Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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中国有色金属学报

ZHONGGUO YOUSEJINSHU XUEBAO

第30卷    第9期    总第258期    2020年9月

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文章编号:1004-0609(2020)-09-2059-16
Ta-W涂层/钛合金体系大气气氛脉冲激光烧蚀行为
彭小敏1,周 凡1,高平平1,王建明1,朱耿立1,彭华凤1,夏长清2

(1. 湖南工程学院 机械工程学院,湘潭 411101;
2. 中南大学 材料科学与工程学院,长沙 410083
)

摘 要: 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。通过脉冲激光加热试验模拟火药气体烧蚀工况,采用有限元温度场数值模拟、X射线衍射分析 (XRD)、扫描电镜(SEM)与能谱(EDS)分析等方法,研究Ta-W涂层/钛合金体系大气气氛循环热加载烧蚀行为。结果表明:脉冲激光加热过程中,高熔点、高热导率(相比纯钛)Ta-W涂层吸收、富集热量对钛合金基体具有热障保护作用,经10~40 s加热,Ta-W涂层使加热区熔透深度从无涂层基体的190~250 μm明显减少至125~180 μm,非加热区平均温度从无涂层基体的350~900 ℃大幅降低至250~500 ℃。由于加热区边缘温度低、温差大、熔体流动性差,利于孔洞及低熔点Al元素富集区的形成,在循环热应力作用下,该区域易成为表面横向和纵向裂纹策源地。钛合金基体加热后熔化层成分偏析严重,形成富Al带、富Mo和Fe区,在循环热应力作用下,富Al带成为截面横向裂纹的策源地;Ta-W涂层试样加热后形成熔化层、熔合层、扩散层组成的微观组织,热时间延长而尺寸逐渐变小的Ta-W涂层颗粒散布于熔化层导致涂层元素富集于此而起到持续保护作用。由于涂层与基体元素互扩散在熔合层形成孔洞(带),在循环热应力作用下,孔洞(带)为起源于表面加热区边缘的截面纵向裂纹的扩展提供便捷路径,且随加热时间(热震次数)的增加,裂纹尺寸增大,并可导致富Ta-W元素层的剥落而失效。热熔化及循环热应力为Ta-W涂层/钛合金体系大气气氛脉冲激光烧蚀失效的主要因素。

 

关键字: Ta-W涂层;钛合金;脉冲激光加热;烧蚀行为;循环热应力

Ablation behavior of Ta-W coating/titanium alloy under laser pulse heating in ambient atmosphere
PENG Xiao-min1, ZHOU Fan1, GAO Ping-ping1, WANG Jian-ming1, ZHU Geng-li1, PENG Hua-feng1, XIA Chang-qing2

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

ISSN 1004-0609
CN 43-1238/TG
CODEN: ZYJXFK

ISSN 1003-6326
CN 43-1239/TG
CODEN: TNMCEW

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