A transformation treatment based on surface effect induced transformation is applied to cold rolled TA10 titanium alloy sheets to change and control transformation texture. This kind of treatment can promote the α-phase nucleation at sheet surface region during cooling and control the growth of surface α-grains into center layer of sheet. The results indicate that as the heating temperature increased, the transformation textures in the final HCP-structured TA10 sheets changed in helium atmosphere from the recrystallization type texture of <11-20>//RD to the transformation type texture of <11-20>//ND. The textures in sheets treated at low transformation temperature of 1000°C reveal texture memory effect, while those treated at high transformation temperature of 1100°C illustrate the effects of both transformation strain and anisotropy in elastic modules of HCP titanium crystals. The surface effect is promoted by cooling gas of helium, which leads to layered structures along sheet thickness direction. The surface region often shows small equiaxed grains with recrystallization orientations, while the center layer reveals coarse grains with either plate-like or equiaxed grain morphology corresponding to transformation orientation or recrystallization orientation, respectively. The special grain boundaries in plate-like α variants are different from those in equiaxed grains. These differences in morphologies, sizes and orientations are explained in terms of the mechanism change of the factors affecting variant selection.
Local shear textures in ASBs of high manganese TRIP steels under high rate straining are determined and the influences of initial microstructure is analyzed using EBSD technique. It is seen that even at the presence of majority of two types of martensite before deformation, ASB is preferred to evolve in austenite, rather than in martenite, due to reverse transformation. Ultrafine grains of thress phases due to dynamic recrystallization are formed and all show shear textures. The less e-martensite in ASB is distributed as islands and its preferred orientation can be found to originate from the variants in matrix. The grain orientation rotation around ASB in multi-phase alloy reveals significant influence of alpha'-martensite on texture in ASB. The mechanism of local texture formation in ASB of high manganese TRIP steel is proposed in terms of the interaction of early TRIP and later reverse transformation.
Basal slip and tension twinning are dominant deformation mechanisms of polycrystalline magnesium at low temperature. However, fracture originates mainly from compression twins or shear bands developed from compression twins. This work compared firstly the morphological difference of two types of twins. Then, the dependence of different deformation mechanisms on initial orientations is computed by Schmid factor analysis and compared with measured matrix orientations of twins. Finally, orientation relationships of compression twins with matrices are determined using EBSD technique and compared with theoretical value.
Microscopy, X-ray diffractometry and EBSD analysis were applied to inspect the relationships between deformation mechanisms and initial textures in polycrystalline magnesium alloys AZ31. It is found that different deformation mechanisms proceed according to theoretic prediction. Basal slips occur when basal planes of grains are tilted toward normal direction(ND) around transverse direction(TD); prism slips dominate when basal planes are perpendicular to TD. {1012} twinning was favored when basal planes are normal to rolling direction(RD) and {1011} twinning is analyzed to be related to the basal orientation of grains.
Microscopy and X-ray diffractometry were applied to inspect the influence of initial texture on dynamic recrystallization and texture formation in AZ31 magnesium alloys during channel die compression. The results show that stress-strain curves, microstructures and textures depend on initial textures. Two types of nucleation sites are detected which are in different proportions depending on initial textures. Dynamic recrystallization proceeds faster in samples with more inhomogeneity. When the basal planes of grains are parallel to rolling plane of sample with scattering around transverse direction, no new texture component occurs and texture is strengthened together with dynamic recrystallization. By other initial textures there are texture changes during hot deformation. New grains rotate gradually to basal orientation at heavy strain.
The microstructure evolution during strain induced ferrite transformation was followed in thermal-simulation tests of clean 08 and 20Mn steels. The influences of carbon equivalence and initial austenite grain size on ferrite grain refinement and the volume fraction of ferrite during straining were inspected. The results revealed that the accelerating effect of ferrite transformation by strain was increased as the carbon equivalence decreased. However, finer ferrite grains were obtained at higher carbon content. At strain of ~1.5 ferrite grains less than 3m and 2m can be obtained in 08 and 20Mn steels respectively. Whereas the ferrite grain refinement in 08 steel was due to both effects of strain induced transformation and ferrite dynamic recrystallization, that in 20Mn was mainly due to strain induced transformation. Heavy strain can produce fine ferrite grains in coarse austenite grained 08 steel, but it would lead to band microstructure in coarse austenite grained 20Mn.
Fe Cr-C cermet was prepared by reaction sintering of ferrochromium and graphite. The exothermic reaction was determined by DTA. The effect of carbon content on the porosity, hardness and oxidation resistance was investigated. The result showed that the cermet with 6 %-7 % of carbon has high hardness and oxidation resistance.