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Compressive deformation was carried out in an Ni-Co-based superalloy with relatively low stacking fault energy (SFE) at 725 °C and a strain rate of 10−2 s−1; the underlying micromechanisms were investigated under true compression strains varying from 0.1 to 1.0. It was found that dislocation slipping accompanied by stacking fault (SF) shearing dominated the compressive deformation under the strain of 0.1 and 0.2. As the strain increased to 0.3 and 0.4, microtwinning was activated and then interacted with dislocations, leading to the formation of dislocation tangles or blocky distorted region. When true strain was further increased to 0.6, abundant subgains (SGs) with polygonous shape appeared and then transformed into nanograins as true strain increased to 1.0. It is demonstrated that high strain and microtwinning are the prerequisites for the evolution of nanograins in the deformed Ni-Co-based superalloy. High strain can produce plentiful dislocations and distorted micro-sized SGs; then the microtwins sheared these distorted regions and refined the micro-sized SGs into nanoscale, which subsequently transformed into nanograins with further deformation. [ABSTRACT FROM AUTHOR]

The hydrogen embrittlement (HE) behavior of a selective laser-melted (SLM) 316L austenitic stainless steel has been investigated by hydrogen charging experiments and slow strain rate tensile tests (SSRTs) at room temperature. The results revealed that compared to the samples without H, the ultimate tensile strength (UTS) and elongation (EL) of specimens were decreased from 572 MPa to 552 MPa and from 60% to 36%, respectively, after 4 h of electrochemical hydrogenation with a current density of 100 mA/cm2. The negative effects of hydrogen charging were more pronounced on the samples' ductility than on their strength. A quasi in situ EBSD observation proved that there was little phase transformation in the samples but an increased density of low angle grain boundaries, after 4 h H charging. After strain was applied, the surface of the H-sample displayed many hydrogen-induced cracks along the melt pool boundaries (MPBs) showing that these MPBs were the preferred areas for the gathering and transferring of hydrogen. [ABSTRACT FROM AUTHOR]

The eutectic cast Al–Si alloys with excellent high-temperature and casting performance are widely used in engine pistons. During frequent starts and stops, the thermo-mechanical fatigue (TMF) is the most important failure cause. Ultrasonic melt treatment (UT) was chosen to compare and investigate the influence of micro-structures on fatigue life and damage mechanisms of as-cast (AC) eutectic Al–Si alloys under TMF loading. After UT, the grain size, primary Si, and intermetallic particles are reduced significantly in the alloy; fatigue life increases obviously. As a result of pilling-up of dislocations, the competitive effects of the critical strain/stress for fatigue crack nucleation can be found. There are two different crack initiation mechanisms under TMF: one is primary Si fracture for AC alloys with limited critical strain/stress for fatigue crack nucleation at fractured Si particles, and the other is primary Si debonding for UT alloys with increasing critical fracture strain/stress. After the crack initiation, the fractured or debonded primary phases provide the advantages for the further development of main cracks for both alloys. The UT alloy (805 ± 253 cycles) has about twice the TMF life of the AC alloy (403 ± 98 cycles). The refinement of micro-structures is instrumental in improving the fatigue resistance and life of TMF for the UT alloy. [ABSTRACT FROM AUTHOR]

The typical microstructure of the laser melting deposition (LMD) additive-manufactured Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy (TC11) contains the heat-affected bands (HABs), the narrow bands (NBs) and the melting pools (MPs) that formed due to the reheating and superheating effects during the layer-by-layer manufacturing process. Characterization results indicated that the coarse primary α lath (αp) and transformed β (βt) structures were located in the HABs, while the fine basketweave structure was formed inside the MPs. The rapid modifications of microstructure and tensile properties of the LMD-TC11 via electropulsing treatment (EPT) were investigated. The initial heterogeneous microstructure transformed into a complete basketweave structure and the HABs vanished after EPT. Thus, a more homogeneous microstructure was achieved in the EPT sample. The ultrafast microstructural changes were mainly attributed to the solid state phase transformation during electropulsing. The tensile properties of the sample were basically stable, except that the yield strength decreased as EPT voltage increased. This study suggests that EPT could be a promising method to modify the microstructure and mechanical properties of the additive-manufactured alloys in a very short time. [ABSTRACT FROM AUTHOR]

In order to obtain the optimum fatigue performance, 35CrMo steel was processed by different heat treatment procedures. The microstructure, tensile properties, fatigue properties, and fatigue cracking mechanisms were compared and analyzed. The results show that fatigue strength and yield strength slowly increase at first and then rapidly decrease with the increase of tempering temperature, and both reach the maximum values at a tempering temperature of 200 °C. The yield strength affects the ratio of crack initiation site, fatigue strength coefficient, and fatigue strength exponent to a certain extent. Based on Basquin equation and fatigue crack initiation mechanism, a fatigue strength prediction method for 35CrMo steel was established. [ABSTRACT FROM AUTHOR]

As common conductive materials, Al wires are used on overhead transmission lines under long-term heating conditions. In this study, the strength degradation behavior and the strength-electrical conductivity relation of the commercially pure Al wires (CPAWs) and the Al-Fe wires (AFWs) annealed at various temperatures were investigated based on the microstructure evolution. The strength degradation rate of the AFW is always higher than that of the CPAW. A linear trade-off relation between strength and electrical conductivity for the annealed Al wires are clarified. The results reveal that the mechanisms behind the trade-off relation between the strength and the electrical conductivity for the annealed CPAWs and the annealed AFWs are the recovery of dislocations and the obvious increase of grain width, which leads to the decrease of strength and the increase of electrical conductivity. The coalescence of precipitate in the AFW leads to the obvious decrease of strength, which results in the higher strength degradation rate for the AFW as compared with that for the CPAW. Consequently, the principle of microstructure design for anti-degradation of Al wire is presented. [ABSTRACT FROM AUTHOR]

The fatigue damage and fracture of metallic glasses (MGs) were reported to be dominated by shear band. While there exist several reviews about the fatigue behavior of MGs, an overview that mainly focuses on shear bands under cyclic loading is urgent, and is of great importance for the understanding of fatigue mechanisms and properties. In this review paper, based on the previous research results, the shear band evolution under cyclic loading including shear band formation, propagation and cracking, was summarized and elucidated. Furthermore, one strategy of enhancing the fatigue property through manipulating the microstructure to suppress the shear band formation was proposed. Additionally, the applications of the effect of annealing treatment and processing condition on fatigue behaviors were utilized to verify the strategy. Finally, several future directions of fatigue research in MG were presented. [ABSTRACT FROM AUTHOR]