Effect of the microstructure generated by repetitive corrugation and straightening (RCS) process on the mechanical properties and stress corrosion cracking of Al-7075 alloy

This study discussed the effect of the heterogeneous microstructure generated through the Repetitive Corrugation and Straightening (RCS) process on the mechanical and stress corrosion cracking behavior of the AA7075. As a result of the RCS process, significant grain refinement was obtained. The average grain size ranged from 126 to 59 µm, for the initial condition and 4 RCS passes, respectively. The yield strength and hardness increased 170% and 15% from the initial pass, remaining almost constant afterward. The evaluation of stress corrosion cracking showed a decrement in the number of cracks of 21.6% and 23.5% between the initial condition and fourth RCS passes. The cracking and pitting corrosion were the dominant mechanisms in the tested samples. The mechanical and corrosion results were also discussed in terms of the microstructural features.Peer ReviewedPostprint (published version

Texture and strain rate sensitivity analysis of solid solution and precipitation hardening aluminum alloys processed by repetitive corrugation and straightening

The potential of improving the mechanical strength by the RCS process is evaluated on the 5754, 6061, and 7075 aluminum alloys, which present different hardening mechanisms related to their respective alloying elements. This work compares the evolution of the texture and the mechanical properties of the different alloys through the RCS processing. The mechanical properties were evaluated by micro-hardness measurements, tensile tests at different temperatures, and strain rates to evaluate the strain-rate sensitivity. The results showed that after two RCS passes, the 6061 and 5754 alloys showed a relatively high strain-rate sensitivity at 300°C. In addition, an increment of 27%, 22%, 15% in hardness was obtained for the 5754, 6061 and 7075 alloys, respectively. Showing the potential of improvement in the mechanical resistance due to the different hardening mechanism. Furthermore, the crystallographic texture was characterized by the obtention of pole figures by X-ray diffraction and the calculation of their orientation distribution functions. The results showed the same trend in the three aluminum alloys, i.e., the initial texture components were conserved, but the texturized volume decreased.Peer ReviewedPostprint (published version

Mechanical, stress corrosion cracking and crystallographic study on flat components processed by two combined severe plastic deformation techniques

Although the current field of application of Al–alloy 7075 (AA7075) is vast, it is still limited due to some drawbacks, especially due to its susceptibility to stress corrosion cracking (SCC). This work aims to evaluate the microstructural, mechanical, and stress corrosion cracking (SCC) behaviors on an AA7075 in flat format deformed by a combination of repetitive corrugation and straightening (RCS) and accumulative roll bonding (ARB) techniques. Four different deformation routes were applied, namely: ARB (A), RCS (R), RCS + ARB (RA) and ARB + RCS (AR). As expected, the efficiency for grain refinement depends on the applied route, in terms of average grain size regarding the initial condition IC): AR > A > RA > R. All conditions resulted in unimodal and widened grain size distributions of micro-, submicro- and nano-metric dimensions. The study of crystallographic orientations showed that route R did not generate any new texture, whereas different preferred orientations were obtained for routes A, RA, and AR. The hardness and three-point bending tests showed an improvement of mechanical strength in the following order: AR > RA > A > R. The cracks per cm2 obtained in the corrosion study indicated that the best SCC resistance was R > A > AR > RA. Based on the above, the best combination of microstructural, mechanical, and SCC properties until one deformation pass was obtained by the single route of the ARB process.Peer ReviewedPostprint (published version

Residual stresses and microstructural evolution of ECAPed AA2017

The mechanical behavior and microstructural evolution of an AA2017 aluminum alloy processed by ECAP with an equivalent simple shear deformation of ∼6 at 200 °C were studied. Samples were characterized by means of scanning electron microscopy (SEM-EDS- EBSD), image-assisted by focus ion beam (FIB), Vickers microhardness and X-ray diffraction (XRD) techniques. During the deformation process, the Al 2 Cu precipitates did not get fragmented or re-absorbed in the Al matrix. After the first ECAP pass, at least 50% of grains displayed an ultrafine size. The EBSD analysis showed an increment of the misorientation angle immediately after the first ECAP pass. The macrotexture evolution was explained in terms of the formation of f1: A 1θ ∗ , A θ , Ā θ , A 2θ ∗ , f2: C θ , B¯ θ , B θ , Ā θ , A θ , A 1θ ∗ and f3: C θ , B θ , B¯ θ , A θ , Ā θ , A 2θ ∗ fibers. The macro-residual stress measurements of the highly deformed samples showed linear sin 2 ψ profiles. The micro and macro-residual stresses were compatible with dislocation rearrangement, in which the annihilation and formation were in quasi-equilibrium. It was found that the highest microhardness value (1176 MPa) and grain refinement (at least 20% of grains showed a size smaller than 100 μm 2 ) appeared after the first extrusion pass. The decrease in hardness, after the second pass and the residual stress stability, could be associated to a dynamic recovery phenomenon

Effect of the Ti/Ta ratio on the feasibility of porous Ti25+x-Nb25-Zr25-Ta25-x (X= 0, 5, and 10) alloys for biomedical applications

Non-toxic biomedical HEAs by powder metallurgy methods have been scarcely studied despite their promising mechanical and biological behaviors. This work studied the microstructural, mechanical, electrochemical, and ion release effects of the Ti/Ta ratio on three porous Ti–Nb–Zr–Ta (TNZT) alloys. The microstructure of the TNZT alloys consisted of semi-equiaxed and micrometric BCC-phases (matrix) with lower contents of HCP phase. Elastic moduli (82–91 GPa), hardness (373–430 HVN), ultimate bending (225–475 MPa), and tensile (119–256 MPa) strength, electrochemical corrosion (4.5–9.6 μm year−1), and ion release (toxicity, 0.9–1.1 μm year−1) were within acceptable limits for implant biomaterials. Increasing the Ti content (and decreasing Ta) was advantageous for improving mechanical strengthening and reducing the elastic modulus. The medium value of elastic modulus may be beneficial to reduce the mechanical mismatch between the implant and the organic tissue. However, the corrosion rate and metallic ion release increased as a function of the Ti content. Besides, the alloy with the lowest Ti content (highest Ta content) showed local corrosion. Based on the above, the porous TNZT alloys with medium and highest Ti contents (30 and 35 wt%) were demonstrated as promising candidates for biomedical implant applications

Repetitive corrugation and straightening effect on the microstructure, crystallographic texture and electrochemical behavior for the Al-7075 alloy

Anti-corrosion susceptibility is one of the top criteria for selecting metallic materials for several industrial applications. This work studies the corrosion performance on an Al-7075 alloy obtained by Repetitive Corrugation and Straightening (RCS). This processing method generated a microstructure formed by randomly distributed micro-, submicro-, and nano- metric grain sizes. The samples exhibited a drop in corrosion resistance for a longer duration in the electrolyte and higher deformation. However, the samples processed by RCS showed better electrochemical stability in comparison with the non-deformed condition. The improvement of electrochemical stability could be associated with the particular microstructure generated during the RCS process.Postprint (published version

Microstructural, mechanical, electrochemical, and biological studies of an electron beam melted Ti-6Al-4V alloy

This work studied the feasibility of an electron beam melting (EBM) Ti-6Al-4V alloy as a biomaterial for implants. Comparisons were made with a wrought forged Ti-6Al-4V alloy. The objective of this work was a detailed description of the microstructural and surface roughness effects on mechanical, electrochemical, and in-vivo biological performances. The EBMed condition showed higher mechanical properties, as well as higher electrochemical and ion release rates. These results were mainly influenced by the lamellar grain morphology and complex crystallographic texture of the EBMed alloy compared to the forged one. The higher area average roughness of the EBMed condition boosted the adhesion, proliferation, and biofilm formation of osteosarcoma (MG63), Staphylococcus epidermidis (S. epidermidis), and Staphylococcus aureus (S. aureus). The mechanical, ion release, corrosion, and in-vivo biological results in both studied conditions met the requirements for orthopedic and dental biomaterials. However, the forged condition is more recommended for patients with clinic stories related to S. epidermidis and S. aureus illnesses

Mechanical and Electrochemical Properties Comparison of Additively Manufactured Ti-6Al-4V Alloys by Electron Beam Melting and Selective Laser Melting

This work involves additively manufactured Ti-6Al-4V alloys, which are widely used in automobile, biomedical, and aircraft components for a comparison of the microstructure–properties relationship between electron beam melted (EBM) and selective laser melted (SLM) alloys after hot isostatic pressing treatment. We carried out microstructural, mechanical, and electrochemical measurements on both alloys. They showed comparable α and β phase contents with slightly higher lattice parameters in the EBM sample compared to the SLM. The EBM sample showed higher yield strength and uniform elongation due to the activation of multistage defects-driven strengthening and strain hardening mechanisms. Cracking during the tensile test nucleated mainly at the α phase near high-mechanical mismatch α/β interfaces. This mechanism was consistent with the reported generation of hetero-deformation-induced strengthening and strain hardening. Both alloys showed similar electrochemical behavior, but the SLM sample was more susceptible to corrosion than the EBM alloy

Findings and perspectives of β-Ti alloys with biomedical applications: Exploring beyond biomechanical and biofunctional behaviour

Early implant failure and bone resorption may occur in load-bearing conditions as a result of stress shielding brought on by a mismatch in the bone-Ti-implant modulus. A review with a novel multidisciplinary perspective is proposed in this work, which considers recent developments of β-Titanium alloys and new trends in novel microstructures, processing techniques, properties of dense and porous substrates, as well as the relationship between all these aspects and performance in service, in terms of improved its biomechanical and bio-functional balance. In addition to highlighting several modern and historical uses for Ti alloys, this review covers many cutting-edge novel β-Ti alloys and uses that promise to exceed historical standards. Also, it deepens through several important properties of these alloys, including toxicity of alloying elements, phase stability, thermo-mechanical processing, heat treatment, surface, and stress-induced modifications. The stiffness, hardness, fatigue and wear resistance, corrosion behaviour, biocompatibility, and manufacturing and surface modification effects on these parameters are also emphasized. In-vitro and in-vivo assays have been added to highlight important aspects of bioactivity and antibacterial behaviour, and future significant research areas are suggested along with new techniques to ensure the successful clinical application of β-Ti alloys

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700