[en] Highlights: • Continuous shape memory alloy NiTi fiber reinforced Al₃Ti composite (CSMAR-Al₃Ti) is fabricated. • Interfacial reaction layer of CSMAR-Al₃Ti composite shows a mixed structure of multi-phases. • Crack propagation can be hampered or blunted by interfacial fine grain strengthening effect of CSMAR-Al₃Ti composite. • The CSMAR-Al₃Ti composite can effectively improve the ductility of Al₃Ti alloy. To improve the ductility of Al₃Ti alloy, the continuous shape memory alloy NiTi fiber (CSMAR) was introduced into intermetallic Al₃Ti matrix for fabricating the novel CSMAR-Al₃Ti composite in this work. Microstructure characterizations demonstrated that the CSMAR-Al₃Ti composite mainly consists of Al₃Ti layer, NiTi fiber, eutectic area and interfacial reaction layer. EBSD results indicated that the eutectic area is made up of Al₃Ti and Al₃Ni phases, the Al₃Ti phase shows a strong [001] crystallographic oriented structure, while the Al₃Ni phase has a non-textured structure. TEM results showed that the interfacial reaction layer between NiTi fiber and eutectic area is a multiple phase mixture, including various Ti-Al and Ni-Al intermetallics. Furthermore, TEM and HRTEM analyses revealed a newly formed Ti₂Ni layer between NiTi fiber and interfacial reaction layer. Tensile test results confirmed that the CSMAR-Al₃Ti composite could effectively improve the ductility of the Al₃Ti alloy. Based on the systematic investigations of interfacial microstructure characterization, mechanical behavior and fracture morphology observation, it is found that the toughening mechanism of CSMAR-Al₃Ti composite is related to the interfacial fine grain strengthening effect with the gradual distribution characteristic. In addition, the excellent metallurgical bonding between fiber reinforcement and matrix is also beneficial to the mechanical properties.

[en] Ultrasonic additive manufacturing (UAM) is an advanced additive manufacturing technique that utilizes ultrasonic energy to rapidly joining thin metal tapes into solid parts in a layer accumulating manner. In this study, the effects of processing parameters on the bond properties of UAM samples were investigated via peel tests, linear weld density (LWD) measurements, microhardness tests and EBSD. The results reveal that, in terms of the overall tendency, the peeling strength and LWD increase with the increasing amplitude and normal force settings. However, a parameter threshold phenomenon and two different mechanisms that affect the bond properties were also observed. Furthermore, the microstructure evolution results show that the development of the interface is closely related to the applied parameters, which can also well explain the bond property variations and the parameter threshold phenomenon. (paper)

[en] In this paper, a novel NiTi shape memory alloy fiber reinforced Mg3AlZn (SMAFR-AZ31) composite sheet was successfully fabricated by laminate structure design combined with hot pressing method using Mg3AlZn (AZ31) foils and continuous NiTi shape memory alloy fibers. The interfacial microstructure of the SMAFR-AZ31 composite sheet was systematically characterized by a high resolution transmission electron microscopy (FEI-TEM Talos F100) combined with an FEI Helios 600i focused ion beam/scanning electron microscopy (FIB/SEM) system. The normal tensile strength of the SMAFR-AZ31 composite sheet was tested using a novel direct tensile sample configuration with the tensile direction perpendicular to prior AZ31 foils. Results showed that a well-densified AZ31 matrix and uniformly distributed NiTi fiber reinforcements were obtained in the SMAFR-AZ31 composite sheet after hot pressing. A continuous interfacial reaction layer consisting of nanocrystalline-amorphous mixture and a few intermetallic phases were formed around the NiTi_f/AZ31 interface. The nanocrystalline was identified as dual phase coexistence grains of MgO and TiO₂, and the amorphous phase was a mixture of Mg–Ti–O and Mg–O. A newly Ti₂Ni intermetallic phase that obeys a specific orientation relationship with NiTi fiber ($\left[\bar{4}2\bar{1}\right]$ NiTi// $\left[\bar{1}12\right]$ Ti₂Ni, (132) NiTi// $\left(1\bar{1}1\right)$ Ti₂Ni with an angle difference of 6.27°) precipitated adjacent to the interface reaction layer. A Ni-rich intermetallic phase identified as AlNi formed at the NiTi_f/AZ31 interface. Furthermore, it is found that large plastic deformation occurred near the interface reaction region in the AZ31 matrix, which is responsible for the successful embedding of NiTi fibers. Compared with the AZ31 laminate sheet without NiTi fibers, the SMAFR-AZ31 composite sheet possessed a superior normal tensile strength, which is attributed to the formation of the amorphous phase at the NiTi_f/AZ31 interface.

[en] In this work, to improve the ductility of Al₃Ti alloy, a multi-phase intermetallic mixture structure was achieved by the post annealing treatments (AT) on the as-fabricated continuous shape memory alloy NiTi fiber reinforced Al₃Ti composite (CSMAR-Al₃Ti). Experimental results revealed that the multi-phase intermetallic mixture structure displays a multi-layer characteristic, including the newly formed intermetallic layer and the eutectic area. Microstructure characterization and formation mechanism confirmed that the newly formed intermetallic layer consists of NiAl, Al₃Ni₂ and Al₃Ti phases, and the eutectic area still consists of Al₃Ni and Al₃Ti phases. The results of compression and tensile tests indicated that the multi-phase intermetallic mixture structure can simultaneously improve the maximum strength and the failure strain of the monolith Al₃Ti alloy. Based on the systematic investigations, it is found that the toughening mechanism is related to the multi-layer characteristic of the multi-phase intermetallic mixture structure, which is beneficial to the crack blunting, crack deflecting and load transformation during the deformation process. Furthermore, the multi-phase intermetallic mixture structure achieved by the 48 h post annealing treatment is the most effective method to improve the ductility of Al₃Ti alloy.

[en] A triple-microstructure with the precipitation of silicide along the α/β phase boundaries and α₂ phase in the Ti-5.8Al-3Sn-5Zr-0.5Mo-1.0Nb-1.0Ta-0.4Si-0.2Er alloy was prepared for improving thermal stability and creep resistance. The alloys were forged at 1050 °C and 1000 °C followed by solution treatment at 1000 °C for 1 h and subsequent ageing at 700 °C for 5 h. The effects of α morphology and precipitation characteristics on the thermal stability and creep performance of high-temperature titanium alloy were investigated. A triple-microstructure with the participation of silicide along the α/β phase boundary and α₂ phase was a promising structure with improved thermal stability and creep resistance. The plasticity loss rate was 25.0% after thermal exposure at 650 °C for 100 h due to the participation and coarsening of α₂ and silicide. Meanwhile, the plastic creep strain was 0.111% during the creep deformation at 650 °C for 100 h with an applied stress of 100 MPa, which was attributed to the inhibition of silicide and α₂ phase for boundary migration and dislocation slipping. Furthermore, the mutual precipitation of coarsening silicide and α₂ phase inside α matrix was a significant reason for the dramatic decrease in the thermal ability, which also worsened the inhibition for dislocation climbing of silicon element during the creep deformation.

[en] Nanostructured alumina/titania composite powders were prepared using nanosized alumina and titania doped with nanosized zirconia and ceria through ball-milling, spray drying and heat treating. The nanostructured reconstituted powders were then cool isostatic pressed and pressureless sintered into bulk ceramic composites. The phase constitution and microstructures of as-prepared ceramic composites were characterized by using X-ray diffractometer and scanning electron microscope. The mechanical properties of the ceramic composites were evaluated by Vickers hardness test, flexural strength test and fracture toughness test. The effects of nano-dopants and sintering temperatures on the microstructures and mechanical properties of the composites were investigated. It was found that nano-dopants had the effects of lowering sintering temperature, accelerating densification, reinforcing and toughening the composites. The maximum flexural strength, fracture toughness and Vickers hardness of the composites with nano-dopants were 51, 20 and 56% higher than that of the composites without nano-dopants. The reinforcing and toughening mechanisms are discussed in detail.

[en] A new titanium-tungsten-bearing hot rolled high strength bainitic steel was developed through the design of chemical composition and rolling processing. The chemical composition of 0.04C-0.1Ti-0.4W (wt%) was determined to make full use of alloying elements through considering the atomic ratio of elements. The rolling condition in the region through austenite recrystallization to austenite non-recrystallization region was adopted to realize a homogenous and fine microstructure. The effects of coiling temperature (CT) on the microstructure, precipitation and mechanical properties of the steel were investigated. Results showed that the average effective grain sizes of bainite ferrite were measured to be 2.2 µm, 1.8 µm and 2.4 µm for the sample of CTs 550 °C, 600 °C and 650 °C, respectively. The precipitates formed during coiling process were identified as nanoscale NaCl-type (TiW)C carbides that contain a high level of Ti and W. As CT increases, the precipitation amount of nanoscale precipitate increases. At the CT of 600 °C, an optimal combination of strength and ductility was achieved (yield strength: 733 MPa; ultimate tensile strength: 806 MPa; uniform elongation: 14.9%; total elongation: 24.4%). In addition, due to re-precipitation of nanoscale carbides, the strength of the steels coiled at 600 °C was obviously increased after tempering at 650 °C for 15 × 10³ s holding, exhibiting superior ageing strengthening effect.

[en] In this paper, the mechanical behavior of a bainite-based quenching-partitioning (BQ&P) steel under high strain rates in a range of 2200–3600/s was studied using Split Hopkinson Pressure Bar (SHPB) experimental technique. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were employed to investigate the microstructural change and fracture behavior. Results show that the stress-strain relation of the steel exhibits obvious strain rate dependence, i.e. strength increases as strain rate increases. After high strain rates deformation, twisting, directional arrangement or crystal rotation appeared for lath (Bainite&Martensite) structure, and a <100> fiber texture was formed, indicating that the slip mechanism operates under high strain rates. As the strain rate increases from 2200-3000 1/s to 3001-3600 1/s, the fracture frequency of samples significantly increases from 33.3% to 77.8%. The fracture of the BQ&P steel is characterized as 45° fracture mode with dimples near impact end and shear river pattern near the other end. Most of blocky retained austenite (RA) underwent martensitic phase transformation in the form of γ→α′ and/or γ→ε→α′ during high strain rates deformation, whereas only partial RA inside a filmy RA underwent martensitic phase transformation. The calculated adiabatic temperature rise, ~100 °C is considered to increase the stability of RA, which results in the occurrence of stress-induced γ→ε transformation under high strain rates. The increased frequency of fracture by increasing strain rates can be attributed into the delayed strain response and embrittlement caused by the martensitic transformation of RA under higher strain rates.

[en] Highlights: • Synthesis of new branched organic molecules bearing double benzotriazole segments. • Corrosion of copper was inhibited by the branched molecules in NaCl solution. • Chemisorption adsorption of the new inhibitors on copper was demonstrated. • Photo and thermal stabilities of the studied new inhibitors were presented. - Abstract: New branched conjugated derivatives with two benzotriazole groups as well as a linear analog containing one benzotriazole segment used as corrosion inhibitors for copper in 3.5 wt% sodium chloride solution containing 90 vol% water and 10 vol% ethanol solvents at 298 K were synthesized. It is shown that the corrosion of copper is inhibited more efficiently by the branched inhibitors. The adsorption mechanism on copper surface was analyzed by Langmuir isotherm and various spectral characterizations, and the results suggest a primary chemisorption adsorption on copper surface. Molecular modeling was performed. Photo and thermal stabilities of the studied inhibitors were investigated.

[en] The interfacial energies of MC/γ-Fe and formation energies of MC carbides have been investigated using first-principles calculations based on density functional theory (DFT). Results show that the replacement of Nb by Mo in the NbC lattice is unfavorable with respect to the formation energy. However, it reduces the lattice parameter of MC and decreases the σ_c_h_e_m_i_c_a_l (interfacial chemical energy) of MC/γ-Fe, thus favoring the formation of complex (Nb, Mo)C carbide. The substitution of Nb by Mo at the interface of MC/γ-Fe system promotes the hybridizations of Mo-1NNFe and C-1NNFe (or 2NNFe) (the first or second nearest neighboring Fe atoms), which leads to a decrease in σ_c_h_e_m_i_c_a_l. The influence of bond energy is estimated using the discrete lattice plane/nearest neighbor broken bond (DLP/NNBB) model. It is found that the reduced is attributed to the much smaller value of e_F_e_-_C-e_M_o_-_C (the difference between Fe-C and Nb-C interactions). The results obtained from the analysis of the precipitates in Nb- and Nb-Mo-bearing steels are in a good agreement with the calculations. (orig.)