STRUCTURE AND PROPERTIES OF NICKEL ALUMINIDE RIBBONS PRODUCED BY RAPID SOLIDIFICATION

The structure and properties of 120-200 mu m thick ribbons of Ni3Al-ba se alloy were studied. The alloy contained, at.%: 6.68 Cr, 0.86 Mo, 1. 14 Zr, 0.98 B. The ribbons were obtained by rapid solidification of mo lten alloy between two rolls. The as-cast alloy has an inhomogeneous s tructure over the length and cross section. The subsurface layer consi sts of equiaxial dendrite cells up to 1 mu m in size. The columnar den drites extend inwards to 5-35 mu m. hr the core of the ribbon there is a region of fine equiaxial grains (cells) with cross-sectional size l ess than or equal to 1-2 mu m. Electron microscopy studies revealed a moderate amount of a bcc phase (beta-NiAl). The contrast between diffe rent regions of the cellular structure suggests that the base of the a lloy is represented by cells with alternating regions of ordered and i ncompletely ordered fee crystal lattice. Dense inclusions the size of =0.1 mu m were observed and identified as nonmetallic inclusions. The tensile properties of the as-cast ribbons vary widely in separate regi ons. The maximum strength data are: UTS = 1832 N/mm(2); YS0.2 = 1105 N /mm(2); delta = 2.27%.