Microstructure evolution and hardness variation of pack-rolled nanocrystalline nickel

The microstructure evolution and hardness of nanocrystalline nickel during pack rolling at room temperature have been investigated. It was found that the roll-bonding side (R) and non-roll-bonding side (NR) behaved quite differently. The hardness of side R is higher than that of side NR. No obvious work softening was observed in either side R or side NR until the strain reached ~ 0.611. Quantitative X-ray diffraction analysis indicated that the grain size in side NR increases faster than that in side R, a result confirmed by transmission electron microscopy. Texture analysis showed that (2 0 0) preferred orientation first strengthens but then weakens in both sides NR and R, while a strong (2 2 0) preferred orientation emerges, particularly in side R. Further texture analysis suggests that dislocation slip is responsible for the texture discrepancy between side NR and side R. The dislocation activity, grain rotation and grain growth are discussed based on the experimental results.     

Scaling of stacking fault energy and deformation temperature on strain hardening of FCC metals and alloys

The strain-hardening behaviour of metals and alloys are significantly affected by the dynamic recovery process, the rate of which can be increased by increases in deformation temperature and/or stacking fault energy (SFE). In the present work, the decay slope of the strain-hardening rate with flow stress as a function of both temperature and stacking fault energy is quantitatively evaluated for several face-centered cubic metals and alloys. A universal and quantitative approach to the scaling of the effects of temperature and stacking fault energy on strain-hardening behaviour is developed, which could be useful for predicting deformation behaviour or for material design.