Transient Creep Deformation Research Articles

高Crフェライト鋼の遷移クリープ変形に及ぼす固溶Mo及びWの効果

高Crフェライト鋼の遷移クリープ変形に及ぼす固溶Mo及びWの効果

Application of the HAI-model to the creep behaviour of particle hardened nickel-base superalloys

The Haasen-Alexander-Ilschner (HAI-) theory of internal and effective stress is combined with the modified threshold stress (σ p) concept in order to describe steady-state as well as transient creep deformation of oxide dispersion strengthened (ODS) nickel-base superalloys under constant strain rate (ġ3) conditions. The microstructurally based model correctly reflects the steady-state relationship of ġ3 and σ at large plastic strains. For any given constant ġ3-value the fine dispersed incoherent Y 2O 3 particles in MA 754 rise the stress level considerably compared to the single-phase solid solution, Nimonic 75, of similar chemical composition. The higher contents of Al and Ti in MA 6000 lead to additional precipitation hardening of coherent γ′-particles and a further increase in stress. However, transient creep can only be modelled by splitting σ p into two additive terms: firstly a constant σ p * value representing the contribution for the mere particle overcoming process and secondly an increasing σ ϱ,p term reflecting the building up of geometrically necessary dislocations during plastic deformation.

Dependence of creep characteristics on temperature and applied stress in Zn-1.0 wt.% Cu during transformation

The change in the transient and steady state creep deformation of zinc-1.0 wt.% Cu alloy was studied under various constant stresses ranging from 45.80 MPa to 56.02 MPa in the temperature range from 473 K to 573 K. From the transient creep results, the peak values of transient creep parametersB andn found in this temperature zone can be ascribed to dissolution ofe-phase (Cu-rich phase). The transient creep parameterB is related to the steady state creep rate\(\dot \varepsilon _{st} \) through the exponentγ. This exponent has been found to range from 0.8 to 0.3. At the dissolution temperature (513 K) ofe-phase, the steady state strain sensitivity parameter has been 0.30±0.01 at the steady state strain peaks which is characteristic of dislocation climb alonge-grain boundaries. The activation energies of the transient and steady state creep in the phase transformation region have been found to be 42 kJ/mole and 63 kJ/mole characterizing the cross slipping of dislocations and dislocation climb along grain boundaries, respectively.

Plastic incompatibility and its accommodation by diffusional flow: Modelling of steady state creep of a metal matrix composite

The creep of a metal matrix composite is discussed by emphasizing the role of an internal stress and its relaxation by diffusion. The internal stress is produced by a difference in strains of plastic character (eigenstrains) between the matrix and dispersoids of the composite. The matrix plastic strain which is caused by slip dislocation activity accumulates the internal stress. The eigenstrain of the dispersoids is brought about by diffusion which occurs to relax the stress. The balance between the accumulation and relaxation of the stress results in a stationary state of creep. When the matrix has a constant flow stress, the stationary creep rate is proportional to the applied stress over a threshold value which is the matrix flow stress multiplied by the volume fraction of the matrix. Transient creep deformation is also examined and, finally, the relation of the present analysis to the Nabarro-Herring and Coble creep is discussed.

Effect of ≡ precipitates on creep deformation in Al2.5wt.%Cu

The change in the transient and steady state creep deformation of aluminium alloy containing 2.5 wt.% Cu was studied under various constant stresses ranging from 30 to 36 MPa in the temperature zone of ≡ precipitates. From the transient creep results, the peak values of the transient creep parameters β and n found in this temperature zone can be ascribed to dissolution of ≡ precipitates. The transient creep parameter β is related to the steady state creep rate ϵ st through the exponent γ. γ was found to range from 0.75 to 0.95. At the dissolution temperature (733 K) of ≡ precipitates, the steady state strain rate sensitivity parameter was 0.3 ± 0.01 at the steady state strain peaks which were characteristic of dislocation climb along ≡ grain boundaries. Microstructural analysis confirmed that the above-mentioned mechanism took place in the dissolution region of ≡ precipitates.

A state variable approach to transient creep deformation in stress reduction experiments

Stress reduction experiments have been widely used to explore the internal state of a creeping material. Although there has been some criticism of the use of this method to measure internal stress directly, data from stress reduction experiments can be used to generate parameters for state variable models that are verified by other means. In this paper the predictions of a state variable approach to stress reduction experiments are explored in detail and compared with previously published data. The state variable model is shown to give a consistent description of the processes involved during the transient deformation, and the predictions and the model parameters are found to compare well with the data obtained by other means.

Etch-Pit Studies of the Dislocation Structures Developed during Creep Deformation of Copper Single Crystals

Dislocation arrangements and substructure formation due to high-temperature creep deformation were investigated in copper single crystals by means of the etch-pit technique. Etch-pit observation was made on the surfaces parallel to the primary slip plane, (111), and to the critical slip plane, (\bar111).At an early stage of transient creep, in some regions, which will be called “region A”, subgrains elongating in the direction of the deformation band (10∼20μ×50∼200μ in size) were seen in the (111) observation. Cell structures (cell size : ∼100μ) were observed in the other regions, which will be called “region B”, adjacent to region A. Regions A and B were bordered along the plane of the deformation band, (\bar101). With the progress of transient creep deformation, the width of the long subgrains in region A increased and the cells in region B changed into well-developed subgrains, decreasing in their size. At the end of transient creep the width of the long subgrains in region A and the size of subgrains originating from the cell structures in region B were 20∼40μ and ∼50μ, respectively. The facts show that the structures in regions A and B tend to become similar with creep deformation. During steady-state creep, little change occurred in the shape and size of the substructures.Many primary dislocations were observed within the subgrains and the cells in transient creep. The primary dislocations, which were generated during instantaneous elongation, decreased in transient creep and increased slightly in steady-state creep.

Transient Creep Deformation of a Semi-Infinite Plate Compressed on a Part of Edge with an Elastic Punch : 1st Report, Compression of Straight Edge by a Flat Punch

Transient Creep Deformation of a Semi-Infinite Plate Compressed on a Part of Edge with an Elastic Punch : 1st Report, Compression of Straight Edge by a Flat Punch