductility.

Technology fusion of metal injection moulding and selective laser melting for the manufacture of complex and multifunctional (hydraulic) components

Selective laser melting (SLM) and metallic injection moulding (MIM) are established processes for the production of high-performance metallic components for small and large series. In the aerospace industry, where very high demands are placed on materials and components, both processes are still considered to be relatively new. In both processes, the conventional titanium alloy Ti-6Al-4V can be used in the form of powder. Currently, both technologies are only considered separately. By fusing components of the same type, multifunctional components with a high lightweight construction potential can be produced.&#x0D; In order to generate direct material fusion, the MIM component must be mechanically processed accordingly. In addition, suitable SLM process parameters must be developed in order to ensure both generative construction and high joint strength. To this end, a characterisation of the joining zone and the static joint strength was carried out. Furthermore, pressure test samples were designed and examined both statically and for fatigue strength. Thus, a high static joint strength could be proven. The compression test samples also withstood a fatigue strength of over 1 million cycles.

High impact resistance of a TWIP β titanium alloy: linking the multi-scale deformation and fracture mechanisms

Titanium alloys with twinning- and transformation-induced plasticity effects display promising mechanical properties, particularly, high impact toughness, unlike conventional titanium alloys. This work focuses on a highly strain-hardenable Ti–Cr–Sn alloy displaying both TRIP and TWIP effects upon quasi-static loading and an average impact toughness of 193 J/cm2, which represents nearly three times the measured value for commercial titanium alloys. To account for this extremely high impact toughness, fracture and deformation features were quantified at different scales using scanning electron microscopy and transmission electron microscopy, particularly a Precession-Assisted Crystal Orientation Mapping system. Examinations evidenced the major role of twins in the fracture process, even on a sub-micrometre scale. The high impact resistance and absorbed energy of this alloy are explained by the positive contribution of dynamical refinement of the β grains with sub-twinning structures, whereas severe stress concentration may eventually contribute to ductile fracture, at least locally.

NiTi shape memory alloy cellular meshes: manufacturing by investment casting and characterization

Recent studies have shown that conventional meshes comprising pure titanium and its alloys can be used to assist the recovery of bone fractures in various parts of the human body, such as the face, jaw, skull and knee. In anticipation of an improved efficiency for these applications and other applications, this work analyses the thermomechanical behaviour of a type of metallic mesh that is fabricated with NiTi shape memory alloys (SMAs), which are smart metals that exhibit functional properties, such as the shape memory effect (SME) and superelasticity (SE). The development of NiTi SMA meshes with different cell designs, good mechanical strength and recoverable deformation to replace titanium meshes and enhance biomedical applications (as well as applications in other fields) can be considered a current technological challenge. In this framework, this study aims to perform the fabrication and mechanical characterization of NiTi SMA meshes produced by investment casting with three different cell geometries (circular, hexagonal and square) in two states (as cast and heat treated). The obtained results show that the manufactured meshes present functional properties even in the as-cast state, as thermoelastic phase transformation and deformation recovery on the order of 6% is demonstrated. The results show that between the heat treatment and mesh cell geometry, the latter factor is the most influential factor in the mechanical behaviour of the meshes. A brief numerical simulation of the tensile behaviour of the meshes is used to deepen the analysis of the influence of cell geometry on their mechanical behaviour. Overall, as-cast meshes with circular and square cells present a high stiffness under tension and bending. The produced meshes show enough thermomechanical features to enhance biomedical applications. These results support the replacement of conventional titanium alloys, which do not possess functional properties, with NiTi SMAs.