MICROSTRUCTURAL FEATURES OF FRICTION WELDED MA-956 SUPERALLOY MATERIAL

The microstructural features of MA 956 friction welds were examined us ing a combination of optical microscopy and transmission electron micr oscopy (TEM). The MA 956 base material contained a uniform distributio n of small diameter (<20 nm) Y2O3 particles. Limited numbers of larger diameter (> 100 nm), spherically shaped Al2O3, Ti(C,N), Y2O3-Al2O3, a nd Al-Ti-Y containing particles were also observed in the MA 956 base material. In the recrystallized region, the grain size was largest at the bondline and increased markedly in the radial direction of the wel ded joint. Increasing the forging pressure from 50 to 150 MPa during t he friction welding operation markedly increased the strain rate and d ecreased the grain size at the joint centerline. The friction welding operation substantially altered the particle chemistry, dimensions, an d shape in the joint region. The number of aluminum-rich or titanium-r ich particles was substantially decreased and large irregularly shaped particles were formed.