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The occurrence of recrystallization will cause catastrophic damage to the structure of the metallic single crystal, which can be avoided by alloying reasonably. In this work, a new strategy is proposed to improve mechanical properties and achieve the structural stability of Mo single crystal during hot deformation. Thermal simulation tests show that the mechanical property of Mo single crystal is significantly improved by adding the Nb element. The Nb element is beneficial to inhibit the dynamic recrystallization of Mo single crystals through blocking the development of high-angle grain boundaries and dislocation cells, leading to Mo-Nb alloy single crystals still retaining monocrystal structure. [Display omitted] • Mechanical properties of Mo single crystal are significantly improved by adding Nb element. • The dynamic recrystallization occurred in pure Mo single crystal, while Mo-Nb alloy single crystals still retain monocrystal structure. • The development of HAGBs and dislocation cells are blocked by Nb atoms. [ABSTRACT FROM AUTHOR]

• The effect of sintering temperature on the mechanical and friction properties of GNPs/TC21 composites were investigated. • A model of the relationship between the interfacial evolution of composites and sintering temperature was established. • The strengthening mechanism of GNPs/TC21 composites was revealed using TEM microstructural analysis. Schematic diagram of microstructure evolution with increasing sintering temperature. (a)Spherical particle sintering model, (b) TC21 spherical particle bonding at lowtemperature sintering, (c) interfacial bonding at medium temperature sintering,(d) interfacial bonding at high temperature sintering. Schematic illustration of the strengthening mechanism of TiC@GNPs bands and TiC particles/plates. (a) Synergistic strengthening mechanism of TiC@GNPs bands and TiC particles/plates, (b) Strengthening mechanism of TiC particles/plates [Display omitted] Graphene nanoplates (GNPs) have been adopted in titanium matrix composite manufacturing and design due to its superior mechanical properties. In this study, Graphene nanoplates reinforced Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-Si alloys (named as GNPs/TC21 composites) were prepared by using spark plasma sintering (SPS), and the effects of sintering temperature on the microstructure, mechanical and wear properties of GNPs/TC21 composites were systematically investigated. The results indicate that the sintering temperatures show a great influence on the interfacial structure. With the increase of sintering temperature from 850 °C to 1050 °C, the interfacial microstructures exhibit three morphographies: (1) The original TC21 particles coated with GNPs (850 °C); (2) A special TiC@GNPs band (900 °C−1000 °C); (3) A discontinuous network structure wrapped by TiC particles/plates (1050 °C). Mechanical and tribological properties of the GNPs/TC21 composites were investigated at room temperature. The optimal SPS temperature was 1000 °C, at which the GNPs/TC21 composites show the best comprehensive mechanical properties i.e. the ultimate tensile strength and yield strength are 1167 MPa and 1041 MPa, the friction coefficient is 0.16275 and the wear loss is 0.0179 g. The improvement of mechanical properties can be attributed to the synergistic strengthening of the load transfer effect of TiC@GNPs bands and the pinning effect of TiC particles/plates. The excellent wear resistance is mainly attributed to the pinning of TiC particles on the surrounding metal matrix and the strengthening and lubrication of GNPs. [ABSTRACT FROM AUTHOR]

• Nb, V and Fe significantly tailor the microstructure and mechanical properties. • Phase stability and energy barrier of phase transformation were responsible for microstructure formation. • Solid-solution and phase-interface strengthening were responsible for various mechanical properties. [Display omitted] Binary Ti-4(Nb, V, Fe) alloys were prepared to investigate the effects of β-stabilizers (Nb, V and Fe) on microstructure formation and mechanical properties of titanium alloys by using experimental and theoretical methods. Microstructure observations revealed that addition of Nb, V or Fe significantly tailored the microstructure under different heat-treated conditions, i.e., furnace-cooled (FC), air-cooled (FC) and water-quenched (WQ). The FC Ti–4(Nb, V, Fe) alloys exhibited the Widmanstätten microstructure and the AC samples showed the spheroidized microstructure. The WQ Ti–4Fe exhibited the microstructure composed of equiaxed β grains and nanoscale ω particles while the WQ Ti–4Nb and Ti–4V showed the martensite microstructure. Differentials of microstructure can be attributed to the effects of Nb, V and Fe elements on the phase stability and energy barrier of phase transformation according to the empirical electron theory (EET) of solids and molecules. Results of tensile tests showed that Nb, V and Fe significantly influenced the tensile properties under the different heat treatments. Both the WQ Ti–4Nb and Ti–4V showed the larger tensile strength than that of the FC and AC sample due to the stronger solid-solution and phase-interface strengthening in martensite structure. The WQ Ti–4Fe sample exhibited the largest tensile strength (1104 MPa) compared to that of the FC (754 MPa) and AC (981 MPa) samples due to the strongest solid-solution and phase-interface strengthening from the ω phase. By executing the methods of the empirical electron theory (EET) of solids and molecules, effects of β-stabilizers (Nb, V and Fe) on microstructure formation and mechanical properties of titanium alloys were revealed on the view of valence electron. [ABSTRACT FROM AUTHOR]

Graphene nanoplates (GNPs) reinforced TC21(Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-Si) (GNPs/TC21) composites were prepared by using spark plasma sintering (SPS). Microstructure, mechanical and tribological properties of the sintered GNPs/TC21 composites were systematically investigated. Microstructural observations demonstrated the formation of a special sandwich interface product is in-situ TiC coated GNPs (TiC@GNPs) bands and TiC particles/plates in the microstructure of the sintered GNPs/TC21 composites. Results of mechanical testing indicated the excellent combination of strength and ductility of GNPs/TC21 composites owing to the dispersion strengthening effects of TiC particles/plates as well as the load transfer between TiC@GNPs bands and TC21 matrix. GNPs/TC21 composite with 0.05 wt% GNPs addition exhibits the relatively excellent mechanical properties, i.e., yield strength of 1017.2 MPa, ultimate tensile strength of 1161.99 MPa and an elongation about 13.2%. Among them, the dispersion strengthening effect of TiC particles/plate was the dominant factor in 0.05 wt% GNPs /TC21 composites. When the GNPs content exceeds 0.1 wt%, TiC particles/plates and TiC@GNPs bands formed at grain boundaries. The excellent combination of strength and ductility of GNPs/TC21 composites owing to the dispersion strengthening effects of TiC particles/plates as well as the load transfer between TiC@GNPs bands and TC21 matrix. Furthermore, additions of GNPs have significantly improved the tribological properties of the sintered GNPs/TC21 composites. The wear loss of 0.05 wt% GNPs/TC21 composite decreased by 21% compared to that of the sintered TC21 alloy. The superior mechanical and tribological performances of GNPs/TC21 composites can be attributed to the unique strengthening effect and the lubricating efficiency of GNPs. This demonstrates that GNPs is an ideal filler for TC21 matrix composites, as the effective lubricant and favorable reinforcement. [ABSTRACT FROM AUTHOR]

Deformation and crack initiation of industrial Ti-6Al-4V titanium alloy sheet were investigated using in-situ scanning electron microscopy (SEM) at room temperature. The results showed that slip band originated from α/α and α/β interfaces when the tension reaches the yield stage, and the slip mode develops from single slip to multi slip and finally the cross-slip occurs. Microcracks initiate primarily at the phase boundary or along the slip band within α phase, cracks are mainly connected along the 45° line. The fracture surface is full of dimples. Intergranular cracking is the main fracture mechanism. [ABSTRACT FROM AUTHOR]

The high cycle fatigue properties of Ti-6.5Al-2.2Mo-2.2Zr-1.8Sn-0.7W-0.2Si with three typical microstructures (equiaxed, bimodal and full lamellar) prepared by carefully controlled isothermal forging and heat treatment procedures are investigated by comparison. Equiaxed and bimodal microstructures exhibit a higher HCF resistance than the full lamellar one and a mismatching of HCF strength with yield strength for equiaxed and bimodal microstructures is observed. Fractography analysis shows crack initiates primarily at the subsurface of ∼30 μm–300 μm for the three microstructures. Interior initiation occurs in 5 specimens of the 19 specimens that were measured. For equiaxed and bi-modal microstructures, the interior initiation samples have significant higher fatigue life than those initiated at (sub)surface under the same fatigue stress, while in lamellar structure, the initiation location shows no such effect on fatigue life. It is found that two factors, i. e. the effective slip length and the intrinsic strength, jointly decide the fatigue crack initiation in the present alloy. The dependence of crack initiation on microstructure is responsible for the microstructural sensitivity of HCF properties. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of ultrahigh strength Aermet 100 steel tempered at five different temperatures in the 472–492 °C range have been studied. The results show that the mechanical properties of Aermet 100 steel are sensitive to the tempering temperature; especially at the temperature of 482 °C, in which significant changes can be observed. At 482 °C, the strength of Aermet 100 steel sharply decreases by 70–100 MPa when the tempering temperature increases by only 5 °C. This is mainly due to the growth of M 2 C carbide at relatively high tempering temperature that can greatly decrease its interface strengthening effect. In addition to strength, the plasticity and fracture toughness of Aermet 100 steel obviously increase at 482 °C when compared with lower tempering temperatures. The rising amplitudes of elongation and fracture toughness can reach 1.7% and 30 MPa m 1/2 respectively. This is attributed to the reverted austenite film precipitated at 482 °C. For one respect, the existence of austenite film between lath martensite can reduce the local stress concentration and the chance of microcrack formation in Aermet 100 steel during deformation, which is responsible for the obvious increase of plasticity. For another respect, the excellent softness, toughness and stability of reverted austenite prompt the advancing crack to divert, branch and blunt or appear “zigzag” route, which results in an increase in the fracture toughness. Aermet 100 steel can achieve the optimum combination of strength, plasticity and toughness at the tempering temperature of 482 °C, which has the yield strength of 1845 MPa, the elongation of 12.9% and the fracture toughness of 113 MPa m 1/2 . [ABSTRACT FROM AUTHOR]

In this study, the effect of surface oxidation behavior on the fracture toughness of Ti–5Al–5Mo–5V–1Cr–1Fe alloy suffered oxidation treatments at the temperatures of 500 °C, 600 °C, 700 °C and 800 °C is studied by means of OM, SEM and EDS analysis. For comparison, the fracture toughness of this alloy suffered vacuum annealing treatments at the temperatures of 550 °C, 600 °C, 650 °C and 700 °C are also investigated. The results show that at the heating temperatures below 600 °C, the fracture toughness values of Ti–5Al–5Mo–5V–1Cr–1Fe alloy suffered vacuum annealing treatments and oxidation treatments show no obvious difference. However, at the heating temperature of 700 °C, the fracture toughness of Ti–5Al–5Mo–5V–1Cr–1Fe alloy undergone oxidation treatment is almost 50 MPa m 1/2 lower than that undergone vacuum annealing treatment. This is due to that at the oxidation temperature of 700 °C, the oxide layer thickness is above 5 μm. In this situation, its influence on the fracture toughness of Ti–5Al–5Mo–5V–1Cr–1Fe alloy cannot be ignored. The existence of oxide layer can decrease the total area of shear lips on the fracture surface, decrease the crack propagation tortuosity and limit the formation of secondary cracks on the side surface of K IC specimen. This can result in a big decrease of fracture resistance, which is detrimental to the fracture toughness of Ti–5Al–5Mo–5V–1Cr–1Fe alloy. [ABSTRACT FROM AUTHOR]

• The segregation and formation of Cu-rich layer are clearer with higher Cu concentration. • The higher copper concentration, oxygen is harder to diffuse through Cu-rich phases. • High Cu concentration contributes to the grain-dissecting behavior which surrounds titanium phase. ga1 "Titanium fire" can cause catastrophic consequences for machinery components made of titanium alloys, especially in the case of aero-engines. As such, there is continuing interests in developing burn resistant titanium alloys. The burn resistant functionality and mechanical strength of titanium alloys rely on their microstructural characteristics that are significantly determined by the alloying components. This work investigated the burn resistant performance of Ti-Cu alloy and analyzed the role of alloying Cu. With sufficient content of Cu in the system, the formation of Cu rich layer cuts off the oxygen transfer pathway and hinders the burning process. Meanwhile, the addition of Cu results in the reduction of chemical kinetics. For the Ti-Cu alloy with insufficient Cu content, the burn resistance is sacrificed by the discontinuous Cu-rich clusters, among which oxygen penetration prolongs the burning process. Apart from the Cu-rich protective layer, various burning processes accompanied with oxidation products are detected via reduced area X-ray diffraction along the burnt cross section. This work provides a comprehensive understanding of the impacts of Cu content on the burn resistant characteristics of Ti-Cu alloy, which offers theoretical foundation of burn resistant mechanism to the design and fabrication of high-performance titanium alloys. [ABSTRACT FROM AUTHOR]

The poor thermal ablation resistance of TC4 alloy limits its use in critical high-temperature applications. In this work, ZrO 2 /TiO 2 composite ceramic coatings were prepared by plasma electrolytic oxidation (PEO) to enhance the ablation resistance of TC4 alloy. The phase compositions, microstructure and ablation resistance of the coatings are significantly influenced by the addition of various concentrations of K 2 ZrF 6 to the electrolyte. The X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDS) techniques were employed to investigate the phase composition, chemical compositions, microstructure, and elemental distribution of the PEO ceramic coatings. The results showed that ZrO 2 /TiO 2 composite ceramic coatings formed on substrate consisted of t-ZrO 2 , ZrTiO 4 , R-TiO 2 , and A-TiO 2 phases. These coatings also exhibited a volcanic-like porous structure. The thermal ablation resistance tests were carried out at 1300 °C for 3000 s, which indicated that the presence of t-ZrO 2 in the coating could improve the ablation resistance of TC4 alloys by inhibiting crack propagation. Moreover, the thermal ablation resistance of the PEO coating prepared with 15 g/L K 2 ZrF 6 was superior to that of other coatings, as indicated by the crack density and weight loss. • High temperature stable structure ZrO 2 /TiO 2 composite coatings which were prepared on TC4 alloy. • The t-ZrO 2 in the coatings prevented the crack propagation during the ablation process at 1300 °C for 3000 s. • A correlation between the t-ZrO 2 and the ablation properties of coating was revealed. [ABSTRACT FROM AUTHOR]

In this work, crack propagation behaviors and fracture mechanism of CT20 alloy with lamellar α at the temperatures ranging from 20 to − 90 °C were investigated and revealed. The results showed the fracture toughness of CT20 alloy was decreased from 430.89 KJ/m2 to 171.67 KJ/m2, and the fracture mechanism was gradually changed from typical ductile fracture to quasi-cleavage fracture with the decreasing testing temperature. The reduction of fracture toughness was mainly influenced by the internal factor (the crack tip plastic zone) and external factor (the tortuosity of the crack propagation path), in which the contribution of the internal factor increased from 87.06% to 95.68% as the temperature decreased. Therefore, the high contribution of the internal factor means the plastic zone at the crack tip could mainly affect the crack propagation behaviors. The lamellar α was found to be deformed by the plastic zone, and then inhibited the crack propagation and deflected its propagation direction at 20 °C, which consumed the additional deformation energy and increased the fracture toughness. With the decline of the plastic zone from 0.526 mm to 0.107 mm, the lamellar α deformation and the crack propagation resistance were significantly reduced at − 90 °C, which accelerated crack propagation and decreased the fracture toughness. • The crack propagation behaviors of CT20 alloy are first investigated from 20 to − 90 °C. • The effect of internal and external contributions on fracture toughness are revealed. • The collaborative effect of both the plastic zone and microstructure are revealed. [ABSTRACT FROM AUTHOR]

Abstract Coarse macrograins have been observed in aerospace components for a high temperature near-α titanium alloy Ti60. The present work was inspired to understand the origin of coarse macrograin and examine how strain affects the macro/microstructure. Thus, thermomechanical processing was conducted in α + β phase field to simulate industrial production. This alloy with a bimodal microstructure was isothermally pre-deformed at 1019 °C and a constant strain rate of 0.1 s−1 to height reductions of 15, 35, 55 and 75%. Heat treatment was conducted following deformation at 1024 °C for 30 min. The results showed that coarse macrograins originated from inadequate recrystallization of prior β grains of initial billet. Deformation in the α + β phase field does not form many new orientation β grains but slightly scatters β grain orientations around the orientations of big prior β grains in small strain samples. Each of different coarse macrograins corresponds to a family of prior β grains with similar crystallographic orientations with about 20° of spread, which is outlined by secondary α (α s) plates having nearly parallel basal planes with similar crystallographic orientations. The size of macrograin decreases with increasing strain, which is consistent with the extent of recrystallization of prior β grain. These understandings can be applied to optimize processing routes for the control of final macro/microstructure and properties in near-α titanium alloys. Graphical abstract Image 1 Highlights • Coarse macrograins may originate from inadequate recrystallization of prior β grains. • Recrystallized β grains formed from subgrains by continuous recrystallization. • Coarse regions can be outlined by α s plates having nearly parallel basal planes. • Long α s percolates the entire big prior β grain, which may reduce fatigue resistance. [ABSTRACT FROM AUTHOR]

To improve the ablation resistance of niobium alloy, plasma electrolytic oxidation (PEO) was introduced to fabricate coatings with different pore structures on niobium alloy by adjusting the applied voltage. The pore volume and shape were investigated by X-ray computed tomography, and the ablation behavior of PEO coatings was also thoroughly discussed. It was found that the ablation behavior of PEO coatings could be divided into the crack propagation stage and the coating peeling stage, which are related to the specific pore structure and ablative oxidation. The stress concentration in the pore tip increased by 60.61% as the pore shape transforms from isolated pores to connected pores, accelerating crack initiation and propagation. Subsequently, oxygen erodes the substrate through connected pores and cracks, which is accelerated by high overall porosity (23.4%) and severe crack propagation, followed by ablative oxidation of the substrate leading to the eventual peeling of the PEO coating. After 15 min of ablation, no coating peeling occurred for the isolated pore structure, while the coating peeling area of the connected pore structure reached 82.1%. Thus, the isolated pores could transfer stress and inhibit further diffusion of oxygen into the coating, improving the ablation resistance of PEO coatings. It is expected that this research would provide feasible ideas for the design and fabrication of ablation-resistant coatings on niobium alloy. • The effect of pore structures on ablation behavior is systematically studied. • The isolated pores inhibit crack propagation and further diffusion of oxygen. • The stress concentration in the connecting pores increased by 60.61% and the coating peeling area reached 82.1%. [ABSTRACT FROM AUTHOR]

By adjusting the particle size of Ti6Al4V(TC4) powders and the distribution of boron particles, a high-performance heterogeneous network structure titanium matrix composites were fabricated through the spark plasma sintering (SPS) technique. In the present work, TiB whisker (TiBw) are in situ synthesized around the boundaries of the small size TC4 (STC4) particles, and formed into a TiBw network structure. The STC4 particles of the network surround the larger size TC4 (LTC4) particles to form a new heterogeneous network structure similar to the shape of a sunflower. The heterogeneous network structure consisted of coarse grain zones (LTC4) and fine grain zones (TiB/STC4) is formed in the microstructure. In light of tensile results, the tensile strength and ductility of TiB/TC4 composites with heterogeneous network structure are about 987.5 MPa and 11.5 %, respectively, which are 16.6 % and 35.3 % higher than those of TC4 alloy. The improvement of mechanical properties is mainly due to the interface strengthening mechanism of heterogeneous network structure and the hindrance and pinning mechanism of reinforcements to dislocation movement. The improvement of ductility depends on the inhibition of crack propagation by the heterogeneous network structure and the existence of high ductility coarse grain zone. [Display omitted] • A titanium matrix composite with heterogeneous network structure was prepared successfully. • Heterogeneous network structure composite achieves the matching of strength and ductility. • The improvement of the strength and ductility is attributed to the fracture mechanism of the heterogeneous network structure. [ABSTRACT FROM AUTHOR]

• Static coarsening behavior was controlled by termination migration and Ostwald ripening mechanism. • The average diameter of Ti 2 Cu phase increased with thermal exposure time. • The loss of ductility is mainly attributed to the coarsening of Ti 2 Cu phase. [Display omitted] The static coarsening behavior of a Ti-14Cu alloy relative to the Ti 2 Cu phase after long-term isothermal thermal exposure was comprehensively investigated. The growth of the precipitated phase is shown to be controlled by the diffusion mechanism characterized by morphological variation during thermal exposure. The static coarsening process is composed of a rapid coarsening stage and stable coarsening stage, and it is primarily governed by volume diffusion of the Lifshitz-Slyozov-Wagner (LSW) model. The rapid coarsening stage is mainly dominated by the terminal migration mechanism, while the stable coarsening stage is governed by the Ostwald ripening mechanism. The rapid coarsening of the Ti 2 Cu phase enhances the effects of precipitation strengthening significantly and simultaneously improves the plasticity of the alloy. However, with stable coarsening, the presence of the high-volume Ti 2 Cu phase in a Ti-14Cu alloy increases the effective slip length during deformation and reduces plasticity. [ABSTRACT FROM AUTHOR]

The mechanical performance of Ti-13Cu-Al alloy is highly determined by its microstructure, which is significantly affected by the cooling process from semi-solid state as it induces peritectic solidification and the subsequent eutectoid transformation of the alloy. This work investigated the effects of cooling rates on the morphology of Ti 2 Cu phase and mechanical properties of Ti-13Cu-Al alloy after cooling from semi-solid state (β+L phase). Different cooling mediums have been considered, including furnace cooling (0.5 °C/s), air cooling (50 °C/s) and water cooling (150 °C/s), corresponding to a slow, normal and rapid cooling process, respectively. It is found that α+Ti 2 Cu phases are uniformly distributed in the alloy after different cooling processes, and the morphology of Ti 2 Cu phase is controlled by the peritectic solidification and eutectoid transformation. Specifically, the thickness and the volume fraction of primary Ti 2 Cu phase are larger than the sample cooling from β phase field when the cooling rate is the same. The morphology of Ti 2 Cu phase varies from "laths + blocky + sheaves" to "short laths + blocky + rodlike" as the cooling rate gradually increases. It is further revealed that the β/L interface provides a fast channel for solute atom diffusion, and the peritectic Ti 2 Cu phase provides a favorable nucleation site for the precipitation of eutectoid Ti 2 Cu. Based on the tensile property and hardness examinations, the mechanical properties of the Ti-13Cu-Al alloy show a clear dependency with the precipitation of Ti 2 Cu phase after cooling from semi-solid state, indicating the importance of cooling mode from semi-solid state on the microstructure and mechanical properties of the alloy. Image 1 • The peritectic Ti 2 Cu will be produced when cooling from semi-solid state (β+L phases). • The peritectic Ti 2 Cu/β interface provides rich nucleation sites for eutectoid transformation. • Active eutectoid Ti 2 Cu will more effectively improve the mechanical properties of the Ti-13Cu-Al alloy. [ABSTRACT FROM AUTHOR]