Because of its high gas velocity and heat input, plasma arc welding (PAW) can penetrate thicker workpieces with a single pass because PAW can operate in the keyhole mode. Compared with electron beam and laser beam welding, keyhole PAW is more cost effective and more tolerant of joint preparation, so that it is widely used in manufacturing structures with medium thickness. However, the keyhole establishment and sustainment during the initial stage of PAW process, i.e., the keyholing process, has a critical effect on the process stability and the weld quality. Thus, modelling and simulating of the keyholing process and its influence on fluid flow and heat transfer in keyhole PAW process is of great significance to completely understand the process mechanism. With considering the interaction between weld pool and keyhole, a three dimensional transient model of fluid flow and heat transfer in weld pool is developed for numerical analysis of keyholing process in PAW. The volume of fluid method (VOF) is used to track the keyhole shape and size. The latent heat and momentum sink due to solidifying and melting are dealt with by enthalpy-porosity technique. Considering the larger ratio of PAW weld depth to width, a combined volumetric heat source model is established, and one of its distribution parameters is adjusted dynamically with the variation of keyhole depth. The evolution of fluid flow and thermal field in weld pool, and the keyholing process are quantitatively analyzed on the stainless steel plates of thickness 8 mm. The feature of fluid flow in weld pool is revealed. The predicted keyhole size at bottom side of workpiece and fusion line at transverse cross-section of welds agree with the experimentally measured results.

T-welded structures of aluminum alloy are increasingly used in automotive, railway vehicles, aerospace and bridges. However, compared with the simple joint, the T-joint of aluminum alloy is more difficultly welded due to its complex temperature distribution and fluid flow mode in the weld pool. Whether using laser welding or the conventional arc welding process, aluminum alloy T-wleded joint is more prone to welding defects such as crack, pore, undercutting, joint softening, and so on. As a promising joining technology, laser+gas metal arc welding (laser+GMAW) hybrid welding not only combines the advantages of laser welding with those of GMAW, but also overcomes their shortcomings, thus having great potential to achieve high efficiency and high quality welding of aluminum alloy T-joint. So far, however, there is a lack of fundamental investigations involving mathematical modelling and understanding of the hybrid welding process of aluminum alloy T-joint. As key factors determining the weld quality, thermal field has a significant influence on microstructure and properties of T-welded joint. In this work, using the numerical simulation method, the temperature distribution in laser+GMAW hybrid welding of aluminum alloy T-joint was studied. Considering the influence of joint form on welding heat flux, an adaptive combined volumetric heat source model for laser+GMAW hybrid welding for T-joint is developed based on macroscopic mechanism of heat transfer. The arc heat flux and heat content of overheated droplet are described using an double ellipsoid body heat source model, and the laser power is regarded as peak density exponentially increasing-conic body distribution. To take into account the effect of inclination of welding gun on heat flow distribution in T-joint welding, the heat source model is rotated by way of coordinate transformation, thus deducing the formula of combined heat source model suitable to hybrid welding for T-joint. The built model is used to calculate the geometry and dimensions in laser+GMAW hybrid both-sided welding for T-joint of aluminum alloy under different welding conditons, and the simulated resluts agree well with the experimental ones, which indicates the accuracy and applicability of the combined model. Besides, the thermal cycles at different positions in hybrid welding for T-joint of aluminum alloy are computed, and the characteristics of the thermal cycles are analyzed, which will lay the foundation for prediction of microstructure and properties of welded joint.

During service, coefficient of thermal expansion (CTE) mismatch between different materials in electronic devices can lead to stress and strain concentration, and the creep and fatigue damage will accumulate, leading to final failure of solder joints. The main constituent of Pb-free solder joint is β-Sn, which is body-centered tetragonal metal. There is big difference in CTE and elastic modulus along different directions of β-Sn, showing strong anisotropy. Therefore, solder joints with different orientations show quite different thermo-mechanical responses. In this study, ball grid array (BGA) assemblies were subjected to thermal cycling, and the orientation of the solder joints was characterized by EBSD to track the orientation evolution in different solder joints. Surface Evolver was adopted to simulate the three-dimensional shape of the solder joint. Based on the shape and grain structure of real lead-free solder joints, the thermal stress and strain distribution in BGA assemblies under thermal loading were computed. Sub-model based on grain numbers and orientation distribution is solved to get the strain distribution of the three typical solder joints. The experimental and simulated results show that grain orientation significantly influences the solder joint reliability and failure mode. For single-grained solder joints, stress and strain concentration is located in the solder bulk near the interface, where recrystallization accompanied with initiation and propagation of cracks.  However, for multi-grained solder joints, the distribution of stress and strain depends on grain orientation. Recrystallization and cracking tend to divert from the interfacial region into the solder bulk along the pre-existing grain boundary. Some special solder joints with grain boundary perpendicular to the interface are not favorable for deformation, exhibiting higher reliability. When the grain boundary inclined at 45^o to the pad, the original grain boundaries produce large stress and strain concentration under combined action of shear stress and anisotropy of Sn grains, accelerating the crack initiation and propagation, and fracture occurred along the original grain boundaries, increasing the probability of early failure.

Electromagnetic brake (EMBr) affects the flow field in mold during the slab continuous casting process. Flow control mold II (FC Mold II) has been developed to resolve the defects of the third generation (flow control mold) of EMBr which the braking effect on meniscus is too strong to make the surface flow excessively stabilize and it would be prone to freezing and related defects. To gain a fundamental understanding of FC Mold II, a mercury physical model was developed to investigate the influence of the magnetic field intensity match on metal flow in FC Mold II based on the\linebreak 1350 mm×230 mm slab continuous casting process in a factory. The flow regime and velocity distribution in mold were measured by ultrasound Doppler velocimeter (UDV) with the maximum magnetic field intensity of the upper pair of magnetic poles B₁=0.18, 0.36 and 0.50 T respectively and the maximum magnetic field intensity of the down pair of magnetic poles B₂=0.50 T, while the mold casting speed is 0.41, 0.52 and 0.82 m/min respectively corresponding to the practical casting speed 1.00, 1.30 and 2.00 m/min respectively. The influences of the magnetic field intensity match on the flow discharged from the nozzle, the flow near the meniscus and the washing intensity to the mold narrow wall were analyzed and studied. The results showed that, when the magnetic field intensity match of the upper and the lower pair of magnetic poles B₁/B₂≤1, with the continuous casting speed increasing, the value of B₁/B₂ should increase in order to get an ideal braking effect. The value of B₁/B₂ should be 0.36, 0.72 and 1.00 respectively when the model casting speed is 0.41, 0.52 and 0.82 m/min respectively. The increasing of the intensity of the magnetic field reduces the “flow passage” effect caused by EMBr, and is conducive to the formation of the plug flow under the electromagnetic braking region.

A new annealing technology has been developed in order to conduct fast steel annealing. The microstructure and texture of the Nb+Ti stabilized interstitial-free (IF) steel and high Nb-IF steel highly cold deformed to a reduction of 94.2% after ultra-rapid annealing (URA) process with heating rates approximately 300 ^oC/s were characterized by means of OM, TEM, EBSD and XRD. The experimental results indicate that the recrystallization process is significantly accelerated and the finish recrystallization temperature is increased after URA. Moreover, the fully recrystallization can be obtained in as short as about 0.41 s, compared with about 4 s in the conventional annealing (CA) process with heating rates approximately 20^o C/s. In the fully recrystallized condition, the grain size and intensity of {445}<231> fiber in the Nb+Ti-IF steel, about 11.2 μm and 15.6, can be observed in one URA cycle, respectively. However, the grain size and intensity of {445}<231> fiber are 13.5 μm and 14.0, respectively, after the Nb+Ti-IF steel is subjected to one CA cycle. On the other hand, the URA has unapparently influence on grain size, within (11.0±0.3) μm in either one URA or one CA cycle, of the high Nb-IF steel, with about 18.0 intensity of {223}<472> fiber. Simultaneously, more random fiber can be found in one URA cycle than in one CA cycle with higher intensity of {223}<472> texture up to 23.9. The grain refining effect in either one URA or one CA cycle is attributed to the mutual interaction of  nucleation density, annealing time and grain boundary migration rate.

The twinning induced plasticity (TWIP) steel has received more and more attention for its outstanding combination of good strength and high ductile. It has been proposed that deformation twinning plays an important role in controlling the deformation behavior. The formation of deformation twins is influenced by deformation temperature, strain rate, pre-deformation, grain size and precipitates. The generation of deformation twins in austenitic steel is closely related to precipitates. However, the relationship between strain hardening rate and precipitates in TWIP steels has not been clarified. In this work, the effect of vanadium carbides on the microstructure, strain hardening behavior and mechanical properties of Fe-Mn-C TWIP steel was investigated. The specimens of Fe22Mn0.6C and Fe22Mn0.6C0.19V TWIP steels with similar grain sizes were fabricated through solution treatments at different temperatures. Mechanical properties were measured by tensile tests, and microstructure evolution was observed by EBSD and TEM. The strain hardening rate (dσ/dε)-true strain (ε) curves of two steels were drawn. The results show that for the Fe22Mn0.6C0.19V steel, the strain hardening rate platform appear when true strain ε>0.14, while the strain hardening rate platform appear when the ε>0.12 for the Fe22Mn0.6C steel. The platform of Fe22Mn0.6C steel is significantly longer than that of Fe22Mn0.6C0.19V steel, The platform of Fe22Mn0.6C0.19V steel disappear quickly as true strain ε>0.21. Tensile specimens of Fe22Mn0.6C and Fe22Mn0.6C0.19V steels were observed by TEM, the results show that both the generation and propagation of deformation twins are inhibited significantly by vanadium carbides.

The development of high performance steels needs to realize the combination of high strength, high plasticity and high toughness. Multiphase microstructure which contains a specific proportion of retained austenite is conductive to enhance the toughness and plasticity of the steel. Making use of the quenching+intercritical reheating-quenching and partitioning (IQ$\&$P) process, a multiphase microstructure which was composed of intercritical ferrite, martensite and well distributed retained austenite (primarily distributed in the prior austenitic grain boundary and the phase boundary) can be obtained in the 0.23C-1.8Mn-1.35Si steel. By means of SEM, XRD and EBSD, microstructures of the steel in different heat treatment stages were characterized. The results indicated that the obtention of the retained austenite was mainly dependent on the following two stages: the first one is the enrichment of the carbon and manganese in the reversed austenite during the intercritical reheating process; the second stage is the secondary enrichment of carbon in retained austenite during the following quenching and partitioning process. After the two stages of element enrichment treatment, more than 10% volume fraction of retained austenite was obtained, and the second stage of treatment plays an important role in the formation and stabilization of the metastable austenite. Due to the strengthening and toughening effect of the widely distrubuted retained austenite, this kind of steel obtained a continuous work hardening ability, and thus achieved a good combination of strength and plasticity. Test results indicated that steel treated by the IQ&P process shows excellent comprehensive mechanical properties: the product of strength and elongation is greater than 26 GPa?%, the yield strength and tensile stength is more than 600 and 900 MPa respectively, the uniform elongationg is above 16\%, and the half thickness size impact toughness at room temperature reaches to 39 J.

Nowadays, the events of bacterial infection are increasingly arising. It is urgent to develop new antibacterial material to fight against the bacteria having resistance to drug. Because the antibacterial stainless steels have both antibacterial property and other excellent combination ones, their development has been obtained rapidly. At present, the copper-containing antibacterial stainless steels are the research focus. It has been reached that the antibacterial effect of those materials is due to the copper-rich phases precipitated from the matrix by aging treatment. Most of studies were performed at single-phase stainless steels, but rarely at duplex stainless steels. It is necessary to study the precipitation process of copper-rich phases in duplex stainless steels for the development of antibacterial duplex stainless steels. In this work, the microstructure and precipitating evolution law of copper-rich phases in the copper-containing duplex stainless steels during antibacterial aging treatment has been analyzed in detail by SEM, XRD and TEM. The results indicate that antibacterial copper-rich phases are precipitated from ferrite and α/γ interfaces, no precipitation in austenite when the duplex stainless steels are aged at temperature ranging from 540 to 580 ℃. The technique parameters of the aging treatment have important effect on the volume fraction and morphologies of precipitated phase. With aging time increasing, the precipitates coarsen, and their morphologies gradually change from spherical particle to rod-like or long-stripe-like grain. When the aging temperature is raised, precipitation speed of copper-rich phases accelerates and they make the change like before. At the same time,  the copper-rich phases gradually turn from metastable state to steady ε-Cu phase with the composition close to pure copper, which has complicated multilayer structure with twisting layers. The Kurdjumov--Sachs orientation relationships between ε-Cu phases and the ferrite matrix followed: (111)_ε-Cu//(110)_α-Fe, [011]_ε-Cu//[001]_α-Fe, (111)_ε-Cu//(121)_α-Fe, [011]_ε-Cu//[012]_α-Fe.

Effects of antibacterial aging treatment on the corrosion resistance of copper-bearing duplex stainless steels were investigated by electrochemical methods. The film-cover method was used to test the antibacterial effect of the materials. The polarization curve test results show ε-Cu and other copper-rich phases become the weak point of the passive film on the surface of the duplex stainless steel, and the sites where the coarse copper-rich phases are precipitated from the matrix are apt to become pitting nucleation source. The proportion of coarse copper-rich phase increases, which makes pitting resistance of the materials worse. EIS test reveals that the presence of ε-Cu and other copper-rich phases in passive film reduces the overall potential and passive film resistance, decreasing the stability of passive film. D-EPR tests show that ε-Cu and other copper-rich phases in grain boundary makes it take on anode characteristic in corrosion process, leading to selectively intergranular corrosion. Compared with austenite, the intergranular corrosion resistance of ferrite decreases seriously because the copper-rich phases are mainly precipitated from ferrite matrix. Antibacterial tests show that the microstructure and volume fraction of copper-rich phases are the key factors affecting the antibacterial properties of the materials. ε-Cu displays the best antibacterial effect, followed by metastable copper-rich phase, solid solution copper is the worst. The more ε-Cu phases are, the more antibacterial effect is.

The effect of Bi contents on the corrosion resistance of Zr-4+xBi (x=0.1%-0.5%, mass fraction)
alloys, which were prepared by adding Bi to Zr-4, was investigated in superheated steam at 400 ℃ and
10.3 MPa by autoclave tests. The microstructures of the alloys and fracture surface morphology of the oxide film
formed on the alloys were observed by TEM, EDS and SEM. The results show that with the increase of Bi content,
the second phase particles (SPPs) are almost the same in size and shape, but increase in amount and vary in
composition, including Zr(Fe, Cr)₂, Zr-Fe-Cr-Bi, Zr-Fe-Sn-Bi and Zr-Fe-Cr-Sn-Bi. Even in the
Zr-4+0.1Bi alloy, Bi--containing SPPs were detected. This indicates that the solid solubility of Bi in α-Zr
matrix of Zr-4+xBi alloys is less than 0.1% at 580 ℃. Moreover, the addition of Bi promotes the precipitation
of Sn which originally dissolved in the α-Zr matrix of Zr-4. Compared with Zr-4, the addition
of Bi makes the corrosion resistance worse, and it becomes more obvious with the increase of Bi content. This
illustrates that the addition of Bi can not improve the corrosion resistance, on the contrary, it brings a harmful
influence. This may be related to the precipitation of the Bi-containing and Bi-Sn-containing SPPs.

Zirconium alloys of a hexagonal close--packed crystal structure have prominent anisotropic characteristic in comparison with metals of a cubic crystal structure and a strong texture is produced in sheet or tubular materials during the fabrication process. The anisotropic characteristic is bound to be reflected on the corrosion behavior of zirconium alloys. In order to investigate the effect of texture and compositions on the anisotropic growth of oxide layer formed on zirconium alloys and clarify the mechanism of improving corrosion resistance by adding Nb in zirconium alloys, Zr-4, N18 and ZIRLO zirconium alloys with different contents of Nb were adopted as the experimental materials. All the plate specimens of zirconium alloys 2 mm in thickness have a similar texture. Corrosion tests were carried out in a static autoclave at 360 ℃, 18.6 MPa in lithiated water with 0.01 mol/L LiOH. The results show that the anisotropic growth of oxide layer on different surfaces of the specimens was only observed for Zr-4 specimen but not for N18 and ZIRLO specimens. The thickness of oxide layer develops much faster on the rolling surface (S_N surface) than that on the surface perpendicular to the rolling direction (S_R surface) and the surface perpendicular to the transversal direction (S_T surface) for Zr-4 specimen after 90-100 d exposure, and the corrosion resistance on the S_R and S_T surfaces was much better than that on the S_N surface. However, for N18 and ZIRLO specimens the anisotropic growth of oxide layer was restrained by the addition of Nb, and the oxide thickness on these three different surfaces was the same after 280 d exposure. Therefore the corrosion resistance of N18 and ZIRLO sheet or tubular specimens was superior to Zr-4 corroded in lithiated water, because the oxide layers grew mainly on the S_N surface of the specimens. If making a comparison among Zr-4, N18 and ZIRLO specimens about the growth rate of oxide layers only on the S_R and S_T surfaces, it is shown that the growth rate of oxide layers increased with the increase of Nb content in these alloys. From a point of view for the improving corrosion resistance, the addition of Nb no more than 0.3\% (mass fraction) is recommended.

Friction stir welding (FSW) of a novel AlCuLi alloy was conducted to investigate the effect of welding parameters on the microstructure and mechanical properties of the joints. The fine and equiaxed dynamically rotation rate increased, the size of the grains in the NZ increased. However, with increasing the welding speed, the size of the grains in the NZ decreased slightly. TEM analyses indicated that most of the precipitates in the NZ dissolved into the matrix during FSW and some coarse precipitates formed during subsequent cooling process. Moreover, many coarse precipitates were observed in the heat affected zone (HAZ) due to the FSW thermal cycle. At a low welding speed of 80 mm/min, the ultimate tensile strength of the joints increased as the rotation rate increased, and could reach up to 442 MPa which was 87% of that of the base metal. All of the joints failed in the lowest hardness zone of the HAZ. At a high welding speed of 200 mm/min, some defects resulting from insufficient material flow were observed on the fracture surfaces. At a low rotation rate, the joints failed along the defects in the NZ and exhibited a low strength. As the rotation rate increased, the size and number of the defects decreased. Therefore, the effect of the defects on the strength of the joints was significantly reduced, and a joint efficiency of 84% was obtained.

Laser shock processing (LSP) is an effective and promising technology for improving surface mechanical properties of metals. The study of the strain behavior of individual phase of advanced engineering materials with polycrystalline and dual-phase microstructures subjected to laser shock processing is an important emerging frontier, which facilitates understanding of the relative roles of intrinsic and extrinsic attributes of microstructure upon strengthening, compared with the strengthening process of metals at the macroscopic scale of deformation. The influence of LSP on the surface layer properties and microstructures of a Ti-6Al-4V alloy has been investigated focusing on the microstructure response of the surface layer of the alloy by means of high efficient Nd³⁺∶YAG ceramic pulse laser with 12.5 J per pulse at 1064 nm and 10 Hz repetition rate. The microstructures response of the alloy are analyzed and characterized with by FE-SEM, TEM and the inverse fast fourier transform (IFFT) algorithm, respectively. The experimental results show that the surface hardness of the laser shocked Ti-6Al-4V alloy can increase 80%, and the compressive residual stress can be over\linebreak 500 MPa. Obvious preference effect between α and β phase is discovered upon strengthening of the alloy under the conditions of the ultra high energy and ultra-high strain rate of laser shock. With the lower shock energy, the deformation strengthening of β phase takes precedence over the other; as the shock energy increasing, both α and β are strengthened simultaneously, whereas, the previously strengthened β phase shows saturated strengthening effect. The results also reveal that dislocation multiplication is the main strengthen mechanism in the laser shocked region, including oriented dislocation projection and dislocation dipoles in the α phase with hcp crystal lattice, but diversified configurations, such as edge-dislocation, extended dislocations and dislocation dipoles presenting in the β phase with bcc crystal lattice. The semi-coherent interface with misfit dislocations between α and β phase boundary is discovered, which plays a synergetic role upon deformation strengthening. Additionally, the strain screening manifestation within the laser shocked region is also discussed, which is regarded as a kind of self-organization phenomenon of deformation defects, and can be attributed to the synthetic effect of the confinement conditions upon laser shocking, the accumulative strengthening mode of single-spot laser shocking process and the differences of strength and crystalline structure between the lamellar α and β phases.

The hot deformation behavior of the T4-treated Mg-6Zn-0.5Zr-0.5Ce alloy was investigated by compressive test using Gleeble 3800 thermal--simulator in the temperature range of 523-673 Kand strain rate range of 0.001-1.0 s^-1. The results show that the flow stress is significantly affected by both deformation temperature and strain rate. The flow stress increases with either decreasing deformation temperature or increasing strain rate. The flow stress value tends to be constant after a peak value appearing at high deformation temperature and low strain rate. In the present work, the average activation energy for the hot deformation has been determinded to be 145.76 kJ/mol using the hyperbolic sine constitutive equation. A feed-forward back-propagation artificial neural network (ANN) has been established and used to investigate the flow behaviors of the alloy. The predicted data by the ANN is in good agreement with the experimental ones. Combing microstructure observation, the processing map for this alloy established on the basis of a dynamic material model indicates that the dynamic recrystallization (DRX) would take place in the range of 648-673 K and 0.1-1.0 s^-1, while under the same strain rate the flow instability would occur due to mechanical twinning when the temperature below 573 K. The formation of interfaces depends on the process of mechanical recovery caused by cross-slip of screw dislocations. The DRX model indicates that DRX of this alloy is controlled by interface migration.

Over the past years, hard wear resistant TiN coatings deposited by magnetron sputtering have gained increasing importance in the field of decorative and cutting tool coatings. With the ongoing trend to multifunctional operating cutting tools, new solutions in the design of tools are demanded. The alloying of TiN coatings with additional elements, for instance, can effectively enhance hardness, wear resistance and so on. Both TiAlN and TiSiN coatings, well-studied nitride systems, yield superior oxidation resistance, and extend the life of cutting tools by significant margins in comparison with TiN coatings. Numerous research activities focus on TiAlN, TiSiN systems, whereas limited efforts have been made to characterize TiMoN coatings. Low coefficient of friction is a common property in various Mo-containing coatings that can react with oxygen in the air into Magneli phase (MoO₃). The effects of Mo alloying on mechanical properties and wear resistance of TiN-based coatings remain to be investigated. TiMoN composite films with various Mo concentrations were deposited using RF reactive magnetron sputtering and characterized by SEM, EDS, XRD, nano-indentation and wearing tester. The results show that TiMoN coatings have fcc structure. When atomic fraction of Mo in total metallic elements (X) is less than 68.37\%, a TiMoN solid solution was formed by dissolution of Mo into the TiN lattice; when X is more than 68.37\%, a TiMoN solid solution was formed by dissolution of Ti into the Mo₂N lattice. With Mo contents increase, preferential orientation change, microhardness increase significantly, the coefficient friction and grain size decrease, friction and wear of TiMoN coatings are excellent. Low coefficient friction can be primarily attributed to the formation of lubricious MoO₃ on the wear track surface in dry sliding wear conditions. The principles of a crystal chemical model relating the lubricity of complex oxides to their ionic potentials can explain this mechanism.

Over the past two decades, interest has been focused on the synthesis of novel nanomaterials with different sizes and different morphologies due to their intriguing chemical, electronic, biosensing, optical and catalytic properties. The biomacromolecules like nucleic acids, proteins, amino acids and peptides have been employed as template for nanomaterial design and synthesis. DNA, which could self-assemble into complex structures such as cubes and squares, is being actively explored for the synthesis of nanomaterials with novel structures and unexpected properties. In this work, the plasmid DNA with 7.5 kB base pairs separated from the bacillus was used as a template to prepare Ag nanoparticles based on the ultraviolet ray (UV) photoirradiation method. The effects of experimental conditions, such as the photoirradiation time and concentration of metallic Ag⁺ ions, on the composition, morphology, and structure of the obtained nanoparticles were detailed studied. The Ag nanoparticles were characterized by using UV--visible light absorption spectroscopy, TEM and EDS. It is found that Ag⁺ and UV are necessary in this preparation based on plasmid DNA. The resulted Ag nanoparticles are fcc structure, and the average diameter of obtained nanoparticles is 25-40 nm. The sizes of nanoparticles increased with the increasing of the photoirradiation time and the concentration of Ag⁺. When the mol ratio of Ag⁺ to base pairs is 4∶1 and the photoirradiation time is 40 min, the obtained nanoparticles are almost ring-shape with inner diameter of 8-10 nm. In synthesizing process of Ag nanoparticles, only plasmid DNA and Ag⁺ ions solution were needed, and the plasmid DNA worked not only as template to drive the formation of the Ag nanoparticles, but also as reducer to reduce the Ag⁺ ions to be metallic Ag. This synthesis method could also be used to prepare other metallic or semiconducting nanoparticles.

Chalcopyrite (CuFeS₂) is the most common copper bearing sulfide in the natural world, and it is also the most widespread copper ore in the world. Pyrometallurgy is used to extract copper from chalcopyrite as main industrial method. However, environmentally friendly metallurgy is advocated because of increasingly serious environmental pollution. The bacterial metallurgy is considered a new clean smelting technology to deal with low--grade and complicated composition metal resources because of short flow, simple operation, low investment and friendly environment. In the process of bioleaching, the formation of oxide film on the chalcopyrite crystal surface hindered the rapid dissolution of chalcopyrite and restricted the large-scale application of copper bioleaching. It is concluded that the oxide film inhibits material exchange between chalcopyrite and leaching liquid on the surface of the chalcopyrite and depresses its leaching rate significantly. In the paper, the advanced surface analysis technologies, such as SEM, XRD and X-ray photoelectron spectroscopy (XPS) are used to observe and analysis the surface layer in the bacterial leaching process. It is studied for the formation of bio-oxide film on the natural chalcopyrite crystal surface, in order to reveal the passivation mechanism of chalcopyrite bioleaching. Through the observation of the microcosmic morphology characteristic changes of chalcopyrite during bioleaching, different chemical composition analysis of surface oxide layer in the different bacterial oxide phase were studied. The results show that the insoluble oxide film inhibits material exchange between chalcopyrite and leaching liquid on the surface of the chalcopyrite and depresses its leaching rate significantly. The results show that the rudiments of oxide film are formed on the surface of chalcopyrite after leaching for 72 h. The oxide layer with certain thickness is formed after 96 h, and the passivation is produced. The compact film is formed after 168 h because bacterial corrosion spots and rillsare formed on the surface of chalcopyrite, and it is begun to produce serious passivation. The variation of chemical state of sulfur element is S^2-→S⁰→S⁴⁺→S⁶⁺. The reaction product, including iron deficiency copper sulfide
Cu$_{1-x}$Fe$_{1-y}$S$_{z}$($x iron oxide (Fe(III)-oxide), iron hydroxide oxide (Fe(III)-O-OH) and
jarosite (KFe₃(SO₄)₂(OH)₆) are formed on the surface
of chalcopyrite in order in the bioleaching process. The chalcopyrite
passive film formed is caused by the stable and compact layer whose main
composition is jarosite, and it produces strong passivation effects on the
chalcopyrite bacterial leaching.