Effects of initial density during laser machining assisted CVI process and its influence on strength of C/SiC composites

Novel laser-assisted chemical vapor infiltration (LA-CVI) technique has been used to improve the density and strength of carbon fiber reinforced SiC composites (C/SiC). Initial density of C/SiC before laser machining played an important role in determining the final density and strength of composites. Results show that final density and bending strength of lower initial density composites were better than that of higher initial density samples after LA-CVI process, while the porosity exhibited opposite behavior. Micro-CT and COMSEL simulation results verify that after LA-CVI process, dense band width of C/SiC with initial density of 1.5 g/cm³ was twice as that of C/SiC with initial density of 1.8 g/cm³. This led to crack propagation bypassing the micro-hole. In conclusion, low initial density when laser machining was carried out resulted in better properties of final composites.