Quasi-Stationary Strength of ECAP-Processed Cu-Zr at 0.5 Tm

Abstract

The influence of the grain structure on the tensile deformation strength is studied for precipitation-strengthened Cu-0.2%Zr at 673 K . Subgrains and grains are formed by equal channel angular pressing (ECAP) and annealing. The fraction of high-angle boundaries increases with prestrain. Subgrains and grains coarsen during deformation. This leads to softening in the quasi-stationary state. The initial quasi-stationary state of severely predeformed, ultrafine-grained material exhibits relatively high rate-sensitivity at relatively high stresses. This is interpreted as a result of the stress dependences of the quasi-stationary subgrain size and the volume fraction of subgrain-free grains.

Effect of severe plastic deformation on creep behaviour and microstructure changes of P92 at 923 K

“…When the grains coarsen with increasing creep strain and approach the size closer to w(d ∼ 0.5-0.6 w s ), the value of n qs is about 5-8. Similar values of n qs were also found in other studies investigating creep behaviour of UFG materials [6][7][8]23]. This creep behaviour was explained and also experimentally modelled by using the simple dislocation model, which was proposed by Blum et al [37].…”

“…An opposite tendency can be found at high stresses. The stress exponent determined fromε-σ creep curves can be called the quasi-stationary stress exponent n qs [7,23]. It can be seen (Fig.…”

“…After normalization and tempering martensitic 9% Cr steels have a fine subgrain microstructure with high dislocation density in the interiors which slows creep rate down [1,5]. The subgrains size coarsen with creep strain until their size reaches a station-*Corresponding author: e-mail address: pkral@ipm.cz ary value expected for the stationary state [5][6][7]. The stationary state is the state when stress and strain rate is constant.…”

“…However, during creep testing under the constant load, the stress and also creep strain are changing. For this reason, the so-called stationary state is sometimes called quasi-stationary (qs) because the changing stress and creep strain lead to small but not negligible microstructure changes [7][8][9].…”

The Effect of Predeformation on Creep Strength of 9% Cr Steel

“…For this reason, SPD techniques provide a unique opportunity to study the influence of significantly different microstructures on creep behavior of metals. Recent results showed that differences in the creep strength of SPD-processed state and its undeformed counterpart depend on the value of plastic strain imposed into the material [ 10 , 11 , 12 , 13 , 14 ], temperature, and applied stress used during creep testing [ 15 , 16 , 17 ].…”