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Owing to excellent high-temperature mechanical properties, i.e., high heat resistance, high strength, and high corrosion resistance, Ti alloys can be widely used as structural components, such as blades and wafers, in aero-engines. Due to the complex shapes, however, it is difficult to fabricate these components via traditional casting or plastic forming. It has been proved that additive manufacturing (AM) is an effective method of manufacturing such complex components. In this study, four main additive manufacturing processes for Ti alloy components were reviewed, including laser powder bed melting (SLM), electron beam powder bed melting (EBM), wire arc additive manufacturing (WAAM), and cold spraying additive manufacturing (CSAM). Meanwhile, the technological process and mechanical properties at high temperature were summarized. It is proposed that the additive manufacturing of titanium alloys follows a progressive path comprising four key developmental stages and research directions: investigating printing mechanisms, optimizing process parameters, in situ addition of trace elements, and layered material design. It is crucial to consider the development stage of each specific additive manufacturing process in order to select appropriate research directions. Moreover, the corresponding post-treatment was also analyzed to tailor the microstructure and high-temperature mechanical properties of AMed Ti alloys. Thereafter, to improve the mechanical properties of the product, it is necessary to match the post-treatment method with an appropriate additive manufacturing process. The additive manufacturing and the following post-treatment are expected to gradually meet the high-temperature mechanical requirements of all kinds of high-temperature structural components of Ti alloys. [ABSTRACT FROM AUTHOR]

This work focused on the effects of laser energy density on the relative density, microstructure, and microhardness of Inconel 718 alloy manufactured by selective laser melting (SLM). The microstructural architectures, element segregation behavior in the interdendritic region and the evolution of laves phases of the as-SLMed IN718 samples were analyzed by optical metallography (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and electron probe microanalysis (EPMA). The results show that with an increase in the laser volume energy density, the relative density and the microhardness firstly increased and then decreased slightly. It also facilitates the precipitation of Laves phase. The variation of mechanical properties of the alloy can be related to the densification degree, microstructure uniformity, and precipitation phase content of Inconel 718 alloy. [ABSTRACT FROM AUTHOR]

2519A aluminum alloy thick plate is a promising structural material in the field of military industries, owing to its low density, high tensile strength and excellent ballistic performance. However, the nonuniformly distributed microstructure along the thickness direction of this alloy leads to delamination cracks, which restrict its further application in light armor fields. In order to understand the mechanism of delamination cracking along the thickness direction, the effect of the microstructure on the mechanical properties of 2519A aluminum alloy in the thickness direction was investigated. The results show that the elongation and critical stress intensity factor values (ΔKcr) of the alloy in the thickness direction are 45.8% and 44.1% lower than the values in the rolling direction, respectively. The low mechanical properties of the alloy may be due to the short distance between the second phase, the weak binding force of grain boundaries and the disharmonious deformation caused by the inhomogeneous distribution of the microstructure. This study provides a basis for improving the mechanical properties and delamination cracking of the alloy along the thickness direction. [ABSTRACT FROM AUTHOR]

• Ancient city wall of Xindeng in Fuyang, China was characterized. • Lime/clay/sand are present in the historical wall. • The results vary greatly among the locations selected. • High volume of aggregates and blue brick leads to great strength. • CaCO 3 and SiO 2 are the major phases present in the historical wall. The goal of this investigation is to characterize the mortar from the ancient city wall of Xindeng in Fuyang, Hangzhou (China), which reveals a history of nearly 1800 years. Several approaches were used to analyze seven specimens obtained from this ancient city wall, and physical properties, mechanical performances, binder/aggregate ratios of these specimens were then determined. However, the mixture compositions as well as the mix design vary greatly among different locations of the city wall. The results indicate that the historical wall is mainly composed of hydrated lime and sand, and parts of the specimens also contain clay. Meanwhile, calcite and quartz are the major phases present in the historical wall mortars with several impurities. Further, the specimens' great strength and large apparent density are related to the abundant aggregates used and the presence of the fragments of blue brick within the specimens. [ABSTRACT FROM AUTHOR]

• Fatigue properties of 2519A Al alloy were obviously improved after DST. • Increased aspect ratio of grain and PFZ width after DST increased the resistance to crack expansion along GBs. • Bridging effect of second phase reduced after DST enhance alloy's fatigue properties. 2519A aluminum alloy thick plates have excellent applications in the military industry due to their superior ballistic resistance and fatigue properties. However, the delamination cracking along the thickness direction of this alloy hinders its further utilization. To address this issue and enhance the fatigue properties of this alloy, the effect of single-stage solid solution treatment (SST) and two-stage solid solution treatment (DST) on the fatigue crack propagation (FCP) behavior in the thickness direction of the alloy was investigated. Compared to the optimum SST, the volume fraction of the secondary phase of the alloy was reduced by 28.6% after DST. The precipitated phases were finer with more uniform distribution, and the volume fraction and number density of the precipitation increased by 47% and 30%, respectively. The DST resulted in a lower fatigue crack growth rate (FCGR) and an increase of 2.92% in the critical stress intensity factor value (Δ Kcr). The crack propagation mode of the alloy after SST was inter/transgranular crack propagation, while it was transgranular after DST. The aspect ratio of grain and the number of secondary phases in the alloy decrease after DST. Meanwhile, the grain boundary (GB) precipitation phase spacing, the precipitation-free zone (PFZ) width, and the spacing between the secondary phases increase. These changes result in decreased crack sources in the alloy and reduced the bridging effect of secondary phases on fatigue cracks, thus improving the fatigue performance of the alloy. [ABSTRACT FROM AUTHOR]

Reactive MgO is a type of eco-friendly material with a lower carbon footprint, as it is produced by calcination of magnesite (MgCO 3) at 750 ℃, much less than that (i.e. 1450℃) needed for calcination of (CaCO 3) to produce clinker for Portland cement. Carbonation can enhance the mechanical properties of reactive MgO-based cementitious materials but will lower the pH value, leading to the neutralization of cement-based materials and further deterioration in rebar passivation. In this study, varying amounts of reactive MgO (0%, 10%, 20%, and 30%) were incorporated into mortars as cement replacements. By adjusting the duration of CO 2 curing (i.e. carbonation curing) and standard curing, it was found that the curing regime involving 36 hours of carbonation curing plus 26.5 days of standard curing led to a higher pH and compressive strength of cement mortars. The pore size distribution was improved as the internal pores of the mortar were filled with carbonation products, which hindered the reaction between CO 2 and alkaline hydration products inside specimens and was conducive to maintaining the alkalinity within the mortar. Therefore, the chloride ion penetration resistance and the mechanical properties of mortar were enhanced. SEM and EDS characterization results indicate that the excessive MgO did not fully participate in carbonation and continuously hydrated to generate Mg(OH) 2. The expansion of Mg(OH) 2 led to crack formation inside the mortar and reduced its strength, which accelerated CO 2 diffusion and further reduced the pH value of reactive MgO-based cementitious materials. • The optimal treatment was investigated for MgO-incorporated cement-based materials by considering carbonation and pH value. • The corresponding effects of MgO dosage on the fresh-state properties of mortars were studied. • Carbonates filled the internal pores of mortar and hindered further reaction between CO 2 and alkaline hydration products. • Carbonation treatment can enhance the chloride penetration resistance of reactive MgO-incorporated mortar. • Carbonation led to the formation of magnesium calcite that was more compact than Mg(OH) 2 crystal. [ABSTRACT FROM AUTHOR]

With the continuous upgrade of weapons, improving the mechanical properties of 7xxx laminated aluminum alloys for tank armor is a very important task. In this study, the 7B52 laminated aluminum alloy was strengthened through the successive solution treatment, large pre-deformation of 50%, and aging process. The yield strength, ultimate tensile strength, and interlaminar shear bonding strength of this alloy remarkably increased to 558 MPa, 593 MPa, and 93.8 MPa, respectively, which exceeded the values obtained after the traditional solution and aging processes. The effect of the large pre-deformation on the microstructural evolution and mechanical behavior of the 7B52 alloy was examined as well. The mechanical properties depended on the presence of dislocations, low-angle grain boundaries, and tiny precipitates in the alloy structure. The introduction of numerous dislocations and low-angle grain boundaries via large pre-deformation were beneficial for the full precipitation of tiny precipitates during the aging process. According to theoretical calculations, precipitation and dislocation strengthening were the dominant strengthening mechanisms. Moreover, because of its finer grain size, higher dislocation density, and larger number density of precipitates, the 7A62 alloy exhibited higher strength increments than those of the 7A52 alloy after pre-deformation. Therefore, a large pre-deformation may serve as an effective method for improving the mechanical properties of 7xxx laminated aluminum alloys for their application in the military industry. • Large pre-deformation enhances the mechanical properties of 7B52 laminates. • The increase in laminate strength is dominated by precipitation strengthening. • 7A62 alloy shows a higher strength increase after pre-deformation than 7A52 alloy. • Plasticity mismatch promotes the void growth and crack propagation processes. [ABSTRACT FROM AUTHOR]