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The mechanical properties of a fine-grained (FG) Ti-6Al-4V extra-low interstitial (ELI) alloy were investigated by tensile tests at 298 K and 77 K. The experimental results indicated that, at 77 K, the alloy exhibits a small uniform elongation of 2.65%, but has a fracture elongation of 19.2%, showing superior post-necking elongation. At 298 K, the alloy displays a single dislocation slipping, β→α″ phase transformation occurred, and 6.35% uniform elongation was obtained, whereas the coupling of dislocation slipping and twinning deformation behaviors dominated at 77 K. The limited uniform elongation is attributed to the absence of martensite phase transformation at 77 K, whereas the decent fracture elongation is ascribed to the resistance offered by twinning against plastic instability. [ABSTRACT FROM AUTHOR]

In this study, the microstructural evolution, distribution, morphology, and change mechanism of an as-rolled Ti2AlNb alloy were quantitatively analyzed by X-ray diffraction and electron backscatter diffraction (EBSD). The results show that after solution treatment at 900 °C, the content of the O phase alloy decreased by 2%, which provided space for the nucleation of the α2 phase, the content of which increased by 2%. After aging treatment at 760 °C, large quantities of acicular O phase and α2 phase were precipitated in the B2 matrix, and the content of the α2 phase increased. As the aging temperature increased to 840 °C, the elongated α2 phases were connected to each other at a specific angle along the grain boundary, extending to the interior of the grain. The hardness reached its maximum value of 402 HV at 760 °C. This study deepened our understanding of the formation of the α2 phase in the microstructure of rolled Ti2AlNb alloy, and investigates the effect of α2 phase content on the hardness of the alloy in more depth. [ABSTRACT FROM AUTHOR]

A novel TiAl alloy was prepared by sintering and forging, and the microstructure and compression properties of the sintered and forged alloys were investigated. The results show that the alloy consists of γ-TiAl and α2-Ti3Al; the microstructure of the alloy in both sintered and forged states is divided into fine-crystal regions and coarse-crystal regions, and the fine-crystal regions in the sintered state consist of slate-like γ grains with a small amount of α2 grains, while the coarse-crystal regions consist of equiaxed γ grains. The fine-crystal regions in the forged state consist of equiaxed γ grains with a few α2 grains, and the coarse-crystal regions consist of equiaxed γ grains. The alloy has lower porosity and a more homogeneous microstructure. The compressive properties of the forged alloy were improved, the compressive strength increased from 1172 to 2349 MPa, and the engineering strain increased from 32% to 42%. [ABSTRACT FROM AUTHOR]

YAG ceramic was brazed to Kovar alloy under a high vacuum of 6–8 × 10−4 Pa. A good contact angle (θ eq = 10.7°) was obtained by wetting AgCuTi filler metal on the YAG ceramic substrate, and the associated interfacial microstructure was characterized. The microstructure of the achieved YAG/Kovar joints brazed by AgCuTi filler was characterized by SEM, TEM and XRD, which was found to be YAG/Y 2 O 3 /(Fe, Ni)Ti/Ag(s, s) + Cu(s, s)/Fe 2 Ti + Ni 3 Ti/Fe 2 Ti/Kovar. The effects of different brazing temperatures on the joint structure were investigated. The thickness of the (Fe, Ni)Ti reaction layer increases, and the banded structure formed by Fe 2 Ti and Ni 3 Ti intermetallic compounds (IMCs) widens with increasing brazing temperature. Nanoindentation and shear tests were used to characterized the mechanical properties of the joints. As the brazing temperature increased, the shear strength of the joints first increased and then decreased. A joint with an optimal shear strength of 51.3 MPa was obtained at 870 °C for 10 min. The nanoindentation test reveals the obvious differences in mechanical properties between phases: (Fe,Ni)Ti phase has higher Young's modulus and hardness than Fe 2 Ti–Ni 3 Ti phase and Ag–Cu eutectic. • YAG and Kovar was brazed with AgCuTi filler metal. • Typical microstructure: YAG/Y 2 O 3 /(Fe,Ni)Ti/Ag(s,s), Cu(s,s)/Fe 2 Ti, Ni 3 Ti/Fe 2 Ti/Kovar. • A contact angle of 10.7° was obtained by wetting AgCuTi filler metal on YAG. • Mechanical properites of the joint were confirmed by nanoindentation and shear strength. • The maximum shear strength of 57.3 MPa was achieved with the parameter of 870 °C/10 min. [ABSTRACT FROM AUTHOR]

The roles of Hf element in the mechanical properties, deformation mode and orientation evolution of the Cu-0.4Cr-0.2Zr-0.2Hf (wt.%) alloys were investigated using both ex-situ and in-situ electron backscatter diffraction (EBSD). The results indicate that the trace Hf element (0.2 wt%) addition into the Cu–Cr–Zr alloys motivates the multiple slip activities. The activation of multiple slip systems indirectly or directly influences the tensile strength, strain distribution and lattice rotation. Firstly, it promotes the generation of dislocations, and thus enhances the work hardening rate, contributing to the improvement of the ultimate tensile strength. Secondly, it inhibits the movement of dislocations to the grain boundaries, and thus hinders the strain localization at the grain boundaries, promoting the homogeneous deformation. Thirdly, the interaction between dislocations on different slip systems restricts the intragranular lattice rotation, leading to the high stability of the grains with Goss orientation in the Cu–Cr–Zr-Hf alloys. The mutual transform between the R-Cube RD orientation and Goss orientation is also observed. This study deepens the understanding of deformation mechanisms and texture evolution of the Cu–Cr–Zr-Hf alloys. • The trace Hf element addition motivates the multiple slip activities. • The multiple slip enhances the working hardening rate, and improves the strength. • The trace Hf element promotes homogeneous deformation. • The mutual transform between the R-Cube RD and Goss orientation are also observed. • The activation of multiple slip systems restricts the intragranular lattice rotation. [ABSTRACT FROM AUTHOR]

Cu-0.4Cr-0.2Zr-0.2Hf (wt%) alloy plates were prepared by cryogenic rolling and intermediate aging process. The effects of intermediate aging and cryogenic rolling on the microstructural, mechanical and textural evolutions were studied by X-ray diffraction, electron backscatter diffraction and transmission electron microscopy. The results show that the combination of cryogenic rolling and intermediate aging resulted in the formation of high-density dislocations, nanoscale deformation twins, deformation bands, and nano-precipitates in the Cu–Cr–Zr-Hf alloys. The nano-precipitates formed during the intermediate aging effectively increase the flow stress, and promote the formation of the nano-twins. Besides, the combination process can both reduce the fraction of the remnant grains and refine the width of remnant grains, promoting the homogeneous deformation of the Cu–Cr–Zr-Hf alloys. The reduction of the remnant grains decreases the Brass component, and increases the S component. The profuse nano-twins and Brass-type shear band contribute to the increase in the Y component. • The intermediate aging both reduce the fraction and the width of the remnant grains. • The intermediate aging effectively promotes the formation of the nano-twins. • The increased nano-twins result in an increase in the Y component. • The reduction in remnant grains lead to the decreases in Brass component. [ABSTRACT FROM AUTHOR]

• Swirl-like phase forms at the joint interface during the USW of Sn coated Cu. • Cu-Sn swirl-like phases greatly enhance the mechanical property of the joint. • Refinement of the phases and grains takes place near the swirl region. • Temperature and diffusivity are higher near swirl region than that of flat region. • Uneven stress and cavitation effect prompt the formation of the swirl phase. Previous studies have shown that sharp physical and chemical changes may induce the formation of swirl-like reaction phases in the ultrasonic spot welding (USW) of different materials. However, the mechanisms have not been well understood. In particular, swirl-like structures have seldom been discovered or discussed in the USW of Cu/Sn. In this study, swirl-like phases were observed in the USW of a Sn-coated T2 Cu plate with different welding energies (300−400 J). The evolution of the microstructure from the flat region to the swirl region was studied, the diffusion coefficient of Cu in Sn and the peak temperature of the interface during welding were theoretically calculated and experimentally verified, the formation mechanism of the swirl-like phases was discussed, and the relationship between the joint properties and welding energies was investigated. The results show that the content of Cu 3 Sn increases, while that of Cu 6 Sn 5 decreases gradually from the flat region to the swirl region and that grain refinement of Cu and IMCs occurs near the swirl regions. The greatly enhanced diffusivity shows that intense atomic diffusion takes place during the welding process. When the welding energy exceeds 300 J, the experimentally measured peak temperatures in the welding processes are higher than the theoretical values. The formation of the swirl-like phase is attributed to the uneven distribution of interfacial stress and the collapse of cavitation bubbles. When the welding energy reaches 400 J, the peak lap shear load of the welded specimen reaches 1008 N, and the associated fractures indicate the combined characteristics of ductility and brittleness. [ABSTRACT FROM AUTHOR]

The Al-Mg-Si-Fe-Cr alloy was subjected to water quenching (WQ) and air quenching (AQ) after solution treatment for 30 min at 843 K followed by a peak artificial aging treatment at 453 K for 8 h. Precipitates of different sizes and precipitate free zone (PFZ) of different widths were obtained. Uniaxial tensile tests were conducted to investigate the effect of the microstructure and deformation temperature on the mechanical properties and deformation behavior of the WQ and AQ samples at 298 K and 77 K. The results showed that the yield strength and work hardening rate of the AQ samples were lower than those of the WQ sample. In addition, the strength and ductility of the two samples are significantly improved at cryogenic temperatures. Furthermore, quasi-in situ electron back scatter diffraction (EBSD) was conducted to investigate the orientation evolution of grains with strains of 1%, 3%, 7% and 10% for the two samples at 298 K and 77 K. The different orientation evolution of the two samples was caused by the nonuniform deformation in the PFZ and grain interior. The dislocation characteristics and fracture morphology were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. Because the rod-shaped precipitates hinder the dislocation movement, no obvious slip traces could be observed on the deformed surface of the AQ sample. In addition, two slip systems are activated for most grains of the WQ sample at 77 K, but only one slip system is activated at 298 K. Due to the weak grain boundaries deformed at 298 K, the stress applied to grains is consistent with the tensile direction. However, the grain boundaries are strengthened when tested at 77 K, and the stress field of the grain boundaries is more complex, resulting in the stress not only in the tensile direction. More slip systems are activated to coordinate the deformation, improving the ductility. TEM images reveal that the deformation of the PFZ is more severe for the AQ sample at 298 K than at 77 K. The deformation in the precipitate-free zone and within the grain was more homogeneous in the AQ sample at 77 K, which increased its ductility compared to the AQ sample at 298 K. • A superior strength-ductility synergy was achieved for a dispersoids containing Al-Mg-Si alloy at 77 K. • The ductility of water quenching (WQ) sample and air cooled (AQ) sample is significantly improved at 77 K. • Two slip systems are activated for most grains of the WQ sample at 77 K, but only one slip system is activated at 298 K. • The deformation is more homogeneous at the PFZ and within the grain for the air cooled (AQ) sample at 77 K. [ABSTRACT FROM AUTHOR]

Layer thickness behaves as a crucial parameter in determining the mechanical properties of multi-layered composites. Recently, a synchronous improvement in the strength and ductility of Ti/Al layered materials was observed with the thickening of Ti layers. To address the underlying mechanism, Synchrotron Laue X-ray microdiffraction and electron backscatter diffraction were performed to study the dislocation behaviors at the initial and large deformation stages. We also developed a mechanistic model to elucidate the influence of layer thickness, as well as to determine the threshold thickness that governs the transition of deformation and fracture behaviors. Our experimental and model efforts suggest that the contribution of layer thickness lies in its role in the dislocation dynamics and strain distribution, which helps with the design of next-generation high-performance layered composites. • A superior strength-ductility synergy was realized with increasing Ti layer thickness. • Two different deformation and fracture behaviors were observed by μLXRD and EBSD. • The threshold of Ti fracture was estimated (img alt="" attrname="Mathedited" dpi="600" id="MPS_37927" mathml="${\sigma }_n/{\sigma }_y^{loc}$" src="http://10.66.13.70/DigiCore/Pageall/Else/JALCOM/168365/images/si%5fimages///si0016.gif" width="4%" />= 40) via a modified mechanistic model and experimental measurements. • The increasing Ti layer thickness, work-hardening exponent, and path direction of cracks improve the mechanical properties. [ABSTRACT FROM AUTHOR]

In this study, TiAl/Ti 2 AlNb laminated composite has been prepared via vacuum hot-pressing sintering. The composite exhibits a good synergy between bending strength and ductility, with a significantly enhanced bending strength value of 910.25 MPa. The fracture characteristics in the TiAl alloy layer, Ti 2 AlNb alloy layer and interfacial α 2 -Ti 3 Al layer are separately elucidated. It is concluded that the slip bands, tunnel cracks (α 2 -Ti 3 Al layer), deflected microcracks (Ti 2 AlNb alloy layer), and microcracks (TiAl alloy layer) are involved in the fracture process. Moreover, the main deformation behaviors consist of dislocation glide and local microcracking. The formation of stack faults and twins is also observed in the TiAl alloy layer. Furthermore, we focus on revealing the relationship between the deformation behaviors and fracture process of the composite. In particular, the strain partitioning and delayed fracture, multistage synergetic deformation mechanisms, and specific microcrack initiation are discussed. These findings are important for investigating the fundamental mechanisms and serving as a guide for the design of high-performance laminated composites. [ABSTRACT FROM AUTHOR]

• A novel TiAl/Ti 2 AlNb laminated composite has been successfully fabricated. • The microstructure evolution in the fabrication process is detailly studied. • A high toughness is achieved and its toughening mechanisms are investigated. TiAl/Ti 2 AlNb laminated composite has been successfully fabricated by hot pressing combined with the foil-foil metallurgy. The corresponding details about the microstructure evolution are discussed, and the metallurgical interface bonding can be achieved in the composite. Fracture toughness tests indicate the fracture toughness of this composite is increased by 77% over the TiAl matrix; meanwhile, the former behaves an enhanced crack damage tolerance ability. At last, the toughening mechanisms of the laminated composite are illuminated in detail. [ABSTRACT FROM AUTHOR]

In this work, the Ti 2 AlNb/TiAl laminated composite is successfully fabricated by hot pressing combined with the foil-foil metallurgy. The microstructure and the orientation relationship of the phases in the interface region, the distribution of strain and hardness along the interface, and the stress releasing mechanisms by the plastic deformation accompanied with two types of dislocation sources near the interface are detailly discussed. The composite presents an obvious yield phenomenon in contrast with the TiAl alloy and shows an improved tensile strength at room temperature. Further, an enhanced strength-ductility synergy at high temperature has been achieved. The synergetic deformation ability between the interface and the base alloys, deformation behaviors, and the effects of the laminated structure on crack distribution and morphology are also carefully investigated. The excellent mechanical performances of the composite are attributed to the outstanding metallurgical interface bonding, the introducing of ductile Ti 2 AlNb alloy into the laminated composite and the well-coordinated deformation ability of the laminated structure. The presented findings provide a new structural design strategy for property optimization of TiAl alloys. [ABSTRACT FROM AUTHOR]