(1. 湖南工程學(xué)院 機(jī)械工程學(xué)院，湘潭 411101；
2. 中南大學(xué) 材料科學(xué)與工程學(xué)院，長(zhǎng)沙 410083)
摘 要: 采用電弧離子鍍(AIP)在Ti-6.48Al-0.99Mo-0.91Fe(質(zhì)量分?jǐn)?shù)，%) 鈦合金表面制備Ta-10W(質(zhì)量分?jǐn)?shù)，%)涂層。通過(guò)脈沖激光加熱試驗(yàn)?zāi)M火藥氣體燒蝕工況，采用有限元溫度場(chǎng)數(shù)值模擬、X射線衍射分析 (XRD)、掃描電鏡(SEM)與能譜(EDS)分析等方法，研究Ta-W涂層/鈦合金體系大氣氣氛循環(huán)熱加載燒蝕行為。結(jié)果表明：脈沖激光加熱過(guò)程中，高熔點(diǎn)、高熱導(dǎo)率(相比純鈦)Ta-W涂層吸收、富集熱量對(duì)鈦合金基體具有熱障保護(hù)作用，經(jīng)10~40 s加熱，Ta-W涂層使加熱區(qū)熔透深度從無(wú)涂層基體的190~250 μm明顯減少至125~180 μm，非加熱區(qū)平均溫度從無(wú)涂層基體的350~900 ℃大幅降低至250~500 ℃。由于加熱區(qū)邊緣溫度低、溫差大、熔體流動(dòng)性差，利于孔洞及低熔點(diǎn)Al元素富集區(qū)的形成，在循環(huán)熱應(yīng)力作用下，該區(qū)域易成為表面橫向和縱向裂紋策源地。鈦合金基體加熱后熔化層成分偏析嚴(yán)重，形成富Al帶、富Mo和Fe區(qū)，在循環(huán)熱應(yīng)力作用下，富Al帶成為截面橫向裂紋的策源地；Ta-W涂層試樣加熱后形成熔化層、熔合層、擴(kuò)散層組成的微觀組織，熱時(shí)間延長(zhǎng)而尺寸逐漸變小的Ta-W涂層顆粒散布于熔化層導(dǎo)致涂層元素富集于此而起到持續(xù)保護(hù)作用。由于涂層與基體元素互擴(kuò)散在熔合層形成孔洞(帶)，在循環(huán)熱應(yīng)力作用下，孔洞(帶)為起源于表面加熱區(qū)邊緣的截面縱向裂紋的擴(kuò)展提供便捷路徑，且隨加熱時(shí)間(熱震次數(shù))的增加，裂紋尺寸增大，并可導(dǎo)致富Ta-W元素層的剝落而失效。熱熔化及循環(huán)熱應(yīng)力為Ta-W涂層/鈦合金體系大氣氣氛脈沖激光燒蝕失效的主要因素。
關(guān)鍵字: Ta-W涂層；鈦合金；脈沖激光加熱；燒蝕行為；循環(huán)熱應(yīng)力
（1. School of Mechanical Engineering, Hunan Institute of Engineering, Xiangtan 411101, China;
2. School of Materials Science and Engineering, Central South University, Changsha 410083, China）
Abstract:Ta-10W (mass fraction, %) coating was deposited on Ti-6.48Al-0.99Mo-0.91Fe (mass fraction, %) titanium alloy by arc ion plating (AIP). Laser pulse heating was used to simulate the heat input and duration in a gun barrel during firing. Finite element analysis of temperate field, XRD, SEM and EDS analysis were carried out to study the behavior of the Ta-W coating/titanium alloy system during laser pulse heating in atmosphere. The results show that Ta-W coating absorbs and gathers heat during heating process for high melting point and thermal conductivity (comparing with the substrate), Ta-W coating can work as thermal barrier to the substrate for absorbing and gathering heat. During 10-40 s heating, the fusion depth obviously decreases from 190-250 μm of the substrate to 125-180 μm of the coating in heated zone and the average temperature sharply drops from 350-900 ℃ of the substrate to 250-500 ℃ in unheated zone after depositing Ta-W coating. Porous and reticular TiO2 and Al2O3 mixed oxides film forms on the substrate surface, but integrated, compact, mainly consisted of β-Ta2O5 and Ta, W-riched oxides film forms on the coated sample. Unlike the static and cyclic oxidation in atmosphere, there are no obviously spalling of the laser pulse heated oxides film for the short heating time. High temperature oxidation is not the main failure factor of laser pulse heated Ta-W coating/titanium alloy system. For lower temperature, large temperature difference and poor fusant fluidity at the edge of heating zone, pores and Al-riched zone, which may be the sources of the transverse and longitudinal cracks under thermal cycling stress, form easily in this zone. Composition segregation is obvious in melted layer of the substrate, which leads to the formation of Al-riched belt and Mo, Fe-riched zone. The Al-riched belt may become the source of the transverse cracks in the cross section under thermal cycling stress. The cross section of Ta-W coated sample is made up of melted layer, fusion layer and inter-diffusion layer after heating. Ta-W coating particles sizes decrease with the heating time increasing, intersperse in the melted layer. Then, the melted layer is rich in Ta and W elements, which maintains the protective effect of the coating during the heating. The pore belts, forming during the inter-diffusion of coating and substrate elements, provid convenient paths for the longitudinal cracks in the cross section under thermal cycling stress. The size of the cracks increases with the heating time, which leads to the spalling of the Ta, W-riched layer. Heat fusing and thermal cycling stress are the main failure factors of laser pulse heated Ta-W coating/titanium alloy system.
Key words: Ta-W coating; titanium alloy; laser pulse heating; ablation behavior; thermal cycling stress
