A Re-examination of grain boundary fracture in Ni₃Al - environmental and alloying effects

The intrinsic room-temperature ductility (approx.23%) of polycrystalline Ni₃Al is considerably higher than previously thought Environmental embrittlement, caused by moisture in ordinary ambient air, reduces significantly the maximum attainable ductility in air. Microcracks (introduced during processing) can also reduce the maximum attainable ductility in air. A consequence of these extrinsic factors is that polycrystalline Ni₃Al is usually found to be quite brittle in air, and very careful experimental procedures are required if its (higher) intrinsic ductility is to be measured. The addition of B essentially suppresses environmental embrittlement in Ni₃Al, thereby improving ductility. The substitutional elements Zr and Hf also improve ductility, but Ti (which is from the same group in the periodic table) does not. The mechanism by which Zr and Hf improve ductility is not known, but they appear to both alleviate environmental embrittlement and enhance grain boundary cohesion.