Densification route and mechanical properties of Si3N4–bioglass biocomposites

The processing route and the final microstructural and mechanical characteristics of a novel biomaterial composite are described. This new material is composed of 70 wt% Si3N4 ceramic phase and 30 wt% bioglass, the later performing as a liquid sintering aid system and simultaneously providing bioactivity characteristics to the composite. The conditions for fabrication of an almost fully dense material ( 98% of relative density) were pursued. Optimised parameters were 1350°C–40 min–30 MPa by hot-pressing technique. The very fast densification rate of the process avoided the crystallisation of the bioglass intergranular phase and therefore its intrinsic properties were maintained. Also, the large amount of glassy phase assured the densification by liquid phase assisted grain rearrangement without Si3N4 phase transformation. The final mechanical properties of the Si3N4–bioglass were as follows: fracture toughness, KIC=4.4 MPa m1/2; Vickers hardness, HV=10.3 GPa; Youngʹs modulus, E=197 GPa; bending strength, σR=383 MPa; Weibull modulus, m=8.3. These values provide an attractive set of properties among other bioactive materials, namely by upgrading the main drawback of bioceramics and bioglasses for high-load medical applications, which is the lack of satisfactory fracture toughness.