On sequences of stable and unstable regions of flow along stress-strain curves of solid solutions—experiments on CuMn polycrystals

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 1993-05, Vol.164 (1), p.230-234
• Main Authors: Kalk, A, Schwink, Ch, Springer, F
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Deformation and plasticity (including yield, ductility, and superplasticity); Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Metals. Metallurgy; Physics
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/0921-5093(93)90668-5

The occurrence and behaviour of boundaries of load instabilities (Portevin-Le Châtelier effect) were investigated in dilute copper-rich CuMn for the temperatures 20°C ⪅ T ⪅ 220°C and for the strain rates 1.2×10 −6 s −1 ⩽ ε ̇ ⩽4.9×10 −4 s −1 . The measured stress-strain curves (with manganese concentration c Mn, T and ε as parameters) yield the critical stresses δ i and the strain rate sensitivity. In two T- ε ̇ intervals, named α and β, two regions of stable and unstable deformation alternate along each deformation curve. The critical stresses depend sensitively on T and ε. Careful evaluations of thermal activation parameters using two different methods provide information about the underlying processes. For interval α we find a single activation energy, and for interval β two different activation energies. Similarly, we determine a single value n≈ 1 3 for the exponent of ε ̇ −1 throughout interval α, whereas we find n≈ 1 3 for lower and n≈ 2 3 for higher stresses for interval β. A theoretical model by Kubin and Estrin ( Acta Metall. Mater., 38 (1990) 697; Phys. Status Solidi B, 172 (1992) 173) explains qualitatively the results for interval α. For interval β we propose two different diffusion processes to act successively along the deformation curves. The n-values indicate that either pipe ( n= 1 3 ) or bulk ( n= 2 3 ) diffusion processes occur.