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:
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.
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.
Ti-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr) is near β titanium alloy, which plays a significant role in manufacturing landing gears and flap tracks in the aerospace industry. This study aims to find out an ...optimal heat treatment to obtain an excellent balance of strength, ductility and fracture toughness. For this purpose, the Ti-55531 alloy was subjected to solution plus aging treatments and mechanical properties tests. Optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM) were adopted to observe the microstructural evolution including morphology, distribution and size. Standard tensile and compact tension (CT) tests were carried out to obtain the yielding/tensile strength (YS, TS), elongation (EL) and fracture toughness (KIC) of Ti-55531 alloy. The effects of solution temperature, aging temperature and time on the microstructural evolution and fractography were analyzed. The relationships between the mechanical properties and microstructures were qualitatively described. The influencing mechanism of plastic deformation and crack propagation path on the KIC were discussed. Simultaneously, the values of YS and KIC were predicted based on mechanical property models, the predicted values were compared with tested data. Finally, an optimal heat treatment was proposed for the Ti-55531 alloy, to obtain a good balance of strength, ductility and fracture toughness.
•An optimal heat treatment of Ti-55531 alloy was obtained in this study.•Precipitation mechanism of lamellar αs phase in the β phase was explained.•Effects of microstructural evolution on mechanical properties and fracture mechanism were analyzed.•Predicted models of yield and tensile strength and fracture toughness were proposed.
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.
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.
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 tensile deformation and fracture behaviors of a new metastable β titanium alloy (Ti–5Cr–4Al–4Zr–3Mo–2W-0.8Fe) with single β phase are investigated by in-situ tensile test under scanning electron ...microscopy. With the increase of deformation degree, in addition to the transition from single slip to multiple slip, the stress induced martensite (SIM) and mechanical twins will also occur to coordinate the overall deformation of the alloy, leading to further work hardening. The slip system activation, slip transfer and grain rotation are closely related to the crystallographic orientation, which can be evaluated by Schmid factor, geometric compatibility factor and misorientation. The dislocation pile-up leads to serious stress concentration and inhomogeneous deformation appeared in the areas near grain boundary, dislocation line and shear band, and the microvoids are easy to nucleate and grow in the above areas and then coalescence into microcracks. The primary crack formed by microcrack extension propagates along the activated slip system in the grain, and deflects as it passes through the grain boundary to coordinate the slip system in the adjacent grain, resulting in the overall crack propagation path being zigzag. Considering the damage prone location and crack propagation path, it can be concluded that the fracture mechanism of the alloy belongs to the intergranular and transgranular mixture.
![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")
