Ablation behavior of Ta, TaC and Ta/TaC coatings on graphite under high-energy laser irradiation

To enhance the ablation resistance of graphite, double-glow plasma surface metallurgy technology was used to efficiently prepare Ta, TaC and Ta/TaC coatings on the graphite. All coatings exhibited a uniform and dense structure, with no microdefects at the interfaces, and the phases of the coatings closely matched the targets. The introduction of the Ta transition layer did not significantly improve the hardness or micro scratch performance of the Ta/TaC coating but greatly enhanced the toughness. Severe ablation occurred on the graphite substrate at 26.5 kW/cm², while noticeable signs of ablation on the Ta and the two TaC coatings was at 61.9 kW/cm² and 70.7 kW/cm², respectively. Although the Ta transition layer did not enhance the ultimate failure power of the Ta/TaC coating, notably, the TaC coating lost its protective function after 10 cycles, whereas the Ta/TaC coating remained protective for 15 cycles, exhibiting superior resistance to cyclic ablation. This can be attributed to the Ta transition layer, which not only prevented crack formation and spalling of the Ta/TaC coating but also maintained the integrity of the coating by flowing and filling the TaC coating. Additionally, the Ta oxides formed during the early cycles also provided a certain degree of protection during subsequent ablation tests. The findings of this study can provide an effective approach for the design and fabricating technology of graphite ablation-resistant coatings.