Effect of TaC particles on the microstructure and oxidation behavior of NiCoCrAlYTa coating prepared by electrospark deposition on single crystal superalloy

doi:10.1016/j.surfcoat.2021.126851

Surface and Coatings Technology

Volume 408, 25 February 2021, 126851

https://doi.org/10.1016/j.surfcoat.2021.126851 Get rights and content

Highlights

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NiCoCrAlYTa/TaC MMC coatings were prepared by ESD on single crystal superalloy.
•
The addition of TaC decreased the thermal conductivity and thermal diffusivity of the MMC electrode.
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The microstructure and oxidation behavior were changed.
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The overall high temperature performance was improved by adding TaC particles.

Abstract

NiCoCrAlYTa/TaC metal matrix composite coatings were prepared on single crystal superalloy (SX) using electrospark deposition (ESD) to improve its high temperature performance. The effect of TaC addition on the coating microstructure, oxidation behavior, wear resistance and physical properties of electrode were investigated. The results showed that, with the addition of TaC particles, the density of electrode increased, while the thermal conductivity and thermal diffusivity decreased. In the electrode, TaC particles were distributed around or embedded into the NiCoCrAlYTa powders, while in ESD coatings, they were distributed homogeneously in both dendrite cores and interdendritic regions. The generation of β-NiAl phase in ESD coating was prevented by adding TaC particles. During 1000 °C/100 h oxidation, the mass gain of coating with TaC addition was lower than that without TaC addition during the first 40 h, and then became higher. The oxidative products were similar, except that θ-Al₂O₃ was relatively more in coating without TaC, while Y₃Al₅O₁₂ was more in coating with TaC addition. The microhardness and wear resistance in both coatings decreased after oxidation, however, it was on the same level for NiCoCrAlYTa coating before oxidation and NiCoCrAlYTa/TaC coating after oxidation. Thus, the overall high temperature performance of the coatings was improved due to the addition of TaC particles.

Introduction

Particle reinforced metal matrix composite coatings (PR-MMC) with wear- and oxidation resistance are widely used in the field of aerospace, especially on the surfaces of moving parts, such as abrasive coatings on blade tips [1,2]. Particularly, MCrAlY alloys are usually selected as the metal matrix to provide the structure strength, oxidation and erosion resistance, while the ceramic particles are generally carbides and oxides, such as WC, ZrO₂, SiC and Al₂O₃ [3]. Among the MCrAlY alloys, NiCoCrAlYTa alloy is increasingly used due to its enhanced adhesion of oxide scale derived from adding Ta element [4,5].

The NiCoCrAlYTa MMC coatings have mainly been produced by spraying processes, such as WC-Co reinforced NiCoCrAlYTa coatings prepared by high velocity oxy-fuel (HVOF) spraying [6], NiCoCrAlYTa-Al₂O₃ coating produced by detonation gun spraying [7,8]. The microstructure and oxidation performance have been concerned. However, due to the different preparation conditions of these coatings, the microstructure and oxidation properties presented a great variety. In general, the spraying processes can obtain coatings with laminated structure owing to the partially melting of the powders, and some oxidation happens during deposition. Though the spraying processes are now dominating the preparation of protective coating on turbine blades, the ESD process may have huge potential in the field of producing abrasive coatings on blade tips of single crystal superalloy (SX), due to its epitaxial growth of dendrites and little heat impact to the SX substrate [9,10].

Xie [11] had investigated the feasibility of producing ESD NiCoCrAlYTa/BN coatings on IN792, a polycrystalline superalloy, and found that the dendrites grew epitaxially until the BN content came to 5 wt%. Wang [10] studied the microstructure of ESD NiCoCrAlYTa/Y₂O₃ coatings on SX superalloy, and found that the operating voltage greatly influenced the morphology of the deposit and the dendrites, and the distribution of the Y₂O₃ particles. Although previous reports have investigated the fabrication and microstructure of NiCoCrAlYTa matrix PR-MMC coatings on polycrystalline superalloy [11,12] and SX superalloy [10], the oxidation performance of this kind of coatings is seldomly reported in literature.

Tantalum carbide (TaC) has a high melting point of 3880 °C and high hardness. Even at elevated temperature, its hardness is not lower than that of diamond [13]. Thus, TaC has been added into metal matrix to produce reinforced surface coatings [[14], [15], [16]]. Xie [12] investigated the effect of TaC content on the microstructure and oxidation property of ESD NiCoCrAlYTa/TaC coating, the results showed that the TaC content did not affect the epitaxial growth of metal matrix, and the oxidation resistance decreased with increasing TaC content. In his work, TaC particles were in the scale of tens of microns, and the addition was higher than 10 wt%. The TaC particles traversed several dendrites, which enlarged the reaction possibility between O and TaC, thus the increased mass gain during oxidation might mainly attributed to the oxidation of TaC particles. However, during MMC preparation by mechanical mixing, there exists a best addition range of ceramic particles, in which the particles are perfectly surrounding the matrix powder [17]. If the TaC particles can be homogenously dispersed in the coating, especially in the dendrite cores, the coating hardness should be enhanced and the oxidation resistance might be under control.

Based on this assumption, submicron TaC particles were added into NiCoCrAlYTa electrode and the NiCoCrAlYTa/TaC coatings were prepared by electrospark deposition on single crystal superalloy. The effect of TaC particles on the microstructure and physical properties of electrodes and oxidation behavior of ESD coatings were investigated.

Section snippets

Materials and methods

TaC particles with diameter in the range of 0.1–1 μm were added into NiCoCrAlYTa powder (nominal composition: Ni-23Co-20Cr-8Al-4Ta-0.6Y, particle size: 45–105 μm) with the weight ratio of 4 wt%, and dry-milled for 3 h in planetary ball mill. Then the MMC powder was sintered and machined to form electrode. The detail of the electrode preparation could refer to the previous work [10].

The thermal conductivity and thermal diffusivity of the electrodes were measured by DLF 1200 (TA Instruments) from

Microstructure and physical properties of electrodes

The microstructure of electrode with and without addition of TaC particles were shown in Fig. 1. As can be seen, both electrodes were consisted of γ (the gray phase), β (the dark phase), TaC (the white particles), and Ni single bond Y phase (the light gray phase), as reported in the previous works [10,18], while the most conspicuous difference was that TaC particles were dramatically increased in amount and mostly distributed in the boundaries between the NiCoCrAlYTa powders in NiCoCrAlYTa/TaC electrode (

Effect of TaC on the microstructure and physical properties

The density of TaC is 14.58 g/cm³ [27], it is easy to understand the increasing density of electrode added TaC particles. The thermal conductivity of TaC is reported to be 27.9 W/m·K at 25 °C [28] and 55 W/m·K at 1400 °C [29], which is larger than that of NiCoCrAlYTa electrode. After the addition of TaC particles, however, the thermal conductivity of NiCoCrAlYTa/TaC electrode was lower than that of NiCoCrAlYTa electrode, as well as the thermal diffusivity, as shown in Fig. 2. The reason might

Conclusions

NiCoCrAlYTa/TaC MMC coatings were prepared by electrospark deposition on single crystal superalloy, and the effect of TaC addition on the microstructure and oxidation properties were investigated. Some conclusions could be drawn as follows:

(1)
TaC particles distributed around the NiCoCrAlYTa powders in electrode, while distributed homogeneously in ESD coating, which was attibuted to the engufment of solidification fronts. The addition of TaC particles decreased the thermal conductivity and thermal

CRediT authorship contribution statement

Wenqin Wang: research framework construction, supervision, validation, writing reviewing and editing.

De Wang: sample preparation, data processing, results analysis and manuscript writing.

Junhao Gao: results anlysis, data processing.

Rui Zhang: writing - review and editing.

Shaojun Deng: results analysis, sample preparation.

Shuyuan Jiang: results analysis.

Donghai Cheng: results analysis.

Pin Liu: results analysis.

Zhenyu Xiong: results analysis.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China [51901090], [51765041], Jiangxi Provincial Natural Science Foundation [2020ACBL214003] and Doctorial Foundation of NCHU [2030009401073]. The authors would also like to acknowledge the colleagues who provided the language help.

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Effect of TaC particles on the microstructure and oxidation behavior of NiCoCrAlYTa coating prepared by electrospark deposition on single crystal superalloy

Highlights

Abstract

Introduction

Section snippets

Materials and methods

Microstructure and physical properties of electrodes

Effect of TaC on the microstructure and physical properties

Conclusions

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgements

Corros. Sci.

Appl. Surf. Sci.

Int. J. Refract. Met. Hard Mater.

Trans. Nonferrous Met. Soc. China

Surf. Coat. Technol.

J. Alloy.Compd.

J. Eur. Ceram. Soc.

Surf. Coat. Technol.

J. Alloy. Compd.

Mater. Charact.

Surf. Coat. Technol.

Surf. Coat. Technol.

Surf. Coat. Technol.

Mater. Sci. Eng. A

Trans. Nonferrous Met. Soc. China

Corros. Sci.

J. Mater. Process. Technol.

J. Alloy. Compd.

Mater. Sci. Eng. A

J. Eur. Ceram. Soc.