Phase Structure, laser pulse heating and short-time high-temperature oxidation behavior of sputtered Ta coating for gun bore application

摘要

In weaponry systems, guns and barrels play a significant role by guid ing ultrahigh-temperature projectiles through narrow cylindrical tube with the high length-to-diameter ratios. During firing, the chemical ammunition substances explode and produce large amounts of gases, leading to oxidation, carbonization and high-temperature erosion for the Fe-based gun bore.Therefore, protective coating is greatly necessary to prolong the service life of the gun bore against this t hermal–chemical– mechanical erosion. Tantalum coating, deposited by magnetron sputtering technology, is a promising candidate for Cr substitute for gun bore applications. In this paper, phase structure of sputtered Ta coating in the negative glow space w as explored. The structure for whole coating/substrate system was substrate → physically gas-absorbed Fe surface → oxygen-enriched TaOX layer → amorphous Ta → α and β dual phase s → single α phase. After the laser pulse heating, microstructure of Ta coating show ed intact, only a few cracks emerge d after 100 laser pulses, indicating thin heat affected zone and thick Fe/Ta inter-connected zone without large-area martensitic transformation. As to electrodeposited Cr coating for comparison, repeated thermal stresses produce d many extra micro -cracks, substrate oxidation and martensitic transformation areas, subsequently leading to crack propagations and final bulk delamination. Moreover, the short -time oxidation behaviour of sputtered Ta coating was studied at 850 °C. W ith the representative columnar structure and quantitative grain boundaries, a rapid oxygen diffusion rate cause d no initial Ta2O5 to form at the surface. The gaps between columns provided spaces for bulk expansion, resulting in almost no opening cracks and delamination s. However, Ta oxidation experience d a Ta2O5 crystallization course from its amorphous state, leading to in situ temperature surging at the crystallization sites. T hen, avalanche delamination behavior happened together with its surrounding coating, and those became independent individuals and finally pulverized after 120-s oxidation.