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In this investigation, a variety of polyurethane composites with different syntactic hollow spheres were prepared by casting method, using 316 L stainless steel hollow spheres and 316 L stainless steel–Al2O3 double‐layer hollow spheres as reinforcements. The sound insulation and absorption properties of polyurethane composites with different syntactic hollow spheres were tested by impedance tube. The effects of the hollow spheres on the acoustic properties of composites were analyzed and compared with polyurethane resin and polyurethane/solid spheres composites. The experimental results reveal that the sound transmission loss of polyurethane can be improved by the addition of hollow spheres, and the range of sound absorption frequency of polyurethane tends to move to lower frequency. Otherwise, the sound insulation and absorption frequency range of polyurethane can be broadened by the effect of 316 L stainless steel–Al2O3 double‐layer hollow spheres. In addition, the compressive strength and stiffness of polyurethane composites have been significantly improved after hollow spheres added. Comparing with polyurethane, the compressive strength and stiffness of PU/316 L–Al2O3 HS increased by 47.9% and 115.9%, respectively. [ABSTRACT FROM AUTHOR]

In this study, heat treatment as a post processing was used in order to improve the microstructures and mechanical properties of Al 0 · 5 CoCrFeNi high entropy alloy (HEA), which fabricated by selective laser melting (SLM). Compared to the microstructure of SLM-ed Al 0 · 5 CoCrFeNi HEA, the strengthening the weakening mechanisms of HEA at different heat treatment temperatures are figured out. Heated at 1073 K for 4 h, the SLM-ed Al 0 · 5 CoCrFeNi HEA shows the 1419 MPa tensile strength. With increasing heat treatment temperature from 1073 K to 1673 K. The content of BCC phase decreases from 34.4% to 14.6%. The average size of BCC phase at grain boundaries increases from 0.497 μm to 2.271 μm, and the average size of BCC phase inside the grains increases from 0.037 μm to 1.216 μm. Moreover, dislocation network disappearance and recrystallization occur at 1173 K and 1373 K, respectively. The boundaries of the dislocation network, as the nucleation sites of precipitation, promote the formation of precipitated phases and form dislocation network wrapped by precipitated phases at 1073 K. The precipitated phases and the dislocation network wrapped by precipitated phases increase the tensile strength of SLM-ed HEA by 65.8%. The low dislocation density in the recrystallized grains change the morphology of the precipitated phases, and the aspect ratio of the BCC phases increases, which made the HEA still maintain a certain tensile strength at 1673 K. • The relationship between heat treatment and the mechanical properties of Al 0 · 5 CoCrFeNi HEA fabricated by SLM was explained. • The evolution of dislocation networks, precipitated phases and recrystallization after heat treatment was systematically studied. • Optimization of mechanical properties of the Al 0 · 5 CoCrFeNi HEA fabricated by SLM through heat treatment. [ABSTRACT FROM AUTHOR]

Effects of electropulsing treatment (EPT) on the microstructure evolution, mechanical properties and crack healing of intermetallic Al 3 Ti alloys were studied in this work. In order to investigate the athermal effect caused by EPT, conventional heat treatment (CHT) was conducted for comparison. The compressive stress-strain curves demonstrated that the failure strains of Al 3 Ti alloy increase under both the EPT and CHT conditions, while the increment of failure strain of Al 3 Ti alloy treated by EPT is higher than that treated by CHT. Fracture surface analysis confirmed that the intrinsic brittle fracture of Al 3 Ti alloy evolves into the quasi-cleavage fracture with increasing frequency of EPT. Based on the systematic investigation into the microstructure evolution, mechanical properties and fracture surface observation, the influence mechanism of EPT on Al 3 Ti alloy was found to be related to the improvements of atomic diffusion and dislocation movement, which results from the coupling of thermal effect and athermal effect by EPT. Furthermore, the thermal compressive stress and athermal effect could heal the local micro-crack and decrease the crack width of Al 3 Ti alloy by EPT. Therefore, EPT can work as a novel method for improving the plastic deformation capacity of Al 3 Ti alloy. [ABSTRACT FROM AUTHOR]

In this study, the ER321 stainless steel is fabricated by wire and arc additive manufacturing (WAAM) assisted with ultrasonic impact treatment (UIT). The mechanical properties and microstructure characterizations of ER321 stainless steel with and without UIT are investigated. It is found that grain structure of ER321 stainless steel is reduced to equiaxed dendrites (with UIT) from coarse columnar dendrites (without UIT). The UIT effectively refines grain sizes that decreases by ∼150% and homogenizes the grain structure of the deposition layers. Simultaneously, the UIT also facilitates the recrystallization that leads to the reduction of dislocation and texture densities. Furthermore, the improvement of grain structure enhances yield strength (∼10.5%), ultimate tensile strength (∼3.7%), microhardness (∼12.5%) and elongation of ER321 stainless steel. The grain boundary strengthening is the main strengthening mechanism, which leads to the yield strength increment of ER321 stainless steel under UIT condition. A way to effectively control grain structure in additive manufacturing-fabricated metal products using an UIT technique is provided in this work. [ABSTRACT FROM AUTHOR]

Abstract: The compressive mechanical properties of Mg–8Li–1Al–1Ce alloy were investigated under quasi-static strain rates (0.0001/s, 0.001/s, 0.01/s, and 0.1/s) and high strain rates up to ∼2700/s at room temperature. The experimental results indicate that the flow stress and strain rate sensitivity increase with increasing strain rate. Microstructure observation by optical microscopy reveals that the distribution of compound Al2Ce is influenced by the strain rate: when strain rate is higher, the compounds Al2Ce distribute in both α and β phases; when strain rate is lower, most of the compounds Al2Ce distribute in β phase and in the boundaries between α and β phases. Furthermore, it is found that the twinning forms in extruded Mg–8Li–1Al-1Ce alloys when deformed at high strain rates, and the amount of twinning increases with increasing strain rate, the deformation mechanism of Mg–8Li–1Al–1Ce alloy at high strain rates is a combination of dislocation motion and twinning. [Copyright &y& Elsevier]

Wire and arc additive manufacturing (WAAM) is a novel technique for fabricating large and complex components applied in the manufacturing industry. In this study, a low-carbon high-strength steel component deposited by WAAM for use in ship building was obtained. Its microstructure and mechanical properties as well as fracture mechanisms were investigated. The results showed that the microstructure consisted of an equiaxed zone, columnar zone, and inter-layer zone, while the phases formed in different parts of the deposited component were different due to various thermal cycles and cooling rates. The microhardness of the bottom and top varied from 290 HV to 260 HV, caused by temperature gradients and an inhomogeneous microstructure. Additionally, the tensile properties in transversal and longitudinal orientations show anisotropy characteristics, which was further investigated using a digital image correlation (DIC) method. This experimental fact indicated that the longitudinal tensile property has an inferior performance and tends to cause stress concentrations in the inter-layer areas due to the inclusion of more inter-layer zones. Furthermore, electron backscattered diffraction (EBSD) was applied to analyze the difference in Taylor factor between the inter-layer area and deposited area. The standard deviation of the Taylor factor in the inter-layer area was determined to be 0.907, which was larger than that in the deposited area (0.865), indicating nonuniform deformation and local stress concentration occurred in inter-layer area. Finally, as observed from the fracture morphology on the fractured surface of the sample, anisotropy was also approved by the comparison of the transversal and longitudinal tensile specimens. [ABSTRACT FROM AUTHOR]

In order to improve the microstructure of the Al 0.5 CoCrFeNi compositionally complex alloy (CCA) prepared by selective laser melting (SLM), the electropulsing treatment (EPT) has been used as a post processing in this study. The strengthening and softening mechanism was analyzed by comparing the microstructure of SLM-Al 0.5 CoCrFeNi CCAs under different EPT parameters. At a 10 s power on time, the substructure size of CCA decreases continuously with increasing voltage. Under 90V/10s EPT, the yield strength increases from 658 ± 10 MPa in the printed state to 748 ± 17 MPa, and the microhardness increases from 265.1 ± 5.6 HV 0.1 to 318.9 ± 5.0 HV 0.1. At 90V/20s EPT, the cellular substructure disappears, and a large number of uniformly distribute BCC phases precipitates inside the FCC matrix. At 90V/30s EPT, recrystallization occurs and the BCC phase coarsen. Dislocation network is the main factor that affects the strength of SLM-CCA. EPT can change the dislocation network structure to enhance the strength of SLM-CCA. Simultaneously, the EPT effectively promotes the transition from FCC phase to BCC phase in a short time. Joule heat and electronic wind force are the main reasons for changing structure and properties of SLM-Al 0.5 CoCrFeNi CCA. This work provides a post-processing method named as EPT to effectively control the microstructure in additive manufacturing CCA products. • Electronic wind force improves mechanical properties by adjusting the dislocation structure in SLM-Al 0.5 CoCrFeNi. • Electropulsing treatment promotes recrystallization and phase transition by reducing thermodynamic potential barriers. • A new EPT technology has been studied, which has broad application prospects in the field of AM-CCAs post-processing. [ABSTRACT FROM AUTHOR]

An optimized continuous ceramic SiC and shape memory alloy NiTi hybrid fibers reinforced Ti-Al metal-intermetallic laminated composite (as-optimized CSMAFR-MIL) was designed and fabricated using vacuum hot pressing sintering technique. The microstructure characterization of the composite was performed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). The formation mechanisms of the intermetallic layer were discussed. Furthermore, the mechanical properties of the as-optimized CSMAFR-MIL composite were measured via tensile tests. The experimental results indicated that the NiTi fibers were exhausted, and the inhomogeneous intermetallic layer was formed containing Al 3 Ni, Al 3 Ti, Al 3 Ti 0.8 V 0.2 intermetallics due to the reactions of Al with NiTi and Ti-6Al-4V alloy. Meanwhile, the intermetallic centerline, which usually appeared in Ti-Al laminated composite, was significantly eliminated in the as-optimized CSMAFR-MIL composite due to the diffusion reaction between NiTi fiber and Al. In addition, the SiC fibers combined well with the intermetallics, and the interfacial phases TiC and Al 4 C 3 were formed around the SiC fiber. Moreover, compared to continuous SiC fiber reinforced Ti-Al metal-intermetallic laminated (CFR-MIL) composite, the as-optimized CSMAFR-MIL composite possessed a good combination of high strength and superior ductility owing to the optimized microstructure of the composite and the mixed fracture mode of intermetallics. [ABSTRACT FROM AUTHOR]

Continuous Al 2 O 3 ceramic fiber reinforced Ti/Al 3 Ti metal-intermetallic laminated (CCFR-MIL) composite was fabricated using a vacuum hot pressing (VHP) sintering method and followed by hot isostatic pressing (HIP). The microstructure characteristics of the interfaces between Ti and Al 3 Ti, as well as Al 2 O 3 fiber and Al 3 Ti intermetallic were analyzed by scanning electron microscopy (SEM). Elemental distribution in the interfacial reaction zones were quantitatively examined by energy-dispersive spectroscopy (EDS). The phases in the composite were identified by X-ray diffractometer (XRD). The mechanical properties of the CCFR-MIL composite were measured using compression and tensile tests under quasi-static strain rate. The experimental results indicated that the residual Al was found in Al 3 Ti intermetallic layer of CCFR-MIL composite. The interfacial reactions occurred during HIP and the reaction products were determined to be Al 2 Ti, TiSi 2 , TiO 2 and Al 2 SiO 5 phases. Compared to Ti/Al 3 Ti MIL composite without fiber reinforcement, both the strength and failure strain of CCFR-MIL composite under both compressive and tensile stress states increased due to the contribution of the continuous ceramic Al 2 O 3 fiber. [ABSTRACT FROM AUTHOR]

The ER321 stainless steel was fabricated by laser and wire additive manufacturing (LWAM) assisted with ultrasonic vibration (UV) under synchronous motion conditions. It was found that the grain structure of ER321 stainless steel varied from coarse columnar dendrites (without UV) to equiaxed dendrites (with UV). And, the UV effectively weakened the texture strength and homogenized the grain structure of the deposition layers. The improvement of grain structure enhanced the microhardness (~10.7%) and yield strength (~11.9%) of ER321 stainless steel. These results show that this innovative manufacturing approach can effectively improve the problem of coarse columnar dendrites in the additive manufactured complex large-scale components. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) is an efficient technique for fabricating large and complex components that are applied in the manufacturing industry. In this study, anisotropic mechanical properties of a low-carbon high-strength steel component fabricated by WAAM were investigated via mechanical testing, and the transversal and longitudinal deformation behavior of the component were studied using the digital image correlation (DIC) method. Additionally, the features of microstructure, texture, and fracture mode of the inter-layer area and deposited area were also investigated to reveal the mechanism of anisotropy. The results showed the mechanical properties of longitudinal specimens were inferior to that of the transversal specimens. Several strain concentration zones in the longitudinal specimen were relevant to the inter-layer characteristics observed from the fracture surface and macrostructure, which was confirmed by the strain evolution recorded by DIC. The inter-layer areas were proved to be the weak link in the deposited component by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) analysis results, including various phase composition, phase morphology, misorientation angle, grain size, Schmid factor, and texture. Finally, based on the fractography analysis, anisotropy resulted from inter-layer zones is also confirmed via the comparison of transversal and longitudinal fracture morphology. [ABSTRACT FROM AUTHOR]