•A mixed equiaxed + columnar prior-β grain microstructure was achieved by 0.05 wt% boron addition.•High-cycle fatigue property was improved significantly in Ti-64-0.05B.•Fatigue crack propagation ...resistance was reduced due to the prior-β grain size reduction and the TiB particle precipitation.
Boron is a powerful grain solute that promotes substantial microstructural refinement in titanium alloys produced by additive manufacturing. However, the fatigue performance of boron refined additive manufactured titanium alloys remained unknown. In this study, a thorough investigation into the high-cycle fatigue life and crack propagation rates of laser direct energy deposited Ti-6Al-4V with a trace boron addition was carried out. The high-cycle fatigue life was significantly improved, as the refined microstructure increased the crack initiation resistance. However, the crack propagation resistance estimated from spectrum loading was reduced, due to the refined prior-β grains and TiB particles.
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.
Herein, the effect of adding Fe and Cr as ternary alloying elements to the Ti–6.4Ni alloy is investigated. Substantial differences in hardness prevail depending on the heat treatment. These are linked to varying microstructures. The formation of a substructure within the α phase is elucidated. The basis for future, novel, and advanced titanium alloys is provided in the results.
Magnesium matrix in-situ composites with hybrid TiC+TiB2 reinforcement are potential materials for automobile and aerospace applications. It is essential to establish the processing map of such ...composites as these materials may undergo several thermo-mechanical processes while manufacturing engineering components. In the current work, AZ91 Magnesium matrix TiC+TiB2 reinforces hybrid in-situ along with its base counterpart were developed and subjected to solutionization followed by peak aging treatment. The safe processing zone for both base and in-situ composite at all heat treatment conditions have been established through processing map based on dynamic materials model (DMM) by conducting hot compression tests at various temperatures (250 °C – 450 °C) and strain rates (0.001 s−1 – 10 s−1). Two regions: stable and instable were identified from processing map for all the material conditions. Dynamic recrystallization is the main dominant mechanism in stable region, whereas instable region is characterized by twin and intergranular cracks. To understand the mechanism of hot deformation behavior, activation energy is calculated based on constitutive model for all material conditions. The developed in-situ composite in peak aged condition is found to possess higher activation energy (∼230 kJ/mol) as compared to base alloy (∼126 kJ/mol). A correlation between constitutive model and processing map have been established with an emphasis on their microstructures.
Display omitted
•TiC-TiB2 reinforced in-situ Mg matrix composite with base counterpart is developed.•The constitutive model and processing maps were established for both materials.•Presence of TiC-TiB2 lead to an improved high temperature efficiency of composite.•Dynamic recrystallization is the main deformation mechanism in stable region.•Twins and intergranular cracks are main reason behind instable region.
Activation difficulty is the key problem limiting the application of TiFe-based hydrogen storage alloys. The addition of transition group elements helps to improve the activation properties of ...TiFe-based hydrogen storage alloy. In our previous work, the Ti1.08Y0.02Fe0.8Mn0.2 alloy exhibits extremely high hydrogen storage capacity (1.84 wt%) at room temperature with excellent kinetic properties, but it still needs an incubation period of about 1500s. In this study, the composition of Ti1.08Y0.02Fe0.8Mn0.2Zrx (x = 0, 0.02, 0.04, 0.06, 0.08) alloys was prepared by electromagnetic induction melting. The quantitative analysis of elements by energy dispersive spectrometer shows that in the second phase region containing Zr, the content of Ti element is significantly higher than that of Fe. Meanwhile, the first-principle calculation on Zr-doped TiFe system indicates that Zr is more attractive to substitute Ti than Fe. Therefore, the doping of Zr partially replaces the Ti. The solubility of Zr in TiFe is limited, when x ≤ 0.04, the alloy consists of pure TiFe phase. When x > 0.4, the excess Zr forms precipitates, which reduces the reversible hydrogen absorption and desorption capacity of the TiFe alloy. The addition of Zr significantly shortens the activation time and reduces the plateau pressure of TiFe alloys. The Ti1.08Y0.02Fe0.8Mn0.2Zr0.04 alloy can be directly activated without the incubation period and its absolute values of enthalpy change (ΔH) and entropy change (ΔS) are minima (ΔH for 23.2 kJ/mol and ΔS for 83.1 J/mol/K).
•TiFe-based alloys doping Zr was prepared by vacuum induction melting.•The solubility of Zr in TiFe is limited and excess Zr forms precipitates.•Adding Zr notably reduces the activation time and plateau pressure of TiFe alloys.•The Zr0.04 alloy can be activated without incubation period and absorb 1.6 wt% H.
(a) Bright-field transmission electron micrograph and selected area diffraction pattern depicting the near-Burgers orientation relationship observed between the α (hcp) and β (bcc) phases in Ti–4Mo ...after heat treatment 950°C-WQ+550°C. (b) TEM bright field image, APT elemental map showing Mo atoms and (c) the corresponding 1-D concentration profile (bin width 0.5nm) across the Mo enriched layer (cylindrical region of interest in (b)) showing very pronounced partitioning of Mo (red) of about 20at% into a ∼20nm thick β lamellar zone, strongly enhancing its stability against phase transformation. Display omitted
We study the effects of different heat treatment routes on microstructure engineering and the resulting mechanical response in a plain binary Ti–4Mo (wt%) model alloy. We observe a broad variety of microstructure formation mechanisms including diffusion driven allotropic phase transformations as well as shear and/or diffusion dominated modes of martensitic transformations, enabling a wealth of effective microstructure design options even in such a simple binary Ti alloy. This wide variety of microstructures allows tailoring the mechanical properties ranging from low yield strength (350MPa) and high ductility (30–35% tensile elongation) to very high yield strength (1100MPa) and medium ductility (10–15% tensile elongation) as well as a variety of intermediate states.
Mechanical testing and microstructure characterization using optical microscopy, scanning electron microscopy based techniques, transmission electron microscopy and atom probe tomography were performed revealing that minor variations in the heat treatment cause significant changes in the resulting microstructures (e.g. structural refinement, transition between diffusive and martensitic transformations). The experimental results on microstructure evolution during the applied different heat treatment routes are discussed with respect to the mechanical properties.
•The effects of process parameters and interactions on the laser repair performance of esophageal tissue were studied by designing laser power, scanning speed, defocusing amount and scanning path ...through orthogonal experiment.•The degree of thermal damage was assessed by calculating the esophageal microtissue characteristic parameters and the degree of collagen thermal deformation.•Laser power and interaction factor laser power and scanning path were the most important factors affecting the burst compression strength.•At laser power of 6 W, scanning speed of 150 mm/s, defocusing amount of 0 mm, and scanning path 3, the bursting pressure strength of esophageal tissue was highest at 93.3 mmHg, and the thermal damage of the tissue was minimum.
To study the influence of laser parameters on the mechanical properties and thermal damage of esophageal tissue, the experiment of laser repair of esophageal tissue incision is made. The effects of parameters including the laser power, scanning speed, defocusing amount, scanning path on the bursting pressure strength of esophageal tissue are analyzed. The influence of different energy densities on the appearance of esophageal tissue morphology, microstructure, and the degree of thermal denaturation of collagen is analyzed. The results showed that the laser power and the interaction factor of laser power × scanning path is the most important factor affecting the bursting pressure strength of esophageal tissues. The optimal parameters are laser power 6 W, scanning speed 150 mm/s, defocusing amount 0 mm, and scanning path 3, the highest bursting pressure strength of 93.3 mmHg is achieved. Meanwhile the esophageal tissues do not show obvious scarring, and the degree of thermal denaturation of tissue collagen is the smallest, which is only 1.6 × 10-5, the texture of the tissue microscopic images is uniformly changed, and the texture clarity is high.
The effect of Gd content on the microstructure and tensile properties of as-cast Mg-Sm-Zn-Zr alloy has been systematically investigated. In the Mg-3Sm-0.5Zn-0.5Zr alloy, the intermetallic compounds ...with multiple morphologies are identified as Mg3Sm phase. In addition to Mg3RE phase, Mg5RE phase originated from Gd addition is observed in Gd-modified alloys. It should be noted that the lattice parameters of all the observed intermetallic compounds are significantly reduced by Zn segregation. The segregation behavior of Zn in Mg3Sm phase is inhibited to some extent by Gd addition due to the electronegativity difference between Sm/Gd and Zn elements. In addition, the increased Gd content effectively leads to much more accumulation of solute atoms in front of the liquid-solid interface during solidification, which can prominently promote nucleation in liquid region and then refine grains. The tensile yield stress of the present alloys is thus improved with increasing Gd addition. Finally, Gd-modified alloys exhibit significantly age-hardening effect, which can be mainly attributed to the high-volume fraction and high density nano-scale precipitates.
The main objective of this research is to prove the viability of obtaining magnesium (Mg) filled polylactic acid (PLA) biocomposites as filament feedstock for material extrusion-based additive ...manufacturing (AM). These materials can be used for medical applications, thus benefiting of all the advantages offered by AM technology in terms of design freedom and product customization. Filaments were produced from two PLA + magnesium + vitamin E (α-tocopherol) compositions and then used for manufacturing test samples and ACL (anterior cruciate ligament) screws on a low-cost 3D printer. Filaments and implant screws were characterized using SEM (scanning electron microscopy), FTIR (fourier transform infrared spectrometry), and DSC (differential scanning calorimetry) analysis. Although the filament manufacturing process could not ensure a uniform distribution of Mg particles within the PLA matrix, a good integration was noticed, probably due to the use of vitamin E as a precursor. The results also show that the composite biomaterials can ensure and maintain implant screws structural integrity during the additive manufacturing process.
•CoNiV fibers with a diameter of 300 μm and a length exceeding 3 m were prepared by multiple-stage cold drawn.•The heat treatment process was optimized to introducing a proper content of κ phase in ...the FCC matrix, resulting in the ultra-high yield strength and tensile strength.•The stress partitioning between the FCC and κ phases during tensile deformation has been analyzed, proving that the κ phase is the main contributor to high strength.•The κ phase elevates local stress within the FCC matrix and promotes the formation of deformation twins.
High/medium-entropy alloys (H/MEAs) are regarded as a potentially viable alternative to conventional metallic fibers for the production of ductile, high-strength fibers, to resolve the inherent trade-off between strength and ductility. The present study involved the cold drawing technique to produce a CoNiV MEA fiber measuring 300 μm in diameter with a length of more than 3 m. The mechanical properties of the FCC matrix can be improved through the inclusion of an appropriate amount of the κ phase via the optimized thermal treatment process. In addition to a yield strength of 1681 MPa and a well-coordinated elongation of 13.4 %, the ideal CoNiV fiber demonstrated a substantial ultimate tensile strength of 1932 MPa. Further calculations revealed that the κ phase, which possesses a substantial Von Mises stress of approximately 2715 MPa and an area fraction of 18.2 ± 1.1 %, was observed to be a primary contributor to the strength. Deformation twins were generated in the FCC matrix as a result of the ultra-high flow stress, which provided adequate ductility. This study offers significant contributions to the understanding of the deformation mechanisms and strengthening effect of the κ phase, thereby facilitating the development of high-performance metallic fibers.
Display omitted
PDF
