ORIENTATION AND HABIT PLANE RELATIONSHIPS FOR CARBIDE AND NITRIDE PRECIPITATES IN MOLYBDENUM (REPRINTED FROM METALLOGRAPHY, VOL 1, PG 195-220, 1968)

Precipitation of group IVa carbides and nitrides (TiC, TiN, ZrC, ZrN, HfC, and HfN) in molybdenum has been studied with electron microscopy. The precipitates display a characteristic platelike morphology, and c ontrast effects suggesting coherent nucleation have been observed. The zirconium and hafnium carbides and nitrides exhibit a cubic {100} hab it plane and an orientation relationship with the matrix characterized as follows: {100}(Mo)//{100}(ppt) [100](Mo)//[110](ppt) [110](Mo)//[1 00](ppt) Platelike precipitates of titanium carbide and titanium nitri de, however, exhibit an apparent {310}(Mo) habit plane. An analysis of the mismatch parameters and an approximate calculation of the relativ e strain energies associated with coherency for various possible habit planes and matrix-precipitate orientation relationships confirm the { 100}(Mo) habit for the zirconium and hafnium carbide and nitride preci pitates. The theory predicts the observed {310}(Mo) habit plane for th e titanium carbide and nitride phases with the following orientation r elationship: {310}(Mo)//{113}(ppt) [113](Mo)//[112](ppt) [100](Mo)//[1 10](ppt).