FORMATION OF SLIP TRACES DURING RECRYSTALLIZATION OF THIN METAL SHEETS

During a study of the mechanical properties of polycrystalline Ni3Al p roduced by recrystallizing B-free Ni3Al single crystals, it was discov ered that {111} slip traces formed during grain growth of cold rolled single crystal thin sheets annealed at 1200 degrees C for 10 hours. Gr ain growth stops when the slip starts. The slip traces are revealed by the formation of thermal grooves at 1200 degrees C. The formation of slip traces seems to be a general phenomenon during the recrystallizat ion of thin sheets of metals, as slip traces also formed on cold-rolle d polycrystalline Cu thin sheets annealed at 922 degrees C for 10 hour s. It is proposed that the residual strains/stresses in the thin recry stallized sheets are responsible for the slip processes and also provi de a primary driving force for grain growth. Slip begins when the grai n size has increased to the point where the yield stress, as determine d by the Hall-Petch relation, equals the residual stress. As the resid ual stresses and strains are relieved by the slip, grain growth stops, and the traces seen in this study are produced. The resulting grain s ize can be controlled by changing the level of the yield stress or the residual stresses thereby changing the critical grain size at which t he two stresses are equal. Thus thinner specimens will have a smaller grain size because the yield stress decreases with decreasing sample t hickness in sheet specimens. Other factors, such as annealing temperat ure or amount of cold-work also directly influence the final grain siz e.