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To enhance the service life and application range of titanium alloys in the aerospace sector, Ti-Zr-B-C coatings with varying B 4 C contents (0–30 wt%) on TC11 titanium alloy was fabricated by laser cladding. The microstructure and anti-ablation were investigated in the present work. The results show that the whisker-like TiB phases and granular TiC and ZrC phases were observed in the coatings due to the in-situ reactions. With increasing the content of B 4 C, the number of reinforcing phases in the coating increased and distributed uniformly, resulting in the improvement of the microhardness up to 803.8HV. Furthermore, due to the formation of TiO 2 -ZrO 2 -B 2 O 3 dense multiphase oxide layer on the surface during the ablation process, the coating with 20 wt% B 4 C exhibited the best anti-ablation at 1400ºC, the mass ablation rate (MAR) and linear ablation rate (LAR) were −2.62 mg/s and 3.67μm/s, respectively, which were just 62.8 % and 50.07 % in comparison with the substrate. This is mainly attributed to the formation of TiO 2 -ZrO 2 -B 2 O 3 layer is beneficial to reduce the infiltration of O 2 and the evaporation of liquid B 2 O 3 , leading to the excellent anti-ablation. • The TiB, TiC and ZrC reinforcing phases were in-situ formed in the Ti-Zr-B-C coating via laser cladding. • With increasing the content of B 4 C, the microhardness of the coating increased gradually. • The coating with 20wt% B 4 C exhibited the best anti-ablation among all the coatings. [ABSTRACT FROM AUTHOR]

Decarburization means carbon in rail material lost in the hot rolled process. It changes the microstructure of rail materials and will influence their rolling contact fatigue (RCF) characteristic. The objective of this study is to explore the effect of decarburized layer on rolling contact fatigue and propagation mechanism of crack under the wet condition using a rolling-sliding wear testing machine. The results show that the crack growth rate on the decarburized rail roller is over 4 times than that on the non-decarburized rail. Small pitting presents on the non-decarburized rail roller, which is dominated by transgranular crack. While, long mouth surface crack dominates on the decarburized rail roller and the cracks mainly grow along the ferrite line or the grain boundary. With the cycles increasing, the surface cracks of decarburized rail roller gradually break and forms spalling damage, eventually expands to bulk spalling. Meanwhile, the crack growth mechanism changes back to the transgranular propagation and propagates in depth with a large angle when the decarburization is worn off. [ABSTRACT FROM AUTHOR]

The Nb-30Ti-18Al alloys doped with the amounts of 0 at%, 1 at% and 5 at% carbon were prepared by arc melting and annealing. The effects of carbon addition on the microstructure and mechanical properties of Nb ss /Nb 3 Al in situ composites as well as the strengthening mechanisms were investigated. The results showed that during annealing at 1200 °C, supersaturated Nb ss decomposed and Nb 3 Al phase precipitated in C-free alloy, while carbide decomposed with the precipitation of Nb 3 Al in C-doped alloys. Furthermore, the orientation relationship of Nb 3 Al phase and the surrounding (Nb, Ti)C was observed in Nb-30Ti-18Al-5C (NA5) alloy. Additionally, with increasing the carbon content, the compressive strength of alloys at high temperature were improved significantly ascribed to the occurrence of solid solution and volume fraction increase of strengthen phase, while the fracture toughness decreased due to the volume fraction decrease of Nb ss . [ABSTRACT FROM AUTHOR]

The in-situ laminated Nb/Nb 5 Si 3 composite was prepared by spark plasma sintering. The microstructures and mechanical properties of the laminated Nb/Nb 5 Si 3 composite were investigated in present work. It could be found that, alternant distribution microstructures of Nb ss and Nb 5 Si 3 layers were observed after sintering. The Nb/Nb 5 Si 3 composite exhibited fracture toughness of 11.2 MPa·m 1/2 , and the predicted fracture toughness was estimated by the Ashby model. Moreover, the deviation of the experimental value from the predicted value was discussed. In addition, the compressive strength of the in-situ laminated Nb/Nb 5 Si 3 composite was measured at 1400 °C and compared with that of the unidirectionally solidified Nb-17.5Si alloy. [ABSTRACT FROM AUTHOR]

A face-centered cubic (FCC) non-equiatomic high-entropy alloy (HEA), Cr 10 Mn 10 Fe 60 Co 10 Ni 10 , is processed via cold-rolling and subsequent annealing at 800 − 1200 °C with different cooling methods. All the annealing treatments lead to fully recrystallized microstructures with various grain sizes and precipitate types. The mechanical properties under uniaxial tension are obtained along with microstructure characterizations of postmortem samples. The sample annealed at 800 °C followed by furnace cooling yields a reasonable combination of high strength and good ductility. The yield strength and ultimate tensile strength are 43% and 19% higher than those of the sample annealed at 800 °C followed by water quenching, with only a uniform elongation ∼ 6% reduction. The yield strength variations of all the annealed samples are explained with a structure-based strength model. After fracture, all the samples show strong 〈 111 〉 texture along the tensile direction. Besides dislocation slip, deformation twinning and multiple phase transitions contribute to high strength and effective work hardening as additional deformation mechanisms. The newly formed hexagonal close-packed and body-centered cubic phases follow the Shoji–Nishiyama and Kurdjumov–Sachs orientation relations with the FCC matrix, respectively. Given the "treatment method − microstructure − mechanical property" relationship in this study, combining the advantages of the steel and HEAs, this kind of Fe-rich HEA bears great potentials to serve under practical conditions. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of columnar-grained copper under casting and drawing conditions were investigated in the present work. It was found that the as-casted copper mainly consisted of continuous columnar grains with orientation preference along <100> and exhibited excellent plastic deformation ability. Moreover, the texture of columnar-grained copper transferred from <100> to <111> during the drawing process. A typical microstructural morphology as multangular-cup feature of as-casted copper as well as drawn copper was observed on the fracture surfaces. With increasing the drawn strain, the texture evolution and the grains broken occurred, leading to a significant increase in the work hardening rate and tensile strength. [ABSTRACT FROM AUTHOR]

A typical Fe-rich non-equiatomic CrMnFeCoNi high-entropy alloy (HEA), Cr 10 Mn 10 Fe 60 Co 10 Ni 10 , and the equiatomic Cr 20 Mn 20 Fe 20 Co 20 Ni 20 HEA, are investigated via plate impact experiments along with in situ free surface velocity measurements. Both the initial and postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. These two HEAs contain a single face-centered cubic phase, are texture-free, and have similar grain sizes. Dynamic yield stress and spall strength of the non-equiatomic CrMnFeCoNi are lower by ∼55 % and 15 % than those of its equiatomic counterpart, respectively. After shock compression, dislocation slips, stacking faults, Lomer-Cottrell locks and nanotwins are found in the postmortem samples of both HEAs. Due to the reduced stacking fault energy in the non-equiatomic HEA, more deformation twins and newly formed hexagonal close-packed phases are found. For spallation, intergranular voids are larger in size but smaller in quantity than intragranular voids for both HEAs. Both intragranular or intergranular voids show strong dependence on grain boundary misorientation. [Display omitted] • Equiatomic and non-equiatomic CrMnFeCoNi are with similar grain size and weak texture. • The yield stress and spall strength of equiatomic alloy are higher. • More nano twins and newly formed HCP phase are found in nonequiatomic alloy. • Ductile spallation occurs. The HAGBs have a higher probability of inducing a void than TBs. [ABSTRACT FROM AUTHOR]

Phase transformation in a metastable body-centered cubic (BCC) high entropy alloy HfZrTiT a 0.53 is investigated via plate impact along with in situ free surface velocity measurements, postmortem microstructure characterizations and first-principles calculations. Impact-induced BCC to hexagonal close-packed transformation is observed. Compared to the single orientation relationship (the Pitsch-Schrader relationship) under quasi-static loading, an additional orientation relationship with higher phase transformation activation barrier is also involved, given the ultrahigh strain rates and complex stress condition under planar impact. [ABSTRACT FROM AUTHOR]

The effects of strain rate on mechanical properties, microstructural evolution and underlying deformation mechanisms of two kinds of interstitial CrMnFeCoNi high entropy alloys (HEAs), (CrMnFeCoNi) 99.5 C 0.5 and (CrMnFeCoNi) 99.0 C 1.0 , are investigated under quasi-static and dynamic tension. Dynamic loading is carried out via a split Hopkinson tension bar system. The pre- and post-deformation microstructures are characterized with electron back scatter diffraction and transmission electron microscopy. Both yield strength and work hardening increase remarkably with increasing strain rate. Plastic deformation in both alloys under quasi-static and dynamic loading are dominated by dislocations, stacking faults, kink bands and deformation twins. Twinning is activated easier under dynamic loading, and twin density decreases with increasing carbon content due to the increased stacking fault energy. The Khan-Liu constitutive model can describe the experimental results for these two interstitial HEAs in a wide strain range. • Both volume fraction and size of the carbides increase with the increase of C content. • The increase of C content and strain rate lead to the increase in σ Y and σ UT. • Twin density decreases with increasing C content due to the increased SF energy. • The Khan-Liu constitutive model is used to describe the deformation. [ABSTRACT FROM AUTHOR]

In this study, two different microstructures were obtained after subsolvus solution treatment (910 °C + 550 °C) and supersolvus solution treatment (1010 °C + 550 °C) in TC21 alloy. The relationship of microstructure with room and high temperature properties was studied. The results showed that at room temperature, both samples after two treatments had high hardness. At room temperature, the subsolvus sample had high tensile strength of 1070 MPa and moderate plasticity and impact toughness, while the supersolvus sample was hard and brittle. The high strength and toughness of subsolvus sample was owing to its clear basket-weave structure within finer β grains which contributes to fine grain strengthening and the increase of crack tortuosity. Poor plasticity and toughness of supersolvus sample could be mainly attributed to its incomplete basket-weave structure, coarse β grains, Widmannstatten α and some coarse α-phase in the grain boundary. Both samples showed excellent high temperature tensile properties and stability at 400 °C, the tensile strength was still as high as 1000 MPa while plasticity was significantly improved. With the tensile temperature increasing to 600 °C, the alloys showed obvious softening as the tensile strength significantly decreased and elongation increased. • TC21 alloys after subsolvus heat treatment showed an obvious basket-weave structure. • The TC21 alloy after subsolvus treatment showed high fracture strength of 1070 MPa with the elongation of 8 %. • Both subsolvus and supersolvus samples showed excellent high temperature tensile properties at 400 °C and 600 °C. • The tensile strength was still as high as 1000 MPa while plasticity was significantly improved during 400 °C tensile. • The tensile strength significantly decreased to about 500 MPa as elongation increased during 600 °C high temperature tensile. [ABSTRACT FROM AUTHOR]

Dynamic equal channel angular pressing (DECAP) and heat treatment are applied to pure Ti to achieve a strength-ductility synergy. DECAP induces a complex multiscale twin structure in Ti including four primary twin types, secondary twins and tertiary twins with multiple variants, and an increased yield strength (58% higher than the as-received Ti). Subsequent annealing at 200 ℃ and 400 ℃ leads to improved ductility and strength. The yield strength (σ y) and total elongation (ɛ t) for the Ti sample processed with DECAP and 400 ℃ annealing are 555 MPa and 30%, respectively, and its σ y ɛ t product is ∼ 45% higher than the as-received Ti. DECAP and subsequent annealing lead to a superior strength-ductility synergy in twinned Ti, providing a novel approach to produce high strength and ductility materials via dynamic deformation and subsequent heat treatment. [ABSTRACT FROM AUTHOR]

• The influence of thermal-cold cycling on dimensional stability of composite. • The microstructure, dimensional change, magnetic property, hardness were analyzed. • The underlying dimensional stabilizing mechanisms of the composite were revealed. • An optimal improvement of dimensional stability of the composite was achieved. Thermal-cold cycling (TCC) treatment was applied to improve the dimensional stability of TiC reinforced steel matrix composite materials in this study. Also, the microstructure, related properties and potential stability mechanisms were investigated. When the TCC cycles were 3, Vickers hardness reached the peak value of 1051.7 HV and relative dimensional change was only 0.012% in a natural service for 30 days. Besides, the retained austenite disappeared and residual stress dramatically decreased from −740 MPa to −357 MPa. It demonstrated that the TiC reinforced steel matrix composite possessed the best dimensional stability after 3 TCC cycles. A variety of stabilizing mechanisms, including martensitic refinement, retained austenite-martensite transformation, carbides precipitation, and residual stress release were observed, hence resulting in a significantly improvement of the dimensional stability of the composite. [ABSTRACT FROM AUTHOR]

• The influence of tempering on dimensional stability of TiC-reinforced composite. • The microstructure, hardness, thermal strain and magnetic property were analyzed. • The underlying dimensional stabilizing mechanisms of the composite were revealed. • An optimal improvement of dimensional stability of the composite was achieved. To improve the service reliability of components prepared by TiC-reinforced steel matrix composite material, tempering treatment was carried out to tailor the microstructure and properties of the composite. The aim of this study was to investigate the microstructure, properties, and dimensional stability of a TiC-reinforced steel matrix composite during tempering and to identify the underlying stabilizing mechanisms. We observed that the metastable retained austenite transformed into martensite and that residual stress released during tempering. The microstructure and properties of the composite reached an optimal state for a tempering time of 10 h. Furthermore, the relative dimensional change, Vickers hardness, thermal strain, and saturation magnetization of the composite were 0.0219%, 960.8 HV, 3.16 × 10−4, and 109.7 emu/g, respectively. Various stabilizing mechanisms, including retained austenite-martensite transformation and residual stress release, were observed during tempering, effectively improving the dimensional stability of TiC-reinforced steel matrix composites. [ABSTRACT FROM AUTHOR]

Plate impact experiments are conducted on a metastable dual-phase high-entropy alloy (HEA) Cr 10 Mn 30 Fe 50 Co 10 with different matrix grain sizes and phase fractions. Free surface velocity histories are obtained along with microstructure characterizations. Postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. Multiple deformation mechanisms are observed, including dislocation slip and stacking fault in the face-center cubic (FCC) phase, dislocation slip and deformation twinning in the hexagonal close-packed (HCP) phase, and the FCC to HCP transformation. For spallation, damage is ductile in nature. Despite different microstructures, micro-voids prefer to nucleate at high-angle grain boundaries within the FCC phase, leading to similar spall strength. Upon shock loading, a dynamic plastic deformation partitioning behavior among the two phases is observed; at high shock stress, denser dislocations in the HCP phase result in increased fractions of voids around the FCC/HCP phase interface and within the HCP phase during spallation damage. • C r10 M n30 F e50 C o 10 with different FCC grain sizes and phase fractions are obtained. • Damage is ductile in nature, spall strengths for different microstructures are similar. • Multiple deformation mechanisms are observed, including FCC to HCP transition. • A dynamic plastic deformation partitioning behavior in two phases is observed. [ABSTRACT FROM AUTHOR]

Three texture-free CoCrNi-based medium-entropy alloys (MEAs) with similar grain sizes, CoCrNi, (CoCrNi) 94 Al 3 Ti 3 and (CoCrNi) 90 Al 5 Ti 5 , are investigated under plate impact loading. Free surface velocity histories are obtained along with microstructure characterizations of postmortem samples. The influences of the addition of minor elements Al and Ti on the microstructures, dynamic mechanical properties and underlying deformation and damage mechanisms of MEAs are elucidated. Compared to the single-phase CoCrNi MEA, spherical nanosized L 1 2 precipitates and micron sized body-centered-cubic phase are found in (CoCrNi) 94 Al 3 Ti 3 and (CoCrNi) 90 Al 5 Ti 5 , respectively. The addition of minor elements Al and Ti leads to an increase in the dynamic yield stress approximately by 70% (to 1.0 GPa) and 130% (to 1.4 GPa) for (CoCrNi) 94 Al 3 Ti 3 and (CoCrNi) 90 Al 5 Ti 5 , respectively, due to the solid solution strengthening and precipitate strengthening. Multiple deformation mechanisms are observed. Planar dislocation glide and stacking faults are the dominant deformation mechanisms for all the MEAs. However, deformation twinning is deactivated in (CoCrNi) 94 Al 3 Ti 3 and (CoCrNi) 90 Al 5 Ti 5 with small additions of Al and Ti. For spallation, damage is ductile in nature for CoCrNi and (CoCrNi) 94 Al 3 Ti 3 , but brittle for (CoCrNi) 90 Al 5 Ti 5 . Under similar shock stress, the spall strength of (CoCrNi) 94 Al 3 Ti 3 is comparable to that of CoCrNi, ∼ 150% higher than that of (CoCrNi) 90 Al 5 Ti 5 because intergranular brittle fracture activation does not require substantial plastic deformation. The minor addition of Al and Ti in medium-entropy alloys significantly affects their dynamic mechanical properties, deformation and damage mechanisms. [ABSTRACT FROM AUTHOR]

In this study, the ageing behaviour of a nanostructured Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr (wt.%) alloy produced by solution treatment followed by high pressure torsion (HPT) was systematically investigated using hardness testing, high resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), elemental mapping, X-ray diffraction (XRD) and XRD line broadening analysis. The HPT-deformed alloy exhibits an ageing response that produces a higher peak-aged hardness at lower temperature and shorter ageing time as compared to the same alloy aged after conventional thermomechanical processing. The HAADF-STEM and elemental mapping reveal extensive segregation of solute atoms along grain boundaries during ageing. A model is developed which shows that the main structures causing hardening for peak-aged samples are the grain boundaries and the segregation of solute atoms formed along grain boundaries. The metastable β′ phase precipitates, which form on ageing of conventionally processed Mg-Gd-Y-Zn-Zr alloy samples, do not form in the present aged samples, and instead equilibrium β-Mg 5 (RE,Zn) phase forms on over-ageing. This altered precipitation behaviour is attributed to the high defect density (e.g. grain boundaries, dislocations and vacancies) introduced by HPT, leading to enhanced diffusion of solutes. The present processing produces an alloy that has a hardness of ∼145 HV. A model of strengthening indicates that whilst grain boundary strengthening provides the largest contribution to strengthening, it is the additional solid solution hardening, cluster hardening, and dislocation hardening that provide the main factors that caused the hardness to surpass that of other bulk processed Mg alloys studied to date. [ABSTRACT FROM AUTHOR]

[Display omitted] • The influence of vibration aging on residual stress relief of composite. • The residual stress, hardness and magnetic property were analyzed. • The underlying mechanisms of the composite were revealed. • An optimal improvement of the composite was achieved. To further improve the long-term service reliability of high-precision inertial instruments prepared with TiC reinforced steel matrix composite materials, vibration aging treatment was carried out to improve the comprehensive properties of the instrument-grade composite. The effects of vibration aging on microstructure, stress relief, hardness, and magnetic properties of the stabilized composite were investigated, and the underlying mechanisms were also elucidated. The results showed that the vibration aging treatment significantly released the residual stress and improved the Vickers hardness of the composite, while also promoting the precipitation of fine carbides in the matrix and the microstructure transformation of metastable retained austenite to relatively stable martensite. When the vibration aging was conducted at 80 °C for 30–60 min, the composite possessed excellent comprehensive properties. During the vibration aging process, various mechanisms, such as residual stress relief, retained austenite–martensite transformation, and carbides precipitation acted on the composite, resulting in a significant improvement in the performance of TiC reinforced steel matrix composite. [ABSTRACT FROM AUTHOR]