1985 Volume 49 Issue 12 Pages 1106-1112
Tensile tests in the temperature range betwean 293 and 1773 K and fractography were carried out on 6×10−4 m thick specimens of Mo-0.3, 0.5, 0.75 and 1.0 mass%Zr alloys nitrided in a purified N2 atmosphere of 0.1 MPa at 1473 to 1773 K, referring to the alloys recrystallized in a vacuum at 1773 K.
The nitrided samples, irrespective of solute content and nitriding temperature, underwent brittle fracture before macroscopic yielding at all test temperatures lower than 1673 K, while the recrystallized alloys showed good ductility. This embrittlement may be attributed to a high stress concentration at grain boundaries near the surface at a depth of ∼10−4 m, built up by dislocation channeling throughout the region containing very thin plate-like ZrN precipitates about 0.5 nm thick. At 1773 K, the nitrided alloys had a fairly good ductility independent of solute content. At such high temperatures, no stress concentration may occur at grain boundaries because of the ease of dissociation and climbing of glide dislocations there.
