The document discusses coating AISI 4140 steel, which is used for rocket nozzles, with thermal barrier coatings (TBC) to improve its thermal resistance. Two TBC materials were tested: Al2O3 + SiO2 composite and pure Al2O3. The coatings were applied using flame spraying. Testing showed that a 50% Al2O3 - 50% SiO2 composition achieved the highest adhesive strength of 16 MPa. X-ray diffraction analysis identified mullite phase formation in this composition after heat treatment. The Al2O3 + SiO2 composite TBC improved the thermal resistance of the AISI 4140 steel for use in rocket nozzles.