W. Fan

Bio: W. Fan is an academic researcher from University of Manitoba. The author has contributed to research in topics: Superplasticity & Texture (crystalline). The author has an hindex of 4, co-authored 5 publications receiving 60 citations.

Anisotropy in flow and microstructural evolution during superplastic deformation of a layered-microstructured AA8090 Al–Li alloy

Abstract: The superplastic forming grade sheets of AA8090 Al–Li alloy were observed to contain layers of different microstructure and microtexture across their cross-section along the normal to the rolling direction (RD). The surface layer (SL) material contained coarse equiaxed grains and the dominance of S {1 2 3}[6 3 4] texture whereas the center layer (CL) material contained fine elongated grains and the dominance of Bs {1 1 0}[1 1 2] texture. Tensile specimens, machined to represent the SL of 0.6 mm thickness from the surface towards center (SL), the CL of 0.6 mm thickness, obtained by removing the material of 0.6 mm thickness from each surface towards center (CL), and full thickness (FL) material of 1.8 mm thick, in a sheet of AA8090 Al–Li alloy, were deformed at optimum superplastic condition of strain rate=1×10 −3 s −1 and temperature=803 K to investigate the effect of loading direction. In SL material, the specimen parallel to RD exhibited maximum and the specimen perpendicular to RD exhibited minimum flow stresses. This trend was reversed in CL material. The anisotropy in flow stress could be explained on the basis of texture in the SL material, but the contribution of grain directionality became important in the CL material. The flow behavior of FL material was found to consist of the composite-like contributions of SL and CL materials.

Effect of layered microstructure and its evolution on superplastic behaviour of AA 8090 Al–Li alloy

Abstract: Superplastic forming grade sheets of AA 8090 Al–Li alloy were observed to contain layers of different microstructure and microtexture across the thickness cross-section. Superplastic behaviour and its relationship to the concurrent microstructural and microtextural evolution of this sheet were studied at 803 K by tensile testing of specimens taken from the full thickness and the near surface and midthickness layers. Initially, the surface layers contained nearly equiaxed and relatively coarse grains with a strong S {123}〈634〉 type texture, whereas the midthickness section had elongated fine grains and a dominant Bs {011}〈211〉 texture. The stress–strain rate (σ–e) curves exhibited minimum flow stress for the full thickness material. Varying levels of grain growth and texture weakening occurred in the above two layers, the extent of which depended on whether the layers were in separated form or as coexistents in the full thickness material. The maximum values of strain rate sensitivity index for the...

Effects of strain rate and test temperature on flow behaviour and microstructural evolution in AA 8090 Al–Li alloy

Abstract: Tensile specimens of superplastic forming grade AA 8090 Al–Li alloy were deformed at constant strain rates in the range 1×10-5–1×10-2 s-1 and at constant temperatures in the range 298–843 K, to investigate their effects on the nature of stress–strain (cσ–e curves and on the concurrent microstructures, substructures, and microtextures. The σ–e curves exhibited flow hardening in the early part of deformation, the rate of which was found to increase with an increase in strain rate and decrease in temperature. Grain growth, cavitation, dislocation interactions, and texture weakening were observed to occur during superplastic deformation. The early part of deformation involved a substantial dislocation slip contribution to flow hardening and to the mechanism for superplastic flow. However, the microstructural evolution facilitated the conventional mechanism of grain boundary sliding and its accommodation by the diffusional process, as suggested by the strain rate sensitivity index and activation energy...

Microtextural evolution during superplastic deformation of AA 8090 Al–Li alloy

Abstract: A brief review of orientation imaging microscopy and an overview of the results of investigations related to textural evolution during superplastic deformation of a recent series of superplastic grade aluminium alloys, and specifically the results of the authors' study on microtextural evolution in AA 8090 Al–Li alloy, are presented. It was observed that the surface layer of the AA 8090 alloy sheet was dominated by S {011}〈634〉 type texture, whereas the midthickness layer was dominated by brass {011}〈211〉 type texture. In the course of superplastic deformation, textural weakening occurred, the rate and extent of which were different in the surface and centre regions, depending upon whether the two layers were deformed separately or as a composite in the full thickness tensile specimen. Textural weakening was generally more extensive at higher test temperatures and lower strain rates. Based on textural evolution and the presence of a large proportion of low angle boundaries, and their near eliminat...

Effect of Composite-Like Microstructure on Superplastic Flow and Concurrent Microstructural Evolution in AA8090 AL-Li Alloy

Abstract: The SPF grade sheets of AA8090 Al-Li alloy were observed to possess a composite-like layered microstructure with different microstructures and microtextures near the surface region and in the mid-thickness region in the longitudinal and transverse directions. Tensile specimens representing the microstructures near the surface in the mid-thickness and full thickness of a sheet were deformed under the optimum superplastic condition of strain rate (∈) = 1 × 10−3 s−1 and T = 803 K. The microstructural and microtextural gradient along the sheet thickness were found to result in the highest flow stress in the mid-thickness material which was dominated (60 v%) by brass (110) [12] texture and elongated grains. Grain growth, transformation of elongated grains into equiaxed grains, texture weakening and cavitation occurred during superplastic deformation. Such microstructural evolution in different zones across the thickness direction was found to influence the nature of stress-strain curves to a varying ex...

Strengthening mechanisms, deformation behavior, and anisotropic mechanical properties of Al-Li alloys: A review

Abstract: Al-Li alloys are attractive for military and aerospace applications because their properties are superior to those of conventional Al alloys. Their exceptional properties are attributed to the addition of Li into the Al matrix, and the technical reasons for adding Li to the Al matrix are presented. The developmental history and applications of Al-Li alloys over the last few years are reviewed. The main issue of Al-Li alloys is anisotropic behavior, and the main reasons for the anisotropic tensile properties and practical methods to reduce it are also introduced. Additionally, the strengthening mechanisms and deformation behavior of Al-Li alloys are surveyed with reference to the composition, processing, and microstructure interactions. Additionally, the methods for improving the formability, strength, and fracture toughness of Al-Li alloys are investigated. These practical methods have significantly reduced the anisotropic tensile properties and improved the formability, strength, and fracture toughness of Al-Li alloys. However, additional endeavours are required to further enhance the crystallographic texture, control the anisotropic behavior, and improve the formability and damage tolerance of Al-Li alloys.

Deformation mechanisms responsible for the high ductility in a Mg AZ31 alloy analyzed by electron backscattered diffraction

Abstract: The microstructural evolution during tensile deformation of an AZ31 alloy with grain size ranging from 17 to 40 µm, at intermediate temperatures, has been studied using electron backscattered diffraction (EBSD) and optical microscopy (OM) as the main characterization tools. Two deformation regimes could be distinguished. In the high-strain-rate regime, the stress exponent was found to be about 6, and the activation energy is close to that for Mg self-diffusion. These values are indicative of climb-controlled creep. In the lower strain rate range, elongations higher than 300 pct were measured. In this range, significant dynamic grain growth takes place during the test, and thus, the predominant deformation mechanisms have been investigated by means of strain-rate-change tests. It was found that the stress exponent varied during the test between 1.7 and 2.5, while the activation energy remains close to that for grain-boundary diffusion. The EBSD analysis revealed, additionally, the appearance of low to moderately misoriented boundaries that tend to lay perpendicular to the tensile axis. The enhanced ductility of this AZ31 alloy in this regime is attributed to the operation of a sequence of deformation mechanisms. Initially, grain-boundary sliding governs deformation; once dynamic grain growth occurs, dislocation slip becomes gradually more important. Dislocation interaction gives rise to the appearance of new interfaces by continuous dynamic recrystallization (CDRX).

On the strain rate sensitivity of high density polyethylene and polypropylenes

Abstract: The strain rate sensitivity of thermoplastic materials namely high density polyethylene (HDPE), homopolymer polypropylene, and high isotactic homopolymer polypropylene and concurrent microstructural evolution is investigated. Strain rate sensitivity index followed the sequence, HDPE>homopolymer polypropylene>high isotactic homopolymer polypropylene. The strain rate sensitivity index parameter of the examined polymeric materials is consistent with the micro-mechanisms of deformation and modes of fracture. Deformation processes in HDPE involved fibrillation and craze-tearing, while homopolymer polypropylene and high isotactic polypropylene were predominantly characterized by craze-tearing and brittle modes of fracture.

The influence of loading rate and concurrent microstructural evolution in micrometric talc- and wollastonite-reinforced high isotactic polypropylene composites

Abstract: The paper describes the response of neat high isotactic polypropylene (iPP) and talc (iPP-T) and wollastonite (iPP-W)-reinforced polypropylenes to tensile loading rate and the evolution of microstructure during plastic deformation. Unreinforced and reinforced polypropylene materials exhibit significant sensitivity to tensile loading rate (strain rate) and the change in strain rate sensitivity index parameter with strain signifies a change in the micromechanism of plastic deformation and mode of fracture. Plastic deformation in neat high isotactic polypropylene is characterized by craze-tearing and brittle mode of fracture, while both talc- and wollastonite-reinforced polypropylenes are characterized by wedge, ridge-tearing, fibrillation, and brittle fracture. The brittle fracture is associated with debonding of mineral particles from the polypropylene matrix. However, yield stress of all the three materials exhibit similar dependence to loading rate and similar activation volume that suggests similarity in the onset of plastic deformation process.

Processing map for hot working of spray formed and hot isostatically pressed Al–Li alloy (UL40)

Abstract: The hot deformation behavior of spray formed + HIPed Al–Li (UL40) alloy was studied using processing map technique. The map has been interpreted in terms of the microstructural processes occurring in situ with deformation, based on the values of a dimensionless parameter η which is an efficiency index of energy dissipation through microstructural processes. An instability criterion has also been applied to demarcate the flow instability regions in the processing map using another parameter ( ξ ). Both the parameters ( η and ξ ) were computed from the experimental data generated by compression tests conducted at various temperature and strain rate combinations over the hot working range (375–575 °C and 3 × 10 −4 to 1 s −1 ) of the present material. The processing map exhibits three distinct η domains without any unstable flow conditions under the investigated temperature and strain rate conditions. The dominant microstructural mechanisms corresponding to these domains were identified to be extended dynamic recovery, grain boundary cavitation and flow localization. The stress–strain, microstructure and hot ductility recorded under the deformation conditions of these domains were correlated to the microstructural processes. The ‘safe window’ for hot working of HIPed UL40 material has been identified based on these results. Further, the significance of HIPing on the hot workability has been enunciated by comparing the results of the present material with the as-spray formed material.