Home About us Contact
|
Home About us Contact | ||
|
|
||
Grain Boundary Sliding (grain + boundary_sliding)
Selected AbstractsHigh-strain-rate Superplasticity in a Nanostructured Al-Mg AlloyADVANCED ENGINEERING MATERIALS, Issue 4 2005B. Q. Han In this work, the authors report high-strain-rate superplasticity in a nanostructured Al-7.5%Mg alloy with a mean grain size of 90 nm processed via consolidation of cryomilled Al-Mg powders. Tensile ductility with an elongation of 291% was observed at a strain rate of 10-1 s-1 and at a temperature of 573 K. Noteworthy is the fact that the microstructure is essentially stable during testing at 573 K. Grain boundary sliding is suggested to be the dominant deformation mechanism in the superplastic deformation of the nanostructured Al-Mg alloy. [source] Creep failure mechanisms of a Ti-6Al-4V thick plateFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2001F. J. Seco The creep failure operating mechanisms of a 17-mm thick plate of a Ti,6Al,4V alloy in various heat treating conditions have been investigated. Specimens in the as-received, mill-annealed, condition (50 min maintenance at 720 °C and air cooled as the final step of the thermomechanical process) showed the lowest creep resistance and their metallographic analysis revealed that the temperature-activated dislocation climb was the mechanism responsible for the failure and that observed holes were generated by plastic deformation, rather than by creep cavitation. Conversely, maximum times to failure were recorded in beta-annealed specimens (1030 °C for 30 min, air cooled and aged for 2 h at 730 °C). The fracture surfaces of these broken specimens exhibited an intergranular morphology that was attributed to grain boundary sliding along the former beta grains. Finally, alpha,beta field-annealed samples (940 °C 4 h, and furnace cooled to 700 °C) possessed intermediate lives between those of mill-annealed and beta-annealed specimens and the failure operating mechanism was diffusional creep by the nucleation and coalescence of the creep cavities generated at the alpha,beta interfaces and the triple points. [source] Superplasticity of a Fine-Grained TZ3Y Material Involving Dynamic Grain Growth and Dislocation MotionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010Guillaume Bernard-Granger Superplastic deformation of a fully dense TZ3Y material, having a starting grain size around 135,145 nm and depleted of any amorphous phase at grain boundaries, has been investigated using compressive creep tests in air in the temperature range of 1100°,1300°C and the real stress range of 50,100 MPa. The key parameters of the creep law have been determined by performing temperature changes at a fixed stress and stress jumps at a fixed temperature. From such experiments, an average value for the apparent stress exponent of around 3 is obtained when the applied stress varied from 50 to 100 MPa and the temperature was kept constant in the range of 1100°,1300°C. The apparent activation energy of the mechanism controlling the creep deformation is evaluated at 577±75 kJ/mol in the temperature range of 1200°,1300°C, for a real stress of 70 MPa. The values of the apparent grain size exponent can be calculated from the initial grain size in the as-sintered samples and the grain size in the crept samples. In all cases, it was determined to be around 2. Observation of the microstructure of the crept samples, using scanning electron microscopy, reveals grain growth but does not show any significant elongation of the elemental grains. Transmission electron microscopy of a sample crept under 100 MPa at 1300°C reveals clear intragranular dislocation activity. This dislocation activity seems to be mainly confined in folds emitted at triple points. Because the creep parameters (experimental and calculated using a simple geometric model) and the microstructure observed are in good agreement, we propose that the creep mechanism involved is grain boundary sliding accommodated by dynamic grain growth and the formation of triple-point folds. [source] Microstructure and Creep Behavior of a Si3N4,SiC MicronanocompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009Monika Ka, iarová The microstructure and its influence on the creep behaviour of carbon derived Si3N4 -SiC micro/nanocomposite tested in bending at temperatures from 1200° to 1400°C in air has been studied. No phase and microstructure change after creep test implied that material is stable at tested temperature range. After creep test only partial crystallization of glassy intergranular phase has been observed. Creep parameters n close to 1, apparent activation energy around 350 kJ/mol together with TEM observation indicated that the main creep mechanisms is solution precipitation controlled by interface reaction in combination with grain boundary sliding caused by the amorphous intergranular phases present in microstructure. However, the grain boundary sliding is hindered by local SiC particles interlocking neighboring Si3N4 grains. [source] Effect of Cation Doping on the Superplastic Flow in Yttria-Stabilized Tetragonal Zirconia PolycrystalsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001Junpei Mimurada The superplastic characteristics of various cation-doped yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) were examined. For 1 mol% cation doping the true stress of Y-TZP is very dependent on the ionic radii of the doped cations; for instance, smaller cation radii give rise to lower true stress when compared with the other compositions for the same grain size, strain rate, and testing temperature. The altered true stress level must be due to the change in diffusivity of the accommodation process for grain boundary sliding caused by the addition of cations in ZrO2. The strain to failure of the doped zirconia is affected by both ionic radius and valence of the dopant cations. [source] | ||||||||||