Revisiting Stacking Fault Energy of Steels
- PDF / 1,703,120 Bytes
- 21 Pages / 593.972 x 792 pts Page_size
- 108 Downloads / 236 Views
TION
STACKING fault, two-dimensional planar defects, is one of the most important crystal imperfections, which is mainly introduced in the material by mechanical deformation and this, in turn, plays a crucial role in the plastic deformation behavior of face-centered cubic (fcc) alloys. The differences in deformation behavior of fcc alloys are strongly dependent due to differences in the stacking fault behavior. However, the strengthening of fcc alloys is strongly dependent on the stacking fault energy (SFE), which generally influences splitting of screw dislocations.[1] Splitting of screw dislocations must be pushed back together before they can cross slip. The cross slipping becomes more difficult as the split in the dislocations increases.[1] The SFE for the Al is so large that splitting is less than one Burgers vector, which is defined as dislocation bands. The partial dislocations separate the slipped and non-slipped areas, while in between one another, they fix a partially slipped area as the stacking fault. Due to stacking fault, dislocations are connected to a certain slip plane so that screw dislocations have a defined slip plane.[1] Metals with wide stacking faults (i.e., low SFE) strain harden more rapidly, twin easily on annealing, and show a different temperature dependence of the flow stress than metals with narrow stacking faults. Metals with high SFE have a deformation substructures of banded, linear arrays of dislocations, which has been reported in detail elsewhere.[2]
ARPAN DAS, Dr. K.S. Krishnan Research Associate, is with the Mechanical Metallurgy Division, Materials Group, Bhabha Atomic Research Centre (Department of Atomic Energy), Trombay, Mumbai, Maharashtra 400 085, India. Contact e-mails: dasarpan1@yahoo. co.in, [email protected] Manuscript submitted February 19, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
SFE is very sensitive to chemical composition of the material and the temperature. According to Otte,[3] faulting in austenite (fcc) is in all cases consistent with a high work hardening capacity of the austenite. The SFE in pure metals and alloys is very important for creep deformation behavior.[2] The smaller the SFE, the spacing between two partial dislocations is greater and cross slipping is even more strongly restricted. Thus, softening becomes more difficult and the stationary creep rate is reduced. This explains the large creep resistance of austenitic steels, which has been documented elsewhere.[1] Constrictions in stacking fault ribbon permit cross slipping, but this requires energy. The greater the width of the stacking faults, the more difficult is to produce constrictions in the stacking faults. This explains why the cross slip is quite prevalent in Al, that has a very narrow stacking fault ribbon, while it is not observed usually in Cu, which has a wide stacking fault ribbon.[2] There is good correlation between SFE and type of texture. High SFE and high temperature deformation favor the Cu-type structure f112gh111i.[2] The SFE plays an important role in determination of critical
Data Loading...
