The morphological evolution and its regularity of γ'  precipitates in the low mismatch alloys powder metallurgy (P/M) FGH98I and FGH96 under different heat treatment conditions were studied systematically. The results show that the morphological instability of γ'  phase can be summarized as the splitting and unstable protrusion. The splitting of γ'  phase is caused by the interaction of anisotropic elastic strain field between γ'  phase and $\gamma$ matrix which is rich in solute atoms. While the irregular morphology of unstabe protrusion is mainly due to the concentration changes of solute atoms in the matrix or in the local places along grain boundaries, leading to the non-equilibrium growth of γ'  phase. The coexist phenomenon of splitting and unstable protrusion, the formation mechanism of fan type structure induced by discontinous precipitation are discussed respectively.

The microstructure and mechanical properties in simulate fusion line of EH40 ship plate steel with high heat inputs were investigated using welding thermal simulation test. The effects of inclusions on the grain size of original austenite and intragranular ferrite (IGF) were analyzed. The results indicate that impact energy of the steels at -20 ℃ was more than 150 J with a heat input of 800 kJ/cm (t_8/5=730 s) and maximum temperature of 1400 ℃ for 30 s. The microstructures of the steel were composed of GBF, IPF and IAF, and the fraction of IAF was over 50%. Lath bainite and granular bainite were not observed. The type and concentration of inclusions were ideal which decreased the growth of GBF. Those inclusions whose diameter were 5-8 μm can also promote the formation of IGF, and sometimes IAF was also formed through the nucleation at Mn-depleted zone.

γ→α transformation is one of the most common and important reactions in steels. Lots of previous experimental researches have already evidenced that hot deformation could refine ferrite grains and remarkably improve strength and toughness of low carbon alloy steels, but relevant theoretical researches, especially quantitative descriptions still need deepening. This work, taking a Fe-0.2C-2Mn alloy as research object, investigated the effect of hot deformation on austenite→pro-eutectoid ferrite transformation by means of both thermo-mechanical experiments and theoretical analyses, in an attempt to provide theoretical basis for further grain refinement in low carbon alloy steels. OM observations showed that finer ferrite grains formed with the increase of strain and decrease of deformation temperature, and hot deformation altered the morphology of pro-eutectoid ferrite; Based on Pillbox model and parabolic growth model, grain boundary nucleation rate and parabolic growth constant were calculated respectively under hot deformation condition, both of which were demonstrated to be accelerated by deformation. Under NPLE mode, ferrite nucleation was enhanced by deformation mainly due to the increase of diffusivity and number of nucleation sites, whereas contribution of stored deformation energy to driving force played a key role under PLE mode. A comparison was made between the strengthening effect of deformation on ferrite nucleation and growth, showing that nucleation was accelerated more significantly at most temperature ranges. Thus the grain refinement mechanism of hot deformation was quantitatively explained.

The effects of N₂ partial pressure on the depth distribution
of residual stresses and mechanical properties in the (Ti, Al)N coatings
prepared by arc ion plating (AIP), were investigated. The results indicate
that the stress distribution was roughly uniform when the coatings were
deposited under lower NN₂ partial pressure. As the partial pressure
increased the stress distribution to exhibited a “bell” shape and the
average stresses of coatings increased remarkably. The mechanism of
stress distribution was analyzed by characterizing the microstructure and
the composition of the coating. The N₂ partial pressure also affected the
hardness of coatings and the coating/substrate adhesion obviously. The
higher the N₂ partial pressure is, the higher the coating hardness but
the lower the adhesion. The stress distribution can be modified and the
adhesion of the coating/substrate can be improved by optimizing N₂ partial
pressure parameter. Finally, the coatings with the thickness over 130 μm
were successfully directly deposited on the substrate through optimizing
the N₂ partial pressure.

DLC films with dispersed high crystallinity CrN nanoparticles were prepared by high power pulsed magnetron discharge plasma ion implantation & deposition (HPPMS-PIID) combined with DC magnetron sputtering (DCMS). The surface morphology, structure and properties of CrN--DLC films with the different currents of C target were studied. The results show that the C content increases as the raise of the current of the C target and clear characteristics of DLC films are found at a higher C content. CrN doped in DLC exists as nanoparticles with highly 200 preferred orientation, and the smallest size of the CrN grains is 42.39 nm. The C1s peak primarily consists of the three peaks that correspond to C-sp², C-sp³ and CN-sp³, and the ratio of total sp³ to sp² is 44.8%. Excellent adhesion between film and substrate with critical load of 66.8 N and high nanohardness up to 24.3 GPa are achieved due to highly energetic ion bombardment and implantation in HPPMS-PIID.

An Al-Ni-Y-Co amorphous and nanocrystalline composite coating was prepared on the surface of the AZ91 Mg alloy by using an automatic high velocity arc spraying system. Its microstructures were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The results show that the coatings compose of amorphous, nanocrystalline and microcrystalline phases, which has a compact structure with low porosity about 1.8%. The average Vickers microhardness and bond strength of this coating are 311.7 HV_0.1 and 26.8 MPa. Its relative wear resistance is about 10 times than that of Al coating and 6 times than that of AZ91 magnesium alloy. The corrosion potential of this coating is more positive than that of Al coating and AZ91 magnesium alloy, and the corresponding corrosion current density value is about 1/2 the same as that of Al coating and 1/5 as that of AZ91 Mg alloy. Especially, compared with the surface on corroded Al coating and AZ91 Mg alloy, the corroded Al-Ni-Y-Co coating has a more flattered surface with less corrosive piting than Al coating. It is confirmed that the Al-Ni-Y-Co coating is an excellent coatinig with higher wear-resistance and\linebreak corrosion resistance.

Five ferrite/bainite (F/B) dual-phase steels with the chemistry of low carbon, high manganese and high niobium, and different volume fractions of bainite (15%-98%) were produced by control rolling+relaxing+ACC processing. With the help of the modified Crussard-Jaoul (C-J) analysis, the effects of soft phase (ferrite) content and its grain size on the work--hardening behavior of the steels and the cooperative deformation relationship between softer phase and harder phase were studied, which was validated by EBSD analysis. The results illustrate that a reasonable proportion of F/B can be helpful to improve initial work-hardening (a high R_t1.5/R_t0.5), reduce the yield ratio, and maintain a high uniform elongation. It is known that the cooperative deformation of ferrite and bainite is the main mechanism for improving the stress ratio and the uniform elongation of the F/B dual-phase steels.

Columnar grains commonly exist in the cast slabs of Fe-3%Si electrical steels and exert, due to their topographic and crystallographic anisotropies, strong influence on the microstructure and texture during following hot-rolling, cold-rolling and annealing. Based on the previous paper addressing the cold-rolling texture evolution in the electrical steels with different alignments of columnar grains, this work illustrates further the recrystallization texture evolution at different annealing temperatures by means of XRD and EBSD techniques. The results show that the recrystallization texture evolution represents, on the one hand, the ‘heritage’ of the initial orientations, concerning the formation of cube and Goss texture. On the other hand, specific features are determined from different types of recrystallized columnar grains specimens, namely, the formation of the {113} texture, the more significant growth of Goss grains than that of cube grains in RD specimens (with initial columnar grains' longitudinal axis being along rolling direction) and the vanishing of {110}<110> grains in TD specimens, which have been scarcely reported in single crystals or in polycrystalline bcc materials composed of equiaxed grains. The dissimilar recrystallization environments lead to distinct evolution of cube texture at various annealing temperature, and the highest intensity of cube texture at low annealing temperature in TD specimen is believed to be related with the strong effect of transverse directional alignments of columnar grain boundaries. Regarding the cube and Goss recrystallization textures, their formation can be explained in terms of the theories of both oriented nucleation and oriented growth. In addition, this study also confirms that {111} texture can be suppressed effectively in the columnar grain specimens after cold--rolling at intermediate reduction and annealing.

The effect of electromigration (EM) on the interfacial reaction in Ni/Sn3.0Ag0.5Cu/Cu solder joints was investigated under a current density of 5.0×10³ A/cm² at 150 ℃. All solder joints were aged at 150 ℃ for comparison purpose. It has been found that the (Cu, Ni)₆Sn₅ intermetallic compounds (IMCs) form at both solder/Ni and solder/Cu interfaces in the as-reflowed state. During aging at 150 ℃, the thickness of interfacial IMC increases with increasing aging time, and no interfacial IMC transformation occurs even after aging for 800 h. The flowing direction of electrons plays an important role in Cu consumption. When electrons flow from printed circuit board (PCB) to chip, the current crowding effect induces a rapid and localized dissolution of Cu pad on PCB and a formation of microcrack at the Sn3.0Ag0.5Cu/(Cu, Ni)₆Sn₅ interface. The dissolved Cu atoms are driven towards anode by EM, and a large amount of Cu₆Sn₅ IMC particles form in solder matrix along the flowing direction of electrons. When electrons flow from chip to PCB, no obvious consumption of Ni underbump metallogy (UBM) has been observed and few Cu₆Sn₅ IMC particles form in solder matrix near the anode interface. There is no evidence of failure induced by EM in solder joints even after EM for 800 h. To sum up, EM enhances the growth of interfacial (Cu, Ni)₆Sn₅ at anode side, no matter how the direction of electrons is. The interfacial IMC at anode side is thicker than that at cathode side. The Ni/Sn3.0Ag0.5Cu/Cu solder joint is prone to fail when electrons flowing from Cu to Ni.

Porous copper with long cylindrical pores has been fabricated by unidirectional solidification of metal-gas eutectic system, which can be used to manufacture a special kind of micro-channel heat sink. The heat transfer performance of the directionally solidified porous copper heat sink with a length of 20 mm along the axial direction of pores was studied. The experimental results show that the directionally solidified porous copper heat sink has excellent heat transfer performance and a heat transfer coefficient of 5 W/(cm²·K) is attainable when a porosity is 29% and mean pore diameter is\linebreak 400 μm, and it shows a larger heat transfer coefficient of 6.5 W/(cm²·K) after cutting the porous copper along the vertical direction of pore axis into two sections alined in the direction of pore axis. Increasing the length of porous copper heat sink along the direction of pore axis will reduce the penetration ratio of pores and then weaken the heat transfer performance of the heat sink. Thus some methods have to be taken to increase the pore length and ratio of penetrating pores when fabricating directionally solidified porous copper heat sink.

Advanced NV-F690 heavy steel plates for offshore structure and shipbuilding have been produced via continuous casting of the slab, thermomechanical control rolling of the plate followed by solutionizing (austenitizing), quenching and tempering (QT) steps. The present work is to reveal the microstructure evolution and evaluate the mechanical properties of 80 mm thick plates subjected to the QT process. The microstructures were characterized with SEM, EBSD and TEM. At quarter thickness ($t$/4) where the cooling rate was rapid, the as quenched microstructures consist of mainly lath--like bainite (LB), between the laths exist fine martensite/austenite (M/A) constituents. At center thickness (t/2), the as quenched microstructures consist of granular bainite (GB)+dislocated LB. The fraction of high angle grain boundary (HAGB) at t/4 of the quenched plate is 67.5% while that at t/2 is 63.0%. After tempering at 650 ℃ for 150 min, the average width of the laths is 0.2 μm at t/4 and\linebreak 0.4 μm at t/2. Cell structures with high misorientations exist in the tempered LB at t/4 while these are absent at t/2. The fraction of HAGB is increased to 71.7% at t/4 while that at t/2 is not significantly changed. Profuse Cu precipitation occurs and the M/A constituents decompose into Cr-Mo containing carbides during tempering. Ductile fracture behaviour is observed even at -80 ℃ at both t/2 and t/4 of the 80 mm thick NV-F690 plate treated by the QT process. The impact toughness at t/4 is higher than that at t/2 due to the predominance of finer LB and higher fraction of HAGB. With the increase of the displacement of the ductile crack propagation, the area with dimples and the size of the dimples increase leading to increased Charpy impact absorbed energy of the NV-F690 plate\linebreak at -80 ℃.

The influence of aging on the hardenability of 7055 aluminum alloy thick plate was investigated by means of end-quench test, optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results show that the hardenability can be improved by long time natural aging before artificial aging. The hardened depth is about 78 mm after natural aging and only about 45 mm after artificial aging, but increased to be about 100 mm after natural and artificial aging. During slow quenching, the coarse η equilibrium phase forms, and the solute concentration and vacancy concentration are decreased, which lead to larger and fewer η' hardening precipitates, thus lower hardness after aging. The long time natural aging before artificial aging is favorable for formation of stable GP zones at slowly-cooled locations, and consequently more amount of dispersed and fine η'  hardening precipitates, which give rise to higher hardness and simultaneously better hardenability.

The effect of heating temperature and holding time on the phase transformation from (Fe, Mn)Al₆ to α-Al₁₂(Fe, Mn)₃Si in AA3104 aluminum alloy during homogenization was studied by BSE and EDS in SEM. The 3D morphology of the eutectic phases heated at 600 ℃ for different holding times was reconstructed by a novel serial sectioning method. Evolution of the microstructure could be revealed in 3D for the first time. Al spots were observed within the α-Al₁₂(Fe, Mn)₃Si phase and counted during different transformation stages. Large number of Al spots disappeared by diffusing into the neighboring matrix after extended heating times, while the volume of the α phase was also decreased at the same time. The microstructure of the α phase after transformation was analyzed, showing ‘duplex interfaces’created by partly transformed particles. The dense holes within α phase particles are believed to promote particle break up during hot rolling of the omogenized material.

The effect of inhomogeneous deformation on twinning behavior during uniaxial compression of AZ31 magnesium alloy at room temperature was investigated with electron backscattered diffraction (EBSD technique. The evolution of twin area fraction in three locations, typical of a dead zone, an easy zone and a free zone with strain was analyzed. The results show that the twin area fractions at the locations in dead zone, easy zone and free zone are different at compression strains less than 8\%. As compression strain reaches 8%, the area fraction of extension twins at these three locations is almost the same, and is about 90\%. Inhomogeneous deformation exerts much effect on the twin area fraction at the locations in the three zones at low strains while exerts little effect at high strains. Twin variant selection in the three zones at 2% strain was also analyzed. The results show that the twin variant activation is governed by the Schmid factor criterion in all the three zones. However, the percentage of grains with two twin variant types in free zone is higher than that in dead zone and easy zone, due to the different stress states in this location.

A microstructure model was established for simulating the microstructure evolution during casting, solid solution and aging process of magnesium alloy casting based on the modified cellular automaton (CA) model. A mechanical property model taking into account the second phase precipitation and strengthening mechanism was developed for Mg-Al alloy. The established models were applied to simulate the microstructure evolution and predict the mechanical properties of a magnesium alloy automobile wheel casting. The results show that the predicted tensile strength is in good agreement with the average measurements, and the predicted yield strength is in good  agreement with the average measurements under as-cast and solid solution state, while there are some discrepancies between the predicted and measured yield strengths under aging state.

The influence of Zn content on the microstructure evolution, texture and mechanical properties of indirect-extruded Mg-8wt.%Sn-Zn alloys have been investigated by OM, SEM, TEM, EBSD, XRD and a standard universal testing machine. The studied alloys were demonstrated to be extrudable at a relatively low temperature (250℃) and a high extrusion speed (2 m/min). During the extrusion process, most of the remained second phase particles present in the homogenized alloy are found to be aligned along the extrusion direction (ED) in the form of stringers after being broken into fragments during the extrusion process. While most of the coarse grains were changed into fine equiaxed grains with average sizes ranging from 10.5 μm to 7.4 μm. The volume fractions of the second phase particles increase with increasing Zn content while the grain size and texture strength decrease with increasing Zn content. These second phase particles are mainly composed of Mg2Sn, having a diameter of submicron and some nano-meter Zn-rich phases. Furthermore, the decrease in grain size can be explained by the Zener drag of fine particles. While, the textural weakening with Zn addition is associated with the decreased fraction of elongated grains retain strong fiber texture. The improvement in strength and reduction in yield asymmetry of the studied alloy were associated with finer grain size, higher fraction of second phase and weaker texture.

The Ti powder forming is more difficult through traditional pressing methods due to inductile and high hardening rate of Ti. Some advanced forming methods, although, are effective for increasing the green density, such as hot--pressing and isothermal--statistic pressing, they are too expensive. In our previous research, it has been demonstrated that compacting high green density of Ti powders would be achieved by high velocity compaction (HVC) which seems to be an attractive candidate that has an excellent balance between performance and cost in forming Ti powders. In this paper, the four Ti powders with average particle size of 150, 75, 48 and 38 μm, namely A, B, C, and D powder, were separately pressed by HVC technology. The influences of particle size on the green density, the maximum impact force and withdraw force in compacting were investigated. The compactability features of the four powders in HVC and the properties of sintered samples were studied. The results show that the green density of compacts obtained by HVC method is related with both particle size and apparent density. At relatively small impact energy, the green density of compacts is mainly determined by the apparent density of powders. While at larger impact energy, it is mainly determined by the particle size. For powders pressed at impact energy lower than 761 J, the highest green density is obtained for compacts made of B powders which has maximum apparent density. With higher impact energy, the highest green density is obtained for compacts made of A powder which has maximum particle size. It is found that the influence of particle size on the maximum impact force is similar to those on the green density, and for the four powders the relationships between the maximum impact force and the green density all comply with Huang Pei-yun equation. Particle size shows no observable influence on withdraw force. The sintered density increases with decreasing particle size of powders, accompanying with grain growth of different degrees. After vacuum sintering at 1250 ℃, nearly fully dense samples can be prepared for the compacts of four powders.