Microstructures and crystallographic features in low temperature brittle fracture of 18Cr-18Mn-0.7N high nitrogen bearing austenitic steel were investigated by means of scanning electronic microscopy. The results showed that there are three kinds of fracture facets on the fracture surface: annealing twin boundary fracture facet, intergranular fracture facet and transgranular fracture facet. Annealing twin boundary facture facet is one of planar and smooth {111} planes, with bent steps on it, and the planar deformations proceeding on the other three sets of {111} planes form a pattern of three sets of straight-lines intersected at 60º on the annealing twin boundary facet. Intergranular facture facet is a kind of smoothly curved facet on which the planar deformations proceeding on {111} planes form a pattern of several sets of curved parallel lines that intersect each other at different angles. Transgranular facture facet is rough and uneven, with steps parallel to {111} plane and river patterns or edge patterns on it, which is the consequence of coalescence of cracks propagating on different {111} planes.

Grain boundary character distributions (GBCD) of type 304 stainless steel, which was strained by cold rolling and then annealed at 1173K, were analyzed by electron back scatter diffraction (EBSD). The results showed that low strain (~6%) followed by long-time annealing (24h~96h) resulted in a GBCD containing a higher fraction of ∑3n (n=1,2,3) boundaries (special boundaries), in which the connectivity of general high angle grain boundary (HAB) network was interrupted significantly by ∑9 and ∑27 segments. Incoherent and coherent 3 boundaries were identified by single-section trace analysis method, which showed that the major part of 3 boundaries were incoherent ones in the optimized GBCD. Further discussion pointed out that the migration and interaction of incoherent ∑3 boundaries might be the mechanism of twin-induced GBCD optimization.

The stress-strain relations of nanocrystalline twin copper with different size grains and twins are studied by using FEM simulations based on the conventional theory of mechanism-based strain gradient plasticity (CMSG). The concept of twin lamellae strengthening zone is proposed in our analysis with a cohesive interface model to simulate grain-boundary sliding and separation. Roles of many material parameters affecting stress-strain curves of polycrystalline twin copper are studied in detail. Furthermore, the effects of both twin lamellar spacing and twin lamellar distribution on the stress-strain relations are investigated under tension loading. The numerical simulations show that: both the strain gradient effect and the material hardening increase with decreasing the grain size and twin lamellar spacing. The distributions of twin lamellae have a significant influence on the general mechanical properties, and the effect will become into small with decreasing the grain and twin lamellar spacing. Finally, the prediction results of FEM are compared with the data of several experiments.

Impact properties of casting Al-0.63wt.%Cu and Al-3.9wt.%Cu alloys subjected to equal channel angular pressing (ECAP) were investigated. It is found that the impact properties of Al-0.63wt.%Cu alloy were enhanced after ECAP. While for Al-3.9wt.%Cu alloy, its impact toughness was not improved, although the tensile strength increased as a result of grain refinement and second-phase dispersion. It is shown that the impact toughness is dependent on the static toughness of the Al-Cu alloys.

Band-like microstructures were observed in directionally solidified Cu-1.0%Cr hypoeutectic alloy at the growth rate ranging from 2m/s to 10m/s and the temperature gradient of 200K/cm in liquid. There are three kinds of band-like microstructures, which are the planar interface plus coupled eutectic, the planar interface plus cellular structure with the growth of coupled eutectic, and cellular interface structure plus coupled eutectic, respectively. The formation mechanism of band-like microstructures has been illustrated by discussing the solute distribution ahead of solid-liquid interface in which the growth rate and alloy composition are changed at the non-steady state in directional solidification. In addition, the density difference between Cu phase and Cr phase is also an available factor to cause the formation of band-like microstructures in directionally solidified Cu-1.0%Cr hypoeutectic alloy.

The corrosion behavior of three Fe-Cr alloys has been examined at 700oC in reducing atmospheres containing constant HCl and two different levels of H2S. Except for Fe-18Cr in the low-H2S gas mixture, in all cases the scales consisted of an outermost porous layer of iron oxides overlaying an inner layer of a mixture of the Fe and Cr oxides and the Fe-Cr spinel plus a zone of internal attack rich in oxygen with little sulfur. An increase of the H2S level in gas mixtures produced an accelerated corrosion for all Fe-Cr alloys, particular for Fe-18Cr. An increase of the Cr content induced the decrease of the corrosion rate in two gas mixtures. The accelerated corrosion induced by sulfur and chlorine is mainly due to the formation of sulfides and chlorides in the scales. The equilibrium partial pressures of chlorine, oxygen and sulfur of the mixed gases were calculated to estimate the possible reactions between the alloy components with the multi-reactant atmosphere and to interpret their corrosion behaviors.

Hot compression tests of TC11 titanium alloy with equiaxed starting microstructure were conducted by using the Thermecmastor-Z hot working simulator. Microstructural deformation mechanisms and the manifestations of flow instability were investigated by means of processing map’ technology based on Murty criterion, and deformation thermomechanical parameters were optimized in the temperature range 990℃～1008℃ and strain rate range 0.001 s-1～70s-1. The results showed that，in phase，the desired deformation thermomechanical parameters were in 990℃～1008℃ and 0.001 s-1～0.02 s-1 with the deformation mechanism of superplasticity，and the optimum deformation thermomechanical parameters were in the order of 990℃ and 0.001 s-1.In phase，the desired deformation thermomechanical parameters were in 1030℃～1080℃ and 0.001 s-1～0.1 s-1 at the strains below 0.6 and in 1020℃～1060℃ and 0.004s-1～0.6 s-1 at the strains beyond 0.6，both of the two regions underwent dynamic recrystallization，and the corresponding optimum deformation thermomechanical parameters were respectively in 1060℃～1080℃and 0.001 s-1 , 1040℃～1050℃ and 0.016 s-1～0.07 s-1. The region of flow instability occurred in the temperature range 1000℃～1080℃and strain rate 4.0 s-1～70 s-1 in phase，and the manifestations of flow instability is non-uniform deformation of grains. In phase , dynamic growth of grains would occur approximately at the strain rate of 0.001 s-1.

Abstract The creep rupture strength, creep damage and characteristics of interfacial failure of dissimilar welded joint between martensite (9Cr1MoVNbN) and bainite steel(12Cr2MoWVTiB) are been investigated by means of argon gas shielded tungsten pulsed arc welding, high temperature accelerated simulation, creep rupture test, in view of dissimilar welded joint between martensite (9Cr1MoVNbN) and bainite steel(12Cr2MoWVTiB).The research results indicate that the interfacial creep damage of undermatching welded joint is very serious, and the interfacial failure occurred, the early failure tendencies are higher than those of overmatching and medium welded joint. The creep damage and early failure tendency of medium matched joint are lower than those of overmatching and undermatching welded joint, and only isolated holes are found in the test. The creep rupture strength ( ) of medium matching joint is almost the same as that of undermatching joint. The creep rupture strength overmatching joint is the least one, therefore, it is reasonable that the medium matched is used for the dissimilar welded joint between martensite and bainite steel. KEY WORDS Martensite heat-resistant steel, bainite heat-resistant steel, dissimilar metal welding joint, creep damage, early failure

A Sol-Gel method was applied to fabricate SiO2 coating on the surface of carbon fibre. By controlling the component of the Sol, the dipping speed, the heating and sintering processes, a crack-free SiO2 coating was obtained. SEM and XPS were used to characterize the structure, morphology and elemental distribution of SiO2 coating, also the interface between carbon fibre and magnesium matrix was characterized by TEM. The oxidation resistance and mechanical properties of carbon fibre with and without SiO2 coating were investigated, the results showed that SiO2 coating enhanced the oxidation resistance ability of carbon fibre, and also SiO2 coating had little influence on its mechanical properties. However, the tensile strength of coated carbon fibre had degraded to 80% after embedded in Mg matrix. Carbon fibre reinforced Mg-based (Cf/Mg) composite was fabricated by gas pressure infiltration process and the results indicated that SiO2 coating could effectively promote the wetting between the molten Mg and carbon fibre.

By using a seed crystal, the TiAl/Ti3Al lamellar orientation was aligned parallel to the growth direction in directionally solidified Ti-47Al alloys. The solidification behavior of hypo-peritectic and hyper-peritectic alloys in TiAl equilibrium phase diagram was studied, and the composition range of successful seeding of TiAl alloys was also determined. Through the lamellar microstructure examination of Ti-47Al alloys directionally solidified from Ti-43Al-3Si seed under the conditions of different growth rates, it was found that a successful seeding requires that the solid/liquid interface must be planer during solidification. This can be achieved by growing crystals at a sufficiently high thermal gradient in the liquid and at a sufficiently low growth rate. It showed that the seeding process easily failed if cells or dendrites formatted, new grains would nucleated or α grains with a preferred growth orientation of <0001> would protrude to the liquid, then the lamellar direction was changed.

Effects of V, Cr and heat treatment on transformation and deformation characteristics of Ti-50.8Ni (atomic fraction, %) superelastic alloy were investigated by differential scanning calorimetry and tensile test. The two-stage reversible transformation ADRDM (A-parent phase, R-R phase, M-martensite) occurred upon heating D cooling in 350-550℃ annealed Ti-50.8Ni alloy. With increasing annealing temperature, the R, M transformation temperature TR, TM of the alloy are first increase then decrease; the M transformation temperature hysteresis ΔTM decreases continuously; the R transformation temperature hysteresis ΔTR is constant. After adding 0.5%V, the transformation type and ΔTR,ΔTM of the alloy do nearly not change, while the TR, TM decrease. After adding 0.3%Cr, the transformation type and ΔTR of the alloy do nearly not change; the ΔTM increases; the TR, TM decrease greatly. The superelastic stress and strain of 400℃ annealed Ti-50.8Ni alloy are 473MPa and 6.4%, respectively. After adding 0.3%Cr, the superelastic stress of the alloy increases, reaches 620 MPa, and the superelastic strain decreases, reaches 3.5%. After adding 0.5%V, the superelastic stress and strain decrease, and reach 388 MPa and 4.9%, respectively. When annealing temperature increases from 400℃ to 500℃, the superelastic stresses of three alloys are all decrease.

Based on the theoretical model of soft reduction gradient, soft reduction gradient for continuous casting slab with different steel grade was investigated. The results show that there is no big change of the range of soft reduction gradient and soft reduction rate for casting steel grades as low carbon, low carbon peritectic, peritectic and medium carbon, which change from 0.26 to 0.16mm/m and 0.37 to 0.22mm/min respectively. The average soft reduction gradient and average soft reduction rate almost have no change as the steel grade changes, which keep the value of 0.21mm/m and 0.29mm/min respectively. It also can be concluded that the soft reduction amount was influenced by steel grade greatly, and it became larger with the increase of temperature range between liquidus temperature and solidus temperature.

Based on the analysis of continuous casting slab soft reduction process, a expression to calculate soft reduction efficiency was deduced, and the effects of soft reduction amount and liquid core thickness on reduction efficiency were investigated. The results show that the reduction efficiency increases linearly with the increase of liquid core thickess as reduction amout is the same, and as the reduction amount is bigger than 2.3mm, the relationship of reduction efficiency η and reduction amount △H can be expressed by η=-0.00902+0.01155△H. For the same thickness of liquid core, the increase of reduction amount will induce the increase of reduction efficiency as reduction amount is less than 2.3mm, while the reduction amount has little effect on reduction efficiency as reduction amount is bigger than 2.3mm.