氧化对热障涂层微观力学性能和界面微结构的影响

发布时间：2018-02-01 08:52

  本文关键词： 热障涂层 微观纳米力学性能 界面微结构演变 失效机理 透射电子显微术　出处：《中国科学技术大学》2016年博士论文　论文类型：学位论文

【摘要】：采用低压/大气等离子喷涂(LPPS/APS)、电子束物理气相沉积(EB-PVD)和多弧离子镀(AIP)方法在镍基单晶高温合金表面制备了NiCrA1Y、NiCoCrAlY、 NiCrAlYSiB三种MCrA1Y涂层和8wt.%氧化钇部分稳定氧化锆(8YSZ)+NiCrA1Y、8YSZ+NiCoCrAlY/20wt.%氧化镁稳定氧化锆(20MSZ)-NiCrAlY三种热障涂层(Thermal Barrier Coatings, TBCs)。借助纳米压痕测试技术,研究了涂层微观力学性能随氧化温度变化规律。以透射电子显微术(TEM)为主要研究方法,结合X-射线衍射(XRD)、扫描电子显微术(SEM)和电子能量散射谱(EDS)等分析手段,研究了1100℃氧化过程中涂层界面微结构演化规律及其涂层失效机制。在NiCrA1Y涂层中加入Co元素,可提高沉积态涂层的硬度并降低其弹性模量,在氧化初期,可同时提高涂层的弹性模量和硬度及其稳定性；加入Si和B元素,可降低沉积态涂层的弹性模量和硬度,但在氧化过程中可稳定涂层的弹性模量和提高涂层的硬度。在沉积状态,因为物相组成、涂层密度和稳定性的不同,20MSZ热障涂层的平均弹性模量和平均硬度都比APS 8YSZ热障涂层的值小；由于存在择优取向织构和多孔隙,沉积态EB-PVD 8YSZ涂层的弹性模量和硬度都比APS 8YSZ的值小,但是随着在氧化初期被烧结,其弹性模量和硬度都得到了提高,比APS 8YSZ涂层的值大。由于涂层与基体间存在元素互扩散和选择性内氧化,导致NiCrAlY涂层经过1100℃恒温氧化后,涂层与基体之间首先生成了两层主要由Cr2O3和α-Al2O3组成的致密热生长氧化物(TGO),Cr2O3层靠近涂层分布,α-Al2O3层靠近基体分布。随着氧化时间延长,因为γ'-Ni3Al的分解,基体内靠近界面区域析出了γ-Al。随着内氮化和内氧化的持续,基体内靠近界面区域进一步生成hcp-AIN和fcc-TiN,期间由于竞争关系,hcp-AIN发生置换反应生成α-Al2O3。随着恒温氧化的继续,TGO层不断增厚且成分中增加了Ni(Al,Cr)2O4、NiO和Y3Al5O12,最终,巨大的热应力集中使涂层在历经1000小时氧化后沿着界面剥离而失效。1 100℃恒温氧化初期,APS 8YSZ+LPPS NiCrA1Y热障涂层的陶瓷层与粘结层、粘结层与基体之间先后生长了分层的TGO膜,对于前者而言,粘附陶瓷层的TGO薄层由α-Al2O3、Cr2O3、NiO和Ni(Al,Cr)2O4混合组成,靠近粘结层的TGO薄层主要由致密的α-Al2O3和/或Cr2O3组成；对于后者而言,紧挨粘结层的TGO薄层由α-Al2O3、Cr2O3和Ni(Al,Cr)2O4混合组成,而贴近基体的TGO薄层主要由致密的α-Al2O3和/或Cr2O3组成。因为基体的强化相γ'分解,而氧分压过低不能氧化分解产物[Al]和[Ti],使得γ-Al和β-Ti在基体内靠近界面区域析出。随着氧化时间延长,粘结层中的富铝相Al2Y和β-NiAl逐渐消失,涂层逐渐退化,加上TGO层的不断增厚、孔隙率提高、成分复杂化以及陶瓷层的相变等因素,导致界面区域产生热应力集中并进而产生微裂纹,由微裂纹的深入扩展和连接,致使粘结层与基体间TGO产生大裂缝,导致热障涂层于3000小时氧化后最终整体失效。MCrA1Y涂层和热障涂层的1100℃C恒温氧化动力学曲线都基本遵循抛物线氧化规律。氧化初期MCrA1Y涂层的平均抛物线氧化常数Kp值约为2.3×10-11g2cm-4s-1,热障涂层的Kp约为1.8×10-11g2cm-4s-1；稳定氧化阶段MCrA1Y涂层的约为6.5×10-12g2cm-4s-1,热障涂层的平均Kp值约为3.5×10-12g2cm-4s-1。涂层的氧化过程遵循氧的吸附、传质和持续补给并使涂层系统发生选择性内氧化的扩散控制机制。涂层的退化即亲氧性金属元素Al和Cr储量逐渐被消耗的过程。而涂层的恒温氧化失效表现为TGO层逐渐生长进而导致界面裂纹的形成、扩展和涂层剥离过程。
[Abstract]:The low pressure / air plasma spraying (LPPS/APS), electron beam physical vapor deposition (EB-PVD) and multi arc ion plating (AIP) method to prepare NiCrA1Y in nickel base single crystal superalloy surface NiCoCrAlY, NiCrAlYSiB three MCrA1Y coatings and 8wt.% yttria partially stabilized zirconia (8YSZ) +NiCrA1Y, 8YSZ+NiCoCrAlY/20wt.% Magnesium Oxide stable oxidation zirconium (20MSZ) -NiCrAlY three (Thermal Barrier Coatings, thermal barrier coating TBCs). Using nanoindentation technique, changes with the oxidation temperature of coating micro mechanical properties are studied. By transmission electron microscopic surgery (TEM) as the main research methods, combined with X- ray diffraction (XRD), scanning electron microscopy (SEM) and electron energy dispersive spectroscopy (EDS) analysis method of 1100 DEG C during the oxidation process of coating interface microstructure evolution and coating failure mechanism. Adding Co element in NiCrA1Y coating, can improve the deposited coating The hardness and the elastic modulus decreased, at the initial stage of oxidation, which can improve the coating hardness and elastic modulus and stability; adding Si and B elements, the hardness and elastic modulus can reduce the deposited coating, but the elastic modulus can be stable coating in the oxidation process and improve the hardness of the coating. In the deposition state, because the phase composition, coating density and stability, the average elastic modulus of 20MSZ coatings and the average hardness of APS 8YSZ thermal barrier coating is small; because of the existence of preferential orientation and multi pore, deposited EB-PVD 8YSZ coating elastic modulus and hardness than the APS 8YSZ value is small, but with sintering in oxidation initially, the elastic modulus and hardness are improved, than the APS values of 8YSZ coating. Because of the existence of element diffusion and selective oxidation of the coating and the substrate, resulting in NiCrAlY coating after isothermal 1100 oxygen After that, the coating and the substrate is first generated dense hot two layer is mainly composed of Cr2O3 and alpha -Al2O3 composed of growth (TGO), Cr2O3 oxide coating layer close to the distribution, a -Al2O3 layer near the substrate distribution. With oxidation time, because the decomposition of gamma'-Ni3Al, the matrix near the interface region of -Al. with continuous precipitation of gamma nitride and internal oxidation and further formation of hcp-AIN and fcc-TiN matrix near the interface region during the competition, hcp-AIN was replaced with -Al2O3. to generate alpha oxidation, increased Ni and TGO layer thickening components (Al, Cr) 2O4, NiO and Y3Al5O12, finally, great thermal stress concentration the coating after 1000 hours after oxidation along the interfacial debonding failure.1 100 constant temperature oxidation stage, the ceramic layer APS 8YSZ+LPPS NiCrA1Y thermal barrier coating and adhesive layer, adhesive layer and the substrate between the first layer of T growth For the former, GO film, TGO layer adhesion of ceramic coatings by alpha -Al2O3, Cr2O3, NiO and Ni (Al, Cr) 2O4 mixture, TGO thin layer near the bonding layer is mainly composed of a dense -Al2O3 and / or Cr2O3; for the latter, next to the TGO thin adhesive layer by a -Al2O3. Cr2O3 and Ni (Al, Cr) 2O4 mixture, TGO thin and close to the substrate is mainly composed of a -Al2O3 compact and / or Cr2O3. Because the matrix strengthening phase of R 'decomposition, and the oxygen pressure too low oxidation decomposition products of [Al] and [Ti], the -Al gamma and beta -Ti in the matrix near the interface. Area. With the oxidation time, rich aluminum bonding layer in phase Al2Y and beta -NiAl gradually disappear, coating gradually degraded, and the TGO layer increased, the porosity increased, and the complex composition of the ceramic layer of phase change and other factors, resulting in the interface region produces thermal stress concentration and micro cracks, by micro cracks the Further expansion and connection, the bonding between the coating and the substrate TGO to produce large cracks, 1100 DEG C isothermal oxidation kinetic curves lead to thermal barrier coating in 3000 hours after the final overall oxidation failure of.MCrA1Y coating and thermal barrier coating are basically follow the parabolic oxidation law. Initial average oxidation parabolic oxidation constant Kp MCrA1Y coated layer is about 2.3 * 10-11g2cm-4s-1 Kp, thermal barrier coating is about 1.8 * 10-11g2cm-4s-1; stable oxidation of MCrA1Y coating is about 6.5 * 10-12g2cm-4s-1, the average value is about Kp thermal barrier coating adsorption and oxidation process of 3.5 * 10-12g2cm-4s-1. coatings follow oxygen, mass transfer and continuous supply and selective diffusion coating system of internal oxidation process of the coating degradation control mechanism. The oxophilic metals Al and Cr reserves gradually by consumption. And the isothermal oxidation coating failure for TGO layer gradually, which led to the growth of the interface The formation, expansion of the crack and the stripping process of the coating.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG174.4
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本文编号：1481459