The near isothermal canned hot extrusion at a temperature close to α transus temperature was used to fabricate Ti－45.5Al－2Cr－2Nb－0.15B alloy rod. Microstructures and tensile properties of samples taken from different locations of the extrudate were compared with each other, and the formation mechanism of extrusion microstructure was investigated in combination with the finite element simulation. It was found that lamellar grains were significantly refined by hot extrusion. Microstructure and tensile elongation were homogeneous along the axial direction of extruded rods, but heterogeneous along the radial direction. The center of rods with coarse fully－lamellar microstructure had low tensile elongation, and the edge of rods with fine near lamellar microstructure had high tensile elongation. Such heterogeneities could not be eliminated in subsequent α solid solution treatment. Lamellar grain size decreased with increasing effective strain. There existed the refined homogeneous microstructure in the regions with effective strain larger than 2.25. The difference of microstructure type was mainly due to different temperatures of different parts of rods during extrusion process. In the edge of rod tails, the γ phase lamellar structure precipitated from α phase was formed due to the chilling effect caused by contacting with the cold die, then the lamellar structure with tortuous boundary was formed in subsequent deformation. Tensile elongation was found to decrease with increasing lamellar grain size, but the poor tensile elongation in the center was mainly attributed to the existence of lamellar grains which lamellar boundaries were nearly perpendicular to the extrusion direction.

The crystallization behavior of annealed metallic glasses during pulsed laser remelting was investigated in this work. The as-casted Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses were annealed at 390, 430, 530, 792 and 902℃ separately. And then these annealed alloys were remelted by pulsed laser. The experiment results show that the alloys annealed at 390 and 430℃ were still metallic glasses, and their crystallization behavior during remelting is similar to the remelting of metallic glass without annealing treatment. The specimens annealed at 530, 792 and 902℃ were completely crystallized. After remelting, the molten pools of these specimens were amorphous. For the specimens annealed at 530 and 792℃, there was no obvious epitaxial growth at the bottom of molten pools. For the specimens annealed at 902℃, there was little primary phase epitaxial growth at bottom of molten pool after one time laser remelting while without epitaxial growth after 11 times laser remelting. The epitaxial growth was caused by the area reserved the composition distribution of CuZr₂ primary phase during laser remelting. So it is hard to obtain epitaxial growth during laser remelting for Zr₅₅Cu₃₀Al₁₀Ni₅m bulk metallic glasses even it has a crystallization substrate because of the slow diffusion. So it is easy to keep molten pool as amorphous state during laser treating Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses.

The coarse-grained pure Al was first pre-fatigued to different fatigue life fractions D(D=2%-75 {%}) at a constant stress amplitude, and then the effect of pre-fatigue deformation on its uniaxial tensile behavior, fracture surface deformation features and dislocation structures were investigated. The results show that with increasing D, the extrusion/intrusion phenomenon on the surfaces of the pre-fatigued coarse-grained pure Al becomes more serious, and the non-uniform deformation in grain interiors is also enhanced, leading to the nucleation of micro-cracks and micro-voids along slip bands (SBs) or at grain boundaries (GBs) as well as their subsequent propagation. As D is as high as 75%, the longer intergranular cracks are produced at triple grain boundary nodes. With increasing D, the fatigue dislocation structures transform from loose cellular structures under annealing state into regular cellular structures and sub-grains, but the size of sub-grains nearly does not change. After the pre-fatigued coarse-grained pure Al specimens were subjected to the uniaxial tension, the yield strengthσ_YS obviously increases, but the change inσ_YS is not so obvious as D increases. Meanwhile, the ultimate tensile strengthσ_UTS first decreases and then increases, and finally sharply re-decreases. However, the pre-fatigued coarse-grained pure Al has poor ability to work hardening. The tensile fracture surface consists of fibrous and shear lip zones, and the number of dimples in fibrous zones increases and the size reduces with increasing D; as D reaches 50%, the number of dimples re-reduces and the size raises, and the fracture surface exhibits tearing characteristics. The sub-structures after the uniaxial tension are mainly composed of sub-grains and cellular dislocation structures inside sub-grains, and with increasing D, the size of sub-grains first reduces and then increases. The formation of fine sub-grains and cellular dislocation structures inside sub-grains results in the fact that the pre-fatigued coarse-grained pure Al has higher maximum uniform percent elongation.

Surface modification experiment of the commercial purity aluminum (α-Al) and Al-Cu-Mg alloyed aviation aluminum alloy 2A02 by laser shock processing (LSP) was implemented. The surface strengthening effect of both the target materials was investigated from dislocation mechanisms of microstructural response by means of TEM method. The results show that the strengthening effect of the two kinds of materials by laser shock processed is significantly different. The strengthening mechanism of α-Al by laser shock can be attributed to the multiplication of a large number of dislocations. With the increase of the impact number of laser shock and the degree of deformation, the new-generated dislocations will pile up and interact with the forest dislocations, and the dislocation lines will gradually evolve into waved-like, or wind into dislocation tangles and dislocation networks. But the hardness curve of the laser shocked (α-Al) will fast and linearly decline due to Bauschinger effect (BE) and stress wave damping. The laser shock strengthening mechanisms of the aging-hardened aluminum alloy 2A02 can be summarized to the enhancement of the matching between the elastic energy of dislocations with the ultra-high energy of laser shock processing due to the higher matrix strength and the dislocation-pinning effect of large number of dispersed precipitates, as well as the complex dislocation networks in between the precipitates constructed by the dislocations induced by laser shock. The matrix strengthened by laser shock processing and the precipitates keep the extra-semi-coherent relationship to coordinate the total deformation, with the number of laser shock increase, dislocation multiplication and the vacancy motion constitutes geometrically necessary boundaries (GNBs), which consists of the sub-grain boundaries to refine the matrix into the nanometer-grains. The strengthening mechanism of surface modification of aluminum alloy by laser shock processing is formed of the internal stress state caused by the combination of the complex dislocation configurations and the Hall-Petch effect of the nanocrystalline grains.

The influences of temperature and Cl^- concentration on the crevice corrosion of grade-2 Ti in the simulated geological disposal environment of high-level radioactive nuclear waste were investigated by potentiodynamic polarization curves, electrochemical impedance spectroscopy, galvanic current monitoring and potentiostatic polarization. The results showed that all the creviced specimens exhibited the passive characteristics in the initial immersion period at 25-95℃. With extending the immersion time, the crevice corrosion of Ti initiated as a result of the gradual aggressive environment (higher Cl^- concentration and more acidification) in the crevice. As increasing the temperature and Cl^- concentration, the galvanic current increased and the crevice corrosion resistance was decreased. In addition, the critical temperature of crevice corrosion decreased with increasing Cl^- concentration and the applied potential. The damage caused by anodic active dissolution in the crevice mainly located near the crevice mouth.

The compound CoSb₃ is one kind of thermoelectric material that has been received more attention due to its potential application in green refrigeration and power generation. The general way to prepare CoSb₃ material is sintering and the solidification behavior of CoSb₃ compound is rarely reported, since this compound is obtained through the peritectic reaction, and there exists phase competitive growth in solidification process. In this work, Bridgman directional solidification and laser rapid solidification experiments on Co-93.0%Sb (mass fraction) alloy were carried out. XRD, SEM and EDS were employed to determine the solidified phases and characterize the microstructure. The results showed that for Bridgman directional solidification, the solidification microstructure of Co-93.0%Sb alloy contained only the CoSb₃ and Sb phases at the solidification rates of 2 and 5 μm/s, whereas at the solidification rates of 20, 50, 100 and 500 μm/s, the microstructure contained CoSb₃, CoSb₂ and Sb phases. Furthermore, the volume fraction of CoSb₃ phase decreased with increasing solidification rate. For laser rapid solidification, the solidification microstructure consisted of CoSb₃, CoSb₂ and Sb phases at the scanning rate of 5 mm/s. As the scanning rate ranging from 10 to 50 mm/s, the microstructure is composed of only CoSb₃ and Sb phases. The critical rate of peritectic phaseCoSb₃ instead of primary CoSb₂ solidified directly from the melt was theoretically predicted to 7.61 mm/s, agreeing well with the experiment result. In addition, the formation mechanisms of peritectic phase CoSb₃ at Bridgeman directional solidification and laser rapid solidification were analysed. The formation of peritectic phase at low solidification rates was due to the local solidification time available for the peritectic reaction, and at high solidification rates higher than 10 mm/s the peritectic phase CoSb₃ was obtained directly from the melt. Therefore to obtain a large volume fraction of peritectic phase CoSb₃,  a low solidification rate is recommended.

Most of the current researches are only limited to the evaluation of high pH stress corrosion cracking (SCC) susceptibilities of pipeline steels at some certain potentials, but the division of the sensitive potential ranges controlled by different SCC mechanisms is rarely reported. When the results of SCC susceptibilities adopted by using the ultimate fracture strength, the reduction-in-area and the elongation rate separately are not consistent, how to evaluate the SCC susceptibilities taking into account both the loss of fracture strength and toughness also needs solving. In this work, the slow strain rate tensile tests were conducted to evaluate the SCC susceptibilities of X80 pipeline steel in concentrated carbonate/bicarbonate solution at different applied potentials. The immersion tests at several constant potentials were used to analyze the potential sensitivity of electrochemical corrosion behavior and its influence on the SCC controlling mechanisms. With the aid of potentiodynamic polarization tests and the thermodynamical calculation, the typical potential ranges of different SCC controlling mechanisms were divided. Considering both of the ultimate fracture strength and reduction-in-area loss, a comprehensive index I_∑ for estimating SCC susceptibility was established and verified. The main results showed that at -580 mV, the ferritic intergranular was corroded preferentially, and X80 steel exhibited remarkable intergranular SCC (IGSCC) with anodic dissolution (AD) as the controlling mechanism. At -750~mV, the ferritic grain was prone to be dissolved causing the occurrence of pitting, but the steel showed very low SCC susceptibility, which indicated that high transgranular SCC (TGSCC) susceptibility could not be triggered only by AD. The open circuit potential E_ocp could be seen as a transition potential between pitting and TGSCC zone, at which the SCC susceptibility was slightly enhanced. At -880 mV, the steel showed tremendous TGSCC susceptibility due to the synergistic effects of AD and hydrogen embrittlement (HE), although it was protected by the applied cathodic potential. And the SCC behavior mainly controlled by HE at -1200~mV, showing quasi-cleavage fracture mode. Therefore, the typical potential ranges could be divided into four categories: -600 —­ -569~mV for IGSCC, E_ocp— -600 mV for pitting, hydrogen evolution potential -1046 mV—E _ocp for TGSCC, and below -1046 mV for HE,i.e., quasi-cleavage cracking. By applying the criteria proposed in acidic soil simulated solution to illustrate the SCC susceptibility in this work, the comprehensive index I_∑ was proved to be reasonable, which provided a supplementary method for evaluating the SCC susceptibility.

PtRu catalyst has long application history in electrochemical field due to the wide prospect in direct methanol fuel cells (DMFCs), but its performance remains to be improved further. There are usually two ways to enhance the catalytic activity of PtRu bimetallic catalyst. One is to add the third metal into alloy; the other is to improve the properties of carbon support. In this work, PtRu and PtRuNi nanoparticle clusters were electrochemically deposited on multi-walled carbon nanotubes (MWCNTs) through a three-step process, including an electrochemical treatment of MWCNTs, electro-oxidation of metal chloride to high valence of metal complex and an electro-conversion of PtRu and PtRuNi nanoparticle clusters on MWCNTs. The structure and elemental composition of the PtRu/MWCNTs and PtRuNi/MWCNTs electrodes were characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray polycrystalline diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic properties of the PtRu/MWCNTs and PtRuNi/MWCNTs electrodes for oxygen reduction reaction (ORR) and methanol oxidation were investigated by cycle voltammetry (CV) method and current-time (CT) method. The results showed that PtRuNi/MWCNTs electrode exhibited a high I_{_f}/I_b (the forward anodic peak/the reverse anodic peak current) value and an appreciably improved resistance to carbon  monoxide (CO) poisoning in methanol solution, so a beneficial effect on the oxygen adsorption in dilute sulphuric acid solution was observed. The high electrocatalytic activity and good stability of PtRuNi/MWCNTs was attributed to the synergetic effect of bifunctional catalysis, three dimension structure and oxygen functional groups which generated after electrochemical activation treatment on MWCNTs surface. The successful preparation of PtRu/MWCNTs and PtRuNi/MWCNTs nanocomposites opens a new path for efficient dispersion of promising electrocatalysts in DMFCs.

Nanocrystalline grains in the surface of reduced activation ferrite/martensite(RAFM) steel were produced by means of surface mechanical attrition treatment (SMAT). Analysis results of XRD and TEM showed that grains after SMAT were nanocrystalline. Experiment results after annealing at 550℃ showed that the nanocrystallines were stable. Abnormal grain growth was observed from the TEM images after tempered for 120 min, and the grain sizes became uniform after tempered for 240 min (about 250 nm). The XRD diffraction peaks of carbides became weaker and boarder indicated that carbides in the surface layer became smaller after SMAT, and smaller MC type carbides were found from HRTEM images after SMAT. The lattice parameters of M₂₃C₆ and MC were 1.0631 and 0.4306 nm calculated from the XRD results. The differences of grain sizes obtained by XRD and TEM could be attributed to the different testing mechanism, different measuring depths and the depth-dependent nanocrystalline microstructure, and results obtained by TEM were more accurate to reveal the real grain size.

The possibility of using Mo as an alloying element in zirconium alloys was considered in terms of its strengthening effect and microstructure refinement effect. However, the impact of Mo addition on the corrosion resistance was not fully understood. In this work, Zr-0.4Fe-1.0Cr-x Mo (x=0, 0.2, 0.4, 0.6, mass fraction,%) alloys with addition of different Mo contents were prepared by vacuum arc melting method and their corrosion resistance in 500℃, 10.3 MPa steam was investigated. Compared with Zr-4, N18 and M5 alloys, the corrosion rate of Zr-0.4Fe-1.0Cr-x Mo alloys was much lower, which was attributed to the large numbers of fine second phase particles in the matrix. Addition of Mo improved the evolution of the oxide film during growth and resulted in the degradation of corrosion resistance. The growth of the oxides remained cubic kinetics in the whole corrosion period (2000 h) for the Mo free alloy, whereas changed from cubic to linear kinetics after a corrosion time of 500--1000 h for the Mo containing alloys.

The high-speed camera was used to observe the behavior of the melt flow in the high-speed laser welding process. The humping formation and the effect of the welding speed on the humping tendency have been discussed, and the suppression methods of humping have also been  studied. The results show that the humping formation undergoes three stages: nucleation stage, growth up stage and solidification stage. During the nucleation stage, the two side streams flow around the keyhole and subsequently converge at the rear of the keyhole. Finally, the wave motion of the liquid metal, which means the nucleus of the humping, is formed in the converging process. During the growth up stage, the valley of the wave is given priority to solidify, which prevents the peak liquid metal from flowing to the rear of the molten pool. The peak of the wave is filled to expand by the front liquid metal. During the solidification stage, the grown-up peak solidifies from the bottom to top, which lifts the solid-liquid interface upward, declines the contact angle, and makes it difficult for the peak liquid metal to spread. With increasing the welding speed, the distance between the converging position at the rear of the keyhole and the laser beam increases, the temperature of the liquid metal at the rear of the keyhole decreases, the surface tension goes up, the peak liquid metal is hard to spread, the humping is apt to nucleate, and humping tendency is increased. Adopting the laser with small spot diameter is helpful to shorten the distance between convergence position and laser beam, and using the trailing beam of the dual beam laser is propitious to increasethe temperature of the liquid metal in the rear of the keyhole.These two approaches are effective in decreasing the surface tension, and suppressing the nucleation of humping.

The constitutive relationships of a 35Mn2 steel during hot compression testing were systematically investigated using three methods. The first method is a conventional hyperbolic sine equation with peak stress dependent constants, the activation energy Q determined by this method is about 278 kJ/mol, very close to the austenite lattice self--diffusion activation energy (270 kJ/mol), indicating the rate-controlling mechanism is dislocation climb controlled by diffusion. The second method is a developed hyperbolic sine equation with strain dependent constants, comparing with experimental results, the correlation coefficient and average relative error ofpredicted and measured values are 0.991 and 4.19%, respectively, indicating that the developed equations can give an accurate estimate of the flow stress for the experimental steel. The third method is a physically based approach accounting for the dependence of the Young’s modulus and the self-diffusion coefficient of austenite on temperature, which is also capable of representing the flow stress of the material as a function of the deformation conditions, but the fitting precision by this method is lower than by the conventional hyperbolic sine equation, and through modification, the fitting precision of the physically based approach is improved in this work.

316L stainless steel is applied to high-temperature environment because of an attractive combination of mechanical properties and corrosion resistance in various aggressive environment. However, the corrosion resistance of 316L was reduced in a particular environment such as water vapor, aggressive sulfur gas which was attributed to the Cr₂O₃ protective scales formed in 316L. The Cr₂O₃ scales are compromised by water vapor due to the formation of volatile Cr oxy--hydroxide species. The Al₂O₃ is more thermodynamically stable in these enviroment than Cr₂O₃. In this work, the effects of Al element on the microstructure, mechanical properties and corrosion resistance of hot-rolled 316L were investigated. Microstructure evolution was observed by OM, EPMA and XRD. Mechanical properties were measured by tensile tests. The resistances to intergranular and uniform corrosion of hot-rolled 316L with different Al content were investigated by means of soaking method at 65%HNO₃ and  5\%H₂SO₄, respectively. The results show that microstructure has changed from single γ to α+γdouble phase. With the increase of Al content in 316L, the yield strength and ultimate tensile strength increased but the ductility decreased. The fracture morphology of tensile was observed by SEM. Which indicated that the fracture mechanism behaved in ductile fracture. Corrosion rate of intergranular and uniform corrosion decreased remarkly as the Al content increased. The optimum Al content in terms of corrosion rate curve was about 2%. Improvment of corrosion resistance was mainly due to Al₂O₃ scale formed in 316L.

The W coatings prepared on structure materials (V-4Cr-4Ti) as plasma facing materials, not only can release impinging thermal power but also can resist erosion under plasma particles bombardment in international thermonuclear experimental reactor. The electro deposition of W in Na₂WO₄-WO₃ melt as a promising technique was studied in this work. The effects of current density on microstructure and mechanical properties of W coating were investigated, and the results show that, with the increasing of the current density, the trend of crystal growth is promoted and the grain size of W coatings increased. The nucleation easily occurs on V-4Cr-4Ti alloy substrate for W atom, and after that, the growth of crystal nuclei is the most important factor for the formation of coatings. When the current density increases to 100 mA/cm², the metallographic structure of W coatings presents columnar or stripy structure, and tooth-like grains were presented in microstructure as current density is lower. The Vickers micro-hardness of W coatings is decreased as increasing current density, and the adhesive strength of the coatings is greater than 59.36 MPa by the tensile test. Although the thickness of tungsten coatings is 10 μm as current density is 10 mA/cm², grain size is less than 5 μm, Vickers hardness, current efficiency and the coatings adhesion are all maximum, and the values are 628.42 HV, 99.71% and 96 N respectively.

The carbon fiber reinforced polymer (CFRP) has been widely used in aerospace and military fields, whereas it is still at its initial stage in the field of automobile manufacturing, wind power generation and so on. One of the main reasons to restrict its wide application is that the strength of metal/CFRP joint is very low and cannot meet the industrial requirements. In this study, an investigation of the laser joining between CFRP and mild steel with Cr electroplating was presented. The influence of Cr plating layer on shear strength of mild steel/CFRP lap joint was studied and the bonding characteristics of the joint interface were analyzed by SEM and XPS. The results show that Cr plating layer can greatly improve the shear force and shear strength of mild steel/CFRP joint. The shear force increases from 2237.37 N to 6127.81 N and the shear strength increases from 9.32 MPa to 22.14 MPa. For the mild steel/CFRP joint without Cr plating, the shear failure happens at the interface. However, for the mild steel/CFRP joint with Cr plating, the shear failure happens at the porosities zone in the CFRP. It means that the Cr plating can improve the interfacial bonding strength. The results of SEM observation and XPS analyses show that the mechanical bonding represented as the ``anchoring effect'' is achieved at the mild steel/CFRP interface both with and without Cr plating. But the chemical bonding is detected only at the mild steel/CFRP interface with Cr plating, which is considered as an important reason that the Cr plating can improve the bonding strength of the mild steel/CFRP joint.

A continuous casting technique was developed to fabricate lotus-type porous alloys. Lotus-type porous Cu-xZn (x=2, 6, 10, mass fraction,%) alloys were successfully fabricated by using the continuous casting technique under a hydrogen gas pressure of 0.6 MPa at various transference velocities. The effects of transference velocity and Zn contents on the porosity and pore diameter were investigated. It shows that, for the porous Cu-2Zn alloy, an increased transference velocity will result in a slightly increased porosity and a decreased average pore diameter. Addition of Zn into pure Cu, on the other hand, will result in an increased average pore diameter. Nevertheless, the pore morphology becomes more and more inhomogeneous with increasing Zn content, and the porosity tends to firstly decrease and then increase. Such tendencies are correlated with the Zn content and the corresponding width of the mushy zone.

Nickel-based superalloy C276 had become one of the alternative materials in simulation loop of thorium molten salt reactor(TMSR) nuclear power system. The strength and plasticity decay of C276 alloy under high temperature environment for long time will directly threatened the security of simulation loop of TMSR. The microstructure of C276 alloy after long-term aging at 700℃ was studied by TEM and SEM with EDS, and the high temperature mechanical performance of C276 alloy after aging was researched at 700℃ with an universal high-temperature materials testing machine. At the same time, the morphology of tensile fracture was analyzed by SEM. The results show that massive block μ phase and M₆C carbides are precipitated after long--term aging with 700℃ at the grain boundaries and within grains of C276 alloy, and the block precipitated phase grains grow up with aging time, some precipitated grains at boundaries extend forward the~interior of based crystal. The alloy is strengthened by the effect of precipitation phase, so the strength is not reduced after long--term aging at 700℃ high temperature. As aging time increases, the plasticity of C276 alloy reduces firstly and then increases to the peak after aging 720 h, and decreases again. However, the plasticity of C276 alloy still maintain well after longer aging time. The high temperature tensile fracture mode of C276 alloy is ductile fracture after long-term aging.