An impression test method for characterization of the flow behavior of superplastic material

The deformation behavior of the superplastic ZnAl eutectoid has been investigated using an impression test at temperatures ranging from room temperature to 548 K. Unlike the conventional method, the flow curve of the superplastic material can be obtained by precise measurements of the displacement of a small cylindrical punch at a predetermined rate into the specimen as a function of applied load. Typically, the flow stress was obtained at a constant penetration rate whereas the strain rate sensitivity was determined by instantaneous changes in the rate of penetration. The value of activation energy for this thermally activated process was found to be 71.1 kJ mol−1 as determined from the flow curve in range II. The temperature and strain rate dependences of flow stress, and the strain rate sensitivity obtained with this impression test, are compared with those of conventional test results. The results suggest that the parameters which are commonly selected as characteristics of superplastic formability can be obtained using the impression test.

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