Search

Asphalt mixture recycled technology (Al-Saffar et al. 2021) is an efficient method for achieving asphalt pavement sustainability. The optimum asphalt content of recycled asphalt mixture is first determined by the Marshall test in this paper. Second, Materials Studio software was used to simulate the interface effect between three different asphalts and aggregate, and the adhesion between asphalt and aggregate was characterised based on the interface energy. The mesoscopic structural characteristics of three asphalt mixtures were then analysed using digital image processing technology. Finally, through three macro experiments, the influence of old asphalt on the mechanical properties of recycled asphalt mixture was studied from a macro perspective. At the microscopic level, the results show that the presence of the old asphalt reduces the adhesion between the asphalt and the aggregate. At the mesoscopic level, the presence of old asphalt reduces the porosity of the asphalt mixture. At the macroscopic level, the addition of old asphalt improves the high temperature and water stability of recycled asphalt mixture while decreasing the low temperature crack resistance. The microscopic and mechanical properties of old asphalt on recycled asphalt mixture are explained on three levels, and new ideas for research on recycled asphalt mixtures are provided. [ABSTRACT FROM AUTHOR]

A Ti1.5Nb1Ta0.5Zr1Mo0.5 (TNTZM) refractory high entropy alloy (HEA) with a cellular structure was successfully fabricated by laser powder bed fusion (L-PBF). Compression testing and cyclic deformation testing results revealed that, in the cellular structure, the cell walls could store dislocations. Furthermore, the local chemical order (LCO) plays a crucial role in controlling dislocations within the cell wall region. The LCO not only facilitates dislocation slip but also generates additional lattice distortion upon stress-induced LCO destruction to enable dislocation pinning. This work offers novel insights into the microstructure of additively manufactured refractory HEAs and uncovers a distinct dislocation regulation mechanism. [ABSTRACT FROM AUTHOR]

A novel (8.5Al3BC + 14.5Al2O3)/Al composite was fabricated with exceptional elevated-temperature properties and stiffness. The composite boasts an average Young's modulus of 99 GPa, with ultimate tensile strength and elongation of the composite at 350°C averaging 188 MPa and 4.4%, respectively. The synergistic strengthening effect of Al3BC and γ-Al2O3 is responsible for the high-temperature properties, while they both contribute to the improvement of stiffness as they have a high initial Young's modulus. This innovative composite design holds promising potential for advancements in material engineering and performance optimization. This work reports a novel fabricated (8.5Al3BC + 14.5Al2O3)/Al composite with prominent elevated-temperature properties and stiffness and reveals the positive contribution of Al3BC and γ–Al2O3 particles to strength-ductility combination at high temperature. [ABSTRACT FROM AUTHOR]

Metals and alloys with heterogeneous microstructures exhibit an enhanced combination of strength and ductility, compared to their counterparts with homogeneous microstructures. Additive manufacturing (AM) techniques offers a new opportunity to induce heterogeneous microstructures in a wide range of metals and alloys, thereby optimizing their mechanical properties. In this review article, we focus on four types of heterogeneous microstructures induced by AM: lamellar, gradient, laminated, and harmonic ones. We will introduce (i) the tailored generation of heterogeneous microstructures, (ii) the effects of characteristic solidification conditions, and (iii) the intricate phase transformation in laser-based AM process. Furthermore, we discuss the features, advantages, and potential applications of the metals and alloys with heterogeneous microstructures made by AM. To conclude, we discuss current challenges and future opportunities in this field. Additive manufacturing offers the opportunity of creating heterogeneous microstructures that enhance the strength-ductility synergy in metals and alloys. We review generation methods, solidification effects, heat treatment, and potential applications. [ABSTRACT FROM AUTHOR]

Calcium hexaluminate (CA6) porous ceramics were prepared by foaming and pore-forming agent methods, with Al2O3 and calcium aluminate cement (CAC) as raw materials and magnesium aluminum spinel hollow spheres (MASHSs) as pore-forming agent. The effects of the amount of magnesium aluminum spinel hollow sphere on the phase composition, bulk density, apparent porosity, flexural strength, microstructure, and thermal conductivity of CA6-based porous ceramics were systematically studied. The pores of such porous ceramics are mainly formed by the enhanced amount of MASHSs and the generation of CA6 phase. The results demonstrate that with the elevation of MASHSs content, the microstructure of the samples transforms from a uniform distribution of closed pores to an interconnected micro-pore arrangement. Notably, the fracture paths transition from cohesive to interfacial interactions between MASHSs. This intricate interplay culminates in a remarkable outcome – our ceramics exhibit thermal conductivities ranging from 0.210 to 0.451 W/(m/k), an augmented gas permeability of 25.96 × 10−11m2, and exceptional compressive strengths reaching up to 22.3 MPa. Overall, this study provides insights into the influence of MASHSs content on the microstructure and thermal-mechanical properties of porous materials, which may contribute to the development of advanced ceramic materials with tailored properties. [ABSTRACT FROM AUTHOR]

The main objective of this study was to examine the combined effect of ground recycled concrete cement (GRC) and thermo-activated recycled concrete cement (TARC) on properties of mortar. The physical, chemical and microstructural tests were conducted to characterize GRC and TARC before mortar mixtures were produced. The microscopic morphology of GRC and TARC revealed uneven edges and a rough surface that is slightly porous. The GRC and TARC powders were used to replace cement in the range of 0-50% at increments of 10% by volume. The fresh, mechanical, microstructure, and durability characteristics of mortar were tested for different proportion of GRC and TARC as partial replacement of cement. The usage of GRC and TARC decreases the workability of mortar marginally. However, the mechanical performance of the mortar mixtures showed an increasing trend when GRC and TARC share increases in the mixture. Predominantly, compressive strength, bulk density, and ultrasonic pulse velocity (UPV) have all been increased by as much as 20% cement replacement. Furthermore, the incorporation of GRC and TARC enhances the mortar's durability properties. The microstructure analysis reveals that 20% replacement (GT20) mix has superior structural compactness. In general, partially substitution of GRC and TARC by ordinary Portland cement improves several characteristics of mortar. This will help solve the most prevalent problems that concrete produces, including the high embedded carbon dioxide creation, the high resource usage, and the high waste generation after demolition. [ABSTRACT FROM AUTHOR]

The aim of this work is to investigate the variations in microstructure, hardness, wear and surface roughness between as-cast and heat treated trace elements added A356 alloy. Alloy A was prepared by adding 1 wt.% magnesium to A356 alloy which was used as the base material for the preparation of alloys with zinc (Zn) and copper (Cu) particles as alloying elements. Other set of samples was fabricated where Cu-coated Zn and Cu were added as reinforcements to base matrix A. The microstructural analysis indicated that the addition of Zn to A356 as an alloying element had a limited effect on controlling the grain size during solidification compared to Cu. The addition of Cu as reinforcement resulted in a higher proportion of pro eutectic α-Al phase, leading to finer grain boundaries. Micro-polishing test was conducted on the alloys and composites by determining the surface roughness (Ra) value using profilometer to study the changes in surface roughness under individual load conditions of 20 and 40 N. In the as-cast condition, the addition of Cu increased the hardness by 39% and 58% over the base alloy, respectively. Age-hardening treatment significantly enhanced the wear resistance properties of unreinforced alloys and composites at both aging temperatures, especially at 100 °C. Composite samples exhibited excellent surface finish (lower surface roughness) compared to alloy samples, attributed to the presence of hard reinforcement particles. [ABSTRACT FROM AUTHOR]

Green oils are plant extract oils such as Karanja, Pinnay, Coconut oil, which are non-corrosive, non-toxic and environmentally friendly, and are capable of replacing petrol oil quenchants. In this study, Pinnay oil, Karanja seed oil and their blends (equal volume in proportion) were used as quenchants. Before quenching for hardening, austenitising was performed at three different temperatures ranging from 890 °C to 950 °C. The effects of austenitising temperature and vegetable oil quenchants on the hardness, room-temperature impact toughness and microstructure of normalised 42CrMo4 steel were determined. Prior to the hardening treatment, the as-received 42CrMo4 steel was subjected to normalising treatment, which enhanced the hardness and toughness properties due to grain refinement of the as-received steel. As the oil viscosity decreases, the hardness increases with marginal alteration in the impact resistance. In all the quenching condition, with an increase in austenitising temperature up to 920 °C, there was an increase in hardness around 7% and decrease in toughness around 37%, whereas at 950 °C there was a decrease in hardness around 24% and an increase in the toughness of the steel around 47% as compared to that of 920 °C. Also, blend oil quenched specimens showed balanced hardness and impact toughness compared to Pinnay oil and Karanja oil quenched specimens. [ABSTRACT FROM AUTHOR]

This study employed laser directed energy deposition (DED) with in-situ ultrasonic vibration to obtain AA7075 deposits. The results showed that with ultrasonic treatment, the grain morphology of DED produced AA7075 was changed from columnar grains with an average area of 1751 µm2 to equiaxed grains of 118.2 µm2, representing a reduction of about 93%. Also, the application of ultrasonic treatment led to the increase of average hardness from 93.1 HV to 110.2 HV, and the increase of average ultimate tensile strength from 226.8 MPa to 314.7 MPa, representing relative increases of 18.36% and 38%, respectively. However, it did not result in a significant reduction of ductility. It is believed that ultrasonic vibration promotes the formation of additional nucleation sites due to cavitation and acoustic streaming, as well as the formation of secondary phase particles at grain boundaries. Both mechanisms effectively augment the mechanical properties of DED produced AA7075. [ABSTRACT FROM AUTHOR]

Achieving grain refinement in the wire-arc directed energy deposition (DED) process of NiTi alloy is highly challenging. We have successfully obtained NiTi alloy with a fine microstructure and observed an improvement in superelastic recoverability by introducing an ultrasound-assisted field during the deposition process. The results show that the average grain size of the NiTi alloy samples decreased from 147.3 to 72.2 µm. Additionally, the recoverable strain of the samples increased significantly from 3.7% to 4.4%. This is attributed to the ultrasonic cavitation and acoustic streaming phenomena during the ultrasound-assisted process, which promotes the columnar-to-equiaxed transition (CET) during the solidification process. Fundamentally, the key to the enhancement of recoverable strain after ultrasound-assisted is that the formation of equiaxial grains provides more strain compatibility to the grain boundaries, which reduces the formation of dislocations during deformation. [ABSTRACT FROM AUTHOR]

Balancing strength and ductility is crucial for structural materials, yet often presents a paradoxical challenge. This research focuses on crafting a unique bimetallic structure, combining nonmagnetic, stainless steel 316L (SS316L) with limited strength but enhanced ductility and magnetic, martensitic 17-4 PH with higher strength but lower ductility. Utilising a powderbased laser-directed energy deposition (L-DED) system, two vertical bimetallic configurations (SS316L/17-4 PH) and a radial bimetallic structure (SS316L core encased in 17-4 PH) were fabricated. Monolithic SS316L, 17-4 PH, and a 50% SS316L/50% 17-4 PH mixture were printed. The printed samples' phase, microstructure, room temperature mechanical properties, and fracture morphology were examined in as-printed conditions. Bimetallic samples exhibited both phases, with a smooth grain transition at the interface. Radial bimetallic samples demonstrated higher mechanical strength than other compositions, except 17-4 PH. These findings showcase the potential of the L-DED approach for creating functional components with tailored mechanical properties. [ABSTRACT FROM AUTHOR]