Strengthening at nanoscaled coherent twin boundary in f.c.c. metals

Abstract

This paper analyses slip transfer at the boundary of nanoscaled growth twins in face-centred cubic (f.c.c.) metals for strengthening mechanism. The required stress for slip transfer, i.e. inter-twin flow stress, is obtained in a simple expression in terms of stacking fault energy and/or twin boundary (TB) energy, constriction energy and activation volume. For nanotwinned Al, Cu and Ni, inter-twin flow stress versus twin thickness remarkably shows Hall-Petch relationship. The Hall-Petch slope is rationalized for various reactions of screw and non-screw dislocations at the TB. Additionally, strengthening at the boundary of nanoscaled deformation twins in f.c.c. metals is analysed by evaluating required twinning stress. At small nanograin size, the prediction of deformation twin growth stress shows inverse grain-size effect on twinning, in agreement with recent experimental finding.

A model for 〈c+a〉 dislocation transmission across nano-spaced parallel basal stacking faults in a HCP alloy

“…Equation (5) is in agreement with the 1/d linear relationship observed in [15,16]. If a pile-up of dislocations against the BSF occurs, the second term on the right side of Equation (1) is replaced by À3:5094 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi d= sin h p sb r 3=2 À r 3=2 0 [18,19]. A similar derivation leads to following tensile flow stress,…”

“…The left end and right end of the loop are pined to the grain boundary where the 〈c + a〉 dislocation is emitted into the first nanospace. From above, the maximum size of the loop within a nanospace is d= sin h. An activation methodology similar to that in the step (1) appears in the recent study of dislocation transmission across twin boundary in nano-twinned FCC metals [18,19]; a loop growth scheme similar to that used in the step (2) was employed in the study of intra-granular dislocation emitted from grain boundaries of nano-grained FCC metals [20][21][22][23].…”

The role of crystallography and the mechanisms associated with migration of incoherent twin grain boundaries

“…3 GBs are of particular importance because they readily manifest in medium to low stacking fault energy materials either through annealing or mechanical twinning [5][6][7]. The presence of the low energy coherent 3 interface can lead to enhanced material properties (such as strength [8][9][10], cracking resistance [6,7,11], and corrosion resistance [12]). Grain boundary engineering (GBE) emerged as a technique to optimize thermomechanical processing routes that enhance properties by increasing the fraction of 3 and other special GB types [6,7].…”

Effect of Surface Mechanical Treatments on the Microstructure-Property-Performance of Engineering Alloys

“…The twin boundary increases the work hardening rate by acting as an obstacle for gliding dislocations [75]. Together, slip transfer at the boundary of nanoscale growth twins in FCC structures also provides the strengthening mechanism and ductility enhancement [76]. It has been demonstrated that the twinning mechanism can simultaneously maintain high strength and ductility of the material.…”