Search

Microstructure and microtexture of a dual-phase (DP) steel was investigated using the electron backscattered diffraction (EBSD) technique. A DP600 steel was produced by 60% cold-rolling a low carbon steel with an initial ferrite pearlite microstructure followed by intercritical annealing at 720°C for 1 h. Kernel average misorientation map of the DP600 steel showed that the density of geometrically necessary dislocations as well as the local misorientation is higher in the vicinity of ferrite–martensite interfaces compared to the middle of the ferrite grains. Microtexture analysis of the cold-rolled steel by EBSD revealed that a strong α fiber and weaker γ fiber texture forms after cold-rolling. After intercritical annealing, the intensity of the α fiber texture is significantly reduced, whereas that of the more desirable γ fiber texture is slightly increased. The maximum texture intensity in the DP600 steel was observed for (112)[110] component in the α fiber, and (111)[123] and (111)[112] components in the γ fiber.

In this research, we investigated microstructural aspects of intergranular and transgranular fatigue crack propagation in an API X65 steel pipelines. For this purpose, the fatigue testing, based on ASTM E647 Standard, was carried out on CT specimens. The micro-texture measurement results showed that fatigue micro-cracks propagates dominantly in transgranular manner through differently oriented grains. It was also observed that most of the grains involved in crack propagation are broken during the crack growth. Coincidence site lattice (CSL) boundaries are considered as crack resistant paths; however, there was an accumulation of Σ3 boundaries around the fatigue micro-cracks showing that such boundaries acts as high energy boundaries during crack propagation. Elongated manganese sulphide inclusion was determined as the most detrimental inclusion for crack propagation due to the highly disordered boundaries between metal matrix and this inclusion. In other words, this type of inclusion may initiate the fatigue crack due to a high stress concentration factor that can provide in some sharp edges. Moreover, it can facilitate fatigue crack growth by reducing the local fracture toughness. Many manganese sulphide inclusions were found on fatigue fracture surfaces.

Vanadium dioxide (VO2) thin films of different thickness have been deposited on Si substrates by using DC magnetron sputtering. The effects of substrate pre-treatment by means of seeding (spin coating and ultrasonic bathing) and biasing on the structure and optical properties were investigated. Seeding results in a smaller grain size in the oxide film, whereas biasing results in square-textured crystals. VO2 thin films of 150 nm thick show a near-zero IR transmission in switched state. Especially, the 150 nm thick VO2 thin film with seeding treatment shows an enhanced switching efficiency.

Vanadium oxides (VO x ) have been widely studied as “smart materials” because of their capability of going through a reversible metal-insulator-transition. They are of considerable technological interests for applications in optoelectronics, ultrafast optical switches, electrochomic devices, and lithium microbatteries. However, vanadium-oxygen system is complicated due to the multivalency of vanadium, which makes preparation of VO x with single stoichiometry difficult. Therefore, structural characterization of vanadium oxides of different stoichiometriesis highly desirable and would provide helpful guideline to both materials preparation and their structural characterization. In the present work, VO x thin films with different stoichiometries under various bonding states were successfully prepared by reactive sputtering with and without post oxidation or reduction and characterized using Raman spectroscopy. Characteristic Raman spectra of single and multi- valence states of VO x including V 2 O 3 , VO 2 , V 6 O 13 , and V 2 O 5 are presented and discussed. The results have demonstrated that high purity VO x thin films with single stoichiometry can be obtained under well controlled conditions.

The impact response of three regions (top, mid and center) across the thickness of AISI 321 austenitic stainless steel plate at high strain rates (>6000 s−1) was studied using the split Hopkinson pressure bar system. The result shows that texture and stored energy heterogeneity across plate thickness influenced the mechanical responses of the investigated steel in these regions. Microstructural evaluation using high-resolution electron backscattered diffraction (HR-EBSD) analysis showed that strengthening in AISI 321 steel originates from the evolution of strain-induced martensite and formation of nano-carbides in addition to plastic deformation by mechanical twinning and slip. This resulted in a desirable combination of high strength and good ductility (approx. 2000 MPa at 0.42 true strain). Phase transformation, dynamic recrystallization and formation of nano-carbides were confirmed within the adiabatic shear band (ASB) region. The average dynamic recrystallized (DRX) grain size in the shear band region is 0.28 µm in comparison to grain size of 15 µm outside the shear bands. The nano-sized grain inside the shear bands is proposed to form by rotational dynamic recrystallization. A comparative study of the alloy's behavior under dynamic and quasi-static compression shows that the stability of austenite is higher at high strain rates and lower at a low strain rate. The strength in the dynamically impacted specimen is compromised as a result of the suppressed evolution of strain-induced martensite and mechanical twin. Martensitic transformation under both loading conditions follows the FCC ɣ-austenite→BCC ά-martensite kinetic path and both phases obey the Kurdjumov-Sachs' {(111)ɣ||(110)ά and ɣ|| ά} orientation relationship.

In this research, two phase brass alloy as one of the most important copper base alloys was processed by equal channel angular pressing as a severe plastic deformation process. The process was performed at 350 °C in route C up to 6 passes. Microstructural study showed that discontinuous recrystallization initiated at the first pass in the alpha phase. Recrystallization fraction enhanced by increasing the amount of strain and grain size decreased to less than one micron after the fifth and sixth passes. Investigations of beta phase showed that recrystallization in this phase began after the third pass and enhanced with increasing the number of passes. Separate investigation of macro-texture for two phases of alpha and beta well proved the different deformation behavior in both phases. Furthermore, it was observed that Goss, Rotated Goss and Rotated cube texture components were dominant for alpha phase, and cube and {112} texture components were dominant for beta phase that had a direct impact on the results of mechanical properties. Micro-hardness and tensile test were used in order to study the mechanical properties of the alloy. The results indicated a massive increase in micro-hardness and tensile strength after the process. Also, total elongation in the processed specimens was higher than expectations in a manner that after the final pass, it reached more than 80% which was only approximately 35% less than the primary anneal specimen.

Spark plasma sintering (SPS) has been recognised, in the recent past, as a very useful method to produce metal matrix composites with enhanced properties if compared with traditional powder metallurgy techniques. Obviously, the materials final properties are strongly related to the reinforcement types and percentages as well as to the processing parameters employed during synthesis. The present paper analyses the effect of microscopic and nanometric alumina particles, blended to pure aluminium in different combinations, on the final properties of metal matrix composites produced via SPS. A strong variation in the microstructural behaviour has been observed by varying the nano to micro alumina particles percentage blended with aluminium ones.

In this study, we applied a thermo-mechanical process to alter the grain boundary characteristic distribution (GBCD) with a view to the feasibility of grain boundary engineering in Incoloy 800H/HT. In order to optimize the GBCD through increasing the low Σ coincidence-site lattice (CSL) boundaries, we applied various thickness reductions with two different rolling modes followed by annealing. We used Electron Backscattered Diffraction (EBSD) to analyze the GBCD and CSL boundaries. We found that the coincidence-site lattice boundaries, particularly Σ 3 and its variants, increased with the pre-deformation level in cross-rolled (CR) samples. In contrast, the fraction of these CSL boundaries had an optimum in 50% reduction for unidirectionally rolled (UDR) samples. In fact, different Σ 3 n interactions led to different GBCD in UDR and CR processed samples. Low to medium deformation with UDR and medium to high deformation with CR on the Incoloy 800H/HT samples showed potential for grain boundary engineering.