Split superlattice reflections are detected in Fe-1 .83C martensite aged at room temperature, indicating the existence of long-period ordered phase. The long-period phase is superperiod of 10 c_M(c_M being the length of c axis of martensite), it is named as γ′-FexC(Ⅱ). For the first time it is found that the superperiod of this long-period phase increases with the increase of temperature, but does not change with aging time. It is also found that the superperiod calculated from the split distance of superlattice spots is not an integral multiple of C_M This is an indication of the coexistence of three long-period ordered phases with superperiod of 10 c_M 12 and 14 c_M, respectively, the interference of diffraction beams from them results in the non-integrality of the split distance of superlattice spots.The calculated intensities of the superlattice reflections are in good agreement with experimental observations. It is suggested that the existence of long-period ordered phase is a result of minimization of lattice distortion energy. The relationship betweenγ′-FexC(Ⅰ) and γ′-Fex C(Ⅱ) is also discussed.

TEM is used to study the interface structure and the thickening kinetics of bainitic ferrite during isothermal transformation of an Fe-30wt-%Ni alloy with the hot stage. It is demonstrated that ferrite possesses ledge morphology with [111]b dislocations at the ferrite/austenite ledge interface. The experimentally measured ferrite thickening rate is shown to be of the same order with those calculated according to Zener-Hillert equation developed for the growth kinetics of ferrite controlled by the volume diffussion of carbon in austenite. All of the results are considered to be support for the ledge growth mechanism for the bainitic ferrite.

Associated with the molecular statics relaxation method，a computer modelling technique was provided for the study of structural characteristics of nanocrystals．By using Fe as a model material，various structural features of a nanocrystal have been studied,and the influences of various factors on the structure have also been discussed．Simulation results indicate that the structure of grain boundaries in nanocrystals is different from those of the amorphous and the gas，or rather，it is a special structure with some degree of short-range order．Morever，the atomic structure of the crystallites is not entirely the same as that in the perfect crystal lattice.

The effect of Sc on microstructure and tensile properties of Al-Li-Cu-Mg-Zr alloy has been studied. The results show that the δ′(Al3Li) and S′(Al_2CuMg) are main strengthening phases in the alloys-Addition of Sc may refine the grain size, reduce the coarsening rate of δ′particles and accelerate the precipitation and uniform distribution of S′phase obviously. Al_3Sc particles and composite Al_3Li / Al_3Sc particles precipitate in the Sc-containing alloys, they are beneficial to the improvement of properties. So,the Sc significantly increases the strength of the alloy, and results in superior combinations of strength and ductility.

The in situ tensile test under TEM for thin foil specimen of brass showed that a lot of dislocations could be emitted from a loaded crack tip and a dislocation free zone(DFZ) could form after reaching equilibrium. The DFZ was a nonlinearly elastic zone with large strain(ε≈0. 1) and the stress in the DFZ might equal to the cohesive strength σ_(th) when the crack tip was sharp enough and an applied stress was large enough. As a result, a nanocrack initiated discontinuously in the DFZ or sometimes at a blunted-crack tip. As soon as the nanocrack nucleated, it would quickly blunt into a void even under keeping constant displacement.

An investigation was made on the high temperature creep and fracture behaviour tested in air and in mixed salt(10% NaCl+90%Na2SO4) environment for both single crystal Ni-base superalloy DD3 without or with Pt-Al coatings. The results show that in mixed salt, Pt-Al coating can improve creep-rupture life, however, in air, no effect on the creep-rupture properties of DD3 at elevated temperature: the creep strength of DD3 would drop suddenly in hot corrosion environment; and owing to the interaction betwween creep and hot corrosion, the formation of corrosion products leads to premature failure of the superalloy. A new fracture model is proposed to explain the creep fracture behaviour of superalloy DD3 at elevated temperatures.

The fracture behaviour of cast irons with graphite irregularity S＝0 and spheroidal graphite iron under three different stress modes was investigated．When the crack was parallel or vertical to the graphite flakes，it would be developed along inside the graphite flakes，i, e the cleavage of(0001) plane of graphite flakes，or propagated along the matrix/graphite interface，i, e decohension between graphite flake and matrix respectively．In the case of spheroidal graphite cast iron with ferrite-bainite matrix，the crack would propagate mainly in ferrite and secondary graphite.

A random fractal model for the crack propagation of free-machining steelsduring impacting transversely was proposed. The random fractal dimension for impact fracture surface was then calculated. And self-similar fractal dimension was also analysed. Experimental measurement is fair agreement with that of random fractal model proposed.