Study On Preparation Technology Of B₄C Coated W Core SiC Fibers

B4C coatings on the W core SiC fibers were prepared via a Chemical Vapor Deposition (CVD) process in order to improve the interfacial reaction between the reinforcement W core SiC fiber and the matrix Ti alloy. The coating temperature, total flow and proportion of reactive gas, takeup speed and other process parameters that affected B4C coatings on W core SiC fibers were studied, and the influence of various process parameters on the tensile strength and elastic modulus of W core SiC fibers, the thickness and surface morphology of B4C coatings were investigated by scanning electronic microscope and tensile test. The experimental results exhibited that it can not obtain B4C coatings below a coating temperature of 1100℃. Under the given process parameters, B4C coated fibers were obtained with a tensile strength close to that of the original W core SiC fiber (~3339MPa). To optimize the process parameters, it should be satisfied that the coating temperature>1210℃and the takeup speed>0.055m/s, or the coating temperature<1210℃and the takeup speed<0.055m/s. Perfect B4C coatings can be obtained when the total flow of reactive gas was 2.25~2.7L/min. The influence of the BCl3 flow on the surface morphology of B4C coatings was small, however, the influence of H2 and CH4 flow was very obvious. The coating temperature was the most important factor of all process parameters, and it affected significantly the tensile strength and elastic modulus of W core SiC fibers, the thickness and surface morphology of B4C coatings. The takeup speed and the total flow of reactive gas affected the tensile strength and elastic modulus of W core SiC fibers, the thickness of B4C coatings. The proportion of reactive gas affected the tensile strength and elastic modulus of W core SiC fibers, the surface morphology of B4C coatings. Finally, the optimal process parameter of B4C coatings on W core SiC fiber was coating at 1210℃, BCl3 flow of 1.2L/min, H2 flow of 0.9L/min, CH4 flow of 0.3L/min, cleaning H2 flow of 1.0L/min, and takeup speed of 0.055m/s.The composite precursors were prepared by Magnetron Sputtering Physical Vapor Deposition (MSPVD) process, and the B4C coated W core SiC fiber reinforced TiAl matrix composite were prepared at a hot press process of 950~1000℃under 30~40MPa for 3~4h. The interface between the reinforcement W core SiC fiber and the matrix TiAl alloy were studied by scanning electronic microscope. The results revealed that the B4C coating acted as a sacrificial layer, and it will effectively reduce the interfacial reaction between the two.