Insight into the ablation behaviors and mechanism of duplex surface treated TC11 titanium alloy via dynamic shot peening and plasma nitriding

Abstract

Titanium alloys demonstrate exceptional mechanical properties and low density, positioning them as potential alternatives to gun steel. Nevertheless, the weak ablative resistance of titanium alloys limits their applications. To address the ablation issue of titanium alloys, an innovative duplex treatment combining shot peening and plasma nitriding was applied to TC11 titanium alloy. The effects of shot peening intensity on the structure, elemental distribution, hardness, and ablation resistance of the nitrided layer were investigated through X-ray diffraction, optical microscopy, surface profilometry, scanning electron microscopy, electron probe microanalysis, transmission electron microscopy, and Vickers microhardness test, respectively. The shot peening pretreatments produced various crystal defects. The defects promote the nitrogen diffusion and thus contribute to a thick and hard nitrided layer (including TiN and Ti₂N phase), which act as a thermal protection shield. On the other hand, it is found that the defects provide aluminum diffusion paths, and forming an aluminum-rich zone, which produced protective Al₂O₃ coating during ablation process. The plasma nitrided TC11 with shot peening intensity pretreatment showed a 91 % reduction in mass ablation compared to untreated specimens, which provides a new clue for improving the ablation and impact resistance of titanium alloys.