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Electrochemical impedance spectroscopy (EIS) of bare type A3 mild steel and silicone-epoxy hybrid coatings/mild steel system in 5 wt.% NaCl solution has been investigated, respectively. The analyses of impedance models and water uptake behaviors of silicone-epoxy hybrid coatings have been studied during the aging process of the coatings. Taking into account the diffusion of oxygen, water and corrosion products as well as the formation of the passive film, six distinguishing impedance models were used to fit the EIS spectra of the coatings on type A3 mild steel. The water uptake was estimated from the Brasher–Kingsbury relation using CPE and two effective capacitances ( C e f f e c t B and C e f f e c t H ) which were also used to calculate the coating thicknesses. A comparison between the coating thicknesses calculated from the effective capacitance C e f f e c t B and thickness gauge measurements suggested a surface distribution of time constant on the surface of the coatings. The use of C e f f e c t B allows estimating the “true” values of water uptake in the silicone-epoxy hybrid coatings.

A series of uniaxial fatigue tests were carried out using specimens containing non-cold expanded and cold expanded holes to assess the effect of split sleeve cold expansion on fatigue behavior of titanium alloy TC4. The fracture surfaces of specimens were observed by scanning electron microscope (SEM). 3D finite element models were also used to analyze the residual stress fields around cold expanded holes. Based on the qualitative finite element analysis (FEA), the multi-axial fatigue lives of the non-cold and cold expanded holes have been predicted by Smith–Watson–Topper (SWT) method and Wang–Brown (WB) method respectively. The effects of the friction between the split sleeve and the hole’s surface were also considered. The results reveal that crack of cold expanded specimen always initiates near entrance face and the crack propagation speed along transverse direction is faster than along axial direction. The lowest compressive stress occurs at the entrance face where crack is preferentially initiated. The mandrel entrance face is the most sensitive region to friction between the split sleeve outer surface and the hole. After cold expansion, fatigue life of TC4 open hole was increased to 1.7–2.2 times. Compared with the result of SWT theory, the result of WB theory is more conservative and reliable.

Water diffusion in a composite coating on 2024 Al alloy was experimentally studied using electrochemical impedance spectroscopy (EIS). The composite coating contained an inner silane film and an outer silicone-epoxy layer. The measured value of water diffusion coefficient of the composite coating by the EIS method was compared to the value predicted using a mathematical model. The results indicated the non-continuity of water concentration at the interface of silane film and silicone-epoxy layer. Considering water concentration jump on the silane film/silicone-epoxy boundary, the diffusion coefficient of the composite coating obtained by validation model was similar to that obtained from the experimental method.

A silicone-epoxy hybrid coating cured with amino silane was developed to provide corrosion protection on 2024 Al-alloy using air spraying. Water uptake characteristics of the silicone-epoxy hybrid coatings were investigated by electrochemical impedance spectroscopy in a 5 wt% NaCl solution. The effect of mixture ratio of silicone-epoxy and amino-silane on the water uptake (solubility, diffusion coefficient and permeation) was studied by using a single frequency (10 kHz) capacitance method. The glass transition temperature (Tg) was also investigated through differential scanning calorimeter (DSC) before and after immersion in the NaCl solution. Consequently, the excess of silicone-epoxy resin or amino silane improved the solubility of water in the coatings. A low water permeation coefficient was obtained with the mixing ratio 8/2 of silicone-epoxy and amino-silane, in which the Tg value was found to be larger than other three mixing ratios before immersion. After immersion for 750 h, the impedance modulus of EFA 2 coating (mixing ratio 8/2) in the low frequency was still close to 108 Ω cm2 that accounts for the good protective performance.

Selective laser melting (SLM) manufactures components through the overlapping of multi-track and multi-layer molten pools of metal powders, resulting in two types of molten pool boundaries (MPBs), “layer–layer” and “track–track” MPBs, remaining in SLM parts. The microstructure of MPBs exhibits a complex and regular spatial topological structure. There is a coarse grain zone below the MPBs and nonmetallic elements (C, O, Si) near the MPBs are in an unstable state. Long and thin columnar grains with the same orientations distribute on two sides of the “layer–layer” MPBs, whereas the columnar grains on both sides of “track–track” MPBs have different orientations. The “track–track” MPBs are short and intersect with “layer–layer” MPBs at some points and form acute angles, where cracks are initiated when applied with external loads. The effect of the MPBs on microscopic slipping, macroscopic ductility and fracture mechanism of the SLM parts made along different directions, which were exerted a tensile loading in the as-built condition without heat treatment, was analyzed and evaluated using slip theory and experiments. The results reveal that the MPBs have a significant impact on the microscopic slipping at the loading, macroscopic plastic behavior and fracture mode, and are one of the main reasons for the obvious anisotropy and low ductility of SLM parts.

The current available selective laser sintering (SLS) and selective laser melting (SLM) systems have relatively small effective building volumes, which do not offer capability to integrally manufacture a large dimension component. Therefore, our research team in Huazhong University of Science and Technology, China, has broken through some key techniques such as the large powder bed preheating system and multi-laser scanning technique, and then successfully developed a series of large-scale SLS systems with effective building volumes up to 1400×1400×500 mm3, and an SLM system with an effective building volume of 500×250×400 mm3. These large-scale SLS/SLM systems will not only offer new capability to make large complex prototypes and products, but also provide higher volume production capability to make numerous small parts rapidly and cost-effectively. In addition, several high performance materials have been developed for the large-scale SLS/SLM systems.

The relationship between the three points bending creep test and the uni-axial creep test on the single crystal superalloy was investigated by using crystal plasticity slip theory with a three-dimensional (3D) finite element model. The purpose of the present work is to build the relationship between bending creep and conventional uni-axial tensile creep in determining crystallographic creep parameters for face centered cubic (FCC) nickel-based single crystal superalloys. To this aim, the bending creep performed on [001]-, [011]-, and [111]-oriented nickel-based single crystal superalloys were respectively investigated, and the data was compared with those obtained with uni-axial tensile creep counterparts. It shows that the determination of crystallographic creep stress exponent is independent of crystallographic orientations, and the results agree reasonably well between bending creep test and uni-axial tensile creep test. The findings may shed some light on understanding of the crystal structures and its time-dependent deformation mechanisms with the bending creep method.

Fastener load-transferred experiments and fatigue tests of the scarfed lap riveted joints with different lap angle were carried out. The fracture surfaces were observed by optical microscope (OM) in this paper. Both experimental and computational studies were described and compared when possible. Based on the qualitative finite element analysis (FEA), the multi-axial fatigue life of the scarfed lap riveted joints has been predicted by Smith–Watson–Topper (SWT) method and Wang–Brown (WB) method respectively. Both of the test results and predicted results show that fatigue life of scarfed lap riveted joints is remarkably increased after introducing lap angle into the faying surface. 8 mm-thick specimens with the lap angle of 1.68 °C exhibit the best fatigue performance, and 20 mm-thick with the lap angle of 3.37 °C do in the present study. Compared with the result of WB theory, the result of SWT theory is more conservative and reliable. For structures’ reliability designs, SWT theory and WB theory are all fallibility.

Bending creep test (based on overhang beam geometry) is investigated by incorporating the important contribution of residual stress. Finite element simulations considering the residual stress is employed to investigate the residual stress behavior of bending creep specimen. We propose several methods to determine the creep parameters directly from the bending creep tests. We considered two cases of residual stress, one is tensile residual stress. The other is compressive residual stress. The present work may shed some light on the influences during bending creep, as well as provide an efficient way to determine material residual stress characteristics.