Materials Science Forum Vols. 706-709

Abstract: The effect of trench aspect ratio and line spacing on microstructure and texture in annealed damascene Cu interconnects has been investigated. The X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) analyses of Cu lines, showed a preferred {111} orientation and the trenches reduce the proportion of high-angle grain boundaries and increase the fraction of coincidence site lattice (CSL) grain boundaries, comparing with the Cu blanket film. In addition, both trench aspect ratio and line spacing can largely affect the microstructure and texture in annealed damascene Cu interconnects.

Abstract: The plastic behavior of the <110>//RD orientations, and specially that of the {001}<110> orientation, under severe cold reductions is addressed. Based on the orientation dependence of the stored energy, the {001}<110> orientation is known to lack from structured misorientation gradients and significant dislocation storage after plastic deformation which makes the former orientation not particularly prone to enhancing the recrystallization process. Recent evidences, however, indicate that {001}<110> orientation plays a relevant role in the origin of {h11}<1/h,1,2> orientations (predominantly {311}<136> and {411}<148> orientations) observed in the recrystallization texture of severely deformed IF steels. The complete understanding of the development of the recrystallized {h11}<1/h,1,2> orientations in IF steels is, therefore, of relevance as it deteriorates the optimum γ-fibre texture required for deep-drawability applications. The plastic instability of {001}<110> grains in a cross-rolled IF steel is evaluated in the present work. The extensive characterization of the deformed substructure along with partially recrystallized data confirmed the oriented nucleation origin of {h11}<1/h,1,2> orientations from deformed {001}<110> grains. Innovative crystal plasticity calculations accounting for the position of the grain boundary plane suggested that the recrystallized {h11}<1/h,1,2> orientations could result from a low Taylor value nucleation criterion.

Abstract: Specimens cut from a cold-rolled IF steel sheet of 1 mm thickness were respectively annealed at 750°C for 20min under a range of DC electric fields (1kV/cm~4kV/cm). The Effect of electric field strength on recrystallization texture of IF steel sheet was studied by mean of X-ray diffraction ODF analysis. It was found that γ-fiber textures were notably enhanced as electric field strength increased. The strength of γ-fiber textures got their peak values as the applied electric field reached to 4kV/cm. The possible reason for such phenomena was discussed in the viewpoint of interaction between the applied electric field and the orientation-dependent stored-energy in deformed metals which is known as the driving force for recrystallization during annealing.

Abstract: Effects of three heating rates, 5, 20/min., and 300°C/sec and decarburization temperature, 700-850°C in primary annealing on the microstructure and magnetic properties of a grain oriented electrical steel were investigated. It was found that the oxide layer thickness and grain size increased with increasing decarburization temperature. However, they decreased with increasing heating rate. On the other hand, injection nitrogen content into steel sheets decreased with increasing decarburization temperature. The percentage of abnormal grain growth obtained a peak value at 800°C in the specimens treated with heating rate less than 20°C per minute. But specimens with rapid heating rate, percentage of abnormal grain growth increased with increasing decarburization temperature. As percentage of abnormal growth increased, magnetic properties got better.

Abstract: A homogenous intensity distribution along the cube texture fibre is important to achieve an easy magnetization in non-oriented electrical steels. Several alternatives have been discussed in literature to achieve this goal namely, tertiary recrystallization (surface energy controlled), decarburization annealing, two step cold rolling (strain induced boundary migration), twin-roll thin strip casting (directional solidification), phase transformation (surface energy anisotropy) and columnar grains formation (selective grain growth). In the present study, a hypoeutectic Al-Si alloy was deposited on the surface of cold rolled Fe-Si steels with a hot dipping simulator and subsequently annealed at 1000°C for different times. This procedure was developed previously in order to enrich the substrate with Al and/or Si and consequently improve their resistivity. Of specific interest was the formation of columnar grains in the low Fe-Si steel after annealing. These columnar grains were found to grow from the surface towards the centre of the substrate. The microstructure and texture in the columnar grains were significantly different than those in the middle of the material. Therefore, the evolution of these features during processing was studied in detail in this work.

Abstract: A two-step rolling-annealing process has been developed to increase the <111>//ND (γ fiber) component in the recrystallization texture of a copper-bearing bake hardening steel. The two step process comprises the first rolling by a low reduction in thickness and subsequent annealing at 780°C, followed by the second rolling by a high reduction and subsequent annealing at 780°C. The first rolling process aims at seeding the γ fiber oriented grains, so that they can grow at the expense of differently oriented grains developed in the second rolling process. In this way the density of γ fiber component in the recrystallization texture of the bake hardening steel much increases compared with that in the conventional one-step rolling-annealing process.

Abstract: Al/Si alloys are considered to be one of the most promising light weight alloys that can be used extensively in aerospace and automotive industry except for the poor tribological behaviour. However, with advancement and precision of the surface coating depositing techniques, new coating design which significantly enhances the tribological properties of the light weight alloys becomes attainable. In this paper, an innovative coating design is presented and thoroughly analyzed using finite elements method. The proposed model consists of Al/Si 319 as a matrix within which the geometrically defined hard Si particles are dispersed on the surface, and a hard coating layer then deposited in between the Si particles so that the lateral movement of the Si particles is constrained. ABAQUS is utilized to model and address the effects of different parameters, such as coating material, the hard coating thickness, and geometrical shape of the Si particles on the fracture and deboning of the entire structure. Two Si particles shapes are studied: circular and elliptical. Three coating materials are investigated: DLC, CrN and Al2O3. Besides, four coating thicknesses of 4 µm , 8µm, 15µm and 20µm are tested. It is found out that there is no single significant parameter which affects the fracture and deboning of Si particles, yet it is the combination of different parameters. The Si particle geometry plays a major role in determining the critical fracture stress with a circular shape outperforms the elliptical shape. The combination the circular Si particles and the CrN as coating material gives the highest critical fracture stress. Finally, DLC does not perform well with the circular Si Particle and it show the highest possible fracture stress with elliptical Si particle

Abstract: This study aims to develop a high-functional photocatalytic film, of which surface is regularly textured by the micro machining technique in order to earn the real surface area. In this work, a regularly textured TiO2 film surface was fabricated by anodic oxidizing a pure titanium plate with regularly arrayed micro cutting grooves, and its wettabilty was evaluated. Micro cutting grooves were machined by a 3-axis NC control precision machine tool with a single point diamond cutter. Anodic oxidation experiments were conducted by using the self-developed equipment with diluted acetic acid as the electrolyte. As a result, it was found that the wettability of the TiO2 film surface regularly textured by synchronized 3-axial micro cutting was superior to those of the mirror finished or irregularly textured surfaces under the irradiation environment by the ultraviolet rays.

Abstract: To evaluate the effect of rolling process on microstructures and textures development, this work was carried out using pure Ta sheets. For this work, conventional rolling (CR) and cross roll rolling (CRR) as a deformation process were introduced, pure Ta sheets were cold rolled to 90% in thickness reduction. After this, to obtain the recrystallized microstructure on cold rolled materials, the recrystallization heat-treatment was performed at 1200°C for 60 min under the high vacuum state. Also, to analyse the grain boundary character distributions of the annealed sheets, electron back-scattered diffraction method was introduced. As an experimental result, increase in strain rate led to the development of texture with its texture component of <111> at conventional rolling and cross roll rolling, in common. Therefore, in this study, we systematically discussed the texture development due to increase in effective strain.

Abstract: A novel method has been discovered for controlling the crystallographic orientation of pure iron using the γ to α phase transformation. When pure iron with clean metal surfaces undergoes the γ to α phase transformation, it develops a strong cube-on-face texture ({100}<0vw>) with the grain size being larger than the sheet thickness. The mechanism controlling the <100> orientation obtained is associated with the fact that the {100} faces are elastically compliant so that the <100> texture can develop in a manner consistent with minimization of strain energy. However, in commercial steels, although so many texture analyses have been conducted, the cube-on-face texture has been rarely observed. According to thermodynamic analysis, surface oxidation in commercial steels appears to be responsible for the deterioration of the <100> texture. This phenomenon can be explained in terms of the modification of the inherent elastic anisotropy of metal surface by the surface oxidation.