A HIGH-RESOLUTION-ELECTRON-MICROSCOPY STUDY OF A GAMMA GAMMA'-ALPHA DIRECTIONALLY SOLIDIFIED EUTECTIC ALLOY .1. THE AS-SOLIDIFIED STATE/

The microstructure of a gamma/gamma'-alpha directionally solidified (D S) eutectic alloy with a nominal solidified composition of Ni-30.26Mo- 6.08Al-1.43V (wt %) was investigated by means of high-resolution elect ron microscopy (HREM) and analytical electron microscopy. The alpha-fi bres exhibited a typical morphology with a rectangular cross-section a nd they displayed the Bain orientation relationship (OR) with the gamm a'/gamma matrix; that is, [0 0 1](alpha)parallel to [0 0 1](gamma), an d (1 1 0)(alpha)parallel to(0 1 0)(gamma,). Misfit dislocations and la ttice strain fields existed at the alpha/gamma' interface for differen t habit planes; that is, (1 1 0)(alpha)parallel to(0 1 0)(gamma,) and (1 0 0)(alpha)parallel to(1 1 0)(gamma,) were analysed. EDAX (Energy d ispersive X-ray) analysis showed that the composition of the gamma-pha se was approximately Ni-4(Mo, Al, V); it contained 90 degrees rotation al domains of Ni-3(Mo, Al, V) with a DO22 structure and Ni-2(Mo, Al, V ) with a Pt2Mo structure.