Abstract:There are three types of cyclic hardening for cyclically deformed interstitial-free (IF) steels. The magnitude of cyclic hardening was unobvious and dislocation cells smaller than 2 lm were very hard to find when total strain amplitude (De/2) was controlled to within 0.1 pct. When De/2 is increased to 0.125 to 0.3 pct, secondary cyclic hardening takes place prior to fatigue failure. De/2 = 0.6 pct, following an initial rapid-hardening stage. Dislocation cells smaller than 2 lm tend to develop near grain bounda… Show more
“…The softening response after initial hardening results from generation of additional mobile dislocations and formation of dislocation cell substructures of lowered internal stresses (Raman and Padmanabhan, 1994). According to Shih et al. (2010), secondary hardening rate and volume fraction of small dislocation cells are directly proportional with strain amplitude in interstitial-free steels.…”
Section: Resultsmentioning
confidence: 99%
“…According to Shih et al. (2009, 2010), while cyclic strain is controlled just above the fatigue endurance limit and cycled to failure, the small dislocation cells prefer to develop near the grain boundaries and at GBTPs for interstitial-free steels. Figure 6. All Euler orientation (SEM-EBSD/OIM) micrographs showing polycrystalline austenite grains’ geometries, configurations and connectivity of (a) base alloy (reference) and cyclically deformed AISI 304LN stainless steel at different strain amplitudes: (b) ±0.50%, (c) ±0.70%, (d) ±0.85%, (e) ±1.0%, (f) ±1.2%, (g) ±1.4% and (h) ±1.6%.…”
Section: Resultsmentioning
confidence: 99%
“…According to Shih et al. (2009, 2010), if the constant strain amplitude is varying from high to low values, the equilibrium between the dislocation multiplication and annihilation may no longer exist. This is in agreement with the present observations.…”
Section: Resultsmentioning
confidence: 99%
“…Moreover, the dislocation substructures and their patterns undergo changes during cyclic plastic deformation (Kuhlmann-Wilsdorf and Laird, 1977; Lukas and Kunz, 2002; Ma and Laird, 1988; Mayama et al., 2008; Mughrabi, 1983, 2006, 2009). It has already been investigated by many eminent scientists that cyclic plastic deformation alters the microstructure in different length scales and causes extreme instabilities with different loading amplitudes (Das et al., 2011b, 2011c; Goh and Yip, 2002; Shih et al., 2010; Yaguchi et al., 2001). Plastic deformation usually results in spatially heterogeneous arrangement/patterning of dislocations in the matrix.…”
Strain controlled low cycle fatigue experiments on multiple specimens are performed by systematically varying strain amplitudes of austenitic stainless steel under laboratory atmosphere. Different dislocation substructures/patterns developed due to strain cycling are characterised, measured by analytical transmission electron microscope and austenite grains’ misorientation, extent of different types of grain boundaries, grain connectivity, slip-system activity are also measured by electron backscatter diffraction experiments. Present investigation clearly reveals the enigma of dislocation patterning through slip system activity during cyclic plastic deformation of austenite at different strain amplitudes. It has been experimentally examined that with the increase in strain amplitude, the activity of single slip system decreases and multiple slip system increases, which in turn help to decrease the dislocation cell size and to vary in their geometric configurations and patterns.
“…The softening response after initial hardening results from generation of additional mobile dislocations and formation of dislocation cell substructures of lowered internal stresses (Raman and Padmanabhan, 1994). According to Shih et al. (2010), secondary hardening rate and volume fraction of small dislocation cells are directly proportional with strain amplitude in interstitial-free steels.…”
Section: Resultsmentioning
confidence: 99%
“…According to Shih et al. (2009, 2010), while cyclic strain is controlled just above the fatigue endurance limit and cycled to failure, the small dislocation cells prefer to develop near the grain boundaries and at GBTPs for interstitial-free steels. Figure 6. All Euler orientation (SEM-EBSD/OIM) micrographs showing polycrystalline austenite grains’ geometries, configurations and connectivity of (a) base alloy (reference) and cyclically deformed AISI 304LN stainless steel at different strain amplitudes: (b) ±0.50%, (c) ±0.70%, (d) ±0.85%, (e) ±1.0%, (f) ±1.2%, (g) ±1.4% and (h) ±1.6%.…”
Section: Resultsmentioning
confidence: 99%
“…According to Shih et al. (2009, 2010), if the constant strain amplitude is varying from high to low values, the equilibrium between the dislocation multiplication and annihilation may no longer exist. This is in agreement with the present observations.…”
Section: Resultsmentioning
confidence: 99%
“…Moreover, the dislocation substructures and their patterns undergo changes during cyclic plastic deformation (Kuhlmann-Wilsdorf and Laird, 1977; Lukas and Kunz, 2002; Ma and Laird, 1988; Mayama et al., 2008; Mughrabi, 1983, 2006, 2009). It has already been investigated by many eminent scientists that cyclic plastic deformation alters the microstructure in different length scales and causes extreme instabilities with different loading amplitudes (Das et al., 2011b, 2011c; Goh and Yip, 2002; Shih et al., 2010; Yaguchi et al., 2001). Plastic deformation usually results in spatially heterogeneous arrangement/patterning of dislocations in the matrix.…”
Strain controlled low cycle fatigue experiments on multiple specimens are performed by systematically varying strain amplitudes of austenitic stainless steel under laboratory atmosphere. Different dislocation substructures/patterns developed due to strain cycling are characterised, measured by analytical transmission electron microscope and austenite grains’ misorientation, extent of different types of grain boundaries, grain connectivity, slip-system activity are also measured by electron backscatter diffraction experiments. Present investigation clearly reveals the enigma of dislocation patterning through slip system activity during cyclic plastic deformation of austenite at different strain amplitudes. It has been experimentally examined that with the increase in strain amplitude, the activity of single slip system decreases and multiple slip system increases, which in turn help to decrease the dislocation cell size and to vary in their geometric configurations and patterns.
“…The advantage of BEI is the sample preparation is easy and the observation region is broad. Huang et al [31,32] successfully observed the dislocation structure of copper and interstitial free (IF) steel regardless of the strain amplitude using this technique. The dislocation structure evolution in ultra-large grain (average grain size of about 600 mm) in pure copper is very seldom reported in the literature.…”
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