In order to optimize the supersonic plasma spraying process more scientifically, it is important to clearly understand the spreading behavior of molten droplet. In this study, the effects of spray ...parameters on the in-flight behavior and spreading behavior of Fe-based amorphous droplets were investigated. Additionally, since the morphology of the splats is a very important factor which determines the final properties of the coatings, the splats in this study were characterized in terms of their circularity, eccentricity, solidity, and spread factor. The porosity and micro-hardness of the Fe-based amorphous coatings were also evaluated. Results show that the spraying power is the most important parameters that influence the surface temperature of the Fe-based amorphous droplets, while the main factor affecting the in-flight velocity is the Ar flow rate. The melting index of in-flight particles reaches the maximum value at the spraying power of 60 kW and Ar flow rate of 110 L/min. The droplets present disk-shaped splats with the lowest solidity and eccentricity, and highest circularity and spread factor with the average velocity of 445 m/s and surface temperature of 2780 K. This is very crucial to reduce the defects of as-sprayed coatings and form fine-lamellar-structured supersonic plasma-sprayed coatings with outstanding mechanical properties.
•Individual splat morphology of Fe48Cr15Mo14C15B6Y2 amorphous coatings investigated.•Spraying power and Ar flow affect surface temperature and in-flight velocity of the particles.•Excess Ar flow and spraying power are detrimental to the melt status of particles.•Droplets form disc-like splat at the average velocity of 445 m/s and surface temperature of 2780 K.•This disc-like splat influences mechanical properties, and thus, coating quality.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Monitoring fatigue crack propagation behavior of ferromagnetic components is very important. In this paper, the tension–tension fatigue tests of center cracked tension (CCT) specimens were carried ...out; the variation regularity of both tangential and normal components of magnetic signals during fatigue process were investigated. The results showed that the initial abnormal signals which appeared at the notch were reversed after cyclic loading. The abnormal magnetic signals became more significant with the increase of fatigue cycles and reversed again after failure. The characteristic parameters, i.e., the peak value of tangential component, Btp, and maximum gradient value of normal component, Km, showed similar variation trends during the fatigue process, which can be divided into three different stages. An approximate linear relationship was found between the characteristic parameters and fatigue crack length 2a. The feasibility of predicting the fatigue crack propagation using the abnormal magnetic signals was discussed. What's more, the variation and distribution of the magnetic signals were also analyzed based on the theory of magnetic charge.
•A novel and passive NDT method, i.e. MMMT method, is proposed.•Both tangential and normal components of magnetic signals were investigated.•The prediction of crack propagation by abnormal magnetic signals was discussed.•A linear relationship was found between the parameters and fatigue crack length 2a.•The parameters can be potentially used to evaluate the crack propagation state.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The generation and propagation of cracks are critical factors that affect the performance and life of large structures. Therefore, in order to minimize maintenance costs and ensure personal safety, ...it is necessary to monitor key structures. The sensor based on ultra-high frequency radio frequency identification (UHF RFID) antenna has the advantages of passive wireless, low cost, and great potential in the field of metallic structure health monitoring. In this paper, aimed at the key parts of a metallic structure, a dual-tag system is used for crack monitoring. In conjunction with mode analysis, the principles of the sensing tag and the coupling principles of the dual-tag are analyzed. Considering that the dual-tag is placed in different methods, the effect of mutual coupling on the sensing performance of the tag is studied. The results show that the frequency of the sensing tag can be tuned by adding the interference tag, and the dual-tag sensor system has reasonable sensitivity. The results also provide potential guidance for the optimal placement of multiple tags in the near-field region.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A new type heat treatment process comprising super-high temperature pretreatment and austempering treatment (S&A treatment) was used to process carbidic austempered ductile iron (CADI). The results ...showed that the netlike eutectic carbides were significantly reduced after super-high temperature pretreatment. Due to the increase in supercooling during super-high temperature pretreatment cooling, the inter-laminar spacing of pearlite was reduced from 300 nm to 100 nm. When the ductile iron with superfine pearlite was reheated, a large amount of Fe3C particles were retained inside the prior austenite grains. After austempering, a superfine ausferrite matrix with a length of 1–3 μm and a thickness of 50 nm was obtained. The main reason for this refinement is the increased number of nucleation-sites for the austenite grains and the retardation-effect of Cr on their growth. TEM results indicated that a possible orientation relationship between bainitic ferrite with a cubic lattice and precipitated Fe3C particles with a orthorhombic lattice is (011¯)α-Fe//(210)Fe3C, and their boundaries are coherent boundaries. The CADI obtained by S&A treatment has an impact toughness 120% higher than the traditional CADI without sacrificing hardness, and has excellent wear resistance under high wear load.
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•The impact toughness of CADI is significantly improved by super-high temperature pretreatment and austempering treatment.•The CADI obtained by S&A treatment has excellent wear resistance under high wear load.•With the rise of reheating temperature, the pearlite decreases gradually, and the precipitated particles are retained.•A superfine ausferrite matrix with a length of 1-3 μm and a thickness of 50 ± 10 nm is obtained.•The boundaries between bainitic ferrite and precipitated particles are coherent boundaries.
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To improve the heat resistance of titanium alloys, the effects of Y content on the precipitation behavior, oxidation resistance and high-temperature mechanical properties of as-cast ...Ti-5Al-2.75Sn-3Zr-1.5Mo-0.45Si-1W-2Nb-xY (x = 0.1, 0.2, 0.4) alloys were systematically investigated. The microstructures, phase evolution and oxidation scales were characterized by XRD, Laser Raman, XPS, SEM and TEM. The properties were studied by cyclic oxidation as well as room- and high-temperature tensile testing. The results show that the microstructures of the alloys are of the widmanstätten structure with typical basket weave features, and the prior β grain size and α lamellar spacing are refined with the increase of Y content. The precipitates in the alloys mainly include Y
O
and (TiZr)
Si
silicide phases. The Y
O
phase has specific orientation relationships with the α-Ti phase: (002)
// (1¯1¯20)
, 110
// 4¯401
. (TiZr)
Si
has an orientation relationship with the β-Ti phase: (022¯1¯)
// (011)
, 1¯21¯6
// 044¯
. The 0.1 wt.% Y composition alloy has the best high-temperature oxidation resistance at different temperatures. The oxidation behaviors of the alloys follow the linear-parabolic law, and the oxidation products of the alloys are composed of rutile-TiO
, anatase-TiO
, Y
O
and Al
O
. The room-temperature and 700 °C UTS of the alloys decreases first and then increases with the increase of Y content; the 0.1 wt.% Y composition alloy has the best room-temperature mechanical properties with a UTS of 1012 MPa and elongation of 1.0%. The 700 °C UTS and elongation of the alloy with 0.1 wt.% Y is 694 MPa and 9.8%, showing an optimal comprehensive performance. The UTS and elongation of the alloys at 750 °C increase first and then decrease with the increase of Y content. The optimal UTS and elongation of the alloy is 556 MPa and 10.1% obtained in 0.2 wt.% Y composition alloy. The cleavage and dimples fractures are the primary fracture mode for the room- and high-temperature tensile fracture, respectively.
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Machine learning combined with traditional experimental methods can promote the efficient research and development of materials. In this work, five kinds of algorithm models combined with a genetic ...algorithm (GA) were used to optimize the compositions of the alloyed high manganese steel. And then the effect of solid solution temperatures on the microstructure, mechanical properties, and impact wear properties of the steel were systematically investigated. The results showed that Categorical Boosting (CB) model exhibited the high validation accuracy (R2 > 0.95, RMSE<4.11, MAE<2.44). Based on the trained CB model and GA, the optimal steel compositions were obtained. The as-cast microstructure of the steel contained coarse austenite, little pearlite and networks and irregular carbides. After water toughening treatment, the pearlite completely dissolved into the matrix and the number of carbides gradually decreased. Compared to as-cast alloy, the austenite grain size significantly decreased, and it decreased first and then increased with the increase of solid solution temperatures. The average impact energy, ultimate tensile strength (UTS) and elongation (EL) of the steel increased and then decreased with the increase of solid solution temperatures. However, the wear loss showed an opposite trend. The steel of water quenching at 1100 °C with an average impact energy of 185.1 J, hardness of 242.4 HBW, UTS of 742 MPa, yield strength (YS) of 458 MPa, and EL of 37.4%, exerted best impact toughness, mechanical properties and wear resistance. It was attributed to the interactions among dispersed small sized second phases, high density dislocations, fine austenite grains and twins.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Reliable lubrication is the key to ensure the safe service of space equipment moving parts, but the tribological performance of most lubricating materials in a vacuum environment is substantially ...degraded. Therefore, graphene/diamond-like carbon (DLC) coatings were prepared on 9Cr18 bearing steel substrates using a combination of radio frequency (RF) magnetron sputtering preparation of DLC coatings and airbrush coating graphene layers, and the structural characteristics and tribological properties of the coatings were comparatively investigated for the different times of graphene layer spraying. The results shows that the graphene surface layer formed a stable bond with the DLC substrate, but there were local wrinkles in the graphene sheets deposited by the airbrush, and the surface roughness of the coating increased with the increase of the spraying times. The graphene/DLC coating with 3 times spraying has relatively excellent tribological properties in vacuum, with an average coefficient of friction of about 0.08 and a wear rate of 4.59 × 10−7 mm3N−1 m−1. Based on the tribological testing results, the mechanism of the friction-reduction and wear reduction of the graphene/DLC coatings in vacuum were analyzed. In general, the graphene/DLC coatings have excellent tribological properties in vacuum and hold significant promise for applications in moving parts of aerospace equipment.
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•Graphene/DLC coatings were prepared on 9Cr18 bearing steel by combined radio frequency magnetron sputtering and gun spraying.•The graphene sheet layer spread unevenly on the DLC coating surface in a wrinkled state, and the roughness increased with the times of graphene spraying.•The non-metric stacking of graphene sheet layers and the formation of "micro-bearings" during the friction process were the main reasons for the excellent tribological properties of the graphene/DLC composite coatings in vacuum.
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Ti-Cu alloys have broad application prospects in the biomedical field due to their excellent properties. The properties of Ti-Cu alloys are strongly dependent on Cu content, microstructures, its ...Ti2Cu phase and its preparation process. The aim of this work is to investigate the effect of Cu content on the precipitation behaviors, mechanical and corrosion properties of the as-cast Ti-Cu alloys. The microstructures and phase evolution were characterized by SEM and TEM, and the properties were studied by tensile and electrochemical test. The results show that the volume fraction of Ti2Cu phase increases with the increase of Cu content. The Ti2Cu phase presents a variety of microscopic morphologies with different Cu content, such as rod, granular, lath and block shaped. The crystal orientation relationships between the Ti2Cu and α-Ti matrix in Ti-4Cu and Ti-10Cu alloys are (103)Ti2Cu//(011¯11)α-Ti, 3¯01Ti2Cu//21¯1¯0α-Ti, and (103)Ti2Cu//(0002)α-Ti, 3¯31Ti2Cu//12¯10α-Ti, respectively. The tensile strength, Vickers hardness and Young’s modulus of the Ti-Cu alloys increase with the increase of Cu content, whereas the elongation decreases. The fracture morphologies of these alloys reveal ductile, ductile-brittle hybrid, and cleavage brittle mode, respectively. The corrosion resistance of the Ti-Cu alloys in SBF solution can be described as: Ti-4Cu alloy > Ti-10Cu alloy > Ti-7Cu alloy. The volume fraction of Ti2Cu phases and the “protective barrier” provided by the fine lath Ti2Cu phases strongly affected the electrochemical performances of the alloys.
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X2CrNi12 ferritic stainless steel has a wide range of application prospects in the railway transportation, construction, and automobile fields due to its excellent properties. The properties of ...X2CrNi12 ferritic stainless steel can be further improved by cold-rolling and subsequent annealing treatment. The purpose of this work is to investigate the effect of cold-rolling reduction on the microstructure, texture and corrosion properties of the recrystallized X2CrNi12 ferritic stainless steel by using SEM, TEM, EBSD and electrochemical testing technology. The results show that the crystal orientation characteristics of the cold-rolled sheet could be inherited into the annealed sheet. The higher cold-rolling reduction could promote the deformed grains rotating into the {111} orientation, increasing storage energy and driving force for recrystallization, which could reduce the recrystallized grain size. The orientation densities of α-fiber and γ-fiber were low at 50% cold-rolling reduction. After recrystallization annealing, a large number of grains with random orientation could be produced, and the texture strength was weakened. When the cold-rolling reduction rose to 90%, the γ-fiber texture at {111} was strengthened and the α-fibers, particularly the {112} component, were weakened after recrystallisation annealing, which could improve the formability of the steels. The proportions of special boundaries, i.e., low-angle grain boundaries and low-Σ CSL boundaries, among the grain boundary distribution of the recrystallized X2CrNi12 stainless steel were higher when the reduction was 90%, especially when the annealing temperature was 770 °C. Additionally, the proportion of LAGBs and low-Σ CSL boundaries were 53% and 7.43%, respectively, which improves the corrosion resistance of the matrix, showing the best corrosion resistance.
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In the case of electrical contact, copper alloys are often unable to withstand arc ablation and premature failure. To solve this issue, Ni-8wt.%Al (Ni–8Al) coatings were successfully prepared on ...copper substrates utilizing the high-speed laser cladding. In addition, the microstructure evolution, microhardness, electric conductivity and arc ablation resistance of the prepared coatings were investigated in detail. As a result, the achieved Ni–8Al coatings were structurally dense with good metallurgical bonding to the substrate, of which the microstructure showed a bottom-up evolution of fine sub-grain structure. Notably, the microhardness of the coating was 191.7 HV0.2, representing an increase of 82.57% compared to the substrate, and the electrical conductivity was 18.03 %IACS, approaching that of pure nickel. Additionally, the increase in ablation currents led to changes in the ablation behaviors and failure mechanisms of both the substrate and coating. At high currents, a huge arc ablation crater appeared in the center of the substrate due to the reaction force of the anode flame and the difference in surface tension between the liquid metal at the center and the edge of the molten pool. Nevertheless, the coatings showed better arc ablation resistance due to the improvement of molten pool stability during arc ablation by the in situ formed Al2O3 layer on the coating surface.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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