EFFECT OF STRAIN RATE ON THE FRACTURE-BEHAVIOR AT 1366-K OF THE BCC IRON BASE OXIDE DISPERSION STRENGTHENED ALLOY MA 956

The tensile behavior of the oxide dispersion strengthened iron-base alloy MA 956 was investigated as a function of strain-rate ranging from 3.3×10-2 to 8.3×10-8 s-1 at 1366 K. All tests were conducted in the longitudinal direction on specimens machined from bar stock. Because of the microstructure of this alloy, all specimens were either single crystals or bicrystals with the boundary parallel to the gage length. Testing revealed that the strength was rather insensitive to strain-rate, the tensile ductility decreased with decreasing strain-rate, and for strain-rates ≤8.3×10-5 s-1, the alloy fractured in brittle manner. Evidence of transgranular cracking perpendicular to the applied stress was observed at all strain-rates; failure at strain-rates ≤8.3×10-5 s-1 was due to cracks which grow by the joining together of cavities ahead of the running crack. This alloy appears to possess a critical stress intensity factor for rapid crack growth. © 1979 The Metallurgical of Society of AIME.