Additive Manufacturing of Silicon Nitride Ceramic Floatation Spheres with Excellent Mechanical Properties

Silicon nitride (Si(3)N(4)) ceramic materials are increasingly being used in deep-sea pressure-resistant applications because of their high compressive strength-to-weight ratio. In the present study, Si(3)N(4) ceramic floatation spheres with an outer diameter of approximately 101 mm are successfully batch produced and evaluated. The implementation method was to prepare Si(3)N(4) ceramic hemispherical housings and pair them together. In order to improve the safety of the joint, the hemispherical Si(3)N(4) housings were gradually thickened from 1.80 to 2.50 mm at the equator near the joining surface, based on a 3D model with additive manufacturing technology. The weight-to-displacement ratio of the prepared floatation sphere is approximately 0.34 g/cm(3). The flexural strength, compressive strength of the material and the collapse strength of a number of Si(3)N(4) floatation spheres were tested to be 1150, 3847, and 205 MPa, respectively, to confirm the reliability of the process. Additional sustained and cyclic hydrostatic pressure tests simulating the full ocean depth working conditions are carried out on several Si(3)N(4) floatation spheres, which perform very well and do not fail.