The influences of EBM processing and post-processing on microstructure, mechanical properties and cracking behaviour in a γ′ precipitation-strengthened nickel-base superalloy DZ125 are critically ...assessed. Results show that a solution treating and ageing (STA) is required to obtain γ′ precipitates with a cuboidal shape. The columnar grain width was found to gradually increase from the bottom to the top of the as-EBM sample having a total build height of 80 mm, whereas there was little gradient in γ′ size. The presence of EBM induced intergranular cracks can be closed by hot isostatic pressing (HIP), however reappearance of intergranular cracks with a much wider crack opening width was observed after STA treatment. EBM induced cracks are classified as liquid-state cracking, as the classic dendritic morphology were found on the cracked surfaces. The post-processing induced cracks can be attributed to the effect of γ′ dissolution and re-precipitation of fine γ′ during the cooling stage of solution treatment. The results suggest that HIP is not an effective approach in healing liquid-state cracks in EBM fabricated γ′ precipitation-strengthened superalloys.
Display omitted
•γ′ precipitation-strengthened Ni-base superalloys are gaining increasing attention for electron beam melting (EBM).•This work represents the first study to reveal the crack reappearance in hot-isostatic-pressing (HIP) post-processed EBM Ni-base superalloy.•EBM induced cracks are classified as liquid-state cracking.•The reappearance of such cracks after post-processing suggests that HIP is not an effective approach in healing liquid-state cracks.
The gas diffusion layer (GDL) in a proton exchange membrane fuel cell (PEMFC) is one of the functional components that provide a support structure for gas and water transport. The GDL plays a crucial ...role when the oxidant is air, especially when the fuel cell operates in the higher current density region. There has been an exponential growth in research and development because the PEMFC has the potential to become the future energy source for automotive applications. In order to serve in this capacity, the GDL requires due innovative analysis and characterization toward performance and durability. It is possible to achieve the optimum fuel cell performance only by understanding the characteristics of GDLs such as structure, pore size, porosity, gas permeability, wettability, thermal and electrical conductivities, surface morphology and water management. This review attempts to bring together the characterization techniques for the essential properties of the GDLs as handy tools for R&D institutions. Topics are categorized based on the ex-situ and in-situ characterization techniques of GDLs along with related modeling and simulation. Recently reported techniques used for accelerated durability evaluation of the GDLs are also consolidated within the ex-situ and in-situ methods.
Display omitted
► This Manuscript deals with Gas Diffusion Layer characterization tools. ► Ex-situ and in-situ methods are identified and grouped. ► Techniques for electrical, thermal, mechanical, surface, bulk properties and durability are discussed.
Tumor extracellular matrix has been associated with drug resistance and immune suppression. Here, proteomic and RNA profiling reveal increased collagen levels in lung tumors resistant to PD-1/PD-L1 ...blockade. Additionally, elevated collagen correlates with decreased total CD8
T cells and increased exhausted CD8
T cell subpopulations in murine and human lung tumors. Collagen-induced T cell exhaustion occurs through the receptor LAIR1, which is upregulated following CD18 interaction with collagen, and induces T cell exhaustion through SHP-1. Reduction in tumor collagen deposition through LOXL2 suppression increases T cell infiltration, diminishes exhausted T cells, and abrogates resistance to anti-PD-L1. Abrogating LAIR1 immunosuppression through LAIR2 overexpression or SHP-1 inhibition sensitizes resistant lung tumors to anti-PD-1. Clinically, increased collagen, LAIR1, and TIM-3 expression in melanoma patients treated with PD-1 blockade predict poorer survival and response. Our study identifies collagen and LAIR1 as potential markers for immunotherapy resistance and validates multiple promising therapeutic combinations.
To enhance the process stability and densification, semi-melt step has been introduced when fabricating the TiC/high Nb–TiAl nanocomposite via electron beam melting. The homogenous TiAl matrix ...microstructure with dispersed nano-scale carbides was realised. During the EBM melt, most TiC nanoparticles dissolved and Ti2AlC formed with near-spherical and rod-like shapes. The particles had an influence on solidification behaviour and the subsequent microstructural degradation. High Nb–TiAl nanocomposites with 1.2 wt% TiC addition exhibited a duplex microstructure with dispersed carbides, while a nearly lamellar microstructure (carbide-free) was found in samples with 0.6 and 0.8 wt% TiC. Furthermore, a lower scanning speed resulted in higher relative density, greater Al loss, increased α2-phase but reduced carbide fractions. The microhardness of 433 ± 10 HV0.2, ultimate tensile strength of 657 ± 155 MPa and fracture toughness of 8.1 ± 0.1 MPa√m in 1.2 wt% TiC/high Nb–TiAl nanocomposite processed by EBM are very promising. In addition, the compressive yield strength of 1085 ± 55 MPa, fracture strength of 2698 ± 34 MPa and strain to fracture of 26.1 ± 1.0%, are superior to those processed by conventional means. The strengthening and toughening mechanisms have been interpreted on the basis of crack path observation.
Display omitted
•Electron beam melted TiC/high Nb–TiAl nanocomposite.•Semi-melt step helps to achieve good process stability and densification.•A homogeneous TiAl matrix microstructure with dispersed nano-scale carbides leading to promising mechanical properties.•The evolution of nano-TiC, solidification microstructure and degradation have been elucidated.
Selective electron beam melting (SEBM) was used to process crack-free Ni3Al-based IC21 alloy (low density superalloy) containing ~85% γ′-volume fraction. There are distinct differences between ...dendrites and inter-dendritic regions with the presence of coarse γ+γ′ eutectic and secondary solidification microconstituents (Cr and Mo-rich) in the latter. The pronounced inter-dendritic eutectic regions suggest that a significant elemental partitioning between the liquid and solid occurred during the SEBM. The terminal liquid is trapped at boundaries between dendrites and grains, as evidenced by the liquid films on cracked surfaces. In contrast to extensive studies indicating the segregation of Zr and B, we show unambiguously the segregation of Si to low melting point liquid films and thereby enhancing the susceptibility to solidification cracking in IC21 produced by SEBM. The tensile specimens extracted from the crack-free IC21 samples exhibit superior properties at room temperature (RT) and 1000 °C. The RT deformation mechanism is characterised by cutting γ′-phase with two paired dislocations and antiphase boundaries in between. At 1000 °C tensile deformation, the well-developed γ/γ′ interfacial dislocation networks are in good agreement with their promising high-temperature performance (σy = 518 ± 10 MPa, σUTS = 560 ± 16 MPa, 20.5% for ductility).
Three-dimensional (3D) topologicalWeyl semimetals (TWSs) represent a state of quantum matter with unusual electronic structures that resemble both a '3D graphene' and a topological insulator. Their ...electronic structure displays pairs of Weyl points (through which the electronic bands disperse linearly along all three momentum directions) connected by topological surface states, forming a unique arc-like Fermi surface (FS). Each Weyl point is chiral and contains half the degrees of freedom of a Dirac point, and can be viewed as a magnetic monopole in momentum space. By performing angle-resolved photoemission spectroscopy on the non-centrosymmetric compound TaAs, here we report its complete band structure, including the unique Fermi-arc FS and linear bulk band dispersion across the Weyl points, in agreement with the theoretical calculations1, 2. This discovery not only confirms TaAs as a 3DTWS, but also provides an ideal platform for realizing exotic physical phenomena (for example, negative magnetoresistance, chiral magnetic effects and the quantum anomalous Hall effect) which may also lead to novel future applications.
Utilization of synchrophasor measurements for wide-area monitoring applications enables system operators to acquire real-time grid information. However, intentional injections of false synchrophasor ...measurements can potentially lead to inappropriate control actions, jeopardizing the security, and reliability of power transmission networks. To resolve this issue, a multisensor track-level fusion-based model prediction (TFMP) has been proposed. It has been demonstrated on a mature wide-area monitoring application, which detect electromechanical oscillations. In this paper, to extract the initial correlation information about attacked oscillation parameters, Kalman-like particle filter (KLPF)-based smoother has been used at each monitoring node. To reduce its computational burden, the KLPF-based smoother is diagonalized into subsystems. The scheme is further supported by the characteristics of moving horizon estimates for handling continuous load fluctuations and perturbations caused by data injections in power grids. Performance evaluations are conducted using different data-injection scenarios in the IEEE New England 39 Bus system. Results show the proposed TFMP accurately extracted oscillatory parameters from the contaminated measurements in the presence of multiple system disturbances and random data injections.
Nature inspired flow field designs for proton exchange membrane fuel cells (PEMFCs) are a relatively recent development in the technology evolution. These novel designs have the potential to show ...dramatic performance improvements by effective distribution of reactant gases without water flooding. Optimization of a flow field requires balancing gas distribution, water management, electron transport, pressure drop and manufacturing simplicity. Computational fluid dynamics (CFD) simulation studies are a useful tool for evaluating nature inspired flow field designs; however, the predictions should be used with caution until validated by an experimental study. Nature inspired flow field designs can be generated using formal mathematical algorithms or by making heuristic modifications to existing natural structures. This paper reviews the current state of nature inspired PEMFC flow field designs and discusses the challenges in evaluating these designs.
► This manuscript deals with the trend on flow field design in the recent years. ► CFD modeling is a useful design tool but limitations should be understood. ► Nature inspired designs are one of the potential optimization approaches.
PDF
