Deformation behaviour of Cu-Zn-Si alloys close to their martensitic translormation temperature
Variations in the pseudoelastic and shape memory effects are described for large-grained specimens of Cu-Zn-Si alloys on altering <br></br><br></br> 1. (a) the amount of strain, and<br></br> 2. (b) the temperature. <br></br><br></br> The progressively decreasing pseudoelastic recovery as the strain is increased is attributed to grain boundary deformation and interaction between different martensite variants. Yield drops were found in the stressstrain curves, but not always the two clearly defined stages reported by Pops. When the temperature was varied, complete pseudoelasticity was not found with temperatures close to <i>M<sub>s</sub></i>, nor with temperatures much higher than <i>M<sub>s</sub></i>, but it was found at intermediate temperatures. The sum of shape memory recovery plus pseudoelastic recovery was close to 100% in general, and the stress for a given strain always increased with temperature. There is evidence that pre-martensitic crystallographic changes occur near <i>M<sub>s</sub></i>, and these are thought to be involved in the shape memory behaviour, the pseudoelasticity being essentially due to stress induced martensite nucleation. The latter is more difficult at higher temperatures and the stress may eventually cause more general yielding instead.<br></br><br></br> Successive cycles of deformation and recovery (strain and temperature constant) increased pseudoelastic recovery, thought to be due to the sweeping out of obstacles; and a two-way memory effect is also reported.
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