Method of fabricating a thermostructural composite material part, and a part obtained thereby

A thermostructural composite material part comprising fiber reinforcement of refractory fibers densified by a refractory matrix obtained by chemical vapor infiltration, with an interphase being interposed between the refractory fibers of the fiber reinforcement and the refractory matrix, wherein the interphase comprises a first continuous interphase layer coating the refractory fibers of the fiber reinforcement, the first continuous interphase layer being of a material selected from pyrolytic carbon, boron nitride, and boron-doped carbon, and having a thickness of not more than 100 nanometers, and a second continuous interphase layer, the second continuous interphase layer covering the first continuous interphase layer and discontinuous grains of a solid carbon or ceramic residue that results from pyrolyzing a resin, which discontinuous grains are interposed between the first and second continuous interphase layers;

• wherein the refractory matrix is in direct contact with the second continuous interphase layer;
• and wherein the first continuous interphase layer is in direct contact with the refractory fibers of the first reinforcement and wherein the discontinuous grains are in direct contact with the first continuous interphase layer.