Duplex stainless steels (DSSs) were processed to have a balanced microstructure containing approximately equal amounts of ferrite and austenite, which exhibit exceptional mechanical properties and corrosion resistance. Lean duplex stainless steel (LDX) 2101 with lower contents of Ni and Mo had been developed in order to further reduce the cost. The coexistence of ferrite and austenite during hot deformation led to a complicated deformation behavior. However, little research had been dedicated to studying the microstructure evolution in LDX 2101 compared with traditional DSSs. In addition, the reported results of microstructure evolution both in ferrite and austenite phases of traditional DSSs exhibited obvious controversy. In the present paper, the microstructure evolution of the LDX 2101 during hot compression at a strain rate of 5 s⁻¹ and 1000 ℃ was studied by electron backscatter diffraction (EBSD) together with TEM. The results showed that continuous dynamic recrystallization (CDRX) occurred both in ferrite and austenite phases by gradual transformation of ow angle grain boundary into high angle rain boundary. In addition, a large number of Σ3 twins appeared after solution anneaing treatment. The hot deformation resulted in a progressive disappearance of the Σ3 twin boundaries in austenite phase. Flow curve characteristics of the LDX 211 during hot deformation were interpreted by the coupling behaviors of the microstructure evolution of its both phases.

In fcc/bcc phase transformation systems, the orientation relationships (ORs) are usually described by parallelism of a set of specific vectors pairs or small deviations from the parallelism. This method often reflects the characteristic feature of the phase transformation correspondence. With the application of the electron backscatter diffraction (EBSD) technique to the measurement of the ORs, the ORs are also evaluated by a rotation matrix or a group of Euler angles. However, this quantitative description does not provide an intrinsic relationship between the crystallography equivalent variants. Thus, self–consistency of the data from different variants with an identical OR is not reflected directly by the data. In this paper, formulas have been derived to convert the OR identified by the relative orientation of a specific st of vectors to the OR described by Euler angles in data from EBSD. This method is useful fr acquiring self–consistent OR of small number of variants. Compared with the fitting method using high–indexed pole figures, which requires existence of many variants, the present method has broader applicability. An application example is given to deermine the OR between two pases in a duplex stainless steel from the measurement data of two variants. A slight deviation from an exact twin relationship between the variants has been characterized.

The excellent combination of strength and elongation and the super work hardening behavior of high manganese TRIP/TWIP (transformation–induced plasticity/twinning–induced plasticity) steels are due to the presence of two kinds of martensitic transformations and their complicated interactions of three phases during deformation. This work investigated the crystallographic characteristics of γ →ε →α' transformation, and in particular, the effects of deformation twins and austenitic grain orientations on martensitic transformation by means of EBSD technique. Results showed that α'–martensite was triggered at the intersection of two ε-martensite variants. Deformation twins were frequently detected near ε–martensite, thus twins promoted the formation of ε–martensite and played n important role during TRIP pocess. However, twinning was affected by austenite grain orientations. It is suggested that austenitic grain orientations with low indices, such as {100}, {111} and {110}, more easily promoted the intersection of ε–variants due to the multi–twinning and thus facilitated further α′–martensite formation than those with high indices. Deformation increased the number of " variants but reduced their sizes and therefore it is difficult for the small strain–induced ε–martensites to transform into α′–martensites smoothly.

In this paper, deformation behaviors of two kinds of martensites (hexagonal and bcc structures) and the influence of austenitic orientations on martensitic transformation in high manganese TRIP/TWIP (transformation–induced plasticity/twinning–induced plasticity) steels during compression were analyzed by EBSD technique. Results showed that, in hexagonal martensites low angle grain boundaries caused by slip and special misorientations such as 93°<7253> were detected in addition to those inherited due to orientation relationship. In bcc martensite, low angle misorientations due to slip were dominant in addition to the special misorientations between α′–M variants or those inherited from austenitic twinsBesides, austenitic orientations affected phase transformation and it was observed that martensite was induced faster in austenitic grains of {110}_γ  orientation than that of {100}_γ  orientation. α′–M orientation changed more obviously in {110}_α' oriented grains because they were unstable during compression. The reasons for the formation of new special misorientations in hexagonal martensite and the influence of austenitic orientation were discussed.

As a precipitation hardened unidirectionally solidified Ni-based superalloy, DZ125 has been extensively applied as structural materials in advanced aeroengine for gas turbine blades and vanes operating at elevated temperatures. The solidification microstructure of alloy plays an important role in determining the alloy's mechanical properties. For a given alloy, the thermal history of alloy melt has an obvious influence on the final solidification microstructure. However, previous researches mainly focused on melt superheating temperature. There are few investigations about the influence of the relaxation process of alloy melt on the solidification structure. In this paper, under the same conditions of processing parameters, e.g.,  olid/liquid interface temperature gradient, withdrawing velocity, by changing the melt holding time, the relaxation phenomenon during melt superheating treatment of DZ125 was investigated. The melt was superheated to 1650 ℃ and kept for 30 min, and then it was rapidly cooled down to 1500 ℃. In order to study the relaxation phenomenon during melt superheating treatment, the melt was held for 15, 30 and 60 min, respectively, and then was withdrawn into the Ga-In-Sn liquid metal bath at a rate of 50 μm/s. The results show that dendrite arm spacing, segregation ratios, size and morphology of γ' phase and γ+γ' eutectic did not change with the increase of the holding time when melt holding time was less than 30 min. But, when melt holding time was prolonged to 60 min, the dendrite arm spacing, γ+γ' eutectic and the size of γ' phase in interdendrite area increased, and the segregation becomes serious, but the γ' phase on dendrite trunk was lightly refined. The morphology of MC carbide mainly showed disconnected blocky and nodule, and unchanged with the prolongation of holding time. These changes in solidification structure should be primarily attributed to the influence of relaxation process on melt structure. When the melt holding time was less than 30 min, there was no evidently change in melt structure. But, further prolonging melt holding time to 60 min, the melt structure had obvious variation. This variation affected the solidification processing and finally solidification structure. Therefore, the variation of melt holding time resulted in the change of solidification structure.

In the last decade, bulk metallic glasses (BMGs) emerge as a new class of metallic materials with disordered atomic structure. Especially, Zr–based BMGs have attracted an increasing attention due to their distinct properties including ultrahigh strength, high elastic strain limit, relatively low Young’s modulus (50—100 GPa) and easy forming ability in viscous state. In addition, Zr–based BMGs displayed a superior corrosion resistance in artificial body fluids and a satisfactory biocompatibility. The combination of these unique properties makes them extremely promising for biomedical applications. The most promising applications for the BMGs are in dentistry and orthopaedics due to their mechanical superiority, where friction and wear properties are clinically important for the performance of the implants in the body. In the present study, a Ni–free BMG plate of Zr₆₀Cu₁₉Fe₅Al₁₀Ti₆ with dimensions of 70 mm×12 mm×1.5 mm was successfully prepared by water–cooled copper mold casting. The friction and wear characteristics of the BMG under sliding in dry air, distilled water and phosphate buffered saline (PBS) have been investigated on a SRV friction and wear tester in a ball–on–plate contact configuration where the upper ball in motion was made of zirconia with 10 mm diameter and the lower stationary plate was made of the BMG. Ti6Al4V alloy was also tested under the same condition for comparison. The wear depth was investigated by a surface profiler and the wear volume was also calculated. The surface morphologes and the component of wear debris were examined by SEM and EDS Compared witte Ti alloy, the BMG exhibits much less volume loss in the PBS solution, demonstrating that the BMG has a better wear rsistance than the Ti alloy, though he former has a larger friction cefficient. The wear mechanism of thBMG is dominated by the corrosion wear with oxidation of the surface and fatigue flake mechanism.

A novel sort of 1500 MPa grade ultra–high strength low alloy structural steel with multi–element of Si–Mn–Cr–Ni–Mo was designed. Effects of four different processes of TMCP (thermo–mechanical controlled processing), controlled rolling+air–cooled, controlled rolling + direct quenching and controlled rolling+direct quenching+tempering at 250℃ on the microstructure and mechanical properties were investigated. The results indicate that the directly quenched steel has a maximum tensile strength of 1890 MPa, yield strength of 1280 MPa and elongation of 13%. After tempered at 250 ℃ for 30 min, the tensile strength of the steel decreased to 1820 MPa, while the yield strength increased to 1350 MPa, which is ascribed to the comprehensive effect of the softening mechanism due to the recoverof dislocation sub–structure and the strengthening mechanism due to the decomposition of retained austenite and "–carbide precipitation. Duplex phase microstructure involving lath bainite, martensite segmented by bainite, and retained austenite was obtained by the process of air–cooling and TMCP, so that it has excellent strength and plasticity. Carbon diffusion phenomenon exists in the quenching process of low–carbon steel. Both the decomposition of retained austenite and the carbon partitioning into austenite from martensite or bainite were found during tempering process. The paper demonstrates that the precipitation particles of cubic structure nucleated in austenite, growing up  and coarsning uring the whole cooling process. Futhermore, the emergence of a lage number of second–phasprecipitation cores was not found in martensite or bainite after phase tansformation.

When a single–phase liquid is cooled into the miscibility gap, it decomposes into two liquid phases. Generally the liquid–liquid phase transformation causes the formation of a solidification microstructure with serious phase segregation. Many efforts have been made to use the liquid–liquid demixing phenomenon for the production of the finely dispersed metal–metal composite materials. It is demonstrated that the only effective method of preventing the formation of the microstructure with heavy phase segregation in monotectic alloys is using the rapid solidification processing techniques. Strip casting may have great potentials in the manufacturing of the bulk materials of this kind of alloys. In this paper, a model was developed to describe the microstructure formation in a strip cast monotectic alloy based on the population dynamic method. The model takes into account the concurrent actions of the nucleation, diffusional growth and motions of the minority phase droplets. The model was nmerically solved together with the controlling equations for the heat transfer, mass transport and momentum transfer to studthe microstructure development in the strip cast Al–Pb alloys. The effects of alloy composition, solidification velocity and melting temperature on the microstructure formation were investigated. The results indicate that with the increase of the solidification velocity, the nucleation position of the minority phase droplets moves towards the solidification interface, the nucleation rate and number density of droplets increase and the average droplet size decreases. All these are favorable for the formation of a well dispersed microstructure. With the increase of the Pb content,  the nucleation position of the minority phase droplets moves away form the solidification interface, the nucleation rate decreases, and the average droplet size increases. These are against the formation of a well dispersed microstructure. With the increase of the melting temperature, the nucleation rate and number density of droplets increase and the average droplet size decreases. These are favorable for the formation of a well dispersed microstructure. But the velocity of the minority phase droplets decreases with the increase of the melting temperature. When the velocity of droplets is negative, samples can not obtain steady state solidification and result in the formation of a microstructure with massive segregation.

The alloy with nominal composition of Ni-30.4Al-34Cr-4.3Mo-0.1Hf-0.05Ho (atomic fraction, %) has been directionally solidified at two withdrawal rates by liquid metal (Sn) cooling (LMC) process. Compared to the as-cast alloy, directional solidification process eliminates primary Cr(Mo) phase. With increasing withdrawal rate from 8 to 15 mm/min, the diameter of NiAl/Cr(Mo) eutectic cell decreases from 115 to 85 μm. In addition, the intercellular spaces and disordered regions become less. In virtue of the disappearance of primary Cr(Mo) phase, the mechanical properties of directionally solidified alloys are better than those of as--cast alloy and are further improved with increasing withdrawal rate.

The high cycle fatigue properties of a new type Ni-based superalloy DZ468 were investigated in this paper. The high cycle fatigue strengths of DZ468 alloy at 900 and 760 ℃ with a ratio of stress R=-1 reach 290 and 300 MPa, respectively. The high cycle fatigue fractures of DZ468 alloy were composed of fatigue source, fatigue district and final stage. Cracks originate from surface, sub-surface and inner defect of sample. At 900 and 760 ℃, stage I and stage II crack propagation could be observed from fatigue fracture, which was caused by the combination action of planar slip, cross slip and climb of dislocations. With increasing of stress value, the crack propagation rate quickly increase. A correlation exists between the crack propagation mode and deformation mode.

Mg–6Li–3Zn alloy was prepared by Jackson’s melting and casting method and the sheets of 1.2 mm in thickness processed by hot rolling at 573 K and cold rolling with a total reduction of more than 92% were obtained. The high–temperature mechanical behavior at temperatures ranging
from 423 to 673 K and initial strain rates ranging from 1.67×10⁻³ to 5×10⁻² s⁻¹ were investigated. The microstructure evolution, such as grains, subgrains, dislocations, cavities and fracture morphology, were investigated by OM, TEM and SEM. Yavari–Langdon model describing the transition between dislocatoviscous glide and dislocation climb was used to construct a new dislocatiocreep mechanism map which consists of Cottrell’s solute atmosphere breakaway dislocation climb regime, dislocation viscous glide regime and Cottrell’s solute atmosphere incorporated dislocation climb regime. A new cavity growth map considering cavity coalescence was obtained according to the cavity growth models. The maximum elongation to failure of 300% was demonstrated at 623 K and an initial strain rate of 1.67×10⁻³ s⁻¹. Significant dynamic recrystallization occurred in band–like structure at 573 K and an initial strain rate of 1.67×10−3 s−1, the subgrain contour was ambiguous and dislocation distribution was relatively uniform. Fracture mode of the alloy at 573—623 K and an initial strain rate of 1.67×10⁻³ s⁻¹ is ductile fracture. It is shown by the dislocation creep mechanism map that the high–temperature deformation mechaism in Mg–6Li–3Zn alloy sheet with bad–like structure at 573 K and an initial strain rate of .67×10⁻³ s⁻¹ is dislocation viscous glide cotrolled by lattice diffusion, the stress exponent is 3 (strain rate sesitivity exponent 0.33) and deformation activation energy is 134.8 kJ/mol, which is the samas the lattice diffusion activation energy of Mg. The cavity growth mechanism of the alloy at 573 K and iitial strain rate of 1.67×10⁻³ s⁻¹ is plasticity controlled cavity growth.

Craze cracks and oxidation appeared on the surfaces of the Mn–Cu weathering steel samples after different soaking times at 1260 ℃in the oxidizing conditions. EPMA result shows that Cu enriches at the interface of matrix/scale, Cu concentration in pearite is higher than that in ferrite. OM observaion shows that decarbonization phenomenon occurred near surface of steel after soaking in high temperature experiments, which resulted in an obvious decrease of pearlite amount, so more Cu segregation in grain oundaies and formed Cu–enriched phase, and caused serous surface crazing at last. Hoever, under the educing conditionthe craze crack phenomenon did not occur after soaking

Tube bulge test is one novel method of determining the stress-strain relations of tubular materials, compared with the traditional tension test, which can give better description of the mechanical properties of tube. Based on the ellipstical surface assumption of the middle free bulge region during hydrobulging, the tube hydrobulge process is analyzed first. The main factors that affect the shape of the tube were determined and analyzed. Results show that the length of tube bulge region and the entrance radius of the die are two key factors that determine the profile of the middle free bulge region. When other conditions are fixed, the ratio of the two semi-radii will decrease as the decrease of the initial length of tube bulge region or the increase of the die radius. It means that the profile of the middle free bulge region after hydrobulging will change from long ellipsoid to sphere and then to flat ellipsoid. The stress-strain curves determined by tube bulge test differ for different length of tube bulge region and the entrance radius of the die, but are all lower than that of traditional tension test along axial direction. The smaller the length of tube or the bigger the entrance radii of the die, the bigger is the difference.

In order to mass-produce the clad steel of stainless/carbon steel at low cost, the new clad steel slab continuous casting process, which uses the combination of long and short submerged entry nozzles and electromagnetic brake in the same mold, was developed. The flow field and concentration field of alloying elements in a clad steel continuous casting mold were studied by combination of experiment and mathematical model. The black sesames dipped in water were used to visualize the flow patterns in the mold. The low Reynolds number turbulent model was used to calculate turbulent viscosity, and the fictitious solidified shell was used to simplify the solidification calculation. The effect of clapboard and electromagnetic brake on the flow field was compared. By comparing experiment with systematical numerical analysis, the reliability and reasonableness of the model proposed were verified. Flow structure and concentration characteristics of alloying element in the mold were obtained, and parameteric studies on the nozzle structure and magnetic flux density were also conducted.

Ti–Al–N coatings with different Ti, Al and N contents were deposited on 1Cr18Ni9Ti stainless steel substrate by vacuum cathode arc ion plating (AIP) method and the as–deposited coatings were annealed under different conditions. The compositions and phases in the as–deposited coatings were lso analyzed and compared. The XRD results showed that the composition of the coatings could be controlled by changing the deposition parameters and dstinct Ti₂AlN phase existed in the annealed coatings. The Ti₂AlN phase could not appear unless the annealing temperature reached 650 ℃. The reactions during the annealing process can be descrbed as AlTi₃N+5Al→TiN+2Al₃Ti and AlTi₃N+3Al→Ti₂AlN+Al₃Ti. The content of Ti₂AlN phase increased slightly by extending the annealing time. The surface morphology and composition of he annealed coating were analyzed by SEM and the friction coefficient of the coating was measured.

Ni–Cu–P and Cr–Cu–P steels are well known as sea water resistance steels, but the effects of alloying elements in steels on corrosion resistance are still not clear. Generally, Cr and Ni are important alloying elements for corrosion resistance but their roles in resisting pitting corrosion still need investigating. In order to understand the effects of Cr and Ni on rust layers and resistance against pitting corrosion, Ni–Cu–P and Cr–Cu–P steels were smelted in vacuum induction melting furnace and examined in the laboratory. Pitting susceptibility of two sea water resistance steels was compared by means of potentiodynamic polarization tests in 3% (mass fraction) NaCl solution. In order to evaluate the pitting propagation of steels, the simulating occluded corrosion cell tests and indoor interval hanging plate tests were performed in artificial sea water and 3% sea salt solution, respectively. The composition of inclusions, corrosive feature and characteristic of rust layer were studied by OM, electron probe micro–analyzer (EPMA), SEM and XRD. The results indicate that Ni–Cu–P steels exhibit stronger pitting susceptibility than Cr–Cu–P steels, and pitting susceptibility of two kinds of steels is not influenced by deoxidizing degrees. The results also suggest that pitting propagation rate of Cr–Cu–P steels is obviously greater than that of Ni–Cu–P steels. In acidified pits, alloying element Ni helps to enhance thermodynamic stability of matrix and improve potential of matrix. However, addition of alloying element Cr tends to lower the potential of matrix in pits. The results of rust layer analysis indicate that the compositions of inner rust layer are Fe₃O₄, α–FeOOH and a small amount of amorphous oxides. However, the rust layer of Cr–Cu–P steels is much more compact than that of Ni–Cu–P steels. It can be observed by SEM and EPMA that Cr in Cr–Cu–P steels is enriched in inner rust layer close to the matrix, while Ni is not found enrichment in inner rust layer of Ni–Cu–P steels.

Biological elements have a significant impact on lifetime prediction of marine carbon steel facilities. Microbe can produce pitting, crevice corrosion, selective dealloying and stress–oriented hydrogen–induced cracking, which accelerate both localized and average corrosion rates of carbon steel.
The formation of microbe films can also reduce the corrosion rate of 25 steel through inhibition of oxygen diffusion and depletion of oxygen in the electrolyte and metal/solution interface. The research on the single effect of microbe on the corrosion behaviors of metal is insufficient up to now. In this work, the single effect of microbe on the corrosion behaviors of 25 steel was studied by comparing the corrosion behaviors of the carbon steel in natural seawater and in serile seawater. The results show that in most of mmerging periods, the bacterial activity at the interface accelerated the average corrosion rate of 25 steel. When the corrosion time was 365 d, the average corrosion rate of 25 steel immersed in natural seawater was 2.6 times that in sterile seawater. However, when the corrosion time was 28 d, the biofilms inhibited the corrosion of 25 steel. The species and contents of microbes significantly influenced the corrosion behavior of 25 steel. The microbes in the corrosion product mainly consisted of pseudomonas, vibrio, crenothrixandleptothrix, thiobacillus and sulfate–reducing bacteria. When the corrosion time was 365 d, flavobacterium also existed in the corrosion product. The contents of aerobe, facultative anaerobe and anaerobe reached the maximum vale when the corrosion time was 28, 91 and 184 d, respectively. The regular change of the contents of microbes with the immerging time led to the different microbe corrosion mechanisms of 25 steel.

The selective laser melting (SLM) was used to process the high–energy ball milled Si₃N₄–Ti (mole ratio of 1∶9) nanocomposite powder in which the average grain sizes of Si₃N₄ and Ti were both less than 20 nm. The TiN reinfrced Ti₅Si₃ matrix in situ composites were prepard by means of the synthesis reaction 9Ti+Si₃N₄=4TiN+Ti₅Si₃ . s the milling time increased, thaverge particle size of te milled Si₃N₄–Ti composite powder decreased and the resultant specific surface area increased. The densification level of laser processed TiN–Ti₅Si₃  composites increased accordingly to 97.2%. The morphologies of TiN reinforcing phase in the corresponding SLM processed structures experienced a successive change from a poly–angular shape to a near–spherical shape and finally to a dendritic shape.