Increase In Grain Boundary Area Research Articles

Effect of Deformation Degree on Microstructure and Properties of Ni-Based Alloy Forgings

The primary objective of this paper is to investigate the influence of deformation degree on the microstructure and properties of a Ni-based superalloy. An upsetting experiment was conducted using a free-forging hammer to achieve a deformation degree ranging from 60% to 80%. The impact of the forging deformation degree on the hardness and high-temperature erosion performance was evaluated using the Rockwell hardness tester (HRC) and high-temperature erosion tester, respectively. The experimental results indicate that as the deformation degree increased, the hardness of the forged material progressively increased while the rate of high-temperature erosion gradually decreased. In order to comprehensively study the mechanism behind the variations in forging performance, optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were employed. The findings reveal that as the deformation degree increased, the presence of small-angle grain boundaries and an increase in grain boundary area contributed to enhanced hardness in the alloy forgings. Furthermore, it was discovered that grain boundaries with twin orientation promoted dynamic recrystallization during deformation, specifically through a discontinuous dynamic recrystallization mechanism. Additionally, the precipitated γ′ phase in the alloy exhibited particle sizes ranging from 40 to 100 nm. This particle size range resulted in a higher critical shear stress value and a more pronounced strengthening effect on the alloy.

Effect of cryorolling and annealing on recovery, recrystallisation, grain growth and their influence on mechanical and corrosion behaviour of 6082 Al alloy

In the present study, recovery, recrystallisation, grain growth, mechanical, and corrosion resistance of 6082 Al alloy subjected to cryorolling (CR) and annealing (AN) treatment were investigated. CR was performed to produce ultrafine grained structure and subsequently, AN treatment was given to investigate its influence on recovery, recrystallisation, and grain growth. The recovery and recrystallisation occurs between 110 and 250 °C and 250–300 °C respectively, where as grain growth starts from 300 °C due to insoluble dispersions (AlMn & AlMnSi) and Mg2Si precipitates in the alloy as evident from Differential scanning calorimetry (DSC), Electron back scattered diffraction (EBSD), hardness and Transmission electron microscopy (TEM) results. CR 6082 Al alloy has showed increased hardness of 120 VHN and ultimate tensile strength of 353 MPa. Annealing of CR 6082 Al alloy at 150 °C exhibited maximum hardness, ultimate tensile strength (UTS) and ductility of 127 VHN, 362.5 MPa, and 11%, respectively. CR of the 6082 Al alloy has produced high density of dislocation and increase in grain boundary area, which enabled the formation of dense oxide film on surface, enhancing its corrosion resistance. CR samples annealed at 350 °C shows excellent corrosion resistance as compared to as deformed Al alloy.

AFM applications to study the morphology of HfO2 multilayer thin films

Atomic force microscopy (AFM) is a technique that has extensively been used to reveal details on surfaces using different scanning techniques. Multilayer hafnium oxide (HfO2) thin films deposited by electron beam evaporation at room temperature on three different glass substrates (including Corning, commercial and wind screen glasses) are discussed for their surface analysis using atomic force microscopy. AFM characterization involves structural morphology, grain size and grain distribution, etc. AFM micrographs show that the films are uniform and crack-free. The average roughness, maximum peak to valley height, root mean square (RMS) roughness, surface skewness and kurtosis parameters are investigated to analyze the surface morphology of HfO2 multilayer thin films. Results show that the RMS surface roughness decreases for commercial glass substrate to Corning to wind screen glass. On the other hand grain size demonstrates an opposite trend. Thus an increase in grain boundary area with decreasing grain size might be associated with the rise in RMS surface roughness. These films show an almost homogeneous and uniform distribution of grains according to AFM images.

Evolution of transformation plasticity during bainitic transformation

Abstract The influences of prior austenitization treatment and the state of applied stresses on the evolution of transformation plasticity strains during isothermal bainitic phase transformation and the resulting microstructures were examined. The key finding is that, upon pre-straining, the amount of transformation plasticity strain under superimposed elastic stresses is dictated by both the prior austenite grain size and the (0.01 % offset) yield strength of the supercooled austenite. Furthermore, the superimposition of internal stresses present due to pre-straining and externally applied stresses results in transformation plasticity strains similar to those obtained when a permanent stress equivalent to the 0.01 % offset yield strength of the supercooled austenite is applied. Another important result is that lower transformation plasticity strains were observed when decreasing the austenite grain size, which is accompanied by an increase in grain boundary area per volume, hindering the growth of preferred variants. Overall, the results clearly lay out the influence of austenite grain size and the particular 0.01 % offset yield strength of the supercooled austenite in limiting the transformation plasticity strains, which has to be incorporated into current models involving bainitic phase transformations.

Grain Size Effect in the Electrical Properties of Nanostructured Functional Oxides through Pressure Modification of the Spark Plasma Sintering Method

Through the use of a high-pressure modification of the spark plasma sintering method, it was possible to consolidate functional oxides (yttria- stabilized zirconia and doped ceria) to high densities and retain a grain size of < 20 nm. The role of the pressure on densification and on the grain size of the sintered samples was demonstrated. The pressure had a marked effect on density at relatively low temperature but an insignificant effect at relatively high temperature. It was found that when prepared with such small grain sizes, these oxides conduct protonically even at temperatures as low as room temperature. The dependence of the protonic conductivity is stronger dependence on grain size than what can be anticipated from a geometric consideration based on an increase in grain boundary area. This observation strongly suggests that factors other than an increase in grain boundary area play a role, a consideration that is being further investigated.

Growth of CuCl thin films by magnetron sputtering for ultraviolet optoelectronic applications

Copper (I) chloride (CuCl) is a potential candidate for ultraviolet (UV) optoelectronics due to its close lattice match with Si (mismatch less than 0.4%) and a high UV excitonic emission at room temperature. CuCl thin films were deposited using radio frequency magnetron sputtering technique. The influence of target to substrate distance (dts) and sputtering pressure on the composition, microstructure, and UV emission properties of the films were analyzed. The films deposited with shorter target to substrate spacing (dts=3cm) were found to be nonstoichiometric, and the film stoichiometry improves when the substrate is moved away from the target (dts=4.5 and 6cm). A further increase in the spacing results in poor crystalline quality. The grain interface area increases when the sputtering pressure is increased from 1.1×10−3to1×10−2mbar at dts=6cm. Room temperature cathodoluminescence spectrum shows an intense and sharp UV exciton (Z3) emission at ∼385nm with a full width at half maximum of 16nm for the films deposited at the optimum dts of 6cm and a pressure of 1.1×10−3mbar. A broad deep level emission in the green region (∼515nm) is also observed. The relative intensity of the UV to green emission peaks decreased when the sputtering pressure was increased, consistent with an increase in grain boundary area. The variation in the stoichiometry and the crystallinity are attributed to the change in the intensity and energy of the flux of materials from the target due to the interaction with the background gas molecules.

ＥＣＡＥ加工したＭｇ‐Ｌｉ‐Ｚｎ合金の引張特性および低温超塑性の発現

In this study, repetitive ECAE processing was applied to Mg–Li–Zn alloys with dual phases consisting of α (Mg solid solution) and β (Li solid solution) phases in order to improve their tensile properties and to achieve low temperature superplasticity by refining both phases and spheroidizing α phase. Such a microstructural change in α. phase is reached by 2–pass ECAE processing at 293 K for LZ101 alloy and 323 K for LZ81 and LZ91 alloys, and subsequent annealing for 1 h at 623 K for LZ81 and LZ101 alloys and 673 K for LZ91 alloy. 4–pass ECAE processing at 293 K for LZ101 alloy and 323 K for LZ81 and LZ91 alloys and subsequent annealing at 398 K for all of the alloys results in grain refinement of β phase. As a result the specimens tested at 293 K show better tensile properties than as-rolled ones. The elongation of as-ECAE-processed specimens tested at 373 K reaches approximately 400% under a relatively low strain rate of about 10−4 s−1 together with low flow stresses, and the specimens have the relatively high strain rate sensitivity exponents of about 0.4. Microstructures of the specimens after tensile test at 373 K reveal that dynamic recrystallization and precipitation occurs in both phases. These results suggest that an increase in grain boundary area through the fine recrystallized grains and precipitation of β phase on the recrystallized grain boundaries of α phase contribute to grain boundary sliding, resulting in the occurrence of superplasticity at 373 K, which is lower than Tm/2.

Recrystallization and Grain Boundary Sliding in a Magnesium Alloy

DURING tensile deformation of magnesium and its dilute alloys in the temperature range 100°–350° C, cells form preferentially close to the grain boundaries1. Afterwards irregular boundary migration occurs and evidence has been presented for the grain boundaries being pinned at their intersections with the cell walls2. This migration results in an increase in grain boundary area and thus the driving force must arise from the difference in stored energy between neighbouring grains. It is unlikely that sliding can occur to any appreciable extent at these irregular boundaries and in these circumstances it is probable that the shearing forces in the vicinity of the grain boundaries are accommodated by increases in the degree of misorientation across the cell walls. Eventually the irregular migration leads to primary recrystallization2–6 along the old grain boundaries and an example is illustrated in Fig. 1.