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Al0.6CoCrFeNiSix high-entropy alloy coatings were obtained by laser cladding on the surface of 45# steel, and their microstructure evolution and wear mechanism were investigated. The surface morphology, element composition, and phase structure were analyzed, and the results showed that an increase in Si content led to a refinement of the Al0.6CoCrFeNiSix alloy coatings with a gradual transition from face-centered cubic (FCC) phase to body-centered cubic (BCC/B2) phase in alignment with the equilibrium phase diagram calculated using Pandat thermodynamic calculation software. The dissolution of Si into the solid solution caused lattice distortion which provided the driving force for this phase transition, while segregation of Si, Fe, and Cr facilitated the formation of Al-Ni-rich B2 phase promoting transformation from FCC to BCC phase. Microhardness improved with increasing Si content, reaching 770 Hv0.2 for the Al0.6Si0.4 alloy coating, demonstrating superior performance, while the wear mechanisms differed among the alloys where abrasive wear dominated in the Al0.6Si0.0, Al0.6Si0.1, and Al0.6Si0.2 alloys, whereas oxidation wear was prominent in the Al0.6Si0.3 and Al0.6Si0.4 alloys. The coating's wear resistance was enhanced due to the formation of a dense oxide film as lubricant resulting from the reaction between Si and oxygen acting leading to significant improvement in the tribological properties. [ABSTRACT FROM AUTHOR]

In this work, the microstructure and mechanical properties of titanium matrix composites were tuned by introducing graphene and alloying elements. The titanium matrix composites reinforced by graphene oxide (GO) and cobalt elements (GO@ Co/TA1) are synthesized by the spark plasma sintering (SPS) technique. Results show that the precipitated Ti2Co phase is almost reticulate distributed in the tissue, while the in situ TiC particles are discontinuously distributed at the grain boundaries. The ultimate tensile strength and yield strength of GO@ Co/TA1 composites are 160% and 126% higher than those of pure TA1, respectively. In addition, composites show excellent ductility where the elongation of GO@Co/TA1 is around 10.95%. Therefore, such enhanced mechanical properties can be attributed to the synergistic strengthening effect of interfacial‐distributed TiC particles and intragranular‐distributed intermetallic compounds (Ti2Co), which would provide a new idea for the design of metal matrix composite. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of powder metallurgy Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloy was investigated by isothermal compression test at the wide temperature range of 7 0 0 – 1 1 5 0 ∘ C, under an intermediate strain rate of 0.1 s − 1 , and with the sample deformation degree of 30%, 50% and 70%. Results suggested that the flow stress was very sensitive to the deformation variables and it decreased with increasing the deformation temperature. Flow localization occurred when the temperature was lower than 8 0 0 ∘ C, accompanied by the dynamic morphology changing of α phase. Dynamic recovery (DRV) features appeared when the temperature was over 8 5 0 ∘ C, while dynamic recrystallization (DRX) took a more important role than DRV for the alloy compressed at 9 0 0 – 1 0 0 0 ∘ C. [ABSTRACT FROM AUTHOR]

Powder metallurgy is a very attractive method for producing titanium alloys, which can be near-net-shape formed and have freedom in composition selection. However, applications are still limited due to product affordability. In this paper, we will discuss a possible cost-effective route, combining fast heating and hot processing, to produce titanium alloys with similar or even better mechanical properties than that of ingot metallurgy titanium alloys. Two titanium alloys, Ti-5Al-5V-5Mo-3Cr (Ti-5553) and Ti-5Fe, were successfully produced from HDH titanium powder and other master alloy powders using the proposed processing route. The effect of the processing route on microstructural variation and mechanical properties have been discussed. [ABSTRACT FROM AUTHOR]

Quasi-static tensile deformation behaviors at room temperature (RT) and 77 K of Ti-3Al-2Zr-1.5Mo alloy with lamellar microstructure were systematically investigated in this study. The experimental results indicated the excellent cryogenic mechanical properties of Ti-3Al-2Zr-1.5Mo alloy with lamellar microstructure. The strength and elongation of the Ti-3Al-2Zr-1.5Mo alloy at 77 K are much larger than those of RT specimen. It demonstrated that the strength, plasticity and strain-hardening rate were improved simultaneously at cryogenic temperature. Microstructural analysis indicated that strong cryogenic twinning induced plasticity (TWIP) effect occurs in the Ti-3Al-2Zr-1.5Mo alloy with lamellar microstructure. The intersection between the substructure and the α/β interface is one of factors to the nucleation of twins at cryogenic temperature. The optimization of the properties of Ti-3Al-2Zr-1.5Mo alloy should be attributed to the significant TWIP effect at cryogenic temperature. In addition, the cryogenic environment weakens the hindering effect of the interfaces on crack propagation. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of deformation and fracture of metastable β titanium alloys is of great significance for improving formability and service life. By combining the in-situ tensile test, TEM characterization and EBSD analysis, the tensile deformation behavior, activation of slip systems, crack initiation, and propagation of a high strength metastable β titanium alloy (Ti-5Cr-4Al-4Zr-3Mo-2W-0.8Fe) with equiaxed microstructure are investigated. The equiaxed microstructure is composed of primary α (αp) phase, transformed β (βt) matrix phase, and secondary α (αs) phase. In contrast to the hexagonal αp grain with limited slip systems, the body-centered βt matrix has more slip systems, however the hindering effect of αs phases on dislocation slip leads to the different deformability of the αp phase and βt matrix. The equiaxed αp grains are more prone to deformation and rotation to coordinate the overall deformation. The shear band leads to the formation of sub-grain boundary and even the fragmentation of αp grains. As a result, the microvoids tend to nucleate at the grain boundary, phase interface, slip band, and shear band. The inhomogeneous deformation in the plastic deformation zone around the crack tip is the primary cause of damage. The crack propagation caused by microvoids coalescence advances along the grain boundaries and phase interfaces in the form of intergranular, and along the activated slip systems and shear bands in the form of transgranular. Pinpointing the situation in the equiaxed microstructure and combining that in other typical microstructures will help to summarize the universal deformation and fracture mechanisms of metastable β titanium alloy, and provide a basis for alloy design and microstructure tailoring. [ABSTRACT FROM AUTHOR]

The impact toughness of a high-strength metastable β titanium alloy (Ti-5Cr-4Al-4Zr-3Mo-2W-0.8Fe) with two typical microstructures is studied by Charpy impact tests. The bimodal microstructure (BM) and the lamellar microstructure (LM) are obtained by the solution and aging treatments and the β annealing, slow cooling and aging treatments, respectively. In the impact crack initiation process, the deformation capacities of the primary α (αp) phase, secondary α (αs) phase and transformed β (βt) matrix in the BM are very different, and the stress gradient at the interface of the three causes the crack initiation. The lamellar α (αl) phase and βt in the LM satisfy the BOR relationship, and the effective slip transfer between α and β phases slows down the crack initiation. Meanwhile, the appearance of deformation twins in the LM improves the crack initiation energy. In the crack propagation process, the lack of coordinated deformation between the α and β phases in the BM leads to rapid crack propagation. In the LM, the deformation of αl and βt is relatively more coordinated, so the severe plastic deformation is only concentrated near the crack and at the interface. The secondary crack initiation and the crack propagation along the twin boundary reduce the stress concentration at the crack tip. The deformation twins and zigzag propagation path can improve the crack propagation energy. To summarize, the alloy with LM exhibits better impact toughness than the alloy with BM. [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]

Titanium alloys are widely used in aerospace, chemical, biomedical and other important fields due to outstanding properties. The mechanical behavior of Ti alloys depends on microstructural characteristics and type of alloying elements. The purpose of this study was to investigate the effects of different Cu contents (2.5 wt.%, 7 wt.% and 14 wt.%) on mechanical and frictional properties of titanium alloys. The properties of titanium alloy were characterized by tensile test, electron microscope, X-ray diffraction, differential scanning calorimetry, reciprocating friction and wear test. The results show that the intermediate phase that forms the eutectoid structure with α-Ti was identified as FCC Ti2Cu, and no primary β phase was formed. With the increase of Cu content, the Ti2Cu phase precipitation in the alloy increases. Ti2Cu particles with needle structure increase the dislocation pinning effect on grain boundary and improve the strength and hardness of titanium alloy. Thus, Ti-14Cu shows the lowest elongation, the best friction and wear resistance, which is caused by the existence of Ti2Cu phases. It has been proved that the mechanical and frictional properties of Ti-Cu alloys can be adjusted by changing the Cu content, so as to better meet its application in the medical field. [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 work, different morphologies and structures of lamellar α are obtained by controlling the cooling rates, i.e., water cooling (WC), air cooling (AC) and furnace cooling (FC), and their effects on tensile properties and impact toughness of a new near α CT20 alloy (Ti-3Al-2Zr-1Mo) are investigated. Results showed that a heterogeneous three-dimensional network lamellar martensite α structure was formed after WC, a mixed structure composed of fine lamellar α/β and a small amount of martensite was formed after AC, and a coarse lamellar α structure was formed after FC. The tensile strength gradually decreased with decreasing cooling rate, and AC had the superior strength-plasticity match (yield strength was 13% higher than FC while their plasticity is equivalent). However, the impact toughness of AC (comparable to that of WC) was about 16% lower than that of FC (90 J/cm2). During tensile deformation, the synergistic effect of the good plasticity of the α colony, the obstruction of dislocations by the colony interface and the plastic deformation of the martensite of the AC contribute to the best strength-plasticity matching. During impact, crack initiates and propagates rapidly at the V-notch root, and the finite element simulation results showed that the plastic deformation was concentrated in a tiny region near the crack tip, resulting in the coordination deformation among the microstructures in AC cannot be fully realized. By contrast, the coordinated deformation of multi-level martensite and the generation of nano twins in WC make its impact toughness comparable to that of AC. The highest impact toughness of FC was attributed to the superior plasticity of coarse lamellae, slip transfer between coarse α and β lamellae, the generation of twins and the formation of a small jagged and large wave-like composite crack propagation path. • Cooling rate has a significant effect on lamellar α morphology and structure of CT20 alloy. • The multi-level lamellar martensitic α structure exhibits better strength-ductility-impact toughness synergy. • Coordinated deformation of multi-level martensite and generation of nano-twins result in high impact toughness. • The overall microstructure's deformation determines tensile properties, while impact toughness depends on the micro-deformation near crack tips. [ABSTRACT FROM AUTHOR]

The effects of lamellar features on the fracture toughness of Ti-17 titanium alloy are studied in the present paper. Three cooling methods were used to prepare different lamellar features of Ti-17 titanium alloy after β forging. Then the same solid solution plus aging treatment were conducted to get the final microstructures. The results show that the microstructure with long and thick needle-like α platelets gets higher fracture toughness as well as strength than the microstructure with short rod-like α platelets. This seemingly “abnormal” phenomenon can be explained based on the theory that the fracture toughness is attributed to two major contributions, namely the crack path tortuosity (extrinsic part) and material plastic deformation along the crack path (intrinsic part). The respective contribution of the plasticity and crack path tortuosity to the fracture toughness of Ti-17 alloy are quantitatively evaluated based on the existent models proposed by previous researchers. The results show that the intrinsic contributions for the three microstructures with different lamellar features do not show a big difference. However, their extrinsic contributions are dramatically different. The microstructure which contains the longest and thickest α platelets gets the most rugged crack propagation path and moderate plasticity among the three microstructures, which results in the highest fracture toughness. Moreover, due to the nature of the near-β Ti-17 alloy, the long and thick α platelets in microstructure also get high aspect ratios, which results in high interfacial strengthening effect. Thus for Ti-17 alloy studied in the present work, the long and thick α platelets in microstructure can realize a good combination of fracture toughness and strength. [ABSTRACT FROM AUTHOR]

In this study, Al 0.9 CoCrNi 2.1 EHEA was prepared by directional solidification at various withdrawal rates from 6 to 120 μm/s. The lamellar eutectic structure is formed containing FCC (L1 2) and BCC (B2) at different withdrawal rates during directional solidification. The solid-liquid interface of the alloy transfers from nearly-planer to cellular eutectic interface and the lamellar spacing decreases from 7.17 μm to 1.65 μm as the withdrawal rate increases. The lamellar spacing is negatively correlated with withdrawal rates which was identified by the Jackson-Hunt model and its growth rate index (0.484) is closely related to the theoretical value (0.5). The tensile experiment demonstrates that the structure of Al 0.9 CoCrNi 2.1 EHEA is finer and the ultimate tensile strength and elongation increase as the withdrawal rate increases. The elongation of Al 0.9 CoCrNi 2.1 EHEA is two times higher than that of the as-cast alloy at the withdrawal rate of 120 μm/s. It is concluded that the formation of the L1 2 phase and Cr-rich precipitated phases in the directional solidified eutectic structure are associated with the enhancement of mechanical properties due to grain refinement at high withdrawal rates. • A lamellar eutectic structure consisting of FCC (L1 2) phase and BCC (B2) phase has been successfully obtained by directional solidification. • The solid-liquid interface transfers from nearly-planer to cellular eutectic interface as withdrawal rates increase, and the lamellar spacing of the eutectic structures gradually decreases. • As Compared to the as-cast alloy, the ultimate tensile strength of the directional solidified Al 0.9 CoCrNi 2.1 EHEA is increased from 932.76 MPa to 1304.49 MPa, and the elongation is increased from 4.79 to 13.34 percent. • Directional solidification of Al 0.9 CoCrNi 2.1 EHEA with excellent elongation at 120 μm/s. • The presence of L1 2 phase and Cr rich precipitated phase has a great influence on the mechanical properties of the alloy. [ABSTRACT FROM AUTHOR]

The microstructure evolution and fracture behavior of Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe (Ti-5321) alloy during BASCA (β annealed with subsequent slow cooling & aging) heat treatment were studied. Three different lamellar microstructures, termed as L1, L2 and L3, were obtained by solution treated at 880 °C for 2 h followed by 0.5 °C/min cooling to 800 °C, 750 °C and 710 °C, respectively and aging at 580 °C for 6 h. Microstructural investigation revealed that the three lamellar microstructures were composed of intergranular precipitation (α GB , α WGB), intragranular α l and β t. Both of the volume fraction of lamellae α and the size of α colonies increased with the increasing furnace cooling time. Both intergranular and intragranular precipitation in L1, L2 and L3 obeyed the Burgers orientation relationship (OR) with adjacent β grain. However, the texture intensity and variant selection degree of lamellar α increased with cooling process owing to the increased amount of α colonies. In addition, the L1 sample, with 15% α l , displayed the lowest fracture toughness value (57.7 MPa·m1/2), while the L3 sample with 61% α l exhibited the highest (114 MPa·m1/2). Although the crack path in all the cases were both translamellar and interlamellar, fracture mode varied from mixed mode (dimples and intergranular cracks) type fracture in L1 to predominantly dimple fracture in L2 and L3. Moreover, the fracture behavior of Ti-5321 alloy was also related to the crystallographic distribution and variation selection of α phase. Crack growth was much easier through continuous α GB layer compared to the discontinuous α GB , especially for the high angled α GB /α GB grain boundary. As a consequence, the higher probabilities of misorientation angles of 90° in L1 and L3 could significantly promote crack deflection compared to L2. • Microstructure evolution and fracture behavior of Ti-5321 alloy during BASCA heat treatment are investigated. • Lamellae α, α colonies and lamellar α play an important role in fracture behavior. • Fracture mode of samples vary from mixed fracture to predominantly dimple fracture with the increased furnace cooling time. [ABSTRACT FROM AUTHOR]

In the current work, deformation behavior and microstructure changes of a new near-alpha titanium alloy in single phase region are investigated. For this purpose, high-temperature compression is carried out in single-beta phase region with different temperatures, strain rates and height reductions. The flow softening behavior can be observed at the strain rates of 0.01s−1 and 0.1s−1, whereas work hardening occurs at the strain rates of 1s−1 and 10s−1. The extents of softening or hardening are strongly influenced by strain rate, but vary only slightly with deformation temperature. Recrystallization and recovery have different impacts under different conditions. Recovery plays a dominate role particularly under high strain rate. By contrast, recrystallization controls microstructure evolution under low strain rate. Alpha phases are precipitated from prior beta grains during cooling after deformation, and there is truly a link among alpha phases. The EBSD analysis indicates that the two adjacent precipitations of alpha may share one common or close (11–20) pole, but the caveat is that the statement is not rigorous due to the smaller scanning areas. Additionally, the drive forces of growth of alpha phases are influenced by their crystal orientations. For the two accompanying alpha phases, it seems the interspersed alpha phase tries to pass through the surrounded alpha phase and grow into a longer structure when they have one common (11–20) pole, while it may be difficult to grow longer when one of (11–20) poles of them have some deviation. [ABSTRACT FROM AUTHOR]

The impact toughness and deformation modes of Ti–6Al–4V alloy with different microstructures, i.e., equiaxed microstructure (EM), bimodal microstructure (BM), fine lamellar microstructure (LM1) and coarse lamellar microstructure (LM2), were studied and revealed in detail. The impact toughness of BM was determined as 85 J/cm2, which was about 70%, 42% and 35% higher than that of EM, LM1 and LM2, respectively. BM possesses a composite-like microstructure containing hard primary α grain (α p) and soft β transformation microstructure (β t). During crack propagation, large plastic deformation occurs within soft β t region, and the deformation of β t was constrained by surrounding hard α p , resulting in kink deformation of β t and local plastic deformation of α p. In addition, {10-12}<-1011> tensile twins with both high and low Schmid factor were activated in α p by the sever kink deformation of β t and impact energy. Furthermore, some α p grains near the fracture surface were crushed significantly by impact loading. As a result, the synergistic effect of these aforementioned factors can effectively dissipate impact energy, correspondingly enhancing the impact toughness of Ti–6Al–4V alloy. By contrast, the crack mainly propagates along the α p 's grain boundary in EM. Moreover, the coordinate deformation ability between α p and β t was weak due to the high content of α p , resulting in a significant reduction of impact toughness. For LM1 and LM2, although {10-12}<-1011> tensile twins and {10-11}<-1012> compression twins were activated, the impact toughness was still lower than that of BM due to little plastic deformation in LM1 and heterogeneous deformation in LM2. These results indicated that the coordinated deformation ability of the microstructure plays an important role in impact toughness of the alloy. [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 wear resistance of titanium alloy, the WC-reinforced composite coatings were prepared on Ti-6Al-4V substrate by laser cladding. The effect of linear energy density (LED: 73.3 J·mm−1-283.3 J·mm−1) on the microstructure, microhardness and wear resistance of the composite coatings were investigated. The evolution of WC during laser cladding was revealed and discussed. It is found that the WC is dissolved by the forms of releasing W and C with increasing LED, and grows into specific shapes according to the Lifshitz-Slyosov-Wagner model. As the LED increases, the retention index of WC decreases (0.91–0.80) and the grain size increases (1.89 μm–5.81 μm) in the composite coating. The microstructure differences lead to the microhardness and brittleness increasement of composite coating. Compared with the Ti-6Al-4V substrate, the maximum microhardness improvement and wear mass loss reduction are 5 times and 25 times by varying LED. The main wear mechanism of composite coatings is abrasive wear. However, additional forms of wear mass loss such as adhesive wear and WC peeling can occur due to LED variation, and further leads to the difference in wear resistance. It is expected that the evolution of WC, which can regulate the microstructure will provide an effective theoretical foundation for the wear-resistance improvement of the laser cladding coatings. [Display omitted] • The evolution process and growth mechanism of WC during laser cladding are revealed. • The effect of linear energy density on the microstructure is summarized. • The WC grows into a specific shape along the habit plane by atomic migration. • The evolution of WC and wear performance response of WC-Co-Cr coating is elucidated. [ABSTRACT FROM AUTHOR]

WC-Co composites comparable to titanium in thermal expansion coefficient can be used as wear-resistant coatings, extending the applications of titanium alloys. This study aims to investigate the effect of laser power on the quality of composite coatings on the Ti-6Al-4 V substrate, and to study the phase constituents comprehensively, microstructural evolution, microhardness, and wear behavior of composite coatings. The experimental results show that there is a good metallurgical bonding between the WC-Co composite coatings with high densification and the substrate. Furthermore, a considerably high microhardness up to 1536 HV 0.5 , and a wear rate of 1.5 g/h were achieved owing to the synergistic effect of excellent metallurgical bonding and fine microstructures of the composite coating under laser power of 2000 W. Based on the experimental results, the process-structure-properties relationship of laser cladded WC-Co composite was established. It is expected to be applied to improve the wear resistance of petroleum titanium alloys in deep and ultra-deep wells. • New phases W 2 C and η-Co were formed under the action of high energy laser density. • The morphology evolution of WC particles with different laser powers was studied. • The distribution of tensile stress eventually leads to spalling of the composite coatings. [ABSTRACT FROM AUTHOR]

A special recrystallization mechanism called ‘particle stimulated nucleation’ (PSN) is found responsible for the pervasive discontinuous dynamic recrystallization (DDRX) in the burn resistant β-stablized Ti–35V–15Cr–0.3Si–0.1C alloy. This might be the first time that PSN is found in titanium alloys. PSN mechanism is studied by transmission electron microscopy (TEM) and Electron Back Scattered Diffraction (EBSD) techniques. Local strain incompatibility between the matrix and the titanium carbides leads to high density of dislocation in the particle deformation zone (PDZ), which provides the ideal sites for PSN. Recrystallized grains produced by PSN is randomly oriented and the microtexture gets weaker as the fraction of DRX increases. [ABSTRACT FROM AUTHOR]

By introducing ceramic SiC particles, Al x CoCrFeNiTi 1-x /SiC (x = 0.5,0.8 in molar ratio) high entropy alloy coatings (abbreviated as Al0.5, Al0.8, Al0.5/SiC, and Al0.8/SiC alloy coating respectively) were fabricated by laser cladding (LC) on the AISI1045 steel in this work. The microstructures, phase constitutions, mechanical and corrosion-resisting behaviors of the as-prepared coatings with and without SiC particles were investigated and compared intensively. It was found that the added SiC particles decomposed into the Si and C during the LC processing, which was verified to have a significant influence on constructing microstructures of the alloy coatings. The cuboidal L2 1 precipitates within the disordered BCC matrix in Al0.5 alloy coating transformed to the coarse lath-like microstructures composed by the L2 1 and FCC matrix in Al0.5/SiC. Simultaneously, the more refined braided network structures were obtained in Al0.8/SiC alloy coating, corresponding to the increased volume fraction of the B2 phase. The microhardness of the Al0.8/SiC alloy coating improved from 637 HV 0.2 in Al0.8 to 718 HV 0.2 , and the coefficient of friction decreased from 0.40 to 0.31 with the SiC addition. In contrast, the SiC particles showed a negative effect on the microhardness of Al0.5/SiC alloy coating from 743 HV 0.2 to 679 HV 0.2 , as a result of coarsened microstructure and increased fraction of the supple FCC solid solution. The friction coefficient reaches its lowest value of 0.29 in Al0.5 alloy coating, and there is a mixture wear mechanism of wear and delamination wear. Furthermore, the pitting potentials of both the Al0.5/SiC and Al0.8/SiC were lower than that of the SiC-free alloy coating. With the dissolution of SiC particles, the prompted spinodal decomposition and enlargement of lattice misfits between phases reduced the coatings' resistance to pitting corrosion. • Ceramic-reinforced composites of Al X CoCrFeNiTi 1-X HEA coatings without cracks were successfully prepared on the AISI1045 steel. • The added SiC particles are verified to have a significant influence on constructing microstructures of the alloy coatings. • Considerably enhanced microhardness and wear resistance were obtained in a SiC-added alloy coating, resulting from the more refined microstructure. [ABSTRACT FROM AUTHOR]

Tensile deformation and damage evolution of a metastable β titanium alloy (Ti–5Cr–4Al–4Zr–3Mo–2W–0.8Fe) with lamellar microstructure are studied by in-situ tensile test under scanning electron microscopy. In the tensile process, the main deformation modes include the dislocation slip, phase interface shear and grain boundary shear, and the geometrical orientation of α lamellae determines the activation of different slip systems and whether the interface shear is involved in deformation. The α lamellae may kink and even fragment under severe deformation. Slip transfer is prone to occur between α lamella and β interlayer that satisfy the Burgers orientation relationship, and the slip lines will deflect and bifurcate as more slip systems are activated and grains rotate. Due to the localized stress concentration and inhomogeneous deformation, the grain boundaries, phase interfaces, tips of β interlayers, junctions of colonies composed of α lamellae and shear bands are all the positions where are easy to generate microvoids. The crack propagates along a zigzag path on account of the synergistic reaction mechanism of critical resolved shear stress, activated slip system, shear band and grain boundary shear, resulting in an intergranular and transgranular mixed fracture mode. [ABSTRACT FROM AUTHOR]

To achieve preferable impact performance of a newly designed high strength Ti-5321 alloy, samples with three kinds of microstructures, i.e., bimodal microstructure (BM), tri-modal microstructure (TM) and lamellar microstructure (LM) were prepared for instrument Charpy tests at room temperature. Results of impact tests indicated that LM presented the higher impact toughness of 37.5 J/cm2 than that of BM (11.25 J/cm2) and TM (25 J/cm2). Moreover, both crack initiation energy and crack propagation energy of LM were obviously raised. Further analysis containing fracture surfaces and the cross-sectional microstructures of the impact samples by the usage of SEM and EBSD provided insights into the influence of microstructure on crack initiation and propagation during impact process. The largely plastic deformation of primary α near the V-notch tip impeded crack initiation and enhanced the crack initiation energy. The interweaved α colonies with high angle boundaries deflected the crack propagation direction and thus increased the crack propagation energy. Besides, TEM analysis showed that the typical deformation characteristic under impact test with high strain rate. Except for dislocation lines, the pile-up of highly dense dislocations, twinning, dislocation cells, sub-grains, shear bands and fragmentation of α phase can be found. These approaches presented in this study could provide certain insights into fabricating typical microstructure in the high strength titanium alloys to ameliorate impact properties. • Lamellar microstructure shows the superior combination of strength, ductility and impact toughness. • Effective crack deflection and compatible deformation of lamellar microstructure can improve the impact toughness. • Dislocation slip, twinning, dislocation cells, shear belts and fragmentation of α phase can be found in the impact samples. [ABSTRACT FROM AUTHOR]