The evolution of the microstructure during plastic deformation was studied in an additively manufactured Ti-15%Nb-12%Zr (at.%) alloy. The applied equivalent strain ranged extremely widely from 8 % to 20,800 %. Strains below 100 % were achieved by uniaxial compression, while the high strains were obtained by the highpressure torsion (HPT) technique. In addition to the as-built material, the same investigation was conducted on the alloy after heat treatment at 550 degrees C for 1 h after additive manufacturing. The as-built alloy had a fully body-centered cubic structure, while the annealing step resulted in the development of a hexagonal close-packed secondary alpha-Ti phase with a fraction of about 10 %. Compression up to a strain of 70 % resulted in an increase in the secondary phase fraction to 12 % and 22 % for the as-built and heat-treated alloys, respectively. HPT processing at high strains yielded a lower secondary phase fraction due to reverse martensitic transformation. The dislocation density increased to 70-100 x 1014 m(-2) when the strain rose to 70 % during compression. The dislocation density reached extremely large values of 600-700 x 1014 m(-2) at a strain of about 20,800 % achieved by HPT. Although the dislocation density increased by two orders of magnitude and nano-crystallization also occurred when the strain increased to 20,800 %, the hardness was enhanced only by 10-30 %. The unexpectedly low hardness increase after HPT was attributed to unique deformation mechanisms such as the kink pair related dislocation motion and grain boundary sliding.

Ti–6Al–4V (wt.%) alloy containing 0.14 wt.% trace Fe and 1 wt.% yttria-stabilized zirconia (YSZ) was manufactured by laser powder bed fusion. In addition to the as-built samples (AB), some samples received post-heat treatments, either by conventional heat treatment (HT) alone or by a combination of HT and hot isostatic pressing (HIP). The HT and HIP processing increased the grain size and the secondary β-phase fraction, and decreased the as-grown dislocation density, leading to a decrease in hardness from about 4500 to 4100 MPa. All three sample types were severely deformed by high-pressure torsion (HPT) to an equivalent strain of ∼208. The differences in the initial microstructures of the three states gradually disappeared as strain increased. The dislocation density increased with plastic deformation, leading to a decrease in the crystallite size and the β-phase fraction. The saturation values of the crystallite size and the dislocation density were about 20 nm and 1016 m−2, respectively, while the β phase practically disappeared at a strain of about 26. Instead, V/Fe-rich regions developed at the grain boundaries of the α phase. The strong initial texture components of ⟨101‾2⟩ and ⟨112‾0⟩ changed to an almost random texture with a weak ⟨101‾1⟩ component during HPT. Due to these changes in the microstructure, the hardness of the three types of samples saturated at similar values within the range of 4500-4700 MPa. The low hardness increase of 5-12% after HPT can be attributed to texture softening which moderated the hardening caused by the defects and small grain size.

Nitrophenyl layers of varying thicknesses were grafted onto an arc-melted Ti 35 Zr 25 Nb 25 (MoTa) 15 high-entropy alloy via electrochemical reduction of 4-nitrobenzenediazonium tetrafluoroborate. A fluorescent peptide derived from bone morphogenetic protein 2 (BMP-2) was then covalently tethered to these films. Electrochemical corrosion behaviour was assessed in 0.1 M NaCl by potentiodynamic polarisation and electrochemical impedance spectroscopy. Grafted nitrophenyl films reduced the corrosion current density ( I corr ) by more than 10-fold and diminished anodic current densities by over 1550-fold, while shifting the corrosion potential ( E corr ) to more positive values. Subsequent BMP-2 coupling further increased the resistive impedance of the coating and eliminated diffusion-limited (Warburg) behaviour. These results demonstrate that, for the Ti 35 Zr 25 Nb 25 (MoTa) 15 alloy in chloride media, sequential nitrophenyl grafting and peptide immobilisation yield a robust, corrosion-resistant and biofunctional surface.

The data presented here aim to show how to analyze crack propagation of a novel metallic matrix composite of Ti-6Al-4V reinforced with 1 wt. % nano-yttria-stabilized zirconia processed by laser powder bed fusion technology. The data was acquired via microstructural observations and electron backscatter diffraction (EBSD) analyses after the quasistatic tensile tests at room temperature. The overall crack path configuration based on the fracture surface observation by scanning electron microscopy (SEM) was first operated, presenting two main regions: (i) local inclined planes (hereafter denoted as “stair-like”), and (ii) region in accordance with the theoretical mode I fracture plane. Thereafter, a series of EBSD data set on a surface obtained after longitudinal cut off operation on one failed piece was conducted at three distinct positions: (i) in the stair-like configuration region, (ii) in the mode I fracture region, and (iii) in the region where the crack path made his transition between these two mechanisms. Since the EBSD data sets were not prone to any post-processing filtering operation, comparison of the observed mechanism with other Ti-6Al-4V alloy processed by additive manufacturing (AM) technology can be easily carried out.

The present work aims to clarify the tensile behavior of a novel metallic matrix composite of Ti-6Al-4V alloy reinforced with 1 wt.% nano-yttria-stabilized zirconia, processed by laser powder bed fusion technology. The as-processed samples were post-processed using notably hot isostatic pressing in order to investigate the most promising material for actual structural applications. The cracking behavior is governed by the activation of prismatic slip systems in primary α-Ti grains. Under horizontal loading configuration (i.e., perpendicular to building direction), average yield stress and ultimate tensile strength of 999 and 1195 MPa have been found, respectively. Strengthening mechanisms caused by (i) solid solution due to raising oxygen concentration and (ii) dispersion hardening have resulted in similar yield stress increases of 108 and 99 MPa, correspondingly. Furthermore, the effect of the texture on the mechanical properties of the investigated material was assessed via a statistical approach, which forecasts a strong strength anisotropy depending on the loading direction. In addition, a particular attention has been paid to the effect of nano-yttria-stabilized zirconia addition on strain-hardening ability, underlining that the enhanced amount of solute oxygen yielded a strong strain hardening in stage II of plastic deformation.

The in-situ chemical grafting conditions of aminophenyl on an equimolar high-entropy HfNbTaTiZr alloy were optimized using an experimental design strategy. A fluorescent ArgGlyAsp peptide molecule was also synthesized and mounted on the grafted aryl group layer as a preliminary investigation toward further alloy biofunctionalization. The chemical composition, anti-corrosion performance and thickness of the aminophenyl/peptide layers were analyzed by X-ray photoelectron spectroscopy (XPS), electrochemistry and transmission electron microscopy (TEM) coupled with energy diseprsive spectrometry (EDS). The grafted aminophenyl and aminophenyl + peptide layers were both inhomogeneous with thicknesses varying between similar to 35 nm and similar to 400 nm and similar to 300 nm and similar to 1250 nm, respectively. The grafted layers did not improve the corrosion potential of the alloy, while compared to the bare alloy, the measured impedance values and anodic current densities of the treated alloys were found to be larger and lower, respectively. Finally, this article presents the first high-resolution microscopic images of a deposited diazonium-based/peptide coating on a solid surface.

This Letter reports on the processing, mechanical properties, electrochemical performance, and toxicity behavior of a multiprincipal element Ti35Nb30Zr29Mo3Ta3 alloy. The recovered centimeter-sized cubes or parallelepipeds were polished before analysis. It was found that the homogeneity and yield stress of the alloys get increased when higher volumetric energy densities are applied during processing. The synthesized alloys also exhibited a Young modulus closer to those of bones than those usually reported on the conventional orthopedic metals (60-80 GPa for this alloy against 110 and 4-30 GPa for the Ti-6Al-4V and bone, respectively). The electrochemical corrosion assays performed at 25 and 37 degrees C, in sodium chloride (NaCl, 0.1 M), deoxygenated high glucose Dulbecco's Modified Eagle Medium (DMEM), and deoxygenated DMEM implemented with fetal bovine serum showed corrosion potentials (E-corr) ranged in the order NaCl(25 degrees C) approximate to DMEM + PBS(37 degrees C) > DMEM(37 degrees C) and impedances much larger in the DMEM and DMEM + PBS media than in NaCl. Finally, pre-osteoblasts cells cultured in the medium conditioned by the alloy did not evidence cytotoxicity effect, because no effects on the cell proliferation and morphology were observed. These data suggest the biocompatibility of this alloy, indicating no acute toxicity, which is a prerequisite for the integration of an alloy as a bioimplant.

The present study compares the efficiency of three different Hot Isostatic Pressing (HIP) post-treatments in reducing the density of defects in Ti-6Al-4V alloy parts fabricated by the Electron Beam Melting process. The HIP treatments are the standard HIP (T = 920 degrees C, P = 1000 bars, t = 2 h), a High-Temperature HIP (T = 1050 degrees C, P = 1000 bars, t = 2 h), and a two-step HIP (held above the beta-transus, rapid quenching, and tempering) treatments. If it is observed that all three HIP treatments do seal internal porosity and increase the final density of the material, they are also shown to differ mainly in significant variations in morphology, porosity and hardness. It is also shown that the observed decrease in density is only partly linked to the decrease in porosity and mainly to the evolution of the chemical composition of the two phases constituting the Ti alloy through the HIP post-treatment as well as the quality of the crystalline structure.

In this study, we report the experimental coarsening kinetics at 850, 900 and 950 degrees C of four complex concentrated alloys in the Al-Ti-Cr-Fe-Co-Ni senary system with different chemical compositions but a similar gamma' (L1(2)) volume fraction (similar to 35 % at 950 degrees C) in a face-centered cubic (gamma, FCC) matrix. The selected alloys were specifically designed to investigate the influence of Fe additions and Ni-Co substitutions on Ostwald ripening kinetics. Atom Probe tomography (APT) was used to determine the compositions of the FCC and L1(2) phases, which agree very well with Calphad calculations at thermodynamic equilibrium. Thermo-kinetic modeling of L1(2) precipitation was carried out using the Prisma module developed by Thermo-Calc and compared with experimental results. Apparent activation energies were determined and discussed in light of diffusion-controlled coarsening models to identify the key parameters affecting Ostwald ripening. We suggest that the abnormally high apparent activation energies results from composition-dependent parameters. When the latter are accounted for, the corrected activation energies for coarsening are in better agreement with available diffusion data.

Objective: The purpose of this research article is to present the functionalization of a new titanium alloy of the system TiNbZr, by the grafting of a bioactive polymer (poly(sodium styrene sulfonate), PNaSS) using the "grafting from" technique to improve the osseointegration. The resulting grafted polymer is covalently bonded to the substrate in this procedure thanks to surface-induced polymerization. Material and Method: Colorimetric assay, Fourier-transform infrared spectra recorded in attenuated total reflection mode (ATR-FTIR), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and water contact angle measurements (WCA) were applied to characterize the surfaces. In addition, the effect of the grafting on the biological response was assessed using MC3T3-E1 pre-osteoblast cells line. Results: This study showed that grafting rates obtained on these new alloy are as good (around 4.5 mu g/cm2) as on classical alloys. In parallel, in vitro biological response study was carried out to assess toxicity, cell viability, and morphology on titanium alloys TiNbZr functionalized. Moreover, results showed superior alkaline phosphatase activity and higher calcium deposition on grafted samples, implying a beneficial effect of the PNaSS in osteoinduction activity. Conclusions: Grafted TiNbZr improves the cell response, in particular, the osseointegration.(c) 2023 AGBM. Published by Elsevier Masson SAS. All rights reserved.

Processing heterogeneous microstructures, especially the so-called harmonic structures consisting of soft core and hard shell regions, is an efficient way to achieve a strength-ductility trade-off in classical metallurgy. In this study, two harmonic samples with the same composition of Ti-24Nb-4Zr-8Sn but different microstructures were processed to exhibit different grain size heterogeneities between the core and the shell. Both samples were consolidated from a ball-milled powder using Spark Plasma Sintering (SPS) but applying two different sintering times, 1 and 60 min. The grain size heterogeneities were higher for the longer SPS sintering time due to the enhanced grain dimension in the core for 60 min consolidation time. The mechanical behavior of the two materials was studied via a monotonic quasi-static compression test. For both harmonic-structured Ti-24Nb-4Zr-8Sn alloys, a high compressive proof stress of about 1 GPa was detected. The strain-hardening rate was higher for the longer SPS time due to the higher grain size differ-ences between the core and shell. A high dislocation density was detected in both mate-rials after compression deformation (several tens of 1014 m-2). The dislocations tend to form cells and LAGBs during compression. The dislocation pile-ups at the core-shell in-terfaces caused a back stress of about 640 MPa after compression at 2-5% strains. The contributions of the different features of the microstructure (grain size, a phase pre-cipitates, and oxygen concentration) to the proof stress were determined. & COPY; 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Download This Paper Open PDF in Browser Add Paper to My Library Share: Permalink Using these links will ensure access to this page indefinitely Copy URL Copy DOI

The cyclic shear study of the Ti-15Mo (wt.%) alloy, with twinning induced plasticity deformation mechanism, shows that whereas conventional {332}<113> twinning is obtained during forward loading, room temperature backward loading in Bauschinger tests are able to cause twins reversion, suggesting that detwinning can act as a proper deformation mechanism. After reversion, the mechanical twins leave behind residual bands with low misorientation (∼2°) in the matrix, and secondary twins. When the backward deformation is continued, new twins of different {332}<113> systems favorable to backward stress are then produced in the microstructure. The formation of the various deformation products is rationalized by trace analysis and calculation of the resolved shear stress on the considered twinning systems.

Pure tungsten is known to be a strong material but very brittle, due to its grain boundary structure. In a quest for improvement of the cold-work capacity of tungsten alloys, pure tungsten powder was doped with 1 wt% nickel. The mixture was consolidated by spark plasma sintering at temperature conditions below and above the Ni melting point. The addition of Ni tends to remove oxygen from W grain boundaries. Spherical particles of WO2 are then formed when the sintering temperature is below the melting point of nickel; while tangled sticks of W oxide encapsulated by a submicron rim of Ni-rich phase are observed when the sintering is carried out above this melting point. Quasi-static compression tests at room temperature have been operated to assess the cold-working capacity of the obtained materials. Ni-doped materials sintered at a temperature below the Ni melting point revealed an increase in the strain at rupture by a factor of six approximately (12 % and 23 % in Ni-doped materials, whereas their W counterparts presents 1.9 % and 3.9 %, respectively), accompanied by a moderate decrease in the compressive strength (1300 and 1250 MPa, in respect with 1615 and 1325 MPa, respectively). The substantially improved mechanical properties of the Ni-doped samples is caused by the combination of the oxygen cleaning at the grain boundaries of the W matrix and local accommodation of the deformation by the created Ni-rich phase. The material consolidated at a temperature higher than Ni melting point underlines the formation of submicron thick ductile Ni-rich phase, accompanied with an improvement of both the strain at rupture and the compression strength of 3.5 times and 25 %, respectively. This configuration is expected to enhance the load transfer between the hard W matrix and the soft Ni-rich phases, which promote the activation of slip activity of the W matrix, in line with the extensive ductile phenomena distinctly observed on the ruptured specimens.

We report on the microstructure and the strengthening mechanisms of additively manufactured parts fab-ricated by directed energy deposition of Ti-6Al-4V(Ti64)powders blended with yttria-stabilized zirconia(YSZ)nanoparticles.These specimens showed refined microstructures as compared to bare as-deposited Ti64,where the α and columnar prior β grain sizes decreased with increasing YSZ content.The YSZ nanoparticles decomposed during the deposition process and led to the formation of yttrium oxide and some excess oxygen in the Ti64 matrix.The decrease in the sizes of the prior β grains could be attributed to the increasing amount of dissolved oxygen and yttrium,which promoted constitutional supercooling.Furthermore,the reduction in the size of the α grains could be ascribed to a shift of the onset of theβ→α+β transformation to a higher temperature and shorter time with increasing concentration of dis-solved oxygen.Finally,the contributions of the underlying strengthening mechanisms for the as-deposited specimens were quantitatively determined.

EXAFS analysis of pure elements, binary and ternary equiatomic refractory alloys within the NbZr-Ti-Hf-Ta system is performed at the Nb and Zr K-edges to analyze the evolution of the chemical local environment and the lattice distortion. A good mixing of the elements is found at the atomic scale. For some compounds, a distribution of distances between the central atom and its neighbors suggests a distortion of the structure. Finally, analysis of the Debye-Waller parameters show some correlation with the lattice distortion parameter δ2, and allows to quantify experimentally the static disorder in medium entropy alloys.

This study discusses the effects of hot isostatic pressing (HIP) post-treatment on Laser Powder Bed Fusion of Ti6Al4V and Ti6Al4V reinforced with 1 wt% and 2.5 wt% of nano-yttria-stabilized zirconia (nYSZ). The bulk parts display a higher density after HIP post-treatment than the as-built counterparts. Besides, X-ray diffraction (XRD) analysis indicates a reduction of the β phase percentage after HIP. An increase in α grain thickness is noticed on both reinforced and unreinforced parts. Additionally, compared to their un-HIPed counterparts, the microhardness decreases after HIP post-treatment by 3%, 11%, 8% and 4% for the as-built Ti6Al4V, stress relieved Ti6Al4V, 1 wt% nYSZ reinforced and 2.5 wt% nYSZ reinforced parts, respectively. The same trend was observed for the yield stress, which decreases by 1%, 4% and 8%, for the as-built Ti6Al4V, stress relieved Ti6Al4V and 2.5 wt% nYSZ-reinforced parts respectively after HIP post-treatment, except for 1 wt% nYSZ-reinforced part, whose yield stress increase by about 7%, which could be attributed to the specific texture evolution within this material. The plastic strain was significantly enhanced after HIP in all materials.

For the first time, four-point bending fatigue behavior of a Ti-6Al-4V alloy reinforced with 1 wt% nano-yttria-stabilized zirconia and processed by laser powder bed fusion was investigated. In a quest for clarification on the effect of the hot isostatic pressing (HIP) on the fatigue outcomes, both untreated and HIPed specimens were studied. The former material indicated relatively modest fatigue resistance mainly due to the presence of inherent processing defects, whereas the latter one revealed a promising fatigue strength in comparison with unreinforced Ti-6Al-4V and exhibited transgranular fatigue crack nucleation provoked by the crystallographic slip in long-length layers of alpha grain.

As the population in modern societies ages and the risks of bone diseases or bone accidents increase, there is a need for a new generation of materials with superior biocompatibility and good mechanical properties. This study combines two innovative metallurgical concepts to provide a material solution for the intended application. To this end, multicomponent and complex concentrated alloy (HEA|CCAs) based on TiNbZr-X (X = Mo, Ta) system is fabricated via additive manufacturing (AM), namely by Laser-Powder Bed Fusion (L-PBF) of gas-atomized pre-alloyed powder. After each stage of development by L-PBF through Taguchi's design of experiments, complete microstructure characterization and mechanical behavior of the resulting samples under different loading conditions are conducted. In addition, mechanical surface functionalization carried out by machining with metrological monitoring is carried out as a pre-step before a chemical functionalization for the suitability of materials developed for the intended application