On the Application of Ball Indentation Test to Characterize Dynamic Strain Aging in Alloy 617M

Abstract

The dynamic strain aging (DSA) behavior of Alloy 617M was exhibited from the compressive ball indentation (BI) tests using spherical indenter in the temperature regime 773-973 K. Type B and B + C serrations were incidentally observed in the load depth of indentation curves measured from BI tests, suggesting that DSA caused by the interaction of dislocations with solute atoms is the dominant mechanism in this temperature range. Notably, the modulus-compensated yield and ultimate tensile strengths were found to exhibit plateaus or even increasing trend with temperature above 673 K. Similarly, the strength coefficient and strain hardening exponent were observed to display anomalous behavior above 673 K. The DSA was further examined by varying the cross-head velocity (indenter speed) in the range 0.003-0.010 mm/s. Interestingly, negative strain rate sensitivity, which was another signature of DSA, was confirmed when the true stress decreased with increasing effective strain rate. The range of temperature of occurrence of DSA as observed from BI tests was similar to that reported from uniaxial tension test, thus signifying the applicability of BI technique to characterize the DSA behavior of materials.