DUCTILE PHASE TOUGHENING OF MOLYBDENUM DISILICIDE BY LOW-PRESSURE PLASMA SPRAYING

The low fracture toughness of MoSi2 at ambient temperature has prompted investigations into new processing methods in order to impart some degree of fracture toughness into this inherently brittle material. In the following investigation, low pressure plasma spraying was employed as a fabricating technique to produce spray-formed deposits of MoSi2 and ductile reinforced MoSi2 composites containing approximately 10 and 20 vol.% of a discontinuous tantalum lamelli reinforcement. Fracture toughness K1C measurements of MoSi2 and the MoSi2-Ta composites were done using a chevron notched four-point bend fracture toughness test in both the as-sprayed condition and after hot isostatic pressing at 1200-degrees-C and 206 MPa for 1 h. Results from the ductile reinforced MoSi2-Ta composites have shown that fracture toughness increases on the order of 200% over the as-sprayed MoSi2 (4.50 +/- 0.173 MPa m1/2 to 9.97 +/- 0.25 MPa m1/2). In addition, a marked anisotropy in fracture toughness was observed in the spray-formed deposits owing to the layered splat structure produced by the low pressure plasma spray process.