Thermal cyclic oxidation and interdiffusion of NiCoCrAlYHf coating on a Ni-based single crystal superalloy

Accepted Manuscript Thermal cyclic oxidation and interdiffusion of NiCoCrAlYHf coating on a Ni-based single crystal superalloy Jinyan Zhong, Jianhua Liu, Xin Zhou, Songmei Li, Mei Yu, Zhenhua Xu PII:

S0925-8388(15)31404-3

DOI:

10.1016/j.jallcom.2015.10.148

Reference:

JALCOM 35703

To appear in:

Journal of Alloys and Compounds

Received Date: 20 August 2015 Accepted Date: 17 October 2015

Please cite this article as: J. Zhong, J. Liu, X. Zhou, S. Li, M. Yu, Z. Xu, Thermal cyclic oxidation and interdiffusion of NiCoCrAlYHf coating on a Ni-based single crystal superalloy, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.10.148. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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According to the figure, it shows that an interdiffusion zone formed under NiCoCrAlYHf coating and a secondary reaction zone formed in third generation single

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crystal superalloy DD10.

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Thermal Cyclic Oxidation and interdiffusion of NiCoCrAlYHf coating on a Ni-based Single Crystal Superalloy

a

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Jinyan Zhong a,*, Jianhua Liu a, Xin Zhoub, c, Songmei Li a, Mei Yua, Zhenhua Xub School of Materials Science and Engineering, Beihang University, No. 37 Xueyuan

Road, Beijing 100191, China

Beijing Institute of Aeronautical Materials, Department 5, P.O. Box 81-5, Beijing

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b

100095, China c

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State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of

Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China _________________________ *

Corresponding authors. Tel: +86-10-82317103. E-mail addresses: [email protected]

Abstract

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(J.H. Liu).

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A NiCoCrAlYHf coating was deposited onto a third generation single crystal superalloy DD10 by arc ion plating (AIP). In the present study, thermal cyclic

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oxidation and interdiffusion of NiCoCrAlYHf coating at 1100

were investigated to

1000 h. The coating surface, interface morphology and phase structure of the organization were characterized by scanning electron microscopy(SEM), energy dispersion X ray spectroscopy (EDS) and X ray diffraction (XRD). An interdiffusion zone (IDZ) and a secondary reaction zone (SRZ) were formed after 300h. Severe inward diffusion of Al, Co and Cr from NiCoCrAlYHf coating and outward diffusion

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of Ni and refractory elements such as Re and W from the superalloy occur at 1100 in air. The SRZ consisting of γ, γ' and topologically closed- packed phase (TCP) was

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formed 60µm distance from the surface of coating in the superalloy after 300h oxidation. Additionally, the development of IDZ and growth of the SRZ was also

observed during thermal cyclic oxidation. Subsequently, interdiffusion coefficients of

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Al were presented by using a modified form of the Boltzmann–Matano analysis. Keywords: Superalloy; Metal coatings; Thermal cyclic oxidation; Interdiffusion;

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Topologically close-packed (TCP) phase; Secondary reaction zone (SRZ)

1. Introduction

With the development of advanced aviation aircraft engines, gas inlet temperature

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rises. It is well known that several generations of heat-resistant Ni based single crystal superalloys have been developed over the past 20 years, specifically for applications within gas turbine engines [1-2]. Compared to the second generation alloy, third

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generation Ni based single crystal superalloy has the advantages of being heat resistant, and it also has high creep strength by the addition of higher levels of

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refractory elements such as Re, W and Mo. However, owing to the restriction of the melting point of single crystal material, further increasing the potential working temperature of the single crystal superalloy has been limited [3-6]. To meet the requirements of an increase of turbine inlet temperature and thermal efficiency in modern advanced gas turbine, thermal barrier coatings (TBCs) are widely used in advanced aircraft engines as high temperature protective coatings, which not only

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have good high temperature oxidation corrosion resistance, but also have the ability to protect the single crystal superalloy from oxidation and corrosion in high

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temperature service [7-9]. Thermal barrier coating system consists of a ceramic top coat with low thermal conductivity and high permeability to oxygen, covering an

alumina-forming metallic bond coat which is resistant to oxidation and corrosion and

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also improves the bonding between the topcoat and the substrate. When thermal

barrier coating is in long-term high temperature atmosphere, thermally grown oxide

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(TGO) would form due to thermodynamics and kinetic. Bond coat provides TGO layer adequate aluminum. TGO effectively isolate substrate and aggressive environment, which greatly reduces the oxidation rate of the substrate. Once the Al content is less than a critical value, an abnormal oxidation reaction might happen to

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damage coating protective properties [9].

At the same time, element interdiffusion between the bond coat and the substrate inevitably occurs during cyclic oxidation tests at high temperature, which results in

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precipitation of refractory element-rich topologically close-packed (TCP) phases in the superalloy. Due to the interdiffusion between the coating and substrate, secondary

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reaction zone (SRZ) and TCP phase form in the superalloy, both of which affect the stability of the coating system and lead to significant reduction in mechanical properties of the superalloy [10-13].The SRZ formation in the substrate results in the degradation of the superalloy creep properties, it is critically important to fully understand the formation mechanism of SRZ and its kinetics. The first step is to understand the interdiffusion processes occurring between the superalloy and the

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metallic bond coat at high temperature which lead to the formation of SRZ and also influence the element distribution [14, 15].

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Third generation Ni-based single crystal superalloy DD10 which contains more refractory elements such as W, Mo and Re has been widely applied as structural

materials in advanced aero engine for gas turbine blades and vanes to improve their

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creep or stress rupture strength at high temperature. However, these elements promote the formation of harmful TCP phase in the superalloy after long-term thermal cyclic

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oxidation [16].It would influence structure instability and lead phase transformation. NiCoCrAlYHf coating (HY5 coating) is a high temperature protective coating and also works as the bond coat material in the TBC system because of its good high-temperature oxidation and hot-corrosion resistance. However, so far little

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attention has been paid to the thermal cyclic oxidation and interdiffusion behaviors between the third generation single crystal superalloy DD10 and HY5 coating. Therefore, the present study aims to investigate the thermal cyclic oxidation and

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interdiffusion behaviors of third generation Ni-based single crystal superalloy DD10 with HY5 coating during thermal cyclic oxidation at 1100℃. Arc ion vacuum plating

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method was adopted to deposit HY5 coating. The coating surface and interface morphology and the phase of organizational structure are analyzed for different thermal cycle times. Cyclic oxidation kinetics and elemental interdiffusion behavior have great significance in engineering and economic value.

2. Experimental procedures 2.1. Substrate material

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The third generation Ni-base single crystal superalloy DD10 was employed as the substrate material and the chemical composition of superalloy and HY5 coating are

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listed in Table 1. The DD10 superalloy was cut into samples and the size is 30 mm×10 mm×1.5 mm which is convenient for the interdiffusion and thermal cyclic

oxidation tests. All of the specimen surfaces were ground on 1000# SiC paper after

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ultrasonic bath cleaning in the solution of alcohol and acetone. 2.2. Preparation of HY5 coating

Ion-Plating Unit) at 1000

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The HY5 coating was deposited by arc ion-plating (A-1000 Vacuum Arc for 90 min. The HY5 coating was about 35 ~ 50µm

thick and exhibited typical morphology of a high temperature oxidation resistant coating. Preparation parameters of coating are shown in Table 2.

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2.3. Thermal cyclic oxidation test and sample characterization

The coated samples were annealed in vacuum at 1100 °C for 300, 600 and 1000h, respectively, with a chamber pressure of 103Pa, to investigate interdiffusion between

1100

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HY5 coating and the superalloy. The cyclic oxidation was performed in air furnace at . All the surfaces of the samples, including side surfaces, were deposited with

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HY5 coating. The samples were held in alumina crucibles and heated at 1100

.

Each cycle included 55 min heating in furnace and 5 min cooling out of the furnace in room temperature. Samples are weighed in a predetermined cycle by an electronic balance (Sartorious BS 224S, Germany) with a precision of 10-4g. The measured data is the average of three parallel samples weight gain by cyclic oxidation. A solution containing HCl and HNO3 at the ratio of 3:1 was used as the chemical

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etchant to selectively dissolve the γ’ phase present in the microstructures, to facilitate the identification of the precipitates. The coating morphology and composition

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evaluation were carried out by scanning electron microscope (SEM, CamScan3100) equipped with energy dispersive spectroscopy (EDS, OXFORD X-Max). X-ray

diffraction (XRD, Bruker D8 Advance, Germany) with Cu Kα radiation at a scan rate

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of 4◦ min−1 was applied to detect the phase of coating.

3. Results and discussion

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3.1. Oxidation kinetics

Cyclic oxidation tests of uncoated DD10 single crystal superalloy lasted for 600h and DD10 superalloy with HY5 coating lasted for 1000h. Applying desiccant method to gain cyclic oxidation kinetics is shown in Fig. 1. Fig. 1a shows that quality of

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uncoated single crystal superalloy during 0 ~ 5h cyclic oxidation increased slightly. The quality is lower than the original quality after 7h cyclic oxidation and then the quality continuously decreased. Because oxidation on surface constantly cracked,

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peeling, and then the exposed surface of the superalloy formed a new oxide film, but weight loss caused by the film peeling was significantly greater than weight gain of

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oxidation. The Ni-based single crystal superalloy without HY5 coating exhibits poor cyclic oxidation resistance. Cyclic oxidation kinetics of are significantly different from uncoated single

crystal superalloy. Fig. 1b shows that weight of single crystal superalloy with HY5 coating grows rapidly during the initial 50 thermal cycles, followed by the growth rate slowed down and the line finally become a straight line. It demonstrates that

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oxidation stage was constant. Fig. 1b also shows that there is a slight increase after a weight loss during the

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experiment, which means that the exposed surface has formed a new oxide film after an oxide film cracking and slight peeling. So HY5 high temperature oxidation

property. 3.2. Morphology and phase structure analysis

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resistant coating improves Ni-based single crystal superalloy oxidation-resistance

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The initial surface of single crystal superalloy is pretty smooth and there is no oxide on the surface. The surface of single crystal superalloy become rough and there is a chartreuse oxide film on the surface after 300h thermal cyclic oxidation. Fig. 2a demonstrates that many large areas of oxide film have fallen off. EDS analysis results

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of oxide film (Fig. 2b) shows that surface element of the superalloy are mainly constituted of elements O, Ni, Al, Co, Cr, Ta, Re and W, oxidation are mainly NiO ,Cr2O3 and small amount of Al2O3.

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The morphology of deposited HY5 coating surface is shown in Fig. 3a. Deposited HY5 coating, which is made up of tiny grains, is compact. As shown in Fig. 3a, size

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of grains is significantly older after 1000h thermal cyclic oxidation and HY5 coating has formed a relatively flat and dense oxide film on which has no surface cracks and no flaking (Fig. 3b).

The cross-section morphology of initial Ni-based single crystal superalloy without HY5 coating is as shown in Fig. 4a. There is no obvious defect in the substrate. There has been small amount of oxidation on the surface of superalloy after 300h and a

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small number of holes inside the superalloy (Fig. 4b). A network of continuous oxidation has been formed on the surface of superalloy after 600h in Fig. 4c. And

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more holes can be clearly seen inside the superalloy. These holes, as a result of Kirkendall effect, caused adhesion of the oxide and the substrate decreased, so that

oxide film peeled from the surface. Kirkendall porosity generated during the element

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diffusion [17].

Fig. 5 shows cross sectional morphology of single crystal superalloy with HY5

oxidation at 1100

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coating under different magnifications after 0,300h, 600h and 1000h thermal cyclic . In Fig. 5a, the deposited HY5 coating thickness is about 35 ~

50µm, the diffusion layer is apparent which is about 5µm thick. After 300h thermal cyclic oxidation, black oxide film on the HY5 coating can be seen in Fig. 5b. XRD

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patterns of HY5coating after 300h thermal cyclic oxidation are shown in Fig. 6. As can be seen in Fig. 6, HY5 coating is consisted of β-NiAl, α-Al2O3 and Cr-rich oxide. It is an advantageous condition in favor of formation of cubic structure β-NiAl phase

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[18].

The TGO throughout thermal cyclic oxidation become clear, complete, and thick.

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Measured values of the average TGO thickness are not greater than 10µm. At the

same time, the thickness of HY5 coating slightly reduced. Al content in HY5 coating is relatively higher than other elements, as well as the element Hf is added to improve the purity and integrity of Al2O3 in TGO, and also inhibits a rapid thickening of TGO.

The formation of TGO effectively prevents external gas diffusing inside the substrate to prolong the life of single crystal superalloy. There is no micro-pores or

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mircocracks occurrence on top of HY5 coatings’ surface. Compared with uncoated Ni-based single crystal superalloy, HY5coating coated substrate has no obvious hole

protect Ni-based single crystal superalloy satisfactorily.

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inside, which indicates that HY5 high temperature oxidation resistant coating could

Fig. 5b, 5c and 5d compare different thermal cyclic oxidation time cross-section

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morphologies of HY5 coating. Three regions can be seen in these figures, they are

HY5 coating, interdiffusion zone (IDZ) and secondary reaction zone (SRZ). Apart

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from this, small amount of γ' phase (Ni3A1) appeared in the HY5 coating (marked by the arrows in Fig. 5b). During the thermal cyclic oxidation, element diffusion occurs in the interface due to the difference of element concentration between HY5 coating and DD10 superalloy. After 1000h thermal cyclic oxidation, the thickness of IDZ 50µm and the amount of γ' phase in the coatings continuously

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increased to

increased. The γ' phase is a face-centered cubic structure, which is a brittle phase, is a kind of intermetallic compounds.

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The formation of γ' phase is induced by the following reactions:

γ-Ni+β-NiAl→γ′-Ni3Al+α-Cr

(1)

3NiAl+3/2O2→γ′-Ni3Al+Al2O3

(2)

This phenomenon was attributed to the transport of Al from the HY5 coating via

diffusion process to the substrate. The phase transformations cause Al depletion in the HY5 coating and the substrate, which might reduce high temperature oxidation resistance ability and also the whole life of the TBCs system [19]. 9

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3.3. Interdiffusion between HY5 coating and superalloy during thermal cyclic oxidation

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The chemical concentrations profiles indifferent cyclic oxidation time are presented in Fig. 7. Fig. 7a presents that all kinds of element concentrations are relatively steady in deposited HY5 coating. As can be seen from the Fig. 7b,

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interdiffusion occurs mainly in the interface between HY5 coating and substrate, which is about 50µm from the surface. Along with cyclic oxidation time, each

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concentrations curve of different elements becomes smooth, which indicates that interdiffusion effect between HY5 coating and substrate leads to the decrease of element concentration, element ratio tend to be more uniform. In addition, the Al Cr and Co content in HY5 coating are relatively high at the beginning, as shown in Fig.

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7a, and they decrease with oxidation cycles as shown in Fig. 7b, 7c, 7d. From the schematic diffusion path, Al from HY5 coating and Ni from the superalloy are transferred through the β phase, while Cr in the γ phase of HY5 coating diffuse into

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the superalloy. With the increase of the oxidation time, Ni concentration becomes more uniform in HY5 coating and substrate. Due to concentrations of Ni, Mo, Ta, W,

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Re are relatively high in the Ni-based single crystal superalloy, they diffuse to the substrate, the element ratio of Ni Mo, Ta, W, Re increase. The element Ta, W and Re ratio of HY5 coating at the surface was measured by EDS are 3.89%, 5.85% and 2.16%, while element Mo does not spread to surface at 1000h. The interdiffusion behavior may change the original chemical composition in the superalloy and also in HY5 coating, thus resulting in decreasing stability of microstructure of superalloy and

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also impact the ability of high temperature corrosion and oxidation resistance [20]. In thermal cyclic oxidation, the surface of HY5 coating formed mainly α-Al2O3.

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Generating α-Al2O3 need to consume a large amount of Al, so content Al of HY5 coating significantly reduced, which is about 12% in deposited state and fall to about 4% at 1000h. Inward diffusion of element Al leads to Al content in the IDZ

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decreasing. Continued interdiffusion between HY5 coating and superalloy results in

new formation of IDZ. New IDZ will lead to a decrease α-A12O3 purity in TGO, thus

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promote the formation of Ni-rich oxide to break stability and protection of TGO. Interdiffusion is element interpenetration due to the thermal motion, the direction is toward the decreasing of element concentration to distribute evenly. It could be self-diffusion of atoms and also can be a foreign diffusion. Two important

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parameters are diffusion coefficient D and diffusion activation energy Q. The diffusion coefficient D is the average number of particles by a certain plane per unit time. The diffusion activation energy Q is the minimum energy of atom transition

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from one position to another position in the atom diffusion process in order to overcome the force of surrounding atoms. The best fit was obtained with an

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exponential relationship between D, Q and temperature which meet Arrhenus relationship:



D = D 0 exp − 

Q KT

  

(1)

For Eq. (1), D is the diffusion coefficient (m2/S); Q is the diffusion activation energy (kJ / mol); D0 is the diffusion factor; K is Boltzmann's constant; T is the absolute temperature (K). 11

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In the vacuum diffusion process, the atom diffusion near interfacial region results in the concentration gradient near the interface changing with distance and time. It is

∂C ∂ 2C =D 2 ∂t ∂x

(2)

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believed that element diffusion process satisfies Fick's second law [21]:

For Eq. (2), C is the volume concentration of the diffusion substance (kg / m); t is

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the diffusion time (s); x is the distance (m).

Matano[22] according to Boltzmann [23], another method is used to calculate

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diffusion coefficient (called Boltzmann-Matano method).

The basic principle of this method is that the diffusion coefficient D suppose as a function of the concentration C, so D = D (C), the equation (1) can be written in the following form:

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∂C ∂ 2 C ∂D ∂C =D 2 + ∂t ∂x ∂x ∂x

(3)

∂D complicates solving D. In this case, by using the relationship of C, x, t and ∂x

x t

substitute into equation (3),

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β=

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diffusion coefficient with law of diffusion at a given time, let C=C (β), D=D (β) and

 dC  β  = − dC d  D 2  dβ 

According to the initial condition: C =0|t=0,x=0, dC 1 C = − ∫ βdC dβ 2 0

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(4)

dC dC = 0 , so = 0, dx dβ

(5)

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Then let β =

x t

substitute into equation (5): C

1 ∫ xdC D=− 0 2 dC dx

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(6)

dC is the slope of curve C = f ( x ) at the concentration of C ; dx

For Eq. (6),

∫

C

0

xdC

is the integral area of curve C = f ( x ) in the interval [0, C]; D is the diffusion

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coefficient at the concentration of C.

Fig. 8 shows Concentration fitted profiles of element Al in different oxidation ; the fitted curve results are consistent with the atomic concentration

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time at 1100

of diffusion couple with changes of distance.

Using equation (6) and fitting curve equation (instead of actual measured value) calculate diffusion coefficient of element Al in different thermal cyclic oxidation time (Fig. 9). Hence, it appears that diffusion of element Al between HY5

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at 1100

coating and single crystal superalloy can be described adequately by:

C

0.16),

D Al600=1.09×10-25exp(284.9C)(0.11

C

0.14),

D Al1000=5.69×10-19exp(198.4 C)(0.09

C

0.12).

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DAl300=4.28×10-24exp(184.8C)(0.11

The diffusion coefficient for element Al increases from 300h to 1000h. The

results show that when temperature is constant, the diffusion coefficient increases slightly with the concentration of element Al in HY5 coating, the range is one order of magnitude. At high temperatures, the interdiffusion is mainly volume diffusion, while short path diffusion increases and diffusion activation energy decrease which results in diffusion coefficient increased significantly. 13

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3.4. Formation of secondary reaction zone Thermal cyclic oxidation at 1100

～accelerates further growth of the SRZ in

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Ni-based single crystal superalloy coated HY5 coating. The continued SRZ growth is evident from Fig. 5b, 5c and 5d. The cross-section morphology and EDS spectra of

secondary reaction zone in Ni-based single crystal superalloy coated HY5 coating are

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shown in Fig.10. Fig. 10a shows an area composing of white stripe and dot precipitates (about 100µm from surface of HY5 coating). This layer under

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interdiffusion zone is thicker and is called secondary reaction zone (SRZ). The SRZ is a region which consists of high density of TCP phases including σ, µ and Laves phases which had primarily a needlelike or rodlike morphology [24, 25]. TCP phase are typically characterized in the form of ‘basket weave’ sheets, which are aligned

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with the octahedral planes in the FCC matrix [26, 27].The TCP phases by EDS analysis (Fig. 10b) are principally composed of high levels of refractory elements such as W (29.54%), Re (28.94%), Cr and Co, while the mass fraction of the element

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Al is pretty low, only 0.7%, which is due to inward diffusion of Al from the coating into the substrate. Inward diffusion of Al causes unstable state of γ phase and the γ

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'phase, the discontinuous phase change occurs. The Al activity of HY5 coating plays a key role in determining the propensity of a specimen to form SRZ [10]. The content Cr in HY5 coating is relatively higher than that in the superalloy,

therefore Cr diffuse into the substrate during thermal cyclic process. However, Cr which diffuse from HY5 coating is not solid dissolved in the γ/γ' phase, it precipitates in form of α-Cr. The refractory elements W, Re dissolve easily in the α-Cr and

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element Al cannot dissolve in α-Cr. The element Re leads to the precipitation of α-Cr [28-31]. In addition, inward diffusion of Al, Cr, Co and outward diffusion of W, Re

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cause the formation of unstable γ/γ' phase. Mo is reported as one of the elements to control SRZ formation, whereas W and Re enhance further SRZ growth with prolonged oxidation at 1100°C [32].

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As is shown in Fig.5 most TCP phases are observed in single crystal superalloy, only a small amount of TCP phase is formed in the coating. TCP phases become

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significantly longer and the number of TCP phase increases with the thermal cyclic oxidation as compared in Fig.5b, Fig.5c and Fig.5d. SRZ areas also become larger and have an internal development of single crystal superalloy with thermal cyclic oxidation. The formation of SRZ below the HY5 coating is undesirable, since it leads

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to significant degradation of mechanical properties of the superalloy [33, 34]. The γ' phase has regular morphology and exhibit a cubic effect in single crystal superalloy without SRZ. Finer γ' phases and good microstructures can keep a high

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level of stress rupture property in superalloy. The γ' phase in SRZ area has grown, coarsened and coalesced obviously as shown in Fig.10. The γ' phase has been unable

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to keep the cube structure and thus causes serious dendritic segregation. And also the increase thickness of γ' phase has a unfavorable effect on bonding strength between

HY5 coating and Ni-base single crystal superalloy. The γ' phase is a major

strengthening phase of superalloy, therefore coarsening of γ/γ' phase will lead a gradation of the mechanical properties [35]. S. Tin et al. [36] have reported that 0.1 wt. % carbon additions could enhance the

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phase stability of superalloy and also inhibit the formation of TCP phases. The present study indicates that adding carbon does have a beneficial effect in suppressing

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the extent of cellular transformation beneath the β-NiAl coating. So, further investigation is needed to find out how to control SRZ formation in superalloys.

4. Conclusions

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NiCoCrAlYHf coating is deposited by arc ion-plating and their thermal cyclic oxidation was systematically investigated. The findings can be summarized as

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follows:

(1) NiCoCrAlYHf coating could protect Ni-based single crystal superalloy very well and improve oxidation-resistance property.

(2) Significant interdiffusion between NiCoCrAlYHf coating and Ni based single , resulting

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crystal superalloy DD10 occurs during thermal cyclic oxidation at 1100

in the formation of both the IDZ and the SRZ. The element Al, Co and Cr diffuse inward from NiCoCrAlYHf coating and element Ni, W, Re, Mo and Ta diffuse

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outward from the superalloy. The element diffusion behavior enhanced with thermal cyclic oxidation.

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(3) When the temperature is constant, the diffusion coefficient of Al increases slightly with the concentration of element Al in NiCoCrAlYHf coating, the range is one order of magnitude. The diffusion of element Al between NiCoCrAlYHf coating and single crystal superalloy can be described adequately by

DAl300=4.28×10-24exp(184.8C)(0.11

C

0.16),

DAl600=1.09×10-25exp(284.9C)(0.11

C

0.14),

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DAl1000=5.69×10-19exp(198.4 C)(0.09

C

0.12).

(4) An 70µm thickness SRZ beneath the IDZ was formed after 300h thermal cyclic . The SRZ consists of high density of TCP phases which had

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oxidation at 1100

primarily a needlelike or rodlike morphology. The TCP phases are principally

composed of high levels of refractory elements such as W and Re, while the mass

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fraction of the element Al is very low. TCP phases become significantly longer and the number of TCP phase increase with thermal cyclic oxidation. High temperature

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oxidation of NiCoCrAlYHf coating coated superalloy led to significant additional growth of SRZ. SRZ areas have an internal development of single crystal superalloy, which lead to significant degradation of mechanical properties of the superalloy.

Acknowledgement

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The authors would like to thank G. Wang and Z.J. Xu for HY5 coating preparation. Financial support from The General Reserve Department of PLA project 813040404-1 is also gratefully acknowledged.

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References

[1] S.G. Tian, Y. Su, B.J. Qian, X.F. Yu, F.S. Liang, A.A. Li, Creep behavior of a

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single crystal nickel based superalloy containing 4.2% Re, Mater. Des. 37 (2012) 236–242.

[2] G. Liu, L. Liu, C. Ai, B.M. Ge, J. Zhang, H.Z. Fu, Influence of withdrawal rate on the microstructure of Ni-base single-crystal superalloys containing Re and Ru , J. Alloys Compd. 509 (2011) 5866–5872. [3] A. Baldan, Review progress in Ostwald ripening theories and their applications to

17

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the γ'-precipitates in nickel-base superalloys Part II Nickel-base superalloys, J. Mater. Sci. 37 (2002) 2379–2405.

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[4] A. Raffaitin, F. Crabos, E. Andrieu, D. Monceau, Advanced burner-rig test for oxidation-corrosion resistance evaluation of MCrAlY/superalloys systems, Surf. Coat. Technol. 201 (2006) 3829–3835.

superalloy between 900 and 1000

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[5] C.T. Liu, J. Ma, X.F. Sun, Oxidation behavior of a single-crystal Ni-base

in air, J. Alloys Compd.491 (2010) 522–526.

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[6] F.H. Latief, K. Kakehi, Influence of thermal exposure on the creep properties of an aluminized Ni-based single crystal superalloy in different surface orientations, Mater. Des.56 (2014) 816–821.

[7] X.L. Chen, Y.F. Zhang, X.H. Zhong, Z.H. Xu, J.F. Zhang, Y.L. Cheng, Y. Zhao,

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Y.J Liu, X.Z. Fan, Y. Wang, H.M. Ma, X.Q. Cao, Thermal cycling behaviors of the plasma sprayed thermal barrier coatings of hexaluminates with magnetoplumbite structure, J. Eur. Ceram. Soc. 30 (2010) 1649–1657.

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[8] Z.H. Xu, S.M. He, L.M. He, R.D. Mu, G.H. Huang, X.Q. Cao, Novel thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/8YSZ double-ceramic-layer systems

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deposited by electron beam physical vapor deposition, J. Alloys Compd. 509 (2011) 4273–4283.

[9] D.F. Susan, A.R. Mardera, Ni-Al composite coatings: diffusion analysis and coating lifetime estimation, Acta Mater. 49 (2001) 1153–1163. [10] B. Bai, H.B. Guo, H. Peng, L.Q. Peng, S.K. Gong, Cyclic oxidation and interdiffusion behavior of a NiAlDy/RuNiAl coating on a Ni-based single crystal

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superalloy, Corros. Sci. 53 (2011) 2721–2727. [11] D. Wang, H. Peng, S.K. Gong, H.B. Guo, NiAlHf/Ru: Promising bond coat

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materials in thermal barrier coatings for advanced single crystal superalloys, Corros. Sci. 78 (2014) 304–312.

[12] M.S.A. Karunaratne, C.M.F. Rae, R.C. Reed, On the microstructural instability

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of an experimental nickel base single crystal superalloy, Metall. Mater. Trans. A 32 (2001) 2409-2421.

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[13] C.M.F. Rae, R.C. Reed, The precipitation of topologically close-packed phase in rheninm-containing superalloys, Acta Mater. 49(2001) 4113-4125. [14] Q.X. Fan, X. Peng, H.J. Yu, S.M. Jiang, J. Gong, C. Sun, The isothermal and cyclic oxidation behaviour of two Co modified aluminide coatings at high

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temperature, Corros. Sci. 84 (2014) 42–53.

[15] B.A. Pint, I.G. Wright, W.Y. Lee, Y. Zhang, K. Prüßner, K.B. Alexander, Substrate and bond coat compositions: Factors affecting alumina scale adhesion,

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Mater. Sci. Eng., A 245(1998) 201–211.

[16] R. Rettig, R.F. Singer, Numerical modelling of precipitation of topologically

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close-packed phases in nickel-base superalloys, Acta Mater. 59 (2011) 317–327. [17] D.K. Das, B. Gleeson, K.S. Murphy, S. Ma, T.M. Pollock, Formation of secondary reaction zone in ruthenium bearing nickel based single crystal superalloys with diffusion aluminide coatings, Mater. Sci. Technol. 25 (2009) 300-308. [18] Z.H. Xu, W.K. Wang, J. Niu, L.M. He, R.D. Mu, K. Wang, Effects of deposition temperature on the kinetics growth and protective properties of aluminide coatings, J.

19

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Alloys Compd. 632 (2015) 238–245. [19] Y.H. Sohna, J.H. Kima, E.H. Jordanb, M. Gella, Thermal cycling of EB-PVD/

mechanisms, Surf. Coat. Technol. 146 –147 (2001) 70–78.

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MCrAlY thermal barrier coatings: I. Microstructural development and spallation

[20] J. Müller, D. Neuschütz, Efficiency of α-alumina as diffusion barrier between

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bond coat and bulk material of gas turbine blades, Vacuum 71 (2003) 247–251.

[21] S.K. Kailasam, J.C. Lacombe, M.E. Glicksman, Evaluation of the Methods for

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Calculating the Concentration-Dependent Diffusivity in Binary Systems, Metall. Mater. Trans. A 30 (1999) 2605–2610.

[22] L. Boltzmann, Wiedemanns Ann. Physik 53 (1894) 959–961. [23] C. Matano, Jpn. J. Physics 8 (1933) 109–113.

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[24] A. Suzuki, C.M.F. Rae, Secondary Reaction Zone Formations in coated Ni-base Single Crystal Superalloys, Journal of Physics: Conference Series 165 (2009) 1–6. [25] T.Q. Liang, H.B. Guo, H. Peng, S.K. Gong, Precipitation phases in the

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nickel-based superalloy DZ 125 with YSZ/CoCrAlY thermal barrier coating, J. Alloys Compd. 509 (2011) 8542– 8548.

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[26] D.F. Lahrman, R.D. Field, R. Darolia, H.L. Fraser, Investigation of techniques for measuring lattice mismatch in a rhenium containing nickel base superalloy, Acta Metall. 36 (1988) 1309–1320. [27] S.B. Kang, Y.G. Kim, H.M. Kim, N.S. Stoloff, The influence of a coating treatment and directional solidification on the creep rupture properties of a nickel-base superalloy, Mater. Sci. Eng. 83(1986) 75–86.

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[28] N. Czech, F. Schmitz, W. Stamm, Microstructural analysis of the role of rhenium in advanced MCrAlY coatings, Surf. Coat. Technol. 76–77 (1995) 28–33.

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[29] W. Beele, N. Czech, W. J. Quadakkers, W. Stamm, Long-term oxidation tests on a Re-containing MCrAlY coatings, Surf. Coat. Technol. 94–95 (1997) 41–45.

[30] C.Z. Xu, S.M. Jiang, Z.B. Bao, J. Gong, C. Sun, Isothermal oxidation behavior

crystal superalloy, Corros. Sci. 51 (2009) 1467–1474.

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of a gradient NiCoCrAlSiY coating deposited by arc ion plating on a Ni-based single

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[31] J.D. Nystrom, T.M. Pollock, W.H. Murphy, A.Garg, Discontinuous cellular precipitation in a high refractory nickel base superalloy, Metall. Mater. Trans. A 28 (1997) 2443–2452.

[32] A.S. Suzuki, K. Kawagishi, T. Yokokawa, H. Harada and T. Kobayashi,

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Prediction of initial oxidation behavior of Ni-base single crystal superalloys by regression analysis, Scripta Mater. 65 (2011) 49–52. [33] N. El-Bagoury, Q. Mohsen, Gamma prime and TCP phases and mechanical

1108–1122.

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properties of thermally exposed nickel-base superalloy, Phase Transitions 84 (2011)

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[34] X.P. Tan, H.U. Hong, B.G. Choi, I.S. Kim, C.Y. Jo, T. Jin, Z.Q. Hu, Characterization of topologically close-packed phases in secondary reaction zone in a coated CMSX-4 single crystal Ni-based superalloy, J. Mater. Sci. 48 (2013) 1085–1089. [35] A.S. Suzuki, K. Kawagishi, T. Yokokawa, H. Harada, Effect of Cr on microstructural evolution of aluminized fourth generation Ni-base single crystal

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superalloys, Surf. Coat. Technol. 206 (2012) 2769–2773. [36] S. Tin, T.M. Pollock, Phase instabilities and carbon additions in single-crystal

Figure and Table Caption

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nickel-base Superalloys, Mater. Sci. Eng., A 348 (2003) 111-121.

Fig.1. The kinetic curves of thermal cyclic oxidation at 1100

(a) Ni-based single

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crystal superalloy for 20h and (b) HY5 coating for 600h.

Fig.2. BSE images of surface morphology of single crystal superalloy DD10 after thermal cyclic oxidation at 1100

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a in (b) respectively.

for 300h (a) are corresponding EDS specra of area

Fig.3. BSE images of surface morphologies of HY5 coatings after thermal cyclic : (a) as-deposited and (b) 1000h.

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oxidation at 1100

Fig.4. BSE images of cross-section morphologies of Ni-based single crystal

superalloy after thermal cyclic oxidation at 1100 : (a)0h, (b)300h and (c) 600h.

Fig.5. BSE images of cross-section morphologies of HY5 coatings after thermal cyclic oxidation at 1100 with different magnifications: (a)0h (b)300h, (c)600h and (d)1000h.

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Fig.6. XRD patterns of HY5 coating after thermal cyclic oxidation at 1100

for

600h.

～after thermal cyclic

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Fig.7. Chemical compositions of HY5 coating at 1100 oxidation.

1100

: (a)300h, (b) 600h and (c) 1000h.

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Fig.8. Concentration fitted profiles of element Al after thermal cyclic oxidation at

Fig.9. Various times of interdiffusion coefficients for Al with the variety of atomic

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contents: (a)300h, (b) 600h and (c) 1000h.

Fig.10. BSE images of cross-section morphology of secondary reaction zone after thermal cyclic oxidation at 1100

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respectively.

(a) are corresponding EDS specra of Point a in (b)

Table 1. Chemical compositions of third generation Ni-base single crystal superalloy DD10 and HY5 coating (mass fraction/%). Table 2. Preparation parameters of HY5 coating.

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DD10 and HY5 coating (mass fraction/%). Co

DD10

Bal.

4

12

HY5

Bal.

18-23

10-15

Al

Mo

W

Re

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Cr

Ta

Y

Hf

6

2

6

5

7

-

-

8-12

-

-

-

-

0.1-0.5

0.2-0.6

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Ni

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Table 1. Chemical compositions of third generation Ni-base single crystal superalloy

1

Table 2. Preparation parameters of HY5 coating. Ub/V

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550-700

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10-30

2

P/Pa

<6.67×10-3

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Fig.1. The kinetic curves of thermal cyclic oxidation at 1100

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crystal superalloy for 20h and (b) HY5 coating for 600h.

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(a) Ni-based single

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Fig.2. BSE images of surface morphology of single crystal superalloy DD10 after thermal cyclic oxidation at 1100

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a in (b) respectively.

for 300h (a) are corresponding EDS specra of area

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Fig.3. BSE images of surface morphologies of HY5 coatings after thermal cyclic : (a) as-deposited and (b) 1000h.

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oxidation at 1100

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Fig.4. BSE images of cross-section morphologies of Ni-based single crystal

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superalloy after thermal cyclic oxidation at 1100 : (a)0h, (b)300h and (c) 600h.

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Fig.5. BSE images of cross-section morphologies of HY5 coatings after thermal

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(d)1000h.

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cyclic oxidation at 1100 with different magnifications: (a)0h (b)300h, (c)600h and

5

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600h.

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Fig.6. XRD patterns of HY5 coating after thermal cyclic oxidation at 1100

6

for

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Fig.7. Chemical compositions of HY5 coating at 1100

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oxidation: (a)0h (b)300h, (c)600h and (d)1000h.

7

after thermal cyclic

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Fig.8. Concentration fitted profiles of element Al after thermal cyclic oxidation at : (a)300h, (b) 600h and (c) 1000h.

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1100

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Fig.9. Various times of interdiffusion coefficients for Al with the variety of atomic

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contents: (a)300h, (b) 600h and (c) 1000h.

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Fig.10 BSE images of cross-section morphology of secondary reaction zone after thermal cyclic oxidation at 1100

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respectively.

(a) are corresponding EDS specra of Point a in (b)

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1) NiCoCrAlYHf coating protect third generation Ni-based single crystal superalloy very well and improve oxidation-resistance property.

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2) Interdiffusion zone and secondary reaction zone are formed during thermal cycling oxidation.

after thermal cyclic oxidation.

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3) Some inward diffusion of Al, Co and Cr from NiCoCrAlYHf coating is occurred

4) Outward diffusion of Ni, W, Re, Mo and Ta and inward diffusion of Al, Co and Cr

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promote the formation of secondary reaction zone.

5) The diffusion coefficient of Al increases slightly with the concentration of

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element Al in NiCoCrAlYHf coating when the temperature is constant.

1