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Four porous corundum‐spinel aggregates were prepared from magnesia and α‐Al2O3 micropowder via the Kirkendall effect. Effects of the particle size of magnesia (PSM, 0–74 μm, 0–15 μm, and 0–44 μm) and firing temperature (1100–1600°C) on the phase compositions, microstructures, pore characteristics of the prepared porous aggregates were investigated. As the firing temperature increased, the PSM influenced the reaction rate of magnesia and alumina, and the sintering process, leading to remarkable changes in the phase compositions, porosity, and microstructure with a negligible impact on the pore size distribution. As the PSM decreased from 0–74 μm to 0–15 μm, the apparent porosity initially increased and then decreased. Relatively compact cyclic spinels formed around the Kirkendall pores in aggregates with 0–74 μm and 0–44 μm magnesia added after fired at 1600°C, as the expansion of spinel formation was inhibited by the high strength of the alumina matrix. Finally, the optimized product is an aggregate with 0–44 μm magnesia added, which exhibits a high total porosity of 32.4%, a low bulk density of 2.69 g/cm3, and a thermal conductivity of 2.178 W/(m·K) at 1000°C, as well as a high compressive strength of 302.5 MPa and a small median pore size of.46 μm. This work provides a promising technique for preparing porous‐corundum‐based aggregates. [ABSTRACT FROM AUTHOR]

Aluminum oxynitride (AlON) ceramics doped with different sintering aids were synthesized by spark plasma sintering process. The microstructures, mechanical, and optical properties of the ceramics were investigated. The results indicate that the optimal amount of sintering aids is 0.06 wt% La2O3 + 0.16 wt% Y2O3 + 0.30 wt% MgO. The addition of La3+ and Mg2+ decreases the rate of grain boundary migration in ceramics, promotes pore elimination, and inhibits grain growth. The addition of Y3+ facilitates liquid‐phase sintering of AlON ceramics. Moreover, the addition of Mg2+ effectively promotes twin formation in the ceramics, which hinders crack propagation and dislocation motion when the ceramics are loaded. Hence, the AlON ceramic doped with 0.06 wt% La2O3 + 0.16 wt% Y2O3 + 0.30 wt% MgO exhibits a relative density of 99.95%, an average grain size of 9.42 μm, and a twin boundary content of 10.3%, which contributes to its excellent mechanical and optical properties. [ABSTRACT FROM AUTHOR]

The formation mechanism and evolution of plastic damage in billet during reduction pretreatment were investigated using laboratory experiments and simulations. The microstructure and damage distribution were observed using reduction pretreatment experiments. Isothermal tension tests were designed to study the mechanism of damage under different deformation temperatures and strain rates. A plastic damage model based on tension tests was established to further analyze damage evolution during reduction pretreatment. Experimental results showed that the distribution of the damage was characterized by microvoids near the surface and microcracks along the grain boundary at the center. With the increase in strain rate, plastic damage above 1050 °C was transformed from grain boundary damage caused by grain boundary slip to inclusion damage caused by dislocation movement. The simulation results showed that the established plastic damage model was reliable and could be used to describe the plastic damage evolution during reduction pretreatment. [ABSTRACT FROM AUTHOR]

Cermet coatings are post-treated by a new surface microcrystallization technology, namely high-temperature-assisted ultrasonic deep rolling (HT + UDR). The process parameters of ultrasonic deep rolling significantly affect the microstructure and tribological properties of the Ni-WC coatings. In this paper, the samples were treated with different preloading depths (0.20 mm, 0.25 mm, and 0.30 mm), and the microstructure and properties of the coatings were characterized by SEM, EDS, X-ray stress analysis, and micro-Vickers hardness testing. An MMW-1A-type friction and wear tester was used for the dry friction and wear test at room temperature, respectively. Compared with the untreated sample, plastic rheology occurred on the surface of the coatings after HT + UDR, showing a phenomenon of "cutting peaks and filling valleys". In the treated coatings, visible cracks were eliminated, and the inside of the coating was denser. The surface hard phase was increased as a "skeleton" and embedded with the soft phase, which played a role in strong and tough bonding. After HT + UDR + 0.25 mm treatment, the surface roughness increased by 68%, the microhardness of the surface layer reached a maximum of 726.3 HV0.1, and the residual tensile stress changed from 165.5 MPa to −337.9 MPa, which inhibited the germination and propagation of cracks. HT + UDR improved the wear resistance of the coating in many aspects. The coating after the 0.25 mm preloading depth treatment possessed the smallest friction coefficient and the lowest wear amount, which is 0.04 and 4.5 mg, respectively. The wear form was abrasive wear, and the comprehensive tribological performance is the best. [ABSTRACT FROM AUTHOR]

Due to the shortage of high-quality fly ash (FA) in Kenya, the successful construction of the Mombasa–Nairobi railway had to rely on the abundant natural pozzolan resources in the country instead. In the work reported in this article, concrete samples produced using 30% FA, 30% fine tuff (FT), 30% fine volcanic slag (FVS), or 10% FA and 20% FVS to replace cement were tested. The hydration activity of the FT was found to be poor. The mechanical properties and durability of the concrete made with FVS were close to those of the FA concrete and optimal performance was obtained from a mixture of FA and FVS. Mercury intrusion porosimetry, X-ray diffraction and differential thermal analysis were used for microanalysis of cementitious systems with 70% cement and 30% FA, 70% cement and 30% FT, and 70% cement and 30% FVS. The results were promising and suggested that the FVS possessed obvious secondary hydration activity and could improve the microstructure of the concrete matrix. It is therefore feasible to use natural pozzolans instead of FA to produce high-performance concrete in railway projects, which would reduce construction costs and help protect the environment. [ABSTRACT FROM AUTHOR]

The microstructure and high temperature mechanical properties of as-cast FeCrAl alloys with varying aluminum contents were experimentally investigated. Crystal phases were identified using X-ray diffractometry and the solidified structures were analyzed, taking into account the freezing range, AlN precipitation and the aluminum addition. A series of tensile tests were conducted at temperatures from 700 °C to 1200 °C and the effects of aluminum content on the stress-strain behavior including peak stress, yield stress and Young's modulus were investigated. The solid-solution strengthening of aluminum is reflected by the increase of peak stress and yield stress with increasing aluminum content at all temperatures, particularly below 1000 °C. Hot ductility is discussed in terms of the variations of the reduction in area value with temperature. Decreased ductility between 800 °C and 900 °C is attributed to ferritic grain coarsening and the precipitation of carbides within the grain boundaries. The occurrence of continuous dynamic recrystallization under the conditions of this study, can play an important role in grain refinement thus increasing the hot ductility of FeCrAl alloys. [ABSTRACT FROM AUTHOR]

The microstructure evolution and mechanical properties under different temperature of as-cast Al-La alloys with varying La contents were investigated by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and tensile test (Gleeble 3500). The results revealed that the phase compositions of Al-xLa (x = 10, 15, 20) alloys were α-Al and Al 11 La 3 . Comparing with Al-10La, the mechanical properties of Al-15La and Al-20La were deteriorated due to the formation of strip-shaped and particle-shaped primary Al 11 La 3 phase respectively. The influence of Al 11 La 3 phase on tensile strength has a downward trend with the increasing temperature, and elevated temperature is more helpful to increase the plasticity of Al-La alloys with high La content. According to the tensile fracture of the three Al-La alloys at temperature range from 200 °C to 500 °C, Al-10La tended to be highly dimples driven, and dimples became larger and deeper with increasing temperature, which demonstrated a growing ability to avoid crack extension. There was a transformation from cleavages to dimples in Al-15La and Al-20La with increasing temperature, but the dimples were small and shallow indicating lower plasticity than Al-10La. [ABSTRACT FROM AUTHOR]

The effect of calcium oxide on the crushing strength, reduction, and smelting performance of high-chromium vanadium-titanium magnetite pellets (HCVTMP) was studied in this work. The main characterization methods of an electronic universal testing machine (EUTM), X-ray fluorescent (XRF), inductively-coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), and scanning electron microscope-energy disperse spectroscopy (SEM-EDS) were employed. The crushing strength was affected by the mineral phases generated during oxidative baking and the subsequently-formed pellet microstructures owing to CaO addition. The reduction and smelting properties of HCVTMP with different CaO additives were measured and characterized with different softening-melting-dripping indices. Although HCVTMP showed the highest crushing strength with CaO addition of ca. 2 wt %, more CaO addition may be needed to achieve high permeability of the furnace burdens and a good separation condition of the slag and melted iron. In the formation process of the slag and melted iron, it can be determined that CaO could have a relationship with the transformation behavior of Cr, V, and Ti to some extent, with respect to the predominant chemical composition analysis of ICP-AES and XRF. With the microscopic examination, the restraining formation of Ti(C,N) and the promoting formation of CaTiO3 are in accordance with the improved melting-dripping indices, including the decrease of the maximum external static load and gas permeability, and the increase of the melting-dripping zone and dripping difficulty. [ABSTRACT FROM AUTHOR]

TA15 Ti-alloy is widely used to form key load-bearing components in the aerospace field, where excellent service performance is needed. Near-β forging technology provides an attractive way to form these complicated Ti-alloy components but subsequent heat treatment has a great impact on the final microstructure and mechanical properties. Therefore evaluation and determination of the heat treatment route is of particular significance. In this paper, for the near-β forged TA15 alloy, the formation and evolution of microstructures under different subsequent heat treatment routes (annealing, solution and aging, toughening and strengthening) were studied and the cooling mode after forging was also considered. Then, the type and characteristics of the obtained microstructures were discussed through quantitative metallographic analysis. The corresponding mechanical properties (tensile, impact toughness, and fracture toughness) and effects of microstructural characteristics were investigated. Finally, for a required microstructure and performance a reasonable heat treatment route was recommended. The work is of importance for the application and development of near-βforging technology. [ABSTRACT FROM AUTHOR]

Strain localization influenced by microstructural features has an important effect on mechanical properties of α + β titanium alloy. To address the effect, a microstructure-based finite element model is established. In this model, regions for primary α (αp) and transformed β matrix (βt) are generated from real microstructures of a two-phase titanium alloy (TA15 alloy); the plastic flow behaviors of these two features are determined directly rather than from single phase alloy. A constitutive equation of αp is developed with consideration of dislocation-obstacle interaction, whereas the constitutive equation of βt is determined by nanoindentation tests. Finally, the calculated stress-strain responses of the alloy are verified by experiments. The simulated results show that strain localization bands (SLBs) have two morphologies: short and long-continuous SLBs. Lots of short SLBs appear mainly in βt and αp when the volume fraction of αp is small and moderate, respectively. Long-continuous SLBs appear mainly in αp when the volume fraction of αp is large. With the increase of αp in SLBs, the strength of the alloy decreases while the ductility increases. By decreasing the disparity of strength between αp and βt, the strain gradient in SLBs reduces and the ductility of the alloy increases. [ABSTRACT FROM AUTHOR]

Abstract: Wettability tailoring of patterned silicon surface has great potential in fields producing integrated circuits, solar cells, sensors, detectors, and micro/nano electromechanical systems. The present paper presents a convenient yet effective method of combining reactive ion etching and catalyzed etching to prepare silicon surface with micro–nano dual-scale pillars. The experimental results indicate that the hydrophilic surface transformed to a superhydrophobic surface when micro–nano dual-scale pillars were formed. The surface preserved superhydrophobicity even when the geometric parameters of the micropillars were changed. Overhangs of water drops on steep micro–nano dual-scale pillars result in superhydrophobicity. This method offers a new way for tailoring the wettability of patterned silicon surfaces. [Copyright &y& Elsevier]

Abstract: Metal undergoes complicated microstructural evolution during hot ring rolling (HRR), which determines the quality, mechanical properties and life span of the ring formed. In this paper, a three-dimensional rigid–plastic and coupled thermomechanical finite element model for HRR was developed and combined with a microstructural evolution model of AISI 5140 steel, on the basis of a DEFORM 3D software platform. The material’s microstructural evolution in the HRR process was thoroughly studied, and the effects of forming parameters (rotational speed of the driving roll, feed rate of the idle roll, initial temperature of the ring and friction factor) on the volume fraction of dynamic recrystallization (DRX), DRX grain size, the volume fraction of recrystallization and average grain size were investigated. The results obtained provide a guide for the quality and process control of HRR. [Copyright &y& Elsevier]

The microstructural evolution and corrosion behaviour of railroad flash-butt-welded U71Mn joints and the effect of heat treatment were investigated via scanning electron microscopy and electrochemical measurements. The joint structures were found to mainly comprise pearlite and a few ferrites. The grains became finer and more homogeneous after heat treatment. Additionally, there was a decrease in the corrosion current density (1.71 × 10−5 A cm−2) and increases in the absolute corrosion potential (0.86 mV) and corrosion resistance (1088.83 Ω−1cm2). This was primarily attributed to the fewer Cl− ions at the homogeneous grain boundaries and fewer oxidation reactions on the joints after heat treatment. The findings of this study explain corrosion failure and will guide the development of corrosion-resistant joints for improved railroad quality.

Precipitation strengthened austenitic stainless steels are widely used in hydrogen related applications. However, their applications may face hydrogen damage resulting in hydrogen-induced delayed failure. Results show that the weld is more sensitive to fracture and hydrogen-induced failure than the matrix. High density curved dislocations, abundant of large size precipitates and considerable γ′ precipitates coarsening are found in the weld. Large size precipitates are found to be major hydrogen traps and preferential microcrack nucleation sites. The γ′ precipitates coarsening make the weld more ductile than the matrix. With the decrease of the applied stress, hydrogen-induced cracking mechanism in the weld changes from brittle transgranular fracture to brittle intergranular fracture. [ABSTRACT FROM AUTHOR]

In this study, Ni/W–TiN composites were fabricated by the pulse current electrodeposition (PCE) method. The effects of TiN concentration on the microstructure, microhardness, and wear properties of the resulting composites were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), microhardness tester, and friction wear testing. Among the four obtained composites, Ni/W–TiN composite prepared at 8 g/L showed the densest and finest surface structure. The TiN contents in obtained Ni/W–TiN composites at 8 and 16 g/L were estimated to 8.1 and 5.4 wt%, respectively. The average Ni/W grain diameter in Ni/W–TiN composite obtained at 8 g/L TiN was recorded as 84.7 nm. The protrusion and depression heights of the composite deposited at 8 g/L were 81.8 and 45.4 nm, respectively. This composite also processed an average microhardness of 897.6 HV, with only a few shallow and narrow scratches on its worn surface, demonstrating its prominent wear resistance when compared to the other three composites. [ABSTRACT FROM AUTHOR]

"SPS pre-sintering + SPS reactive hot extrusion" (SPSHE) is a promising technique for manipulating the orientation of TiB whiskers (TiBw) in discontinuously reinforced titanium matrix composites (DRTMCs). In the current study, (12.4 vol % TiBw +2.9 vol % TiC)/Ti6Al4V composites were prepared using SPSHE technology, successfully achieving both the normalization of TiBw orientation and a high aspect ratio. Specifically, the [010] axis of TiBw was aligned with the extrusion direction, and the average aspect ratio was 24.86. Tensile tests were conducted on the DRTMC samples at temperatures of 873 K, 923 K, and 973 K. The results demonstrate that SPSHE significantly enhances the high-temperature strength of the composite. At 873 K, the DRTMC exhibited an exceptionally high tensile strength of 732.2 ± 20 MPa. The main strengthening mechanisms of the DRTMC include load transfer strengthening from TiBw and TiC particles, solution strengthening, fine grain strengthening and dislocation strengthening. Moreover, at 873 K and 923 K, the dominant failure mode of the reinforcement was a load-bearing fracture. However, as the test temperature increased to 973 K, a mixed failure mode of load-bearing fracture and interface debonding was observed in the reinforcement. [ABSTRACT FROM AUTHOR]

TiB/Ti6Al4V composite was prepared using spark plasma sintering followed by bidirectional reaction hot rolling. The TiB whiskers were synthesized in situ during the rolling process, thereby preserving a relatively high structural integrity. TiB whiskers were distributed within the composite in three distinct locations: intragranular, intergranular, and transgranular distribution. After eight passes of vertical bidirectional reaction hot rolling, the average grain size of the matrix was refined to 1.36 μm, and the grains exhibited random crystallographic orientations. Tensile properties in different directions demonstrated high consistency, with a strength of 1220 MPa ± 30 MPa and an elongation of 8.0% ± 0.5%. The primary strengthening mechanisms in the composite included grain refinement, dislocation strengthening, and load transfer strengthening from the TiB. • Dense TiB 2 /Ti6Al4V billets were achieved via SPS. • A multi-pass bidirectional in-situ reaction hot rolling method was employed to prepare TiB/Ti6Al4V composite. • The TiB/Ti6Al4V composite showed consistent strength and ductility in all directions. [ABSTRACT FROM AUTHOR]

Abstract Al–Si–Mg alloys manipulated by in-situ synthesized nanoparticles have been prepared by casting method in this work. The addition of different contents of refiners promoted the obvious grain refinement of the Al–Si–Mg alloys. It was found that 0.10 wt% refiners addition caused a significant and efficient refinement on α-Al (from 1675 µm to 199 µm) and Mg 2 Si in the inoculated Al–Si–Mg alloys. The morphology of the eutectic Si in the inoculated Al–Si–Mg alloys transformed from needle-like structure to a fibrous one, and the mean size sharply decreased (from 26.56 µm to 11.89 µm) and increased a little with the increase of FeBSi amorphous refiners content. Tensile property tests showed that both strength and ductility of the alloys were improved by the addition of FeBSi amorphous refiners. The yield strength, tensile strength, fracture strain and elongation of the alloy inoculated with 0.10 wt% FeBSi amorphous refiners for 20 min were 226 MPa, 343 MPa, 18.4% and 16.7%, compared to those of the uninoculated alloy (170 MPa, 289 MPa, 13.7% and 12.2%), respectively. It was found that the Fe 2 B and Fe 3 Si nano-sized particles which were crystallized from FeBSi amorphous refiner contributed to the grain refinement of α-Al, resulting in higher strength. Moreover, grain refinement shortened the atomic diffusion distance and refines Mg 2 Si. The grain refinement and spheroidization of eutectic Si enhance uniform deformation during tension, and reduce the possibility of crack initiation and expansion, thus improving the plasticity. Graphical abstract fx1 Highlights • The inoculated Al–7Si–0.3Mg alloy appeared as 199 µm fine grains. • The inoculated alloy reached 226 MPa, 343 MPa, 18.4%(δ) and 16.7%(ε f). • This work achieved the refinement of α-Al and Mg 2 Si and the spheroidization of eutectic Si. • The Fe 2 B, Fe 3 Si had better lattice mismatch with α-Al and eutectic Si. [ABSTRACT FROM AUTHOR]

The individual effects of Y and Nd elements on the precipitate-free zone (PFZ) development and the dislocation creep mechanism of a Mg-4Y-3.5Nd alloy were investigated using tensile creep loading at 553 K. Some of the samples were treated with a solid solution (WNS) and others were treated by peak aging (WNA). Before creep, no precipitates were found in the WNS sample, whereas both lamellar binary phases and platelet ternary phases were found in the WNA sample and PFZs were already formed. After creep, cross slip and pyramidal < c + a > slip were detected as the dominant creep mechanisms in the WNS sample under all stress regimes. Only cross slip dominated the creep of the WNA sample under low-stress regimes, whereas pyramidal slip also became dominant under high-stress regimes. Dynamic precipitation of ternary phases was observed, and PFZs gradually developed in the WNS sample under all stress regimes. Ternary phases persisted in the WNA sample under all stress regimes, but the dissolution of binary phases and widening of PFZs were significant under high-stress regimes. Consequently, greater creep resistance was achieved in the WNA sample under low-stress regimes but in the WNS sample under high-stress regimes. Compared to Mg-7.5Y and Mg-3.5Nd binary alloys, the synchronous addition of Y and Nd to form a Mg-4Y-3.5Nd alloy diversified the slip types. The Y element reduced the widening rate of PFZs, but it could not thoroughly prohibit the formation of PFZs. The Nd element accelerated both static and dynamic precipitation, but it also triggered the rapid widening of PFZs. • Individual effect of Y and Nd elements on creep behavior of Mg-4Y-3.5Nd alloy is revealed. • The Y element delays PFZ widening while the Nd element promotes dynamic precipitation. • The synchronous addition of Y and Nd elements diversifies the active slip types. • Static precipitates are stable and aging strengthening is effective under low stress. • Precipitate dissolution and PFZ widening weaken creep resistance under high stress. [ABSTRACT FROM AUTHOR]

In this work, 3.5 vol% TiB/Ti6Al4V composites with aligned TiB whiskers are synthesized by spark plasma sintering-hot extrusion (SPSHE). The effects of deformation temperature and deformation amount on the microstructure evolution and tensile properties are systematically investigated in composites. The results suggest that the dispersion of TiB whiskers is gradually improved with the deformation increasing from 30%, 50%–70%. TiB whiskers obtain a highly consistent orientation as the composite is deformed by 70%. The multiplication of more dislocations induced by TiB whiskers provides the driving force for dynamic recovery and dynamic recrystallization of the composite during SPSHE. In addition, the matrix microstructure of the composite is composed of α phase, β phase and interface L phase. The interface L phase decreases the mean free path of dislocation slip and improves the strength of the composite manipulated by SPSHE. The tensile strength (1294 ± 20 MPa) and elongation (5.0% ± 0.5%) of the composite with a deformation amount of 70% at 950 °C are well combined. According to the analysis results of the microstructure and fracture, the strengthening mechanism of the composite is the TiB load transfer strengthening effect and the matrix strengthening effects including interface L phase strengthening, fine grain strengthening, substructure strengthening and texture strengthening. [ABSTRACT FROM AUTHOR]