Investigation Of Mo Alloy Cladding On C/C Composites And Its Microstructure

The anti-oxidation coating of carbon/carbon composites at medium-high temperature have been studied abundantly, but the coating serving for ultra-high temperature (over1800℃) still remained further investigation. Ir coating, as one of the best candidate anti-oxidation coatings, is however easy to peel off and results in failure during the serving period due to the coefficient of thermal expansion mismatch with C/C. In this paper, surface modification was adopted to solve the problem of thermal expansion mismatch. The Mo alloy coatings on C/C composites were prepared by two different surface cladding methods. The microstructure and the micro-mechanical properties of the coatings were investigated by XRD, SEM, microhardness tester and nanoindentation.The Mo-Cr alloy was coated on C/C composites by vacuum cladding technique. The10%wt Cr coatings presented more crack defects, interestinglyt, the20%Cr coating was relatively complete, which metallurgically bonded with C/C, however a few micro holes were found in the outside of the coating. The coating was composed of Mo, Cr7C3, Mo2C, MoC. Cr diffused from alloy to C/C and concentrated at the interface and formed chromium carbide, which generated the Cr-rich transition layer. The microhardness of coatings increased as the increasing of Cr content, which reached1633HV peaked at20wt%Cr.Prepared by argon arc cladding, Mo-Ti alloy coating was bonded effectively with C/C through the conical interfacial structure. The cladding layer consisted of MoTi solid solution, Mo, Mo2C and TiC. From C/C substrate to the outside of cladding coating, the microstructure transformed planar crystal to cellular/dendrite crystal. The microhardness of coating decreased first then increased and remained steady gradually. With the Ti content increasing, the hardness of the coatings increased and reached at989.3HV.The micro-mechanical properties were investigated by nano-indentation technique. The hardness and elastic modulus of different phases in cladding coatings could be achieved by the load-distance curve obtained from measurement. The hardness of the Cr-rich phase and Mo-rich phase of Mo-20wt%Cr coating were respectively18.6GPa and8.4GPa while elastic modulus were355.4GPa and322.4GPa. The average hardness and elastic modulus of Mo-rich phase of Mo-20%Ti coating were8.5GPa and280.5GPa, separately. With the increase of Ti content, the hardness and elastic modulus of coatings increased and arrived at27.2GPa and338.8GPa, respectively. In the10s load-keeping process, three kinds of coatings appeared displacement, specifically the Mo-20wt%Ti coating showed more potential to resist indentation deformation.