The microstructure characteristics and deformation behavior of 304L stainless steel during tensile deformation at two different strain rates have been investigated by means of interrupted tensile tests, electron-backscatter-diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The volume fractions of transformed martensite and deformation twins at different stages of the deformation process were measured using X-ray diffraction method and TEM observations. It is found that the volume fraction of martensite monotonically increases with increasing strain but decreases with increasing strain rate. On the other hand, the volume fraction of twins increases with increasing strain for strain level less than 57%. Beyond that, the volume fraction of twins decreases with increasing strain. Careful TEM observations show that stacking faults (SFs) and twins preferentially occur before the nucleation of martensite. Meanwhile, both ɛ-martensite and α′-martensite are observed in the deformation microstructures, indicating the co-existence of stress-induced-transformation and strain-induced-transformation. We also discussed the effects of twinning and martensite transformation on work-hardening as well as the relationship between stacking faults, twinning and martensite transformation.

Twinning and martensite in a 304 austenitic stainless steel

Effect of stacking-fault energy on deformation twin thickness in Cu-Al alloys

Molecular dynamics simulations of shock compression of nickel: From monocrystals to nanocrystals

This chapter reviews the results of a large number of shook loading experiments utilizing a common design and a constant shock pulse duration of 2 µs. It is shown that dislocations, dislocation cells, planar dislocation arrays, stacking faults, twins, twin faults, and point defects all contribute in specific systems to residual shock strengthening. Shock-induced microstructures are determined primarily by the stacking fault free energy. High stacking-fault free energy metals and alloys are characterized by dislocation cell structures while low stacking-fault free energy metals and alloys (with the fcc structure) are characterized by planar dislocation arrays, stacking faults and twins in {111} planes. High stacking-fault free energy metals and alloys also twin according to critical shear stress criteria, and the (001) orientation is the initial orientation where twinning occurs. Residual shock microstructures and specific lattice defects induced by the peak shock pressure are shown to be related to resisdual hardness and engineering yield stress. Body-centered cubic metals and alloys are characterized by irregular dislocation arrays as a result of the more numerous slip planes, although twinning also occurs in bcc metals.

F. Greulich

Papers

Effect of Grain size, dislocation cell size and deformation twin spacing on the residual strengthening of shock-loaded nickel