Advanced Materials Research Vols. 15-17

Abstract: Micro-orientation data of a high purity Al rolled up to total thickness reduction of 80% at room temperature were determined using SEM-EBSD technique, conceptions of describing substructure information, such as subgrain misorientation (θcry), and average misorientation (θenv) of circumjacent subgrains for a special subgrain, etc., were suggested and corresponding GCDP-OI soft package was developed. It is found that the subgrains sizes increase rapidly from about 2 to 7 μm with increasing misorientations from 1° to 15°, and the total number frequency of which is more than 95%. However, taking into account local features of subgrais, whose sizes for Dcry/Denv > 1 are 2 times larger than that for Dcry/Denv < 1 on the same misorientation levels below 20°, and the relationships between misorientations and sizes are consistent with that if Dcry/Denv > 1, θcry/θenv > 1, vice versa.

Abstract: The textures and nanomechanical properties of nanocrystalline Fe-50wt%Ni foil fabricated by using an electroforming method were investigated. The as-deposited texture was characterized by major <100>//ND and minor <111>//ND fibre components. Annealing of the as-deposited specimen resulted in the texture change that the <111>//ND fibre texture developed strongly with decreasing <100>//ND intensity. The elastic modulus and hardness were investigated by nanoindentation test, and these experimental results were compared with the theoretical predictions based on an elastic self-consistent (ESC) polycrystal model. Annealing led to an increase in the elastic modulus and a strong decrease in the hardness. At the low ratio of indentation depth to the specimen thickness, the theoretical predictions of the elastic modulus in the sample thickness direction showed a good agreement with experimental results.

Abstract: Two polycrystal models are implemented into the finite element code to model texture development for pure Al under uniaxial tensile deformation and cold rolling deformation with EBSD data. Both models predictions in tensile deformation are reasonable agreement with the experimental data. Texture development under cold rolling predicted by the finite element model is more approximate to the measurement than Taylor-type model. Some other ideal orientations are failed to be predicted.

Abstract: This paper investigates the changes in deformation mechanisms of commercially pure titanium over a range of temperatures for different orientations relative to the initial rolling texture. Samples from grade 1 titanium plate were tested in plane strain compression (PSC). Extremes of orientation relative to the predominant split basal texture were tested at temperatures from 25°C to 700°C. Specimens were subsequently examined using X-ray texture analysis and electron back-scatter diffraction (EBSD). Changing the orientation resulted in substantial yield stress anisotropy. This was found to be largely related to the orientation of the dominant texture relative to the most favorable orientation for the easiest slip mode (prism slip), and significantly but to a lesser extent on differences in twinning behaviour. The most important difference in twinning was the operation of {1012} tensile twinning in c-axis tension and {1122} compression twinning in c-axis extension. Calculations indicated that at low temperature both of these twinning modes accommodate a significant amount of strain. Twinning was also found to be the most significant factor affecting work hardening behaviour, with reorientation hardening occurring for some sample orientations. As temperature was increased above ~350°C {1011} twinning became the dominant twinning mode, but its contribution to the strain was not as large as the low temperature twinning modes, and the total amount of twinning decreased with temperature. The decrease in twinning with increasing temperature led to a reduction in the difference in work hardening behaviour. The quantitative information gathered in the course of this work is discussed in the context of mechanical property prediction.

Abstract: We demonstrated the production of tin oxide (SnO2) one-dimensional (1D) nanostructures on silver (Ag)-coated substrates by the thermal evaporation of Sn powders. Scanning electron microscopy revealed that the product consisted of 1D nanomaterials with average diameters or widths in the range of 50-1300 nm. X-ray diffraction and high resolution electron microscopy coincidentally indicated that the nanostructures were mainly single-crystalline rutile structure of SnO2. The PL measurement with the Gaussian fitting showed visible light emission bands centered at 579 nm and 624 nm.

Abstract: A Co-20at%Ni polycrystal produced by electrodeposition was studied in its detail using orientation microscopy. By analyzing the local crystallographic texture, grain morphology and the grain boundary character on three distinct sections of the film, we have obtained a complete understanding of its microstructure. The microstructure and grain morphology is very complex, consisting of grains elongated in deposit direction, clusters of coarse and fine grains and further very fine structures. The deposition parameters generate a strong (1120)//ND texture and the columnar grain reveals inner orientation gradients along the growth direction

Abstract: The effects of strain path reversal under hot working conditions on the microstructure and crystallographic texture in the near-α titanium alloy Timetal-834 have been studied using high resolution electron backscatter diffraction (EBSD). The main objective of the work was to investigate the potential effect strain path may have on breaking up the well known clustering of similarly orientated primary alphas grains in the alloy, which significantly reduces its low cycle dwell fatigue lifetime. Deformation was carried out using forward torsion to an equivalent strain of 0.9 and forward/reverse torsion of two equal steps to produce a total strain of 0.9. The tests were performed at a typical industrial forging condition of 990°C (~50% alpha, ~50% beta) at an equivalent tensile strain rate of 2s-1. Investigation of the microstructure showed the primary alpha grains to align with the direction of torsion for the forward test and return to an equiaxed shape on strain reversal, though a significant numbers of deformation twins are formed and retained after the full strain reversal. Analysis of the texture of the starting material showed the typically clustering of primary alpha grains, which upon forward torsion and forward/reverse torsion did not break down. This indicates that during a typical forging operation the clustering of similarly orientated primary alpha grains inherited from the as-received billet will not be reduced. This suggests that improved in-service performance of this alloy can only be achieved by reducing the clustering upstream in the manufacture of the billet.

Abstract: The microstructure evolution of near-alpha IMI834 titanium alloy during hot working in the beta phase temperature regime has been investigated with regard to the effects of deformation and heat treatments. Typical cogging conditions were simulated through compression testing at temperatures of 1025°C-1100°C, strain rates of 0.01s-1-1s-1, and post- deformation heat treatments up to 4h. An analysis of flow behaviour and as-deformed microstructures revealed mechanisms of dynamic recovery and recrystallization in operation during deformation. However, complete grain refinement was not achieved through dynamic recrystallization and subsequent heat treatment was required for microstructure homogenization through metadynamic recrystallization and grain growth. The mechanisms of dynamic and metadynamic recrystallization are considered through quantitative measures of beta grain size and available literature models.

Abstract: New α+β type titanium alloy with Ti-4.5Al-6Nb-2Mo-2Fe was developed on the basis of using biocompatible elements and eliminating the cytotoxic ones such as Vanadium, while achieving the desirable mechanical properties such as appropriate strength, cold workability and low superplastic forming (SPF) temperature. The present study was conducted to investigate the effect of yttrium addition of less than 0.05% into this alloy on static and under superplastic deformation grain growth behavior. The new alloy bar manufactured by α+β processing and annealed at 1073K yielded extremely fine two-phase microstructure with α grain size around 2μm. Specimens were heated at temperatures of 1048, 1073 and 1098K and kept for times between 3.6 to 172.8KS. Yttrium forms in-situ Y2O3 particles, and the presence of these particles yield finer two phase microstructure due to their retardation effect on β phase grain growth. Grain growth behavior during hot deformation was investigated by hot compression test in use of a hot working simulator of THERMEC-Master Z. Strain rate was varied from 2×10-2 to 2×10-4S-1 and strain was 0.69. Grain size of both α and β phases increased with a reduction of strain rate, and Y2O3 particle was also effective to retard grain growth under hot deformation. It was confirmed from comparison of grain growth during isothermal heating with and without hot deformation that grain growth was much accelerated by deformation. All of these results were discussed based on grain growth mechanism or model for two-phase microstructures as well as superplastic deformation mechanism.