Wire-feed electron beam additive manufacturing (EBAM) is a promising manufacturing process for fabrication large-scale, fully dense and near net shape metallic components. However, limited knowledge ...is available on the wire-feed EBAM process of titanium alloys. In this work, the Ti-5Al-2Sn-2Zr-4Mo-4Cr near β titanium alloy sample was fabricated by the EBAM process and the effect of subtransus solution and aging treatment on the microstructure evolution and mechanical properties was investigated. The results reveal that the volume fraction of the primary α decrease dramatically from 48.6% to 8.9% with increasing the solution temperature from 750 °C to 850 °C. The ultimate tensile strength and yield strength increase monotonously with increasing of the solution temperature, while the elongation and reduction of area change conversely. The thickness of the secondary α (αS) increases significantly from 28.6 nm to 120.1 nm with the aging temperature increasing from 550 °C to 710 °C. The volume fraction and thickness of αS are sensitive to the aging temperature and strongly influence the mechanical properties. The quantitative relationship between the microstructure and mechanical properties was established. As a good result, the tensile properties of the post-deposition heat treated alloy at 400 °C can meet the standard requirements for wrought counterpart.
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•Wire-feed electron beam additive manufacturing of Ti-5Al-2Sn-2Zr-4Mo-4Cr near β titanium alloy was conducted.•The volume fraction and thickness of α phases can be tailored by adjusting the temperature of solution and aging treatment.•400 °C tensile properties of the post-deposition heat treated alloy can meet the requirements for wrought counterpart.•Quantitative relationship between the phase volume fraction, phase size and mechanical properties was firstly established.
Multiwall carbon nanotubes (CNTs) – carbon fibers (CFs) hybrid materials were produced by directly growing CNTs on CFs by means of chemical vapor deposition. For the latter, the oxidative ...dehydrogenation reaction of C2H2 and CO2 was applied, which allows growing CNTs without damaging the CF surface. Uni-directional nano-engineered carbon fiber reinforced composites (nFRCs) were fabricated by impregnating these hybrid materials with epoxy. The nFRCs subjected to single fiber push-out tests revealed a decrease of the interfacial shear strength (IFSS) of about 36% compared to the carbon fiber composites without CNTs. By means of transverse three-point bending tests performed on pre-notched composite beams inside a scanning electron microscope, the fracturing behavior parallel to the fibers was studied in-situ. The nFRCs showed significantly reduced fiber/matrix debonding while CNTs pull-out, CNTs bridging as well as matrix failure occurred. These results demonstrate that the presence of CNTs in nFRCs affects the stress distribution and consequently the damage initiation as well as the damage propagation. The presence of CNTs suppresses the stress concentration at the fiber/matrix interface and reduces the debonding of CFs from the matrix. However, our results indicate that the stress concentration shifts towards the CNTs' ends/matrix interface and causes promoted matrix failure leading to lower IFSS.
The failure behaviors of 3D woven composites (3DWC) under biaxial tensile loadings are investigated through a combined experimental and numerical approach in this paper. Appropriate biaxial cruciform ...specimen of 3DWC is first designed according to the experimental requirements. The biaxial tensile experiments are conducted on a servo-hydraulic biaxial testing facility, and then the full-field strain distributions and crack morphologies of cruciform specimens are analyzed in detail. For the multiscale geometric reconstruction of 3DWC, a full-thickness mesoscopic RVC is first extracted from the periodic woven architecture, and then a novel full-scale geometric modeling method is developed to reconstruct the biaxial cruciform specimens of 3DWC. Particularly, in conjunction with the micromechanics of failure theory, a multiscale damage model is proposed to simulate the biaxial failure behaviors of 3DWC. With the stress amplification factor, a transfer relationship between mesoscopic and microscopic stresses is established, and then the damage states of matrix and fibers within yarns can be separately determined. By comparing the experimental and predicted results, the realistic damage mechanism of 3DWC under biaxial tensile loading can be elucidated.
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In the Arctic, the fatigue properties of marine steels under low temperatures and complex loads are essential for the safety of ship navigation. In this study, the fatigue crack growth (FCG) ...characteristics of EH36 and EQ70 steels are explored under low-temperature mixed mode (I + II) through experiments and numerical simulation. Experimental results show that the FCG life and the crack growth retardation (CGR) effect of both steels correlate positively with the loading angle and negatively with the temperature. The prediction results for FCG path indicate that the Maximum Tangential Stress (MTS) criterion provides accurate predictions for loading angles less than 45° in low-temperature mixed mode (I + II), while the Richard model is more suitable for the loading angle of 60°. The simulation results show that, when the crack deflects, KII decreases rapidly in magnitude while KI gradually increases and becomes dominant. The SEM results for the FCG fracture surfaces in both steels revealed that the roughness of the fracture surface is positively correlated with the loading angle, moreover clear transition regions are observed between the pre-crack and crack growth regions.
•The FCG life of EH36 and EQ70 steels positively correlates with loading angles.•A transition region exists before the crack deflection.•The MTS criterion is more accurate to predict FCG path at 30° and 45°.•Low-temperature mixed-mode loading triggered a crack growth retardation effect.•The fracture roughness of both steels correlates positively with loading angle.
The fracture behaviour of grains and grain boundaries plays an important role in the design of novel ceramics with improved macromechanical deformability. This was investigated first time in a ...dual-phase high-entropy carbide/boride ceramic, using microcantilever bending, linear beam theory and micro/nanofractography. Microcantilevers were focused ion beam milled from the carefully polished sample surface with random locations containing both carbide and boride grains and grain boundaries in the beam volume. Scanning electron microscopy-based fractography analysis revealed that the bending strength of grain/phase boundaries varies in the range of 0.9–6.7 GPa, depending on the orientation and location of the boundaries in the beam. The fracture of carbide grains was found to be initiated mainly on submicron size volume defects with strength values of 4.5–9.5 GPa, while the fracture origin in most boride grains was identified as surface defects introduced by specimen preparation, which resulted in higher fracture strengths of 9.0–12.3 GPa.
Although single crystal gallium arsenide (GaAs) is a technologically important semiconductor material, its mechanical behavior is poorly understood. In this study, the Vickers microindentation ...technique was leveraged with a quantitative fractographic approach to determine the fracture energy and toughness corresponding to various crystal planes. Cracks preferentially propagated along the {110} planes associated with the primary crack system {110} / 〈110〉. The normalized fracture toughness was used to calculate the directional fracture energy on the {001} plane and was consistent with a theoretical model based on calculating the number of broken bonds.
Creep behavior in interlaminar shear of an advanced SiC/SiC composite with a self-healing matrix was investigated at 1300℃ in laboratory air and in steam. The composite was processed via chemical ...vapor infiltration (CVI). The composite has a self-healing oxidation-inhibited matrix comprising alternating layers of silicon carbide and boron carbide and is reinforced with laminated woven Hi-Nicalon™ fibers. Fiber preforms were coated with pyrolytic carbon followed by a boron carbon overlay. The interlaminar shear properties were evaluated at 1300℃. The creep behavior was examined for interlaminar shear stresses ranging from 13 to 20 MPa in air and in steam. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. Creep run-out (defined as 100 h at creep stress) was achieved at 13 MPa in air and in steam. Presence of steam had little influence on creep strain rates and creep lifetimes. However, larger creep strains were accumulated in steam than in air. The retained properties of all specimens that achieved creep run-out were characterized. Composite microstructure and damage and failure mechanisms were investigated.
This work introduces a novel, fractographic method to extend the current, state-of-the-art, fractographic techniques to chemically strengthened (CS) glasses with large, surface flaws. The proposed ...method uses proven relationships based on dimensional analysis to correlate the flexural fracture strength to newly-introduced, fractographic length-scales. The technique requires knowledge of the residual stress profile and access to standard visualization tools such as optical microscopes. The proposed methodology was validated on three sets of aluminosilicate CS glass plates with depth of the compressive layer (DOL)ranging between 28~54μm and surface stress 980–1140 MPa, and one set of untreated plates. For the CS and untreated glass plates considered, the proposed fractographic technique estimated the fracture strength within (2 ± 11)% of experimental values, which is comparable to the accuracy of fractographic techniques currently used for annealed, brittle specimens.
In this study, linear friction welding is applied to join JIS-S45C medium carbon steel with ferrite and pearlite structures at temperatures above and below the A1 point. Additionally, low-strain-rate ...tensile tests are conducted both in air and with a cathodic hydrogen charge to evaluate the hydrogen-embrittlement susceptibility of the linear friction-welded joints under both joining conditions. Results of hydrogen thermal-desorption analysis show that the hydrogen-charging conditions in this study simulated atmospheric corrosion conditions. The joining zone of the above-A1 joint comprises fine martensite and ferrite, whereas that for the below-A1 joint comprises ultrafine ferrite and cementite. In air tensile tests, both joints fractured in the base-metal region, thus suggesting the high reliability of the joints. In the hydrogen-charged tensile test, the above-A1 joints exhibit premature fracture at the joining zone. By contrast, the below-A1 joints exhibit base-metal fractures, thus suggesting that the joints are highly reliable in a hydrogen environment. Fracture-surface observations show that the above-A1 joints exhibit cleavage fractures in the martensite-dominated region. Tensile tests on heat-treated martensite S45C specimens show that their fracture strength decreased significantly in a hydrogen environment. Therefore, the joint fracture is due to the significant decrease in the fracture strength of martensite formed in the above-A1 joints in the hydrogen environment. The linear friction-welded medium carbon steel joints below the A1 temperature can ensure reliability even in a hydrogen environment.
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