Evaluation of Failure Micromechanisms of Advanced Thermal Spray Coatings by In Situ Experiment

2014 ◽  
Vol 606 ◽  
pp. 187-190 ◽  
Author(s):  
Radek Mušálek ◽  
Catalina Taltavull ◽  
Antonio Julio Lopez Galisteo ◽  
Nicholas Curry
Keyword(s):  
Thermal Spray ◽  
Thermal Spray Coatings ◽  
Three Point Bending ◽  
Spray Coatings ◽  
Barrier Coating ◽  
Failure Evolution ◽  
Inhomogeneous Character ◽  
Coating Microstructure ◽  
Service Conditions

Identification of failure mechanisms of thermal spray coatings by means of traditional fractography of failed parts is often troublesome. Reason for this is a highly inhomogeneous character of the coating microstructure and harsh in-service conditions which may hinder evidentiary fractographic marks. In this study, failure evolution of advanced thermal barrier coating (TBC) prepared by plasma spraying was studied in-situ at high magnification in a scanning electron microscope under well-defined laboratory conditions of three-point bending (3PB).

Image-Based Modeling for Assessing Thermal Conductivity of Thermal Spray Coatings at Ambient and High Temperature

2006 ◽  
Author(s):  
Y. Tan ◽  
A. Sharma ◽  
J. P. Longtin ◽  
S. Sampath ◽  
H. Wang
Keyword(s):  
Thermal Conductivity ◽  
High Temperature ◽  
Thermal Spray ◽  
Process Parameters ◽  
Thermal Spraying ◽  
Thermal Spray Coatings ◽  
Analysis Model ◽  
Element Analysis ◽  
Spray Coatings ◽  
Coating Microstructure

Thermal spray coatings are used extensively for protection of engineering components and structures in a variety of applications. Due to the nature of thermal spraying process, the coating thermal, mechanical, and electrical properties depend strongly on the coating microstructure, which consists of many individual splats, interfaces between the splats, defects and voids. The coating microstructure, in turn, is determined by the thermal spray process parameters. In order to relate coating process parameters to the final coating performance, then, it is desirable to relate coating microstructure to coating properties. In this work, thermal conductivity is used as the physical parameter of interest. Thermal conductivity of thermal spray coatings is studied by using an image analysis-based approach of typical coating cross sections. Three coating systems, yttria stabilized zirconia (YSZ), molybdenum, and Ni-5wt.%Al are explored in this work. For each material, thermal conductivity is simulated by using a microstructure image-based finite element analysis model. The model is then applied to high temperature conditions (up to 1200 °C) with a hot stage-equipped scanning electron microscope imaging technique to assess thermal conductivity at high temperatures. The coating thermal conductivity of metallic coatings is also experimentally measured by using a high-temperature laser flash technique.

In Situ Temperature Measurement Using Embedded Micro-Thermocouples in Vacuum Plasma Sprayed Multi-Layered Structures

1998 ◽  
Author(s):  
C. Verdy ◽  
B. Serio ◽  
C. Coddet
Keyword(s):  
Thermal Spray ◽  
Thermal Spray Coatings ◽  
Spray Coatings ◽  
Spray Process ◽  
Vacuum Plasma ◽  
Copper Coatings ◽  
Plasma Sprayed ◽  
Spraying Process ◽  
Infrared Pyrometer

Abstract The integration of thermocouples into thermal spray deposits and especially into vacuum thermal spray coatings could provide temperature monitoring between the substrate and the coating or between two different coatings during the spray process and later during post treatments and service life. Thermocouples of 251µm in diameter were made using Chromel® and Alumel® wires. Electrical insulation was obtained using a ceramic cement. Astroloy and Copper coatings were successfully sprayed over these sensors and the temperature given by an embedded thermocouple was compared to the response of an infrared pyrometer during the spraying process.

An ASM Recommended Practice for Evaluation of Young’s Modulus and Poisson’s Ratio of Thermal Spray Coatings Bonded to a Substrate

2000 ◽  
Author(s):  
J.R. Shadley ◽  
E.F. Rybicki ◽  
Y. Xiong ◽  
R.T.R. McGrann ◽  
A.C. Savarimuthu
Keyword(s):  
Young’S Modulus ◽  
Thermal Spray ◽  
Poisson’S Ratio ◽  
Young's Modulus ◽  
Thermal Spray Coatings ◽  
Poisson's Ratio ◽  
Spray Coatings ◽  
Recommended Practices ◽  
International Thermal Spray

Abstract In situ values of Young's modulus and Poisson's ratio for thermal spray coatings are needed to evaluate properties and characteristics of thermal spray coatings such as residual stresses, in-service stresses, bond strength, fracture toughness, and fatigue crack growth rates. It is important to have methods documented in detail so that people can follow the document and use the methods. Such a document requires more pages than are allowed in conference proceeding and journal papers. Thus, Recommended Practices and Standards describing these methods are needed. Currently, there is not a recommended practice or standard for evaluating Young's modulus and Poisson's ratio for thermal spray coatings. The ASM International Thermal Spray Society has recognized this need and formed a committee on Recommended Practices for Thermal Spray Coatings. This paper describes one of the recommended practices being written by the Mechanical Properties Evaluation Subcommittee of the Recommended Practices Committee. The specimen is a coated substrate in the form of a cantilever beam. The method is easy to use and inexpensive. The equipment needed is a vise or clamping fixture, strain gages, a strain indicator, a micrometer, a ruler, a hanger, and a set of weights. The specimen is easy to machine and spray. The loading is easy to apply and remains constant during readings. The method can be used to evaluate Young's modulus and Poisson's ratio in tension or compression. A description of the method, a verification, and a sensitivity analysis was done and published in Reference [1]. Some of the details of implementing the method and the data sheet are presented here.

In-Situ Observation and Ae Analysis of Microscopic Fracture Process of Thermal Spray Coatings

1998 ◽  
Author(s):  
K. Akita ◽  
G. Zhang ◽  
S. Takahashi ◽  
H. Misawa ◽  
S. Tobe
Keyword(s):  
Thermal Spray ◽  
Bonding Strength ◽  
Thermal Spray Coatings ◽  
Fracture Mechanisms ◽  
In Situ Observation ◽  
Spray Coatings ◽  
Thermally Sprayed Coatings ◽  
Thermally Sprayed ◽  
Sprayed Coatings

Abstract Microscopic fracture mechanisms of thermal spray coatings under bending stress are investigated. Samples of thermally sprayed coatings were made using three distances. The sprayed powder was pure molybdenum. Vertical microcracks occur in lamellae and subsequently, these cracks join together and form vertical macrocracks in the samples sprayed with a short spraying distance. On the other hand, horizontal microcracks occur at the lamellae interfaces, and these cracks link together in the samples sprayed with a long spraying distance. These tendencies can be explained in terms of the hardness of the lamella and the bonding strength between each lamella. It is clarified that the bonding strength between each lamella corresponds to the applied strain at the point of rapid increase of the AE event count. The amplitude and rate of AE beyond the point of rapid increase are high in the coatings which formed macrocracks. It is concluded that the coating which has high resistance to crack formation has a high point of AE increase, low AE amplitude and low AE increasing rate.

Using In Situ Atomic Force Microscopy to Investigate the Kinetics of Corrosion of WC–Co–Cr Cermet Coatings Applied by High-Velocity Oxy-Fuel

2006 ◽  
Vol 129 (1) ◽  
pp. 55-68 ◽  
Author(s):  
V. A. D. Souza ◽  
A. Neville
Keyword(s):  
Atomic Force Microscopy ◽  
Thermal Spray ◽  
High Velocity ◽  
Thermal Spray Coatings ◽  
Aqueous Corrosion ◽  
Cermet Coatings ◽  
Force Microscopy ◽  
Spray Coatings ◽  
Atomic Force

Most of the early applications of thermal spray coatings were focused toward providing a remedy to excessive wear degradation. However, as the introduction of such coatings into wider industrial sections increases there is also exposure to other potential degradation processes—aqueous corrosion is one such process. The complex microstructures in cermet coatings have been shown to translate to complex modes of corrosion attack. In this paper an electrochemical test methodology to probe the local/microaspects of corrosion initiation and propagation will be described. A new electrochemical cell has been devised in which the corrosion can be followed “live” and in “real-time.” The surface is subjected to in situ imaging by atomic force microscopy which shows that not only the binder (Co, Cr) corrodes in high-velocity oxy-fuel thermal spray coatings but also the hard phase, with oxidation and dissolution of WC∕W2C taking place. Also potentiostatic tests indicated that the corrosion of WC-based coatings follows an Arrhenius relationship enabling the determination of activation energy (Ea) for the corrosion of WC and demonstrating that the oxidation and dissolution of WC are temperature, particle size, potential, and pH related

scholarly journals Sliding Wear of Conventional and Suspension Sprayed Nanocomposite WC-Co Coatings: An Invited Review

2021 ◽  
Author(s):  
R. Ahmed ◽  
O. Ali ◽  
C. C. Berndt ◽  
A. Fardan
Keyword(s):  
Wear Rate ◽  
Thermal Spray ◽  
Sliding Wear ◽  
Failure Modes ◽  
Thermal Spray Coatings ◽  
Annual Growth Rate ◽  
Total Energy Consumption ◽  
Wear Performance ◽  
Wear Rates ◽  
Spray Coatings

AbstractThe global thermal spray coatings market was valued at USD 10.1 billion in 2019 and is expected to grow at a compound annual growth rate of 3.9% from 2020 to 2027. Carbide coatings form an essential segment of this market and provide cost-effective and environmental friendly tribological solutions for applications in aerospace, industrial gas turbine, automotive, printing, oil and gas, steel, and pulp and paper industries. Almost 23% of the world’s total energy consumption originates from tribological contacts. Thermal spray WC-Co coatings provide excellent wear resistance for industrial applications in sliding and rolling contacts. Some of these applications in abrasive, sliding and erosive conditions include sink rolls in zinc pots, conveyor screws, pump housings, impeller shafts, aircraft flap tracks, cam followers and expansion joints. These coatings are considered as a replacement of the hazardous chrome plating for tribological applications. The microstructure of thermal spray coatings is however complex, and the wear mechanisms and wear rates vary significantly when compared to cemented WC-Co carbides or vapour deposition WC coatings. This paper provides an expert review of the tribological considerations that dictate the sliding wear performance of thermal spray WC-Co coatings. Structure–property relationships and failure modes are discussed to grasp the design aspects of WC-Co coatings for tribological applications. Recent developments of suspension sprayed nanocomposite coatings are compared with conventional coatings in terms of performance and failure mechanisms. The dependency of coating microstructure, binder material, carbide size, fracture toughness, post-treatment and hardness on sliding wear performance and test methodology is discussed. Semiempirical mathematical models of wear rate related to the influence of tribological test conditions and coating characteristics are analysed for sliding contacts. Finally, advances for numerical modelling of sliding wear rate are discussed.

Effects of Phosphorus and Carbon Contents on Amorphous Forming Ability in Fe-based Amorphous Alloys Used for Thermal Spray Coatings

2013 ◽  
Vol 44 (6) ◽  
pp. 2573-2580 ◽  
Author(s):  
Jeonghyeon Do ◽  
Seungmun Jung ◽  
Hyuk-Joong Lee ◽  
Byeong-Joo Lee ◽  
Gil-up Cha ◽  
...  
Keyword(s):  
Thermal Spray ◽  
Amorphous Alloys ◽  
Thermal Spray Coatings ◽  
Spray Coatings
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