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Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17 titanium alloy with small surface defects. The microstructure, micro-hardness and room temperature tensile properties of laser additive repaired (LARed) specimen were investigated. The results show that, cellular substructures are observed in the laser deposited zone (LDZ), rather than the typical α laths morphology due to lack of enough subsequent thermal cycles. The cellular substructures lead to lower micro-hardness in the LDZ compared with the wrought substrate zone which consists of duplex microstructure. The tensile test results indicate that the tensile deformation process of the LARed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and fracture in the laser repaired zone with a mixed dimple and cleavage mode. The tensile strength of the LARed specimen is slightly higher than that of the wrought specimen and the elongation of 11.7% is lower.

The biomedical co-continuous (β-TCP+MgO)/Zn-Mg composite was fabricated by infiltrating Zn-Mg alloy into porous β-TCP+MgO using suction exsorption technique. The microstructure, mechanical properties and corrosion behaviors of the composite were evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical testing, electrochemical and immersion test. It was found that the molten Zn-Mg alloy had infiltrated not only into the pores but also into the struts of the porous β-TCP+MgO scaffold to form a compact composite. The Zn-Mg alloy contacted to the β-TCP+MgO scaffold closely, and no reaction layer can be found between the alloy and the scaffold. The compressive strength of the composite was as high as 244 MPa, which was about 1000 times higher than that of the original porous β-TCP+MgO scaffold and 2/3 of the strength of the Zn-Mg bulk alloy. The electrochemical and immersion tests in simulated body fluid (SBF) solution indicated that the corrosion resistance of the composite was better than that of the Zn-Mg bulk alloy. The corrosion products on the composite surface were mainly Zn(OH) 2 . Appropriate mechanical and corrosion properties indicated that the (β-TCP+MgO)/Zn-Mg composite fabricated by suction exsorption would be a very promising candidate for bone substitute.

The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti–5Al–2Sn–2Zr–4Mo– 4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by the thermal history of LAM process. Primary α (αp) with different morphologies, secondary α (αs) and martensite α′ can be observed at different positions of the LAMed specimen. Annealing treatment can promote the precipitation of rib-like α phase or acicular α phase. As a result, it can increase or decrease the microhardness. The as-deposited L-direction and T-direction specimens contain the same phase constituent with different morphologies. The tensile properties of the as-deposited LAMed specimens are characterized of anisotropy. The L-direction specimen shows the character of low strength but high ductility when compared with the T-direction specimen. After annealing treatment, the strength of L-direction specimen increases significantly while the ductility reduces. The strength of the annealed T-direction specimen changes little, however, the ductility reduces nearly by 50%.

The sliding electrical contact behavior of AuAgCu brush on Au plating was investigated at various normal loads and sliding speeds. The contact voltage drop and electrical noise between the two brushes were measured and the resistance waveforms were recorded. The morphologies of the worn surfaces and wear debris of the brush and plating were observed. The results show that the contact voltage drop and electrical noise decrease with the addition of load whereas increase drastically with increasing sliding speed. With the electrical current in vacuum, the wear process of AuAgCu brush on Au plating involves adhesion, transfer of gold from the plating to the brush, rolling of wear debris between contact surfaces and arc-induced melt at the contact edge, and this gold-on-gold sliding electrical contact system is reliable within experiment period.

The nanocrystalline and amorphous Mg2Ni-type alloys with nominal compositions of Mg2Ni1-xMnx (x=0, 0.1, 0.2, 0.3, 0.4) were synthesized by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are obtained. The structures of the as-spun alloy ribbons were characterized by XRD and HRTEM. The electrochemical hydrogen storage characteristics of the as-spun alloy ribbons were measured by an automatic galvanostatic system. The electrochemical impedance spectrums (EIS) were plotted by an electrochemical workstation. The hydrogen diffusion coefficients (D) in the alloys were calculated by virtue of potential-step measurement. The results show that all the as-spun (x=0) alloys hold a typical nanocrystalline structure, whereas the as-spun (x=0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg2Ni-type alloy. The substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving the discharge capacity and the electrochemical cycle stability. With an increase in the amount of Mn substitution from 0 to 0.4, the discharge capacity of the as-spun (20 m/s) alloy increases from 96.5 to 265.3 mA·h/g, and its capacity retaining rate (S20) at the 20th cycle increases from 31.3% to 70.2%. Furthermore, the high rate dischargeability (HRD), electrochemical impedance spectrum and potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with raising the amount of Mn substitution.

The crystal detachment behaviors from a chilling solid surface with vibration were investigated using a transparent NH 4 Cl-70%H 2 O alloy. The nucleation experiments of NH 4 Cl-70%H 2 O alloy were performed on a chilling surface generator with various vibration frequency from 20 to 1 000 Hz and vibration acceleration from 10 to 100 m/s 2 . The results indicate that the crystal detach rate increases and the grains are refined with increasing vibration acceleration under a certain vibration frequency. It is interesting to note that, when the frequency is 50 Hz, acceleration is 100 m/s 2 , the crystal detach rate increases sharply and the grain refinement effect is strengthened. A special grain refinement phenomenon can be observed, when the vibration acceleration and frequency are up to a critical value. A power-based definition was introduced in order to describe the relationship between the vibration parameters and imposed power on the system. It is found that a power criterion exists for the grain refinement in the current system.

Morphological evolution of non-dendritic microstructure during the solidification of succinonitrile-5%water (SCN-5%Wat) transparent alloy under mechanical stirring was experimentally investigated. The incubation time for the formation of non-dendritic microstructures decreased rapidly and the microstructure was gradually refined with the increase of stirring rate and cooling rate. When the stirring rate and cooling rate were low, the incubation time for the formation of non-dendritic microstructures decreased obviously with the increase of the melt undercooling. When the stirring rate was high, the effect of the melt undercooling on the incubation time for the formation of non-dendritic microstructures was weak. The morphology of primary microstructures had an important influence on the subsequent morphological evolution of these microstructures during the isothermal holding of the melt without stirring. It was found that when there were dendrites in the undercooled melt, the dendrites would be dissolved and the final microstructure would be replaced by the re-nucleated globular crystals if the stirring time was long enough.

Nanocrystalline Mg2Ni-type alloys with nominal compositions of Mg20Ni10-xCux (x = 0, 1, 2, 3, 4, mass fraction, %) were synthesized by rapid quenching technique. The microstructures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The hydriding and dehydriding kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The results show that all the as-quenched alloys hold the typical nanocrystalline structure and the rapid quenching does not change the major phase Mg2Ni. The rapid quenching significantly improves the electrochemical hydrogen storage capacity of the alloys, whereas it slightly impairs the cycling stability of the alloys. Additionally, the hydrogen absorption and desorption capacities of the alloys significantly increase with rising quenching rate.

The effects of cooling rates corresponding to different diameters of the steel mould and laser surface melting (LSM) on the as-cast microstructures of Mg-9Al-xSi (x=1, 3) (mass fraction, %) alloys were investigated by XRD and OM. The results show that obvious refinement of the alloy microstructure is obtained with increasing cooling rate by conventional ingot metallurgy. However, no evident modified morphologies of both dendritic primary Mg2Si and Chinese script eutectic Mg2Si in the Mg-Al-Si alloy occurs. Surprisingly, the morphologies of Mg2Si phases within the laser-melted Mg-Al-Si alloy transform drastically from both coarse Chinese script shape for the eutectic Mg2Si and dendrite for the primary Mg2Si to fine spherical particles with an average size of about 3 μm due to the rapid cooling of the melted layer, and the Mg2Si particulates distribute more uniformly in the α-Mg matrix.

The effects of isothermal holding time on the semisolid microstructure of Mg-9Al-1Si (mass fraction,%) alloy were investigated. The research results indicate that the Mg-9Al-1Si alloy with non-dendritic microstructure can be produced by the semi-solid isothermal heat treatment. With holding time varying from 5 to 30 min, the volume fraction of liquid is gradually enlarged from 29.3% to 38.6%, the morphology of α-Mg grains changes from initial dendritic shape to spherical types and their average sizes increases from 41.1 to 56.1 μm. In addition, during the isothermal heat treatment, the eutectic Mg2Si phase changes from the initial Chinese script shape to granule and/or polygon shape in Mg-9Al-1Si alloy. The modification of Mg2Si phase is possibly attributed to a shift of the eutectic composition of the liquid in semi-solid slurries, towards lower silicon contents with increasing Al content due to a redistribution of Al during isothermal heat treatment.

AZ61 alloys with different levels of Al5Ti1B master alloy additions were prepared by conventional casting method. The effects of Al5Ti1B contents and holding time on microstructures and microhardness of AZ61 alloys were studied by XRD, OM and microhardness testing techniques. The results show that when the addition level of Al5Ti1B master alloy is less than 0.5% (mass fraction), the average grain size of the alloys decreases with the increase of Al5Ti1B content at the same holding time. But the grain size increases somewhat with further addition of Al5Ti1B. The average grain size of the alloys decreases with the increase of the holding time as it is less than 30 min at the same addition level of Al5Ti1B. It is considered that TiB 2 particles can serve as the heterogeneous nucleation sites of α-Mg during solidification, and heterogeneous nucleation is the main reason for the grain refinement of AZ61 alloys. The microhardness of the refined AZ61 alloys with 1.0% Al5Ti1B addition is increased by about 8%.

The Mg2Ni-type alloys with nominal compositions of Mg20Ni10-xCox (x=0, 1, 2, 3, 4, %, mass fraction) were prepared by melt-spinning technology. The structures of the alloys were studied by XRD, SEM and HRTEM. The hydrogen absorption/desorption kinetics and the electrochemical performances of the alloys were measured. The results show that no amorphous phase forms in the as-spun Co-free alloy, but the as-spun alloys containing Co show a certain amount of amorphous phase. The hydrogen absorption capacities of the as-cast alloys first increase and then decrease with the incremental change of Co content. The hydrogen desorption capacities of as-cast and spun alloys rise with increasing Co content. The melt spinning significantly improves the hydrogenation and dehydrogenation capacities and kinetics of the alloys. The substitution of Co for Ni clearly enhances the discharge capacities of the alloys and the cycle stability of the as-spun alloys.

The La-Mg-Ni system PuNi 3 -type La 0.5 Ce 0.2 Mg 0.3 Co 0.4 Ni 2.6– x Mn x ( x =0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the rapid quenching on the structure and electrochemical characteristics of the alloys were studied. The results obtained by XRD, SEM and TEM indicate that the as-cast and quenched alloys mainly consist of two major phases, (La, Mg)Ni 3 and LaNi 5 , as well as a residual phase LaNi. The rapid quenching does not exert an obvious influence on the phase composition of the alloys, but it leads to an increase of the LaNi 5 phase and a decrease of the (La, Mg)Ni 3 phase. The as-quenched alloys have a nano-crystalline structure, and the grain sizes of the alloys are in the range of 20–30 nm. The results by the electrochemical measurements indicate that both the discharge capacity and the high rate discharge(HRD) ability of the alloy first increase and then decrease with the variety of quenching rate and obtain the maximum values at the special quenching rate which is changeable with the variety of Mn content. The rapid quenching significantly improves the cycle stabilities of the alloys, but it slightly impairs the activation capabilities of the alloys.

In order to investigate the influences of the stoichiometric ratio of B/A (A: gross A-site elements, B: gross B-site elements) and the substitution of Co for Ni on the structures and electrochemical performances of the AB3.5–4.1-type electrode alloys, the La-Mg-Ni-Co system La0.75Mg0.25Ni3.5Mx (M=Ni, Co; x= 0, 0.2, 0.4, 0.6) alloys were prepared by induction melting in a helium atmosphere. The structures and electrochemical performances of the alloys were systemically measured. The results show that the structures and electrochemical performances of the alloys are closely relevant to the B/A ratio. All the alloys exhibit a multiphase structure, including two major phases, (La, Mg)2Ni7 and LaNi5, and a residual phase LaNi2, and with rising ratio B/A, the (La, Mg)2Ni7 phase decreases and the LaNi5 phase increases significantly. When ratio B/A=3.7, the alloys obtain the maximum discharge capacities. The high rate discharge(HRD) capability of the alloy (M=Ni) monotonously rises with growing B/A ratio, but that of the alloy (M=Co) first mounts up then declines. The cycle stability of the alloy (M=Co) monotonously increases with rising B/A ratio, but it first decreases slightly then increases for the alloy (M=Ni). The discharge potential of the alloy (M=Ni) declines with increasing B/A ratio (x > 0.2), but for the alloy (M=Co), the result is contrary. The substitution of Co for Ni significantly ameliorates the electrochemical performances. For a fixed ratio B/A=3.7, the Co substitution enhances the discharge capacity from 365.7 to 401.8 mA·h/g, the capacity retention ratio (S100) after 100 charging-discharging cycles from 50.32% to 53.26% and the HRD from 88.65% to 90.69%.

The average lamellar spacing and interface undercooling in steady-state irregular eutectic growth were estimated based on the Jackson and Hunt's analysis by relaxing the isothermal interface assumption. At low growth rates, the average lamellar spacing and average interface undercooling are dependent only on the characteristic thermo-physical properties of a binary eutectic system. For a general Al-Si eutectic, it is found that the eutectic characteristic length based on the present non-isothermal analysis is consistent with that obtained from isothermal analysis; however, the average interface undercooling is remarkably different between them, and such discrepancy in average interface undercooling increases with increasing of growth rate. The measured interface undercooling obtained from literature is reasonably interpreted by present non-isothermal analysis.

The La 0.7 Mg 0.3 Ni 2.55- x Co 0.45 Cu x ( x =0, 0.1, 0.2, 0.3, 0.4) electrode alloys were prepared by casting and rapid quenching. Ni in the alloy was partially substituted by Cu in order to improve the cycle stability of La-Mg-Ni system (PuNi 3 -type) hydrogen storage alloy. The effects of substituting Ni with Cu on the microstructures and cycle stability of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the substitution of Cu for Ni is favourable for the formation of an amorphous in the as-quenched alloy, and this leads to an obvious refinement of the as-quenched alloy gains and a growth of the lattice constants and cell volumes of the as-cast and quenched alloys. The results obtained by the electrochemical measurement indicate that the cycle stability of the alloys significantly rises with the incremental variety of Cu content. When Cu content changes from 0 to 0.4, the cycle lives of the as-cast and quenched (30 m/s) alloys are enhanced from 72 to 88 cycles and from 100 to 121 cycles, respectively.

In order to improve the electrochemical performances of La-Mg-Ni based electrode alloys with PuNi3-type structure, a trace of boron was added in La0.7Mg0.3Ni2.55Co0.45 alloy. The La0.7Mg0.3Ni2.55Co0.45(x=0, 0.05, 0.1, 0.15 and 0.2) alloys were prepared by casting and rapid quenching. The electrochemical performances and microstructures of the as-cast and quenched alloys were investigated. The effects of rapid quenching on the microstructures and electrochemical performances of the above alloys were investigated. The results show that the as-cast and quenched alloys are composed of (La, Mg)Ni3 phase, LaNi5 phase and LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloys containing boron, and the Ni2B phase in the B-contained alloys nearly disappears after rapid quenching. Rapid quenching increases the amount of the LaNi2 phase in the B-free alloy, but it decreases the amount of the LaNi2 phase in the boron-containing alloys. The effects of rapid quenching on the capacities of the boron-containing and boron-free alloys are different. The capacity of the B-free alloy monotonously decreases with increasing quenching rate, whereas the capacities of the B-contained alloys have a maximum value with the change of the quenching rate. The rapid quenching can improve the stability of La-Mg-Ni based electrode alloy but lowers the discharge plateau voltage and decreases the plateau length. The effect of rapid quenching on the activation capabilities of the alloys was complicated.