DYNAMIC STRENGTH AND STRAIN RATE EFFECTS ON FRACTURE-BEHAVIOR OF TUNGSTEN AND TUNGSTEN ALLOYS

An investigation of the stress-strain response as a function of strain rate, spall strength, and dynamic fracture behavior of pure W, W-26Re, W-Ni-Fe and W-Ni-Fe-Co has been performed. Spall strength measurements, obtained in symmetric-impact tests, showed an increase in spall strength from 0.4 GPa for pure tungsten to 3.8 GPa for 90W-7Ni-3Fe. Concurrent with the increase in spall strength was a change in fracture mode from cleavage (for pure W) to a mixture of transgranular and intergranular fracture for the alloyed systems. Compression testing performed at strain rates from 10(-3) s-1 to 3000 s-1 showed that pure tungsten exhibits a large strain rate sensitivity and almost no work hardening at tested strain rates. In contrast, W-26Re and W-Ni-Fe-Co displayed significant work hardening at all strain rates.