Mechanical properties at ambient and cryogenic temperatures of Al-Cu-Li alloy are required for design and fabrication of liquid hydrogen and liquid oxygen tanks of satellite launch vehicles. In the ...present work, bead-on-sheet, friction stir welding was carried out with three different rotation speeds. The yield and strain hardening behaviors of the welds were evaluated in temperature range of 20 K to 298 K. Both yield stress and strain hardening ability in the specimen increased with decrease in testing temperature. The dependence of yield stress on temperature was modeled on the basis of thermally activated dislocation mobility, while that of strain hardening was modeled on the temperature dependence of dynamic recovery rate parameter. The recovery parameter followed an Arrhenius-type relationship with temperature. The model parameters determined from the experimental data were further used to simulate the stress–strain curves at different sub-zero temperatures for the friction stir welds.
Two grades of austenitic stainless steel, type 304 and 316L, were cold rolled to different reductions by unidirectional and by cross rolling. Subsequent solutionizing of the cold rolled samples ...produced noticeable textural differences in type 304, but insignificant differences in type 316L. Both the solutionized materials had however the same trend in grain boundary character distribution (GBCD): an increasing fraction of random boundaries with an increasing pre-solutionizing reduction percentage. The degree of sensitization (DOS) was measured by the double loop electrochemical potentiokinetic reactivation (DL-EPR) test in both the alloys. The susceptibility to intergranular corrosion was assessed by the standard weight loss technique (practice B, A262 ASTM) in type 304 alloy. These increased with increase in random boundary concentration, but then dropped significantly beyond a ‘critical’ concentration—a pattern observed in both the grades. Such a pattern may be explained from a balance between nucleation rate of Cr-carbides and grain boundary Cr-flux, though postulating an exact model is premature at this stage. The present study, however, demonstrates a clear possibility of remarkable improvement in DOS and IGC through extreme grain boundary randomization.
An algorithm is used to estimate mesoscopic strains in a deformed polycrystalline material. This requires comparison of microstructures before and after imposed macroscopic plastic deformations, in ...order to estimate the local/mesoscopic strains from the displacements of identifiable grain boundary segments. The algorithm was applied to lightly plane strain compressed (PSC) polycrystalline zirconium. Very large (up to 1.2) near-boundary mesoscopic shear strains were estimated. These were well above the estimated measurement uncertainties and remarkably larger than the extremely small (0.01–0.04) PSC strains imposed. Opposing local shears, on both sides of a grain boundary, appeared to compensate each other. Direct correlations were noted, in the same grain, between mesoscopic shear strains and (i) in-grain misorientations and (ii) subsequent grain fragmentation.
Fully recrystallized Zircaloy-4 was cold rolled to 20% reduction in thickness. The deformed microstructure had fragmented and non-fragmented grains. Fragmentation represented deformation-induced ...refinement in grain size. Typically, the fragmented grains had more misorientation and were finer than the as-received grains. The deformed samples were subjected to 650°C annealing for different time periods, followed by water quenching.
Based on experimental observations, three distinct stages of annealing were noted. Stage I caused changes in the misorientations of the non-fragmented grains, while the fragmented regions remained unaffected. This was also the most effective stage for residual stress relief. In stage II, discontinuous recrystallization and grain coarsening consumed the fragmented regions. This stage provided the highest softening. Finally, stage III created recovery-induced grain refinement of the larger non-fragmented grains. A combination of indirect and direct observations thus provided a complete picture of the annealing related microstructural changes in a moderately deformed commercial Zirconium alloy.
Polycrystalline diamond films (∼10 μm thick) were grown on five different silicon (Si) substrate orientations by microwave plasma chemical vapor deposition. The selected Si substrates had a range of ...f(θ): 0.18–0.65. It is to be noted that f(θ) scales inversely with the packing density of the interface. As f(θ) decreased, three changes in the polycrystalline diamond microstructures were observed. (i) At the film surface -fiber texture increased but -fiber dropped. (ii) A novel reconstruction technique was proposed and tested for faceted microstructures. The reconstructed microstructures revealed that the observed texture changes, with a decrease in f(θ), was accompanied by elimination of very fine facets. (iii) Noticeable differences in Raman estimated stress gradients were also observed: the lowest stress gradients for more closed packed substrates.
AISI 316L austenitic stainless steel was deformed at different strain and strain paths. The twin boundaries in the deformed microstructure had two possible origins: decay of original annealing twins ...and generation of deformation twins. Assuming that rotations of grains, specifically grains on both sides of a twin boundary, are responsible for the twin decay, a simple model was proposed to bring out the domain of relative twin generation. A biaxial strain path, in general, was associated with strong twin generation - an association or dependency linked to the texture estimated values of Taylor factor. Formation of strain induced martensite was also observed to be strain and strain path dependent and was more in biaxial strain path.
Microstructural studies on Alloy 693 Halder, R.; Dutta, R.S.; Sengupta, P. ...
Journal of nuclear materials,
October 2014, 2014-10-00, 20141001, Letnik:
453, Številka:
1-3
Journal Article
Recenzirano
Superalloy 693, is a newly identified ‘high-temperature corrosion resistant alloy’. Present study focuses on microstructure and mechanical properties of the alloy prepared by double ‘vacuum melting’ ...route. In general, the alloy contains ordered Ni3Al precipitates distributed within austenitic matrix. M6C primary carbide, M23C6 type secondary carbide and NbC particles are also found to be present. Heat treatment of the alloy at 1373K for 30min followed by water quenching (WQ) brings about a microstructure that is free from secondary carbides and Ni3Al type precipitates but contains primary carbides. Tensile property of Alloy 693 materials was measured with as received and solution annealed (1323K, 60min, WQ) and (1373K, 30min, WQ) conditions. Yield strength, ultimate tensile strength (UTS) and hardness of the alloy are found to drop with annealing. It is noted that in annealed condition, considerable cold working of the alloy can be performed.
The evolution of microstructure under static annealing was studied for mid-thickness section of a twin-roll-cast (TRC) magnesium alloy. Annealing was performed at 300°C and 500°C for different times. ...Microstructural evolution was quantitatively analyzed, from optical micrographs, using grain path envelope analysis. Additional information from electron backscatter diffraction (EBSD) was used for addressing the possible mechanism(s). It was found that the TRC structure had a bimodal grain size, which was preserved even after annealing at 300°C. However, the annealing at 500°C led to a unimodal grain size. This difference in the grain size distribution created a contrasting behavior in the normalized standard deviations. This was primarily attributed to a competition between recovery and recrystallization, and their respective dominance at 300° and 500°C. A deformation induced recrystallization recovery (DIRR) model was proposed. The proposed model could successfully address the experimental microstructural evolution.
•Annealing of twin roll cast (TRC) magnesium alloy was done at temperatures of 300°C and 500°C.•TRC had bimodal structure. Bimodality preserved for annealing at 300°C. Annealing at 500°C led to unimodal structure.•Grain evolution was described based on the competition between recovery and recrystallization.•Deformation induced recrystallization recovery (DIRR) mechanistic model was developed.
In this study, the bainitic microstructure of a furnace-cooled electro-slag-refined 5% Cr steel was studied by the electron backscattered diffraction (EBSD) technique. The pole figures suggest a ...strong orientation relationship close to the Nishiyama–Wassermann type, i.e. there are 12 variants of the bainite sheaf that emerge from the three Bain correspondences. The microstructure consists of the bainite variants arranged in four sheaf colonies or morphological groups. Each sheaf colony, in turn, is made of one crystallographic group composed of 3 variants of bainite – one from each of the three Bain correspondences. Computations based on the phenomenological theory of martensitic crystallography (PTMC) show that the observed morphology is a product of stress-coupled autocatalytic nucleation. The 〈111〉Austenite 3-variant tension-coupled sheaf group predicted by the computations is the one that is experimentally observed.
Using X-ray diffraction line profile analysis (XRDLPA) approach the radiation response of FCC Ni-Cr-Fe based alloy 690 to 1.5 and 3 MeV Ni2+ ion damage was quantified in terms of its microstructural ...parameters. These microstructural parameters viz. average domain size, microstrain and dislocation density were found to vary anisotropically with fluence. The anisotropic behaviour is mainly attributable to presence of twins in pre-irradiated microstructure. After irradiation, surface roughness increases as a function of fluence attributable to change in surface and sub-surface morphology caused by displacement cascade, defects and sputtered atoms created by incident energetic ion. The radiation hardening in case of 1.5 MeV Ni2+ irradiated specimens too is a consequence of the increase in dislocation density formed by interaction of radiation induced defects with pre-existing dislocations. At highest fluence there is an initiation of saturation.
Display omitted
•Effect of self ion damage on FCC Ni-Cr-Fe based alloy quantified in terms of microstructural parameters.•Ion irradiation results in inhomogeneous microstructure.•Radiation hardening, anisotropic change in domain size, micro-strain and dislocation density with fluence.•Presence of twins in pre-irradiated microstructure responsible for anisotropy.•Same trend of variation in microstructural parameters with fluence in both 1.5 MeV and 3 MeV Ni2+ irradiation.
