EFFECT OF CARBON ON STRUCTURAL CHANGES IN Ni3Al PHASE

The paper presents X-ray diffraction and metallographic researches of a carbon influence on structural changes in Ni3Al phase. Base alloys were made maintaining the nominal atomic ratio of Ni:Al = 3:1. Next, carbon was introduced into the individual liquid alloys at a rate of 0.2, 0.25, 0.5, 0.75, 1 and 1.25 wt. %. Final castings were cut into pieces and specimens for microscopic and X-ray diffraction examinations were prepared. Their phase composition was analysed as well as the structural changes occurring within the Ni3Al phase. Some changes along the lattice constants of the Ni3Al phase were noticed, and they amounted to 0.3580 nm and 0.3589 nm for 0.2 wt.% C and 1.25 wt.% C, respectively. In the alloy consisting 1.25 wt.% C, the presence of graphite of the (001) atomic plane was noticed. Its existence is connected with exceeding the solubility limit of carbon in the Ni3Al phase. This result was also confirmed by metallographic researches, in which numerous precipitates of graphite of both lamellar and nodular shape were observed to exist.