Experimental design in the deposition of BN interface coatings on SiC fibers by chemical vapor deposition

Boron Nitride (BN) coatings deposited by chemical vapor deposition (CVD) have been increasingly used as an interface material for SiC/SiC composites. In this work, the CVD of BN was investigated using a statistical design of experiments (DOE) approach. In order to determine the most significant parameters for the process a two-level screening design (Plackett–Burman) was employed. The deposition pressure, gas mixture dilution factor, deposition time, and the reaction gas flow ratios were found to be the most significant factors that influenced coating thickness. To optimize the deposition process, a three-level surface response design (Box–Behnken) was used with the aim of producing a predictive mathematical model of the process. The generated response surface modeling (RSM) showed that deposition time had the greatest effect on coating thickness while, temperature–time and temperature–NH3/BCl3 interactions may be large at low/high NH3/BCl3 ratios and high deposition time, respectively. Tensile strength was strongly influenced by the deposition temperature and deposition time. The response model showed the dependence of tensile strength on coating thickness, NH3/BCl3 gas flow ratios and time. The model interaction plots suggested a dependence of temperature–gas flow ratio on tensile strengths of BN coated SiC fibers.