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
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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The cyclic oxidation behaviors of the as-cast Ti-1100-xNb (x = 0.5, 1.0, 1.5, 2.0) alloys exposed at 650 °C for up to 100 h were systematically investigated. The aim of this work is to explore the ...in-depth oxidation mechanism by using the oxidation kinetics and the structure of the oxide products. The oxidation kinetics were determined by thermogravimetrically, and the microstructure and composition of the oxidation scale were studied by using XRD and SEM. The results demonstrate that Nb can significantly improve the oxidation resistance. However, the average weight gains of the alloys decrease firstly and then increase with the increase of Nb content. The oxidation kinetics obeys a parabolic model. The Ti-1100-1.0Nb alloy has the lowest k
value, which is 5.7 10
g
cm
s
. The surface oxidation products are mainly composed of massive or acicular rutile-TiO
, Ti
O (x = 3, 6), NbO
and Al
O
. Besides, Al
(MoO
)
oxide is also presented on the oxidation surface of the Ti-1100-1.5Nb alloys. Ti-1100-1.0Nb alloy shows the best oxidation resistance property revealed by combining weight gains and EDS-SEM element content profiles analysis. The interaction of Nb, O, Ti, and other elements retarded the diffusion of O atoms into the alloys, which improves the oxidation resistance.
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The Ti/SiC gradient material with Mg2Si additive was designed and fabricated by reaction sintering. The structure, microstructure and properties were investigated systematically. The result indicated ...that the Ti/SiC gradient material contained six layers with Ti-rich and Si-rich regions. The relative density decreased from 98.32% to 88.73%, and it increased to 97.28%. Besides, the harness increased from 532.97 HV to 571.32 HV and reduced to 228.14 HV with the increase of Ti content. The fracture toughness of the SiC layer was 6.74 MPa m1/2, and it decreased to 4.91–5.39 MPa m1/2 at the layers containing Ti. The shrinkage rates increased during heating, and it slowed down at the holding stage. The densification primarily occurred at the heating and holding stages. The densification mechanism is the pore displacement controlled by lattice diffusion. Ti5Si3 synthesized by the reaction between Ti and SiC shows the incoherent interface to the Ti grain.
•A novel Ti/SiC gradient material was fabricated.•The structure, microstructure and properties were investigated systematically.•The reaction mechanism was clarified.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
For improving the wear resistance of Al-30Si-5Cu coating, in this study, the composite coating in-situ synthesized TiC-TiN-TiN0.8C0.2/Al-30Si-5Cu (TiCN/Al-30Si-5Cu) was prepared used TiH2-graphite ...aggregates as raw materials and plasma spraying technology. The effect of in-situ synthesized ceramic reinforcements on the coating was researched in detail. The results showed that during the plasma spraying process, TiH2 decomposed and chemically reacted with graphite to form TiC. Additionally, some Ti also reacted with N2 and O2 in the air to form TiN and TiO2. The phases composition of TiCN/Al-30Si-5Cu composite coating were α-Al, β-Si, θ-Al2Cu, β-Ti, TiC, TiN, TiN0.8C0.2, TiO2, as well as amorphous CNX and residual graphite. The TiC-dominated ceramic phases and β-Si were uniformly distributed in the coating, which were tightly bound to the α-Al matrix. Because of the exceptionally rapid cooling rate during the coating preparation, a minor amount of submicron Si particles were also generated. The microhardness, elasticity modulus, and fracture toughness of TiCN/Al-30Si-5Cu composite coating appeared improvements compared to those of Al-30Si-5Cu coating. The TiCN/Al-30Si-5Cu composite coating exhibited smoother friction coefficient curve, along with lower friction coefficient and wear volume in comparison to the Al-30Si-5Cu coating. This suggested that the ceramic reinforcing phases in-situ synthesized led to a notable advancement in the wear resistance of the TiCN/Al-30Si-5Cu composite coating. The wear resistance of TiCN/Al-30Si-5Cu composite coating demonstrated an increasement of 78.3 % over the substrate and 28.2 % over the Al-30Si-5Cu coating. Under the dry friction test conditions outlined in this study, the wear mechanism of the TiCN/Al-30Si-5Cu composite coating included abrasive wear and fatigue wear, coupling with a minimal amount of oxidative wear.
•In-situ synthesized TiC-TiN-TiN0.8C0.2 were achieved using TiH2-graphite agglomerates.•The TiC-dominated reinforcements were evenly distributed and tightly bonded with α-Al.•TCN/Al-30Si-5Cu coating had better mechanical and wear resistance properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To reveal the effect of laser remelting on the high-temperature oxidation resistance of high-entropy alloy (HEA) coating, an AlCoCrFeNi HEA coating was prepared on AISI 1045 steel by plasma spraying ...technology and then remelted by laser remelting process. The microstructure of the coatings before and after remelting was characterized, and oxidation experiment was carried out at 900 °C for 100 h. The results showed that, after laser remelting, the porosity of AlCoCrFeNi HEA coating decreased from 4.8 % to 0.3 %. Moreover, the phase compositions of the coating after remelting were the same as that before remelting, which were still dominated by a single BCC solid solution structure. After oxidation, the oxidation weight gain of the remelted coating was slightly greater than that of the as-sprayed coating. Nevertheless, uniform and dense multilayer oxide films were formed on the remelted coating surface, leading to the lower oxygen content in the remelted coating and at the interface of remelted coating/substrate. Therefore, laser remelting can effectively improve the ability of AlCoCrFeNi HEA coating to hinder oxygen at high temperature and prevent the substrate from oxidation.
•Laser remelting improved the coating's ability to hinder oxygen at high temperature.•Uniform and dense multilayer oxide films were formed on the remelted coating surface.•The order of oxides formation and distribution of different oxide films were discussed.•The oxidation behavior was studied from the aspects of oxidation thermodynamics and kinetics.
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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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