Abstract
Molybdenum sheets with two types of elongated coarse-grain structures (trade name: TEM) were developed by heavy duty rolling and recrystallization treatment of sintered molybdenum bodies with lmass% La2O3. One type has spindle-like grains (S-TEM) and the other has stacked plate-like grains (P-TEM). Three-point bending tests were carried out on S-TEM and P-TEM at 77K to 300K, to investigate the effects of grain structure on their ductile-to-brittle transition characteristics such as maximum strength and ductile-to-brittle transition temperature (DBTT).
The aspect ratio (LRD/W) of grains on the perpendicular plane to the rolling direction and the number of grains (Ng)along the normal direction of sheets were estimated as parameters of the grain structure. The following results were obtained.
(1) Molybdenum sheets with elongated coarse-grain structures (S-TEM and P-TEM) had a higher fracture strength at low temperatures and a lower DBTT, than pure molybdenum and TZM with equiaxial-grain structures.
(2) Cracks are initiated at a fine equiaxial-grain near the surface of the specimen and propagated across elongated coarse-grains remaining on the cleavage-fractured surface.
(3) Fracture strength increased and DBTT decreased with Ng, of S-TEM.
(4) P-TEM with fewer residual fine equiaxial-grains had a lower DBTT and higher maximum strength.
