The ageing responses of selective laser melted Al-7Si-0.6Mg alloy with different solid solution treatment times are investigated in this work. Silicon particles with random crystallographic ...orientations are the dominant precipitates at the direct aged condition. With 1 or 8 h solid solution treatment, the precipitation sequence resembles that of cast/wrought Al-Si-Mg alloys. However, the main precipitates at the peak-aged condition are different and are premature B′ (1 h) and β″ (8 h), respectively. These unusual precipitation pathways are attributed to the uniaxial strains in the Al matrix, suggesting new heat treatment procedures required for selective laser melted alloys.
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•Post-HIP heat treatment led to refined microstructure and improved tensile properties.•Deformation occurred mainly by forming stacking faults in γ′ at RT and elevated temperature.•Net-shape HIPed ...RR1000 failed in a transgranular fracture mode.
A nickel-based superalloy powder RR1000 has been hot isostatically pressed (HIPed) and heat treated to produce different microstructures. Microstructures were investigated using a scanning electron microscope (SEM). Tensile testing was performed at room temperature and 700°C and the deformed samples were examined using SEM and transmission electron microscope (TEM). It was found that in the as-HIPed condition the microstructure consisted of coarse and irregular-shaped primary and secondary γ′ together with a low volume fraction of fine γ′ (<50nm in diameter). Solution treatment below the γ′ solvus followed by air cooling resulted in the formation of finer cuboidal secondary γ′ (350–750nm) and medium-sized spherical tertiary γ′ (100–200nm). This led to an improvement of both the 0.2% yield strength and ultimate tensile strength. Ageing of the solution-treated or of the as-HIPed samples at 760°C resulted in the precipitation of a high population of fine γ′ (around 50nm) which further increased the strength. Within the resolution limit of the current TEM analysis, deformation at room temperature seemed to occur mainly by dislocations cutting through secondary γ′ and very fine γ′, accompanied by the formation of stacking faults within these precipitates; most of the medium-sized tertiary γ′ precipitates in solution-treated and aged samples were not cut through but were surrounded by dislocations. Deformation at 700°C happened by dislocations cutting through γ′ precipitates and γ matrix, leading to the formation of extended stacking faults across both γ and γ′. It is suggested that the optimum treatment of the current powder superalloy is to solution-treat and age after HIPing; this results in properties which are comparable with those of thermomechanically processed samples.
The improved understanding of the factors that control microstructure and properties of TiAl alloys is reviewed together with current work aimed at developing both wrought and cast products. It is ...suggested that the choice of alloy composition is perhaps far simpler than the complex literature would suggest and the factors that underlie alloy choice will be explained. These factors include the processability of the alloy as well as the properties and examples will be given where this dual approach of defining both processability and properties is central to the successful application. In addition other aspects of processing that will be discussed include cost-effective processing, accuracy of compositional control and control of processing conditions appropriate for the specific alloy. Some current applications of TiAl components are summarised before considering some of the challenges still remaining for TiAl-based alloys.
Under the background of carbon neutrality and large‐scale penetration of renewable energy, the integrated local energy system (ILES) has been extensively recognized as an effective way to reduce ...carbon emissions and improve renewable energy consumption level due to its high energy utilization and multiple energy complementarity. Hence, an optimal low‐carbon scheduling model of ILES considering oxygen‐enriched combustion plant (OECP) and generalized energy storages (GESs) is proposed in this paper to reduce the carbon emissions, improve the renewable energy consumption level and reduce the operating costs of ILES. More specifically, the cooperation mechanism between OECP and power to gas (P2G) is established to maintain a high carbon capture level during peak load periods; the GESs under the background of ILES is modelled, which can make full use of the multiple energy complementarity to improve the renewable energy consumption level of ILES. Case studies are performed on an IES that consists of an IEEE 33‐bus distribution network, a 44‐node district heating network and a 20‐node natural gas network to verify the effectiveness and advantages of the proposed model.
Laser powder bed fusion (LPBF) is a timely important additive manufacturing technique that offers many opportunities for fabricating three-dimensional complex shaped components at a high resolution ...with short lead times. This technique has been extensively employed in manufacturing Ti-6Al-4V parts for aerospace and biomedical applications. However, many challenges, including poor surface quality, porosity, anisotropy in microstructure and property, and difficulty in tailoring microstructure, still exist. In this paper, we review the recent progress in post-process treatment and its influence on the microstructure evolution and material performance, including tensile, fatigue, fracture toughness, creep, and corrosion properties. The contradictions in simultaneously achieving high strength/ductility and strength/fracture toughness/creep resistance have been identified. Furthermore, research gaps in understanding the effects of the emerging bi-modal microstructure on fatigue properties and fracture toughness require further investigation.
Platform heating is one of the effective strategies used in laser powder bed fusion (LPBF) to avoid cracking during manufacturing, especially when building relatively large-size components, as it ...removes significant process-induced residual strains. In this work, we propose a novel and simple method to spare the elaborate post-processing heat treatment typically needed for LPBF Al-Sc alloys without compromising the mechanical properties. We systematically investigated the effects of LPBF platform heating at 200 °C on the residual stress relief, microstructure, and mechanical performance of a high-strength Al-Mn-Sc alloy. The results reveal that LPBF platform heating at 200 °C is sufficient to largely relieve the process-induced residual stresses compared to parts built on an unheated 35 °C platform. Meanwhile, the platform heating triggered the dynamic precipitation of uniformly dispersed (1.5-2 nm) Sc-rich nano-clusters. Their formation in a high number density (1.75 × 10
m
) resulted in a ~20% improvement in tensile yield strength (522 MPa) compared to the build on the unheated platform, without sacrificing the ductility (up to 18%). The improved mechanical properties imply that platform heating at 200 °C can strengthen the LPBF-synthesised Sc-containing Al alloys via in situ aging, which is further justified by an in situ measurement study revealing that the developing temperatures in the LPBF part are within the aging temperature range of Al-Sc alloys. Without any post-LPBF treatments, these mechanical properties have proven better than those of most Al-Sc alloys through long-time post-LPBF heat treatment.
Functionally graded lattice structures produced by additive manufacturing are promising for bone tissue engineering. Spatial variations in their porosity are reported to vary the stiffness and make ...it comparable to cortical or trabecular bone. However, the interplay between the mechanical properties and biological response of functionally graded lattices is less clear. Here we show that by designing continuous gradient structures and studying their mechanical and biological properties simultaneously, orthopedic implant design can be improved and guidelines can be established. Our continuous gradient structures were generated by gradually changing the strut diameter of a body centered cubic (BCC) unit cell. This approach enables a smooth transition between unit cell layers and minimizes the effect of stress discontinuity within the scaffold. Scaffolds were fabricated using selective laser melting (SLM) and underwent mechanical and in vitro biological testing. Our results indicate that optimal gradient structures should possess small pores in their core (~900 µm) to increase their mechanical strength whilst large pores (~1100 µm) should be utilized in their outer surface to enhance cell penetration and proliferation. We suggest this approach could be widely used in the design of orthopedic implants to maximize both the mechanical and biological properties of the implant.
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•A macroscale thermal modelling strategy has been developed by combining a published characteristic time-based heat input (CTI) model with an adaptive mesh re-mapping method.•The ...strategy is capable to accurately capture the peak temperatures of the thermal cycles induced by deposited tracks.•The predicted temperature histories agree well with in-situ measurements by thermocouples in both the printed part and powder bed.•Case studies demonstrate that our strategy can improve computational efficiency at least 6 times.
Numerical modelling is an effective tool to investigate the rapid temperature cycling in laser powder bed fusion. However, the high computational cost limits the modelling of part-scale components due to the significantly different scales between the highly local energy input region and the global field response region. This study presents a macroscale finite element thermal simulation strategy with a track-scale resolution by combining the recently developed characteristic time-based heat input (CTI) model with a currently proposed adaptive mesh re-mapping method. Due to the uniformly distributed power density along the scan direction in the CTI model, the optimized mesh strategy allows one element to capture the temperature solutions over the majority of a scan track except at the two ends. The adaptive mesh re-mapping method is used to map simulated results from a previous scan track model to a current scan track model with a new mesh configuration. This strategy has been implemented for a Ti-6Al-4V part with the dimensions of 20×40×3mm3. The predicted temperature histories agree well with the in-situ measurements at the points in both the printed part and powder bed. Three case studies demonstrate that our strategy can improve computational efficiency between 6 and 30 times.
This paper deals with the problem of bipartite consensus for Takagi-Sugeno fuzzy multiagent systems on multilayer cooperation-competition networks and its application to image communication. Fuzzy ...control laws are proposed by using relative output measurements between neighboring agents, where additive couplings are considered to show the different layered-interactions. Sufficient conditions for bipartite consensus of the multilayer networks with signed graphs are obtained by using the signed graph theory, Lyapunov stability theory and Takagi-Sugeno fuzzy systems theory. Then, coupled chaotic Lorenz systems over multilayer signed-networks are illustrated to show the effectiveness of the obtained results. Finally, a new multiagent image communication system is constructed based on the bipartite consensus of the fuzzy multilayer coopetition multiagent network, in which two agents in different layers for point-to-point communication use the output measurements from their own and neighboring agents as the synchronous encryption/decryption keystreams. The experimental results show that the proposed multiagent image communication system has excellent performance against some classical attacks.
In view of the high gas pressure and low permeability of deep coal seam, it is difficult to control gas, which affects the safety production of coal mine. The technical scheme of hydraulic fracturing ...to improve the permeability of coal seam is put forward, and the gas drainage technology is used to control the gas emission of coal seam. The fracturing effect under different water pressure, different gradient fracturing times, and in situ stress is analyzed by using 3DEC (3-Dimensional Distinct Element Code) discrete element software. The simulation analysis and field verification results show that the coal seam gas pressure increases linearly with the buried depth. In situ stress characteristics and hydraulic strength are the key factors affecting the effect of hydraulic fracturing. The fracturing radius increases with the increase of flow. When the construction pressure of hydraulic fracturing test is 18 MPa, the distance between fracturing hole and drainage hole is 8.5 m. The actual measurement shows that after hydraulic fracturing and gas drainage, the maximum gas emission is reduced by 51%, and the average gas emission is reduced by 58%.
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