钛合金表面Ta-W涂层的制备及循环氧化行为

Preparation of Ta-W coating on titanium alloy and its oxidation behavior

采用电弧离子镀（AIP）在Ti-6.48Al-0.99Mo-0.91Fe（质量分数,%）钛合金表面制备Ta-10W（质量分数,%）涂层。通过扫描电镜（SEM）与能谱（EDS）分析、透射电镜（TEM）分析、电子探针分析（EPMA）,X衍射分析（XRD）,划痕及纳米压痕试验,研究钛合金基体与Ta-W涂层经900℃大气循环氧化前后的物相组成、组织形貌及性能,讨论涂层/基体的氧化行为。结果表明：沉积态Ta-W涂层连续、均匀、致密,由颗粒细小（≤50 nm）的α-Ta（W）堆积成100~250 nm的等轴晶组成,硬度为14.4~15 GPa,与基体的临界载荷为58.5 N;经900℃大气循环氧化后,钛合金表面形成带裂隙的层状Ti O2、Al2O3疏松混合氧化膜,氧化膜明显脱落;Ta-W涂层能明显提高钛合金的抗循环氧化性能,形成以β-Ta2O5为主的致密氧化膜;随着氧化的进行,氧化膜中Ti O2、Al2O3含量增加并出现Al Ta O4、Al WO4相,氧化膜始终保持完整;氧化过程中,基体中Ti、Al元素及涂层中Ta、W元素互扩散,在界面形成Al Ta2、Al2Ta3、Al3Ti、TixW1-x相,O元素扩散并固溶于基体,在近界面基体处形成厚度逐渐增加的富Ta、W、Al、O、α-Ti固溶体（稳定）区,涂层元素向氧化膜和基体扩散而被消耗为其失效的主要原因。

Ta-10W（mass fraction, %） coating was deposited on Ti-6.48Al-0.99Mo-0.91Fe（mass fraction, %） titanium alloy by arc ion plating（AIP）. Scratch test, nano indentation test, SEM, EDS, TEM, EPMA and XRD analysis were carried out to study the phase composition, microstructure and properties of the substrate and coating before and after cyclic oxidation at 900 ℃ in air. The oxidation behavior of the coating/substrate was discussed. The results show that the as-deposited Ta-W coating is continuous, uniform and compact with fine α-Ta（W） particles（≤50 nm） aggregating to form 100-250 nm equiaxed grains. The coating with hardness of 14.4-15 GPa and critical load of 58.5 N is obtained from the scratch test. Laminar Al2O3 and Ti O2 mixed scale with fissuring is formed and desquamated obviously on the substrate after cyclic oxidation at 900 ℃ in air. Ta-W coating can evidently improve the cyclic oxidation resistance of the substrate. An integrity and compact scale, which is mainly made up of β-Ta2O5, formed on Ta-W coating. With the oxidation going on, the contents of Ti O2, Al2O3, Al Ta O4 and Al WO4 in the scale increase. The coating elements（Ta and W） and substrate elements（Ti and Al） interdiffuse during the oxidation. Al Ta2, Al2Ta3, Al3 Ti, TixW1-x phases form on the interface. With the diffusion of Ta, W, Ti, Al and O, α-Ti solid solution layer（stabilized layer） forms in the substrate near the interface. The degradation of Ta-W coating mainly attributes to the consumption of coating elements to form scale and dissolve in the substrate.