A ceramic matrix composite is formed from a non-oxide ceramic and continuous ceramic fibers. The matrix includes a hafnium donor in the matrix in an amount sufficient to harden the composite at elevated temperatures to prevent ablation of the composite. The matrix also includes a boron donor in the matrix in an amount sufficient to lower the glass transition temperature of the composite to flow over cracks formed in the composite. The method to form the matrix is selected from polymer infiltration pyrolysis, chemical vapor infiltration, and sequential polymer infiltration pyrolysis and chemical vapor infiltration.