The effects of boron on mechanical properties and corrosion resistance in $Ni_3Al$ polycrystal alloys were investigated.
The ingots of $Ni_3Al$ with various boron additions (0, 0.05, 0.1 wt%) were prepared by vacuum induction melting using high purity Ni, Al and AlB (3.3 wt% boron mother alloy) and remelted to homogenize the composition of those alloys under vacuum condition.
In general, the $Ll_2$ type intermetallic compound $Ni_3Al$ has been known to be so brittle so far and its corrosion resistance is also not good in the grain boundaries.
In this work, $Ni_3Al$ polycrystals without boron did not exhibit any ductility at room temperature and showed inter-granular corrosion behavior.
But a small addition of boron improved mechanical properties and corrosion resistance of $Ni_3Al$ polycrystals considerably. Especially 0.1 wt% boron added $Ni_3Al$ could be bent with no signs of fracturing and showed about 38% elongation. But yield strength was decreased about 5Kg/㎟.
It was found by scanning electron microscopy that fracture mode and corrosion behavior changed from the intergranular one to the transgranular type due to the effect of boron. In effect, boron appeared to be effective element which suppress the intergranular fracture and corrosion behavior by strengthening the grain boundaries of $Ni_3Al$ poly-crystal alloy.
