Materials Science Forum Vols. 702-703

Abstract: Bulk properties of polycrystalline structural and functional materials are controlled by the grain boundary microstructure defined by the grain boundary character distribution (GBCD) and grain boundary connectivity, because of percolation-dependent grain boundary phenomena. It has been found that there is a close relationship between microscale texture and grain boundary microstructure. Since percolation-controlled grain boundary phenomena are involved and playing key roles in the generation of various kinds of bulk properties, the relationship between texture and grain boundary microstructure can be effectively used as a powerful tool in development of high performance structural and functional materials by Grain Boundary Engineering (GBE).

Abstract: Grain boundary texture evolution in case of two of the Zr based alloys (Zircaloy-4 and Zr-2.5\%Nb) was studied. In case of Zircaloy-4, grain boundary texture evolution during $\beta$ $\to$ $\alpha$ phase transformation was monitored. Direct evidence of variant selection during this transformation is presented. In case of Zr-2.5\%Nb alloy, considerable increase in $\alpha/\beta$ interfaces following Burger's orientation relationship was noticed with increasing annealing time at 700 \textdegree{}C.

Abstract: The origin and role of S3 boundaries during dynamic recrystallization (DRX) and grain boundary engineering (GBE) of a Ti-modified austenitic stainless steel (alloy D9) is studied. Hot deformation tests were carried out on solution-annealed (SA) specimens to study the DRX behavior whereas a series of cold deformation and annealing were performed on SA specimens to realize GBE microstructure. A linear relationship between the area fraction of DRX and the number fraction of Σ3 boundaries was observed during hot deformation. This high fraction of Σ3 boundaries could account for the formation of coherent annealing twins by “growth accidents” during DRX. For certain combinations of cold deformation and annealing, a significant increase in S3 boundaries was observed. In contrast to hot deformation, majority of these new S3 boundaries during cold deformation and annealing were formed by geometrical interactions between the pre-existing Σ3 boundaries. The role of the S3 boundaries during DRX and on tailoring microstructure through grain boundary engineering approach is discussed.

Abstract: In the present study diffusion bonding of γ-TiAl intermetallic with Ti-6Al-4V alloy was carried out in high vacuum. The diffusion bonding was performed at temperatures of 800°C and 850°C under the constant pressure of 40MPa and at varying time. The interfacial microstructure formed during the diffusion bonding was analysed by SEM and TEM. The elemental distribution characteristics across the interface were also studied by X-ray EDS analysis. From EDS results obtained, some regions were rich in aluminium and some regions were rich in vanadium. Also there are some compositional variations such as chromium and niobium close to the interface zone. However, the composition gradient was not gradual across the interface. Strong evidence has been found for the solute re-distribution in a more localized manner.

Abstract: The recrystallization (Rex) texture of cross-rolled 3.3% Si steel was similar to the deformation texture approximated by {100}. The deformation texture of cross-rolled 99.99% copper was approximated by major {110} plus minor {001}. Its Rex texture was approximated by major {110} plus minor {001}. The results have been discussed based on the strain-energy-release-maximization model.

Abstract: Desirable magnetic properties for grain oriented electrical steels are low core loss and high magnetic flux density. These properties are closely related with sharpness of {110} texture. This Goss texture develops by abnormal grain growth during secondary recrystallization annealing. Based on experimental results, a general suggestion which estimates the magnetic properties after completion of secondary recrystallization from a primary recrystallized texture can be proposed. For a material to have better magnetic properties after completion of secondary recrystallization, it should have a primary recrystallized texture in which there are not only large number of ideal Goss grains, but also lower frequency of low angle grain boundary around those Goss grains.

Abstract: The texture can be evolved through the γ to α transformation by cooling in Fe-Si alloy systems. Oxygen in the annealing atmosphere hampers the evolution of the texture. The texture evolution is associated with the fact that the {100} faces are elastically compliant so that the texture can develop in a manner consistent with minimization of strain energy. By alloying Mn to Fe-Si alloys, the texture evolves in relatively high oxygen containing annealing atmosphere. The role of Mn in the texture evolution appears to be preventing formation of surface oxides, which modify the elastic modulus of metal surface, thereby suppress the development of the correct texture.

Abstract: Magnetic properties of electrical steels such as magnetization behavior and electrical losses are mainly related to chemical composition, crystallographic orientation and microstructure. By now, several models have been proposed to empirically correlate magnetic properties and affecting parameters. A quantitative model based on physical understanding of the interaction between the magnetic field variables (e.g. domain structure) and local microstructural variables (e.g. grain orientation and misorientation, grain boundary plane inclination) is still missing. To obtain a better understanding of the interaction between grain boundaries and domain walls, the magnitude of free pole density at grain boundaries was taken into account. Experimental results from 3-dimentional EBSD experiments were employed to measure the grain boundary orientation for several samples with different chemical composition and grain size. The free pole density was calculated using the relative misorientation between adjacent grains, and was included in a model together with grain size, magnetocrystalline anisotropy energy and silicon equivalent. By comparison with the experimental results of the magnetic induction measured at low, medium and high magnetic fields, is shown that the magnetization behavior can be more accurately predicted when the above mentioned phenomena are taken into account.

Abstract: To identify the relationship between grain orientation and precipitation of MnS/AlN particles during hot deformation, cylinder samples containing columnar grains in electrical steels were prepared with different angles between columnar grain axis and sample axis. They were heated at 1360°C and compressed at 1100°C for 50%. Grain orientations and the precipitation states are determined using XRD, EBSD, EDS and SEM. Results indicate a general behavior of less precipitates in <100> and more precipitates in <111> grains. In addition, more precipitates were observed in samples with grain boundaries perpendicular to compression axis.

Abstract: Fe₈₁Ga₁₉ sheets were produced by conventional rolling procedure. Recrystallization texture dominated with strong Goss ({110}) was successfully obtained through sheet thickness by primary recrystallization annealing. The development of Goss can be attributed to the favorable shear band morphology and deformation texture derived from the applied specific rolling process.