Many crystalline solids fail by cleavage at low temperatures. and by plastic processes at high temperatures. In the transition region cleavage failure occurs at stresses increasing with increasing temperature. reflecting a decrease in yield stress. and a consequent increase of plasticity around the crack tip. Crack tip plasticity blunts the crack and shields it through compressive stresses in the plastic zone. This paper gives a brief review of a model of the brittle-ductile transition in which the shielding is calculated from a plastic zone formed by the generation (from a source). motion and interaction of dislocations moving on a slip plane containing the crack tip. and obeying a velocity/stress/temperature law. The application of the model to experiments is discussed.

Elemental mapping with a high spatial resolution is indispensable to characterization of the nanoscale microstructure in the research of materials science. In the present paper, Gatan Model 678 Imaging Filter, which has been attached to HF-2000 FEG TEM, has been employed to study the microstructures at namometer scale in several materials.

Fine structure of bainite, morphology and distribution of carbide in steels and morphology of bainite in Cu-Zn-Al alloy have been investigated with TEM. Interfacial structure ledges and interfacial lattice images of Cu-Zn-Al alloy have also been observed with HREM. Addition of minor alloying elements can fine the structure of bainitic ferrite markedly. The bainitic ferrite is composed of subunits or subchunks. The carbides with different morphologies are distributed between the laths. inside the plates and at the boundaries of subunits. There are abundant fine structures in bainitic ferrite. In the primary bainite of Cu-Zn-Al alloy there are interfacial structure ledges. whose heights are within 3-40 nm.corresponding to 15-200 atomic layers. The phase reaction mechanism of bainite is discussed in this article.

Al-Si-Fe-Cu-Ma alloy has been produced with spray deposition technology.The microstructures of the alloys under spray deposited, extruted and T6 heat treated conditions have been investigated. The mechanical properties at room temperature and 200° have been measured. The strenghening and fracture mechanisms of the alloy have been put forward.

In order to investigate the modified effects the specific conductivities of Al-Si-Mg alloys added by Sb, Sr and RE elements were measured respectively. The results show that the specific conductivities of alloys modified by Sb and Sr have high values, while the specific conductivity of alloy modified by RE displays low values and that the farther the distances from the bottom of the ingots, the smaller the specific conductivities of the Sb or Sr modified alloys are. It is indicated that solid solution treatment at 535℃ increases the specific conductivity of the unmodified alloy, but decreases the values of the Sb or Sr modified alloy and the higher the specific conductivity, the higher the impact toughness of the ingots is.

The alloying behavioUrs of Mg, Ca, Y, La and Ce in Ni3Al have been determined by X-ray diffraction measurement. It is found that Mg, Ca, Y, La and Ce atoms occupy the Al site in the L12structure. Besides, the additive atoms can further increase the long-range order degree for Ni3Al and this increment becomes more pronounced in the sequence of Mg, Ca, Y(La-Ce). Finally, the lattice parameters of the Ni3Al alloys with the alloy additions have also been determined. It is found that the lattice parameters of Ni3Al increase linearly with increasing elemental content. and this increment becomes more pronounced in the sequence of Ma, Ca. Y, La-Ce.

The deformation and fracture characteristics of nickel-base single crystal superalloys at high temperatures, which are in plates with different thickness and in different crystallographic orientations, have been studied. The macro-results show that the thickness effects are dependent on the test temperature. The strength increases with decreasing thickness at 1000℃, while the strength increases with increasing thickness below 950℃. At 1000℃, the dependence of strength on crystallographic orientation is not distinct. The micro-results show that [001] plate specimens at 1000℃ are in void-related ductile fracture model, and the rest specimens are in micro-face fracture model. And it is confirmed that the microface are crystallographic slip plane, and voids on the faces have important effects on the fracture.

The crystal defects and the recovery behaviour in quenched and deformed Fe-Cr-Ni austenite alloys were investigated by the methods of positron lifetime and Doppler line shape measurement. The mechanism of defects recovery and their interaction were discussed. The process of dynamic interaction between vacancy-type defects and the impurity atoms was also discussed according to the changes of the positron lifetimes.

Single-edge-notched tension (SENT) specimens under constant load amplitude were used to obtain the small crack growth information via an acetate replica method. The observed results show that more cracks are surface ones and initiated at inclusion-particles or voids on the surface of the notch. Steel 30CrMnSiNi2A does not exhibit a significant short crack effect when stress ratio R=0. But a slight small crack effect was observed at R=-1, and the short cracks can grow below the long crack threshold. Using the closure crack growth model and a microstructural defect as an initial crack, the small crack growth rate and the total fatigue life can be predicted and the predicted results are in reasonable agreement with experiments.

Studies were made on the nucleation of creep cavities and propagation of creep cracks in steel 20Cr11MoVNbNB at 550-650℃. Results show that creep cavities are mainly nucleated at the big particles of undissolved Nb (C, N) and M23C6 carbides, both of which exist at prior austenite grain boundaries and lath martensite boundaries. It is also found that creep creacks crossed the prior austenite grain boundaries and lath martensite boundaries along the direction normal to applied stress, propagated into the grains, and finally leaded to the transgranular fracture.

In situ TEM tensile experiments show that the principal reason for the poor ductility at room temperature of TiAl base alloys with lamellar structure is the lack of slip systems, eventhough (1/2)＜110] ordinary dislocations exhibit good mobility and (1/6)＜112] deformation twinning is activited in some γ-lamella phase. The key to improve the room temperature ductility of TiAl base alloy is to operate other slip systems apart from (1/2)＜110]{111).

The fracture behaviour of weld metal of ferrite-austenite duplex stainless steel was investigated by constant deformation rate tensile test. It is shown that the origin of cracking relates with hydrogen and oxide inclusions in the weld metal. The propagation of cracks is a discontinuous process, the fracture appearance is different in each stage. The γ-phase resists the advance of cracks, and γ sheet within δ grains often forms tearing ridge, the γ-phase between δ grains often forms dimples. Transgranular cleavage fracture is more easily formed in the weld metal with higher hydrogen and nitrogen content.

The behaviours of intergranular corrosion on the rolled 316L and cast 317L implant stainless steels were studied by using SEM in the process of corrosion fatigue in Hank physiological solution. It was concluded that the initial fatigue cracks engender at the corroded granular boundaries and propagate along intergranule first and then transgranule under the fatigue stress. The intergranular corrosion is not due to the chrome-deficiency induced by the precipitation of carbide at the granular boundary but due to non-sensitized intergranular corrosion.

The variations of displacement field and strain field around notch tip of brass specimen during stress corrosion crack in 1mol/L NH4OH+5g/L CuC12 solution were investigated by the laser moire interferometry method. The results indicate that the anodic dissolution (corrosion) increases the plastic zone around notch tip of specimen and the plastic deformation amounts of the various points in plastic zone i.e. the anodic dissolution can facilitate the local plastic deformation around the notch tip of specimen.

The plasma sprayed coating zone (Ni-Cr-B-Si) on an Al-Si alloy surface was remelted by a 5 kW CO2 laser. SEM and TEM analysis showed that there is crystalline and amorphous coexistent region. As the annealing effects caused by heat transfer of following melt and latent heat of crystallizing, some Ni3Al nano-crystallites (2-5 nm) formed and some of them grew gradually into globular grains (0. 1-0.2μm). The hardness in amorphous region is up to HV 1235 which is 3 times as high as that of plasma sprayed coating zone.

Si3N4 thin film has been deposited on the matrixes of carbon steels, alloy structure steels, speed steels and stainless steels by using a direct current plasma chemical vapor deposition (DC-PCVD) device under controlling processing parameters. Component,structure, morphology and hardness of the film were measured. This thin film consists mainly of the component of Si3N4 with amorphous structure.

The superplasticity behaviours of Ni3Al alloy with 10-30 pm grain sizes were investigated. The superplastic flow with a maximum elongation of 256% and strain rate sensitivity of 0.3 to 0.7 were observed at temperature range from 900 to 1100℃ and initial rate 2.1 ×10-4 s-1. As combined with optical and TEM observations, it is suggested that a continuous recovery and recrystallization process took place and superplasticity may arise from this process.

According to the corrected macro-dynamics data of irradiation process by using low-voltage mercury lamp with monochromatic 254 nm, the formation reaction of Cu2O ultrafines in a liquid environment is regarded approximately as one-order reaction. Comparing macro-dynamics of ultraviolet radiation with those of γ-Ray radiation from 60Co and high energy γ-Ray radiation translated from the electron beam in the 200 MeV linac of the synchroton facility, it is well known that there are some resemblances among those processes,i.e. The preparing process of Cu2O ultrafines by using ultraviolet radiation in a liquid environment contains both the photochemical effect and the reductive effect of solvated electron produced by ultraviolet radiation. The latter is similar to that of solvated electron produced by γ-Ray radiation.