Beneficial from small-size effect, super-high specific surface area and a large amount of defects and dangling bonds on the surface, nanoscale metals exhibit superior chemical activities than traditional bulky counterparts. Nevertheless, it is the high reaction activities of nanoscale metals that in turn make them vulnerable to be oxidized and corroded, which is a main obstacle in their applications. In liquid solutions or liquid-involving multiphase environment, corrosion on nanoscale metals is ubiquitous so that it remains a crucial issue before nanoscale metals are widely employed in real applications. Due to the low-dimension and small-size of nanoscale metals, it is a huge challenge of studying their corrosion behaviors since the experimental and theoretical methods are significantly different from those on bulky metals. In the present paper, recent studies on environmental stability and corrosion behaviors of nanoscale noble metals (Pt, Ag), transition metals (Cu, Ni, Fe), active metals (Al, Mg) and semi-conductor metal (Ge) have been reviewed. Meanwhile, analysis and expectations of theoretical and experimental innovations have also been stated for the further study the corrosion on nanoscale metals.

Deep-sea hydrothermal area has a lot of mineral resources, and study the corrosion behavior of metal in deep-sea hydrothermal area is useful for marine resource development. Electrochemical impedance spectroscopy, linear polarization, potentiodynamic polarization and Mott-Schottky analysis were used to study the electrochemical properties of 2205 steel in 20 MPa hydrostatic pressure 3.5%NaCl solution with different temperatures. Corrosion morphologies and corrosion products of 2205 steel after electrochemical tests were analyzed by SEM, EDS and white light interferometry. The results show that 2205 steel has good pitting resistance under 25 ℃ in simulated hydrothermal area, pit occurred on the surface of 2205 steel after the solution temperature reaching 65 ℃, crack-shaped pit occurred on the surface of 2205 steel under 150 and 200 ℃. Pit occurs in austenite phase at 65 ℃, and occurs in ferrite phase at 100~200 ℃. Impedance and linear polarization resistance of 2205 steel first decrease and then increase with temperature increasing in simulated hydrothermal area, and impedance and linear polarization resistance under 150 ℃ are lowest. Pitting potential of 2205 steel first negative shift and then positive shift, and carrier density of passive film formed in simulated hydrothermal area increase with temperature increasing.

It is very important to find out the mechanism of composition in steel. Many efforts have been put on the study of the effect of Si and Mn elements on the microstructure and mechanical properties of middle Mn steel, transformation induced plasticity (TRIP) steel and quenching and partitioning (Q&P) steel. But fewer studies were focused on the mechanism of Si and Mn contents in a press hardening steel. In this work, the microstructures after hot rolled and the fine martensite structure after hot stamping in ultra-high strength press hardening steel (PHS) with different Si and Mn contents were studied by OM, SEM, EBSD and TEM. The results showed that there are a great influence of Si and Mn contents on the microstructure and mechanical properties of PHS after hot rolled. The yield strength of the PHS increases from 552 MPa to 751 MPa, the ultimate tensile strength (UTS) increases from 757 MPa to 1124 MPa, and the microstructures are different with the Mn content rose from 0.57% to 1.21% and the other components remained the same. The UTS of the steels goes up as the Si content goes up from 0.25% to 0.38%, and the yield strength and the elongation show a fluctuation trend. After simulating hot stamping process at 950 ℃ and holding 5 min, the microstructure of the steels with different compositions is martensite, but it is different in the fine martensite structure and the average size of sub-grain; after hot stamping process, the comprehensive mechanical properties of the steel B with 0.30%C, 0.34%Si and 1.21%Mn are the most outstanding, the yield strength is 1161 MPa, the UTS is 1758 MPa, and the elongation is 6.5%; after hot stamping process, the microstructure of the steel B is fine lath martensite, and there is a large amount of dislocation in the martensite lath, and precipitates a small number of carbide. The mechanical properties of the ultra-high strength press hardening steels designed in this work is not obvious correlation before and after hot stamping process, and it is just a slight difference in martensite fine structure which is beneficial to controlling the performance stability of the mass industrial production.

As a new steel, nanobainite steel has favourable strength and good plasticity, but the bainite transformation needs a longer time, so as to severely slow production efficiency down. So, the research of acceleration methods of bainite transformation is of significance. In this work, in order to accelerate the bainite transformation rate, the 20% compression pre-deformation at 300~850 ℃ and isothermal transformation at 300 ℃ were conducted on a thermal simulator. The effects of pre-deformation temperature on nanobainite transformation kinetics and microstructure of the medium carbon nanobainite steel were investigated. The results showed that pre-deformation process obviously shortened the incubation time of bainite transformation. Low pre-deformation temperature could accelerate bainite transformation at whole isothermal region, while high pre-deformation temperature accelerated bainite transformation at the initial stage, and hindered bainite transformation at later stage. Bainite ferrite lath thickness was increased with decreasing pre-deformation temperature. The pre-deformation process increased the frequency of small angle grain boundary of bainite transformation microstructure, and the frequency of small angle grain boundary of low pre-deformation temperature was higher than that of high pre-deformation temperature. The kinetic parameters n of bainite transformation was calculated by the analytical model, the model of nucleation and growth were identified, the pre-deformation process changed the nucleation position of bainite transformation. The crystal corner nucleation was mainly obtained through low pre-deformation temperature, and the crystal edge and the crystal face nucleation were mainly obtained through high pre-deformation temperature.

In recent years, in order to develop the higher strength steel, the idea of increasing the strength of the hot rolled ferritic steel via complex Ti microalloyed technology has been widely accepted and applied, such as Ti-Nb, Ti-Mo, Ti-Nb-Mo and Ti-V-Mo. It is important to know the thermodynamics and kinetics of complex Ti contained precipitates for controlling the precipitation behavior of carbides and improving the mechanical properties of complex Ti microalloyed steels. In this work, according to the classical nulceation and growth kinetics theory and the solubility products of various carbides in austenite/ferrite (γ /α) matrix, the precipitation-time-temperature (PTT) curve, nucleation-time (NrT) curve and the nucleation parameters of (Ti, V, Mo)C carbides in γ /α matrix of Ti-V-Mo complex microalloyed steel were obtained through the theoretical calculation. Moreover, the effects of deformation stored energy and the amount of strain-induced precipitation in γ matrix on the precipitation kinetics of (Ti, V, Mo)C were discussed. The results showed that the PTT diagrams of (Ti, V, Mo)C in γ /α matrix showed "C" shape curve, while the NrT curves showed inverse "C" shape curve. The nose temperature of (Ti, V, Mo)C in γ matrix is about 1020~1050 ℃. Increasing the deformation stored energy of γ matrix moves the PPT curve to the upper left. In addition, the NrT curve of (Ti, V, Mo)C precipitated in α matrix moves towards to the lower right by properly increasing the amount of strain-induced precipitation in γ matrix. The maximum nucleation rate temperature of (Ti, V, Mo)C in ferrite is around 630~650 ℃ from the theoretical calculation, which agrees well with the result of experimental observation.

With the rapid development of Chinese high-speed railway system, the urgent demand for lighter weight structures is increasing, and aluminum alloys are widely applied into manufacturing the railway train and critical safety components. As a medium strength aluminum alloy, the 7020 aluminum alloy shows a great potential. Hybrid laser welding has currently become one of the most important welding techniques for medium and high strength aluminum alloys. Nevertheless, intrinsic defects such as pores and shrinkages physically determine the fatigue resistance of the welded joint. Based on in situ synchrotron radiation X-ray computed microtomography (SR-μCT), the population, location and size of gas pores within AA7020 hybrid welded joints are firstly identified and counted. The critical size of gas pores, affecting the fatigue properties of welded joints, is acquired by combining the statistical results of the pores and the average grain size of the hybrid weld. Meanwhile, the qualitative relationship between pore size, effective stress and fatigue life is discussed through in situ fatigue life data via SR-μCT and fracture morphology. By using the finite element analysis, detailed works have been performed on the stress state near the pores of different positions inside the joint. Through the simulation analysis, the stress concentration coefficient around the pores firstly increases, then decreases, and finally tends to a stable trend as the location of the pore-like defect is transferred from the surface to the inside. Besides, the influence of porosity on fatigue crack initiation, fatigue crack growth and sudden breaking process is also analyzed using fatigue crack growth experiment. In conclusion, the results show that the critical pore size of hybrid laser welded joint can be qualitatively identified as 30 μm; the SR-μCT and fracture analysis show that larger surface and sub-surface pores are more likely to initiate fatigue cracks, and the fatigue crack propagation experiment further shows that the porosity has very little effect on the long crack growth but significant influence on the crack front.

Magnesium and its alloys have become increasingly attractive in the automotive, 3C products and aerospace industries because of their advantages such as low density and high specific strength. In recent years, rare earth-Mg alloys have attracted much attention due to their high mechanical properties at room and elevated temperatures. Adjusting the microstructures by deformation treatment is a common method to improve the mechanical properties of Mg alloys. The microstructure especially the size, volume fraction and distribution of second phases in rare earth-Mg alloys will be changed during deformation treatment, which has a great effect on the corrosion resistance of Mg alloys. However, the studies on the effect of deformation treatment on the corrosion resistance of rare earth-Mg alloys are far away from sufficient. In this work, the corrosion behavior of cast and forged Mg-5Y-7Gd-1Nd-0.5Zr (EW75) alloys were studied by using SEM, XRD, mass loss measurements and electrochemical tests. The results indicate that the second phases are distributed along the grain boundaries of cast and forged EW75 alloys. Meanwhile, the second phases in forged EW75 alloy are finer and lower volume fraction than that in cast EW75 alloy. The micro-galvanic corrosion of the forged EW75 alloy is weaker in comparison with the cast EW75 alloy owing to the smaller size and lower volume fraction of second phases as well more compact surface film, resulting in the better corrosion resistance.

The hexagonal close-packed (hcp) metal Be has many potential applications. Much attention has been attracted on its mechanical properties and deformation mechanism. It has been found that the deformation mechanism involves the dislocation slip, twinning and their interaction, which are controlled by temperature, strain rate and initial texture. Typically, the softening and hardening behaviors in mechanical properties can be respectively induced through the elevated temperature and high strain rate. However, the microstructures engineering for properties tailoring in Be is still an open question. In this work, the effect of different initial microstructures on mechanical properties of polycrystalline beryllium was investigated, and the underlying mechanism was revealed by OM, SEM and in-situ neutron diffraction measurement. Three different kinds of microstructures have been achieved in Be by different pre-deformation strategies: (i) room temperature (RT) and the strain rate of 10^-3 s^-1, (ii) 600 ℃ and 10^-3 s^-1, and (iii) RT and 10³ s^-1, respectively. The mechanical properties of the polycrystalline Be are consequently tailored. The results show that, the compressive mechanical response is the hardest for the sample quasi-statically pre-deformed at RT, while is the softest for the dynamically pre-deformed one. The sample quasi-statically pre-deformed at RT possesses the "weak texture" type of initial microstructure, for which the (00.2) plane preferentially bears the compressive strain during the microscopic mechanical response; due to the combined effects of the initially preferred microstructure and induced dislocation, this sample exhibits the relatively obvious deformation-hardening with respect to the other ones. The sample dynamically pre-deformed at RT has the "strong texture" type of initial microstructure and some micro-voids; the (00.2) plane also mainly bears the compressive strain during the microscopic response; however, the deformation-hardening effect is weakened because the existing micro-voids participate the stress partition. The sample quasi-statically pre-deformed at 600 ℃ possesses the "random orientation" type of initial microstructure; each plane for this sample bears the compressive strain equally at the preliminary stage during the microscopic response and then the lattice strain for (11.0) plan increases with the increase of loading stress; for such case, the deformation accommodation inside the sample becomes relatively easier due to the decreased dislocation density. It suggests that the controllable mechanical properties can be realized through collaborative configurations of microstructures at different scales. The material properties can be customized through the microstructure engineering to meet the particular service requirements.

The micro-actuater materials are needed urgently in micro-electro-mechanical systems (MEMS) which are developing rapidly. The melt-spun Ti-Ni shape memory alloy ribbons have become candidate materials since their fast heat response and large acting density. The bulk Ti-47Ni (atom fraction, %) shape memory alloy is an ideal material to make thermosensitive actuators since its one-stage martensitic transformation and small temperature hysteresis. In order to develop the micro-actuator materials with fast response using in MEMS, the chilled Ti-47Ni alloy ribbons were fabricated by melt-spinning in this research. The effects of the roller speed and the annealing processes on microstructure, phase composition, phase transformation behaviors and shape memory effect of Ti-47Ni alloy ribbons were investigated by CLSM, XRD, DSC and bending test. The results show that the microstructure of as-cast and 300~800 ℃ annealed Ti-47Ni alloy ribbons fabricated under different roller speeds is vertically and horizontally arrayed columnar. The higher the roller speed, the finer the grain is. The annealing processes do nearly affect the microstructure of the alloy ribbons. The composition phases of Ti-47Ni alloy ribbons are martensite (B19' phase, monoclinic structure) and parent phase (B2 phase, CsCl-type structure). The B2→B19'/B19'→B2 type one-stage martensitic transformation occurs in Ti-47Ni alloy ribbons upon cooling and heating, the martensitic transformation temperature and the reverse martensitic transformation temperature are about 54 and 81 ℃, respectively, and the temperature hysteresis is about 27 ℃. With increasing the roller speed, the martensitic transformation temperatures of the alloy ribbons decrease, and the recovery rate of shape memory of the alloy ribbons increases. With increasing the annealing temperature, the transformation behaviors of the alloy ribbons change a little, and the recovery rate of shape memory changes in the range of 93%~98%. The as-cast and annealed Ti-47Ni alloy ribbons are all of excellent shape memory effect.

The method to deeply undercool alloy melts far below the liquidus temperature by eliminating heterogeneous nucleation sites inside is frequently used in studying non-equilibrium solidification behavior, preparing quasi-crystal, amorphous alloy and other metastable materials. Previous work on the solidification of Co-(18.5~20.7)%B (atomic fraction) alloys indicated that metastable Co₂₃B₆ phase instead of stable Co₃B phase was formed as the primary phase from the melts undercooled by larger than 60 K. To know whether Co₂₃B₆ phase can still primarily form from the deeply undercooled melt of Co₇₅B₂₅, the nominal composition of Co₃B phase, the Co₇₅B₂₅ alloy melt was undercooled to different degrees using the glass fluxing technique, and the solidification path was identified by analyzing the microstructures and cooling curves of the samples. There was nothing other than α-Co and Co₂B phases to form during solidification, indicating that not only the peritectic reaction of L (liquid) and Co₂B into Co₃B, predicted by the Co-B phase diagram, but also the formation of Co₃B as primary phase at large undercooling were inhibited. The peritectic reaction did not occur even though the solidification was designed to occur at a very small undercooling and a cooling rate decreased to 5 K/min.

Continuous basalt fiber (CBF) is a new type of performance outstanding inorganic nonmetallic material. In comparison with carbon fibers, basalt fibers exhibit greater failure strain as well as better impact and fire resistance with less poisonous fumes and 50% cost reduction. It is also known that basalt fibers display higher mechanical properties, better chemical stability and superior thermal and electrical insulation as compared with glass fibers. Basalt fiber has been widely used as a reinforcing composite material for construction industry and for preparation of polymer matrix composites. As high-performance low-cost reinforcements, basalt fibers should have a great potential for strengthening metal matrix composites (MMCs) and reducing their preparation cost. However, so far, few reports focused on the investigation on metal matrix composites reinforced by continuous basalt fibers, especially for lack of feasible fabrication technologies. Thus, in the present work, two-dimensional continuous basalt fiber cloth and Al-12Si alloys foils were selected as raw materials and alternately stacked to obtain a sandwiched structure. Subsequently, vacuum pressure infiltration was utilized to fabricate aluminum matrix composites reinforced by continuous basalt fibers (CBF/Al) with volume fraction of 65% successfully. Influence of infiltration parameters on microstructure evolution of resulting aluminum matrix composites was investigated and formation mechanism of multi-layered structure of CBF/Al composite was clarified. Moreover, mechanical properties of the multi-layered CBF/Al composite were evaluated. The results showed that when the infiltration parameters were 660 ℃, 10 MPa and 10 min, fully dense CBF/Al composite could be achieved and the novel composite displayed a unique multi-layered structure, namely continuous basalt fibers in forms of cruciform crossing distributed within aluminum alloys matrix. It is noteworthy that no obvious chemical reaction happened between continuous basalt fibers and Al-12Si alloys, and sound metallurgical bonding interface between them was obtained due to the interdiffusion of Al and Si elements. Unfortunately, mechanical properties of multi-layered CBF/Al composite did not reach a desired level, which was attributed to (i) decreasing of effective load-carrying capacity due to the imperfect distribution manner of continuous basalt fibers and (ii) deteriorating of intrinsic mechanical properties at high temperature.

The synthesis of nanostructures catalytic electrode for hydrogen evolution reaction (HER) plays an important role in national economy such as chlor-alkali industry, chemical power supply and fuel cell. Electro-splitting of water powered by electric energy has attracted extensive attention because this process can convert electric energy into chemical energy for easier storage and delivery. In this work, a facile and direct synthesis of NiCo₂O₄ nanoneedles and MoS₂ nanoflakes grown on 316L stainless steel meshes substrate by two step hydrothermal method was reported. Initially MoS₂ nanoflakes grown on the stainless steel (SS) meshes, and then NiCo₂O₄ nanoneedles were grown on MoS₂/SS meshes at optimum conditions using hydrothermal method. The prepared nanostructures were characterized by SEM, TEM and XRD. Then a three-electrode system was used to test the property of HER. The results show that the as-prepared electrode exhibits good catalytic behavior towards HER. The onset overpotential and Tafel slope are 65 mV and 108 mV/dec respectively. When the current density reaches 100 mA/cm², the overpotential is 219.6 mV. Furthermore, the composite structure exhibits good cycle stability in the same experimental conditions.

Various metals, such as uranium and plutonium, have the potential to form hydride phases while environment develop so that they are exposed to low standard of hydrogen in a long time storage environment. The generation of hydride phases has safety implications, for instance the potential to cause unintended thermal excursions and to adversely alter mechanical properties. So the reaction of alloys between hydrogen is of signi?cant industrial interest. The hydrogenation kinetics characteristics of Ce-La alloys have the similarity with some actinide materials. Investigating the growth kinetics of Ce-La alloy hydride reaction sites is of fundamental importance to the development of predictive model of hydriding behavior. In this work, the effect of La content (0~10%, mass fraction) on hydriding kinetics of Ce-La alloys was studied by pressure consume curve, and the effects of La content on surface morphology and oxidation film structure of Ce-La alloy were observed by in situ OM, XRD and Raman spectra. The results show that doped La can shorten the induction period and accelerate the nucleation rate, so as to accelerate the hydriding rate. Furthermore, doped La can cause the lattice expansion and promote the formation of oxygen vacancy in the oxidation film. The apparent activation energies of pure Ce and Ce-10La alloy are 51.12 and 41.53 kJ/mol, respectively, suggesting that the diffusion barrier of hydrogen in the oxidation film of Ce-10La alloys is lower. The oxygen vacancy and the lattice expansion caused by doped La may promote the diffusion ability of hydrogen in the oxide film. Hydrogen diffusion through the oxide film decides the hydriding rate. So doped La accelerate the hydrogenation.

It is easy to corrode the steel structural materials. In view of this problem, the Al-Ni-Zr amorphous and nanocrystalline composite coating with high amorphous volume was prepared by high velocity arc spraying on the 45 steel. The microstructure, macroscopic corrosion performance and microzone corrosion performance of the composite coating was investigated. XRD, SEM with EDS and TEM were applied to confirm that the gray zone of the composite coating microstructure was the amorphous enrichment zone. It was found by the scanning Kelvin probe microscopy (SKPM) that the corrosion failure order of each phase of the composite coating was arranged in order of the aluminum rich phases, the oxidation phases and the amorphous phase. The microhardness of the composite coating was about 364 HV_0.1 which was greater than that of 45 steel. The EIS fitting results showed that the charge transfer resistance of the composite coating is 2~4 times of the aluminum coating and 45 steel. It has two time constants in the spectrum. The corrosion failure behavior of the composite coating in the low frequency was controlled by the diffusion process, which was related to the accumulation and diffusion of the corrosion products. The potentiodynamic polarization curves fitting results indicated that the self-corrosion potential of the composite coating was higher than those of the aluminum coating and 45 steel. And the self-corrosion current density of the composite coating was about 1.08 μA/cm², which was 7/100 and 1/3 of that of the aluminum coating and 45 steel, respectively. According to the corrosion morphology of the composite coating, there was no obvious pitting. A large number of NaCl crystals were attached to the surface of the aluminum rich phase region as the preferred corrosion zone. But the surface of the amorphous enrichment zone was smooth. At the same time, the corrosion pits, micro-cracks and pitting enrichment occurred on the surface of the composite coating, which was mainly related to the effects of Cl^- erosion and swelling.

The materials design and fabrication based on predicting microstructure have been drawn increasing attention from scientists and engineers. Martensite microstructure, which is well observed in many materials, has significant influence on physical and mechanical properties of the materials. Some experimental studies have been launched to understand the featured microstructure and its evolution in martensitic transformations (MT). Meantime, numerical approaches are often employed to assist the experimental studies due to the complex and nonlinear nature of MT. The phase field method is one of the most powerful tools in predicting microstructure. Due to the diffuse-interface description, phase field method can be used to simulate arbitrary morphologies without tracking the interface. As a consequence, the interface must contain enough elements to obtain reasonable results by using finite element method. On the other hand, the width of the interface is several orders smaller than its real counterpart. More computational resources are required to resolve the phase field variables at the interface with the system size increased. Therefore, the simulation is restricted in smaller system even with state-of-the-art computer power. For arbitrary model formulations, the interfacial energy depends on the interfacial width and other specific properties of materials. However, the phase field models of martensitic transformation do not have enough degrees of freedom to increase the interfacial width without changing the interfacial energy. In the present study, a scalable phase field model by introducing a global modified function is constructed to study MT, the modified function takes into account the inhomogeneous nature of order parameter gradient across the interfacial region. Through adjusting the free energy density and gradient coefficient, meanwhile keeping the interfacial energy density unchanged, the interfacial width and system size are increased, yet the MT feature can be fully characterized. The simulation results show that the modified phase field model can well solve the drawbacks such as fast growth rate of martensite, artificial orientation relationship between the variants of martensite, and disordered martensite microstructure in large scale system.