It is challenging to simultaneously achieve nearly full density and high strength in refractory alloys using selective laser melting (SLM). In this study, the achievement of ultrahigh-strength ...resulting from nearly full density has been reported in beta-type titanium alloy by controlling the melt pool mode in SLM. The melt pool mode was divided into the conduction and keyhole modes, which were determined from the macroscopic morphology of the melt pool in the SLMed Ti-34.2Nb-6.8Zr-4.9Ta-2.3Si (wt%) (TNZTS) alloy single tracks in combination with the keyhole threshold (P·V−0.5 = 251.3 W (m⋅s−1)−0.5) calculated theoretically. Compared with condition mode, the keyhole mode has higher porosity and inevitably causes poor mechanical property. Fortunately, by optimizing the SLM process parameters predicted via the keyhole threshold, an ultrahigh-strength and nearly full density (99.7%) TNZTS alloy with conduction mode was obtained by SLM. The alloy exhibited an ultrahigh compressive yield strength of 1286 MPa, which was higher than the majority of the beta-type titanium alloys reported so far. The microstructural analyses indicated that the ultrahigh-strength TNZTS alloy consisted of a thin shell-shaped (Ti, Nb, Zr)2Si (S2) phase (20–50 nm) around the columnar β-Ti grain boundaries together with an ultrafine dot shaped (Ti, Nb, Zr)5Si3 (S1) phase (50–300 nm) in the β-Ti matrix. The ultrahigh strength resulted from high-density dislocations and the effective dislocation blockage by the semi-coherent S1 and coherent S2 phases, thereby leading to the dislocation-strengthening and hardening effect. The strategy utilized in this study provides the fundamental guidelines for generating refractory metallic alloys with high density and excellent performance.
In this work, the correlations between the growth mechanism and properties of micro-arc oxidation (MAO) coatings on titanium (Ti) alloy were studied using different electrolytes. The adhesion and ...tribological properties of MAO coatings were evaluated by thermal shock tests and ball-on-disk friction tests, respectively. Results show that the growth mechanism as well as adhesion and tribological properties of MAO coatings are greatly influenced by electrolytes. In silicate electrolyte, the growth of MAO coatings is dominated by the deposition of silicate oxides and mostly characterized by outward growth. As a result, the coatings exhibit poor adhesion, but the presence of silicate oxides in the coatings is beneficial for improving the wear resistance. In phosphate electrolyte, the coating growth mainly results from the oxidation of the substrate and is more characterized by inward growth, resulting in high adhesion but low wear resistance. Employing the mixed silicate and phosphate electrolyte, however, is a feasible way of optimization to get relatively both high adhesion and improved wear resistance.
•The properties of MAO coatings are determined by growth mechanism.•The coating growth mechanism is influenced by electrolytes.•Silicate and phosphate electrolytes are comparatively studied.•The outward growth and inward growth are emphasized.
Implants with bioactive coatings are becoming increasingly popular in bioengineering. The incorporation of silver nanoparticles into the oxide layer supports the antibacterial effect. This article ...describes the surface modification of Ti15Mo alloy subjected to the plasma electrochemical oxidation (PEO) process in baths containing Ag compounds: Ag2O, Ag3PO4, and Ag3PO4+ Ca(PO4)2 to incorporate antibacterial silver particles into the oxide layer on the surface of the tested alloy. Scanning electron microscopy revealed changes in the surface porosity of the obtained oxide layers. Energy dispersive analysis, Raman spectroscopy, and X-ray electron spectroscopy determined the chemical composition and distribution of elements on the sample's surface. The tests showed the presence of embedded silver particles and uniform distribution on the surface. The bioactivity of the obtained layer was tested by adhesion tests of bacteria and fungi: Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), and Candida albicans (ATCC 2091).
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•Two different Ag sources were used to form PEO layers.•PEO baths consisted of Ag-containing suspensions.•Bioactive Ca, P and Ag were successfully introduced into Ti15Mo surface during PEO.•Ag incorporated PEO coatings exhibited bacteriostatic effect.
Commonly used high-temperature near-alpha titanium alloys contain Al, Zr and Si as their alloying elements. Significant losses of mechanical properties and cleavage mode failures are evident due to ...the presence of Ti3Al and S2 types of zirconium silicides ((TiZr)6Si3) in these alloys. We developed a new alloy (Ti-6.5Al-3.0Sn-4.0Hf-0.2Nb-0.4Mo-0.4Si-0.1B) by replacing Zr with Hf to avoid the formation of zirconium silicides. Aging at 700 °C for five hours successfully eliminated the Ti3Al phase and substantially improved the room-temperature ductility. Tensile tests were carried out at room temperature and at 650 °C. The mechanical properties of the present alloy were significantly improved compared to those of existing high-temperature titanium alloys under testing at ambient and elevated temperatures.
TiCsub.x/Al composites were successfully prepared in this study by dissolving graphite particles in Al-Ti melt based on the principle of a solid–liquid in situ reaction. It was observed that the ...microstructure of the TiCsub.x/Al composites changed with changes in the reaction temperature and graphite particle size. With an increase in reaction temperature, the TiCsub.x particles in the TiCsub.x/Al composites transitioned from a spider-like distribution to being evenly dispersed in the Al matrix. Additionally, the morphology of the TiCsub.x particles changed from polygons of various sizes to quasi-spherical shapes with a uniform particle size, while the presence of Alsub.4Csub.3 and Alsub.3Ti in the matrix diminished. The size variation of the graphite particles had minimal impact on the particle size and stoichiometric ratio of TiCsub.x generated in the sample. Furthermore, an appropriate graphite particle size was found to mitigate the agglomeration and residue of graphite particles during the in situ reaction.
The structure and energy associated with interfaces between the BCC and HCP lattices (beta and alpha phase, respectively) in titanium alloys with commonly used beta stabilizers were analyzed. For ...this purpose, the crystallographic structure of the matching facets of broad, side and end faces was described using misfit dislocations and structural ledges which compensate the mismatch in atomic spacing of the alpha and beta phases. The effect of the beta/alpha transformation temperature due to various concentration of beta stabilizers on periodicity of misfit dislocations and structural ledges was estimated. The van der Merwe approach was used to calculate energy of different matching facets. An increase in the percentage of beta-stabilizing elements was found to result in a decrease in the lattice-parameter ratio (a.sub.beta/a.sub.alpha) and an increase in the energy of all faces. The dependence of the interface energy on the a.sub.beta/a.sub.alpha ratio was for the first time quantified, and insight into the preferred shape of alpha-phase precipitates was obtained. Author Affiliation: (1) Institute for Metals Superplasticity Problems, Russian Academy of Sciences, Khalturin 39, 450001, Ufa, Russia (2) Belgorod National Research University, Pobeda 85, 308015, Belgorod, Russia (3) Air Force Research Laboratory, Materials & Manufacturing Directorate, 45433-7817, Wright-Patterson Air Force Base, OH, USA (a) mma@imsp.ru Article History: Registration Date: 02/05/2021 Received Date: 08/03/2020 Accepted Date: 01/31/2021 Online Date: 03/09/2021 Byline:
Laser solid forming (LSF) is a newly developed additive manufacturing which offers a less material waste and reduction in lead-time for fabricating aerospace titanium alloys components. In this ...paper, two types of block with different build dimension (section geometries) were fabricated by LSF with same processing parameters. The corresponding microstructure, texture, and tensile properties were investigated systematically. The results show that the samples exhibits similar columnar β grains morphology and 〈100〉 fiber texture, but very different α variant characterizations (morphology and texture) due to the different thermal history they experienced respectively. The fine basket-weave microstructure with weak texture can be obtained under the fast cooling conditions, while the colony microstructure shows a strong transformation texture as a result of variant selection in the relative slow cooling rate. The α characterizations depend strongly on the competition growth mechanism between the αWGB (grin boundary Widmanstatten structure) and αI (intragranular α nuclei) during cooling process. The presence of αGB (grain boundary α layers) enhances the nucleation of certain variants in β→α phase transformation. Tensile results reveal that fine basket-weave microstructure has relative high strength and ductility with dimple fracture mode. The colony microstructure shows a feature of dominant brittle fracture appearance and results in low tensile ductility.
Aim
To compare the ProTaper Next (PTN) system with a replica‐like and a counterfeit system regarding design, metallurgy, mechanical performance and shaping ability.
Methodology
Replica‐like (X‐File) ...and counterfeit (PTN‐CF) instruments were compared to the PTN system regarding design (microscopy), phase transformation temperatures (differential scanning calorimetry), nickel‐titanium ratio (energy‐dispersive X‐ray spectroscopy), cyclic fatigue, torsional resistance, bending strength, and untouched canal areas in extracted mandibular molars (micro‐CT). anova, post hoc Tukey’s and Kruskal–Wallis tests were used according to normality assessment (Shapiro–Wilk test) with the significance level set at 5%.
Results
Overall similarities in design and nickel‐titanium (Ni/Ti) ratio were observed amongst instruments with the X‐File having a smoother surface finish. PTN and PTN‐CF had mixed austenite plus R‐phase (R‐phase start approximately at 45 ºC and near 30 ºC, respectively), whilst X‐File instruments were austenitic (R‐phase started at approximately at 17 ºC) at room temperature (20 ºC). PTN‐CF had the greatest inconsistency in the phase transformation temperatures. Time to fracture of PTN‐CF X2 and X3 was significantly shorter than PTN and X‐File instruments (P < 0.05), whilst no difference was noted in maximum torque to fracture amongst the tested systems (P > 0.05). X‐Files and PTN‐CF had a stress‐induced phase change during bending load. Mean unprepared surface areas of root canals were 25.8% (PTN), 31.1% (X‐File) and 32.5% (PTN‐CF) with no significant difference amongst groups (P > 0.05).
Conclusion
Similarities amongst the systems were noted in the Ni/Ti ratio and maximum torque to fracture, whilst differences were observed in the design, phase transformation temperatures and mechanical behaviour. The ProTaper Next counterfeit instruments could be considered as the less secure system considering its low‐cyclic fatigue resistance. Apart from these differences, the unprepared canal surface areas, obtained with the tested systems, were similar.
A study has been undertaken to verify the feasibility of using powder-bed fusion additive manufacturing to fabricate Ti-5Al, Ti-6Al-7Nb, and Ti-22Al-25Nb alloys from elemental powders. Selective ...Laser Melting was used to produce bulk samples from mechanical mixtures of elemental powders for Ti-5Al, Ti-6Al-7Nb, and Ti-22Al-25Nb alloys. For Ti-Al-Nb system, annealing was carried out at 1050–1350 °C for 1–3,5 h followed by furnace cooling. The systematic characterization of the samples was done using scanning electron microscopy (SEM), optical microscopy (OM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and tensile testing. It was shown that using elemental powders it is possible to synthesize titanium alloys by Selective Laser Melting. In case of Ti-5Al, powder-bed fusion of powders resulted in a homogeneous microstructure, while for Ti-6Al-7Nb and Ti-22Al-25Nb a subsequent heat treatment at 1350 °C temperature is required to fully dissolve niobium particles.
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•Titanium alloys were synthesized from elemental powders by additive manufacturing.•Microstructure and tensile properties of obtained alloys were studied.•Proper heat treatment needed for Nb diffusion in Ti-Al-Nb system.•Ti-22Al-25Nb alloy is prone to cracking during SLM.
•The very high cycle fatigue strength of titanium alloy fabricated by additive manufacturing is much lower than that of the traditional process.•Combining with the weak zone, ΔKFGA is analyzed, and ...it is found that the size of the FGA plastic zone was similar to the width of the martensitic laths.•Failure critical dimension is obtained and a new fatigue life relationship is established based on defect characteristics.•Based on probability statistics, the influence of maximum defect size on fatigue behavior is discussed.
Tensile and fatigue behaviors of selective laser melted titanium alloy were investigated in the as-built condition. The alloy has a high defect density, and its tensile properties are comparable to those of wrought alloys, but the fatigue strength is significantly reduced. The FGA plastic zone is similar to the martensite laths width. The critical size of fatigue failure is analyzed by the K-T diagram. A new value is obtained based on the defect characteristics. Using the probability statistical, the maximum effective size of the defect considering the shape was calculated, and the competitive relationship of the defects was analyzed by volume density.
![Synthesis of TiC[sub.x]/Al ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2075-4701/small "Synthesis of TiC[sub.x]/Al Composites via In Situ Reaction between Al[sub.x]Ti Melt and Dissolvable Solid Carbon")
![The Effect of [beta] Stabil...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1073-5623/small "The Effect of [beta] Stabilizers on the Structure and Energy of [alpha]/[beta] Interfaces in Titanium Alloys")
