Loading rate effects on ductile-phase toughening in in-situ niobium silicide niobium composites

This paper reports on brittle silicide intermetallics such as Nb5Si3 significantly toughened by Nb particles incorporated during in-situ processing techniques. Ten-fold increases in toughness as well as resistance-curve behavior have been realized at conventional testing rates with these ductile Nb particles. Under more rapid loading rates the efficiency of the body-centered cubic (bcc) Nb particles in enhancing the toughness may be affected due to the strain-rate sensitivity of the Nb and/or the possible strain-rate sensitivity of interfacial debonding. Toughness tests conducted at loading rates of 0.0042 to 8.5 mm/sec have indicated a significant sensitivity to testing rate, with a drop in fracture toughness from 28 to 9 MPa √m over this range accompanied by a change in fracture mode from primarily ductile to cleavage failure in the Nb