Microstructure, mechanical properties and machinability of particulate reinforced Al matrix composites: a comparative study between SiC particles and high-entropy alloy particles

In this study, 2024Al matrix composites reinforced by SiC particles (SiC-2024Al) and nanocrystalline high-entropy alloy particles (HEA-2024Al) fabricated by powder metallurgy were systematically compared for the first time. There is a significant difference in microstructure and mechanical properties as well as machinability between two kinds of composites. In term of microstructure, when the volume fraction of reinforcements was 10%, both SiC-2024Al and HEA-2024Al composites showed a homogeneous particle distribution in the matrix. With the increase of reinforcement content, HEA-2024Al composites presented denser microstructure than that of SiC-2024Al composites. The composites with 10, 20 and 30 vol.% HEA reinforcements all showed better plasticity than that of the SiC-2024Al composites with same volume fraction of reinforcements, which was related with better particle distribution and interface bonding. However, the strength showed the opposite tendency in the two kinds of composites. Selecting 10SiC-2024Al and 10HEA-2024Al composites as examples to explore the difference in the yield strength of two kinds of composites, it is ascribed to the dislocation punched zones around interface between the Al matrix and reinforcements, which was analyzed in detail by a combination of calculation, nanoindentation tests and finite element analysis. Additionally, HEA-2024Al composites showed better machinability than those of SiC-2024Al composites. This work provides insight into the application of particulate reinforced Al matrix composites

The Kernel Based Multiple Instances Learning Algorithm for Object Tracking

To realize real time object tracking in complex environments, a kernel based MIL (KMIL) algorithm is proposed. The KMIL employs the Gaussian kernel function to deal with the inner product used in the weighted MIL (WMIL) algorithm. The method avoids computing the pos-likely-hood and neg-likely-hood many times, which results in a much faster tracker. To track an object with different motion, the searching areas for cropping the instances are varied according to the object’s size. Furthermore, an adaptive classifier updating strategy is presented to handle with the occlusion, pose variations and illumination changes. A similar score range is defined with respect to two given thresholds and a similar score from the second frame. Then, the learning rate will be set to be a small value when a similar score is out of the range. In contrast, a big learning rate is used. Finally, we compare its performance with that of the state-of-art algorithms on several classical videos. The experimental results show that the presented KMIL algorithm is faster and robust to the partial occlusion, pose variations and illumination changes

Supported Ionic Liquid Silica as Curing Agent for Epoxy Composites with Improved Mechanical and Thermal Properties

The present study aims to improve the mechanical properties of epoxy composite by incorporating supported ionic liquid silica (IL-silica). The IL-silica not only showed improved interfacial interaction and reinforcement, but also served as cure agent of epoxy composites. The differential scanning calorimetry analysis revealed that epoxy composites could be successfully cured with IL-silica without any routine curing agents. IL-silica/epoxy composites presented higher mechanical and thermal properties compared with epoxy composite containing un-functionalized silica (u-silica). The dynamic mechanical analysis showed that the storage modulus of composites significantly increased with the addition of IL-silica in comparison to that with added u-silica, as well as the variation of Tg parameter. The incorporation of IL-silica simultaneously enhanced the tensile strength, toughness, and thermal stability of the epoxy composites. The considerable improvements in mechanical and thermal properties are ascribed to the improved dispersion of IL-silica and the enhanced interfacial interactions between epoxy matrix and IL-silica by strong covalent bonding, which results in an effective load transfer

The Influence of A Mo Addition on the Interfacial Morphologies and Corrosion Resistances of Novel Fe-Cr-B Alloys Immersed in Molten Aluminum

The influence of a Mo addition on the interfacial morphologies and corrosion resistances of novel Fe-Cr-B alloys in molten aluminum at 750 °C was systematically investigated using scanning electron microscopy, X-ray diffractometer, electron probe microanalysis, and transmission electron microscopy. The results indicated that Mo could not only strengthen the matrix but also facilitate the formation of borides. Furthermore, the microstructures of Mo-rich M2B boride changed from a local eutectic net-like structure to a typical coarse dendritic structure and a blocky hypereutectic structure with increasing Mo addition. This was true of the blocky Mo-rich M2B boride, rod-like Cr-rich M2B boride and the corrosion products, which had a synergistic effect on retarding of the diffusion of molten aluminum. Notably, the corrosion resistance of the Fe-Cr-B-Mo alloy, with an 8.3 wt.% Mo addition, was 3.8 times higher than that of H13 steel

Structure and Flame-Retardant Actions of Rigid Polyurethane Foams with Expandable Graphite

In this paper, rigid polyurethane foams that were filled with expandable graphite (RPUF/EG) composites were prepared by the liquid blending method, and then the structure and flame retardancy performance of materials were investigated through optical microscope, scanning electron microscope, limit oxygen index, cone calorimeter, thermogravimetric analysis coupled to fourier transform infrared spectrum, and X-ray photoelectron spectroscopy. The results showed that a large number of EG could be good to the exhibition of flame retardancy of RPUF, where the optimal material was found at loading 15 phr EG that showed an increased limit oxygen index value and a decreased calorific or fuming value. TGA coupled FTIR and XPS revealed that EG could disassembled before RPUF under heating treatment, and it could form a pyknotic and enahnced residual carbon layer on RPUF surface after the fire, which restricted the transfer of gas, like oxygen or heat into PU matrix, finally resulting in the promotion of flame retardancy of RPUF

Tailoring Microstructure And Tensile Properties Of Low-cost AlCrFeNi-based High-entropy Alloys Via Co And/or Ti Addition

Al-Cr-Fe-Ni high-entropy alloys (HEAs) have low cost but suffer from intrinsic brittleness, leading existing research to concentrate on compressive properties. This study explores alloying strategies to improve tensile properties for these HEAs. Minor elements including 5 at.% Co, 5 at.% Co + 3 at.% Ti, and 5 at.% Co + 5 at.% Ti are added to investigate their impact on microstructure, tensile properties, and solidification behavior for Fe30Ni35Cr21.25Al13.75 HEA. The addition of both Co and Ti has a synergistic effect on the alloys; however, it does not alter the types of phases present, as the face-centered cubic (FCC), body-centered cubic (BCC), and B2 phases are maintained. Specifically, the increase of Ti content promotes the transformation of the primary phase from FCC to BCC and causes the BCC phase to undergo spinodal decomposition. The addition of Co alone decreases the strength, whereas the synergistic combination of Co and Ti enhances the yield strength (from ∼571 MPa to ∼625 MPa) and ultimate tensile strength (from ∼1112 MPa to ∼1288 MPa). Nonetheless, the total elongation is only reduced by 1.5% with this combination. Specially, introducing 5% Ti into the alloy instantly renders it brittle. These results provide valuable insights into improving the mechanical properties and understanding the solidification behavior of low-cost Al-Cr-Fe-Ni HEAs through synergistic alloying

Determination of fluoride component in the multifunctional refining flux used for recycling aluminum scrap

In this paper, the optimum fluoride component in the multifunctional refining flux used for recycling aluminum scrap was determined. Theoretical analysis of solid fluxing shows that strong stripping ability of oxide layer on aluminum surface for the flux and appropriate interfacial tensions between Al melt / inclusion (σM-I), flux / inclusion (σF-I), and flux / Al melt (σF-M) are indispensable for making the flux achieve the properties of covering, drossing, and cleaning simultaneously. In term of four preliminarily selected fluoride salts, i.e., KF, AlF3, K3AlF6 and KAlF4, the results of interfacial tension measurements indicates that, combined addition of A-type fluoride (KF) and B-type fluoride (AlF3, K3AlF6 and KAlF4) to equimolar NaCl-KCl can just offset the shortage of single addition of KF which means worsening the separating effect of flux from melt surface and weakening the wettability of flux on the inclusions due to the lower σF-M and the higher σF-I respectively. Additionally, coalescence behaviors of aluminum droplets in molten fluxes reveals that, KF, K3AlF6 or KAlF4 possesses stronger stripping ability of oxide layer, while the stripping ability of oxide layer for AlF3 is weaker. Ultimately, the combination of KF with K3AlF6 or/and KAlF4 is ascertained to be an optimum selection for fluoride component in the multifunctional refining flux