THE INFLUENCE OF HYDROSTATIC-PRESSURE ON FRACTURE OF SINGLE-CRYSTAL AND POLYCRYSTALLINE NIAL

Effects of pressure on the tensile ductility of single-crystal and polycrystalline cast and Powder Metallurgy (PM) NiAl are examined. Simple pressurization does not measurably influence the ductility of any of the materials, despite the pressure-induced generation of mobile dislocations in the polycrystalline cast/extruded NiAl. Tension testing with a superimposed pressure did increase the ductility of the materials tested, albeit to different levels. The fracture strain of the single-crystal NiAl did not increase appreciably when tested under pressure, while significant pressure-induced ductility increases were obtained in the PM and cast materials, with 11 pct strain being attained for the cast material tested at 500 MPa. The fracture mode of the polycrystalline samples changed from primarily transgranular (TG) at 0.1 MPa to predominantly intergranular (IG) at 500 MPa. The increases in ductility and changes in fracture appearance are discussed in light of the probable effects of pressure on fracture nucleation and propagation, while the results are additionally compared to existing models.