Micro and Macroscopic Approaches to Residual Stress Generation Mechanism of Thermal Spray Coatings

2000 ◽  
Author(s):  
S. Tobe ◽  
Y. Andou ◽  
M. Ando ◽  
S. Kuroda ◽  
K. Akita
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Thermal Spray ◽  
Stress Measurement ◽  
Coefficient Of Thermal Expansion ◽  
Steel Substrate ◽  
Generation Mechanism ◽  
Thermal Spray Coatings ◽  
Stress Generation ◽  
Spray Coatings

Abstract Microscopic and macroscopic residual stress measurements and a finite element method (FEM) for stress analysis of thermal spray coatings have been carried out to investigate the residual stress generation mechanism. The residual stresses of one splat, laminated two splats and coatings were measured by a micro-beam x-ray stress measurement system and the macroscopic residual stresses were measured in-situ by the curvature change of the thin substrate plate during and after spraying. Two coating materials were employed in this study to deposit the coatings. One is molybdenum of which the coefficient of thermal expansion (CTE) is smaller than that of steel substrate and the other is 80%Ni-20%Cr alloy which has higher CTE than steel. The substrate was preheated up to 550°C just before spraying. The residual stresses of the splat and a coating are fundamentally the same level. The FEM analysis on the residual stress was also useful and by the comparison of two measurement results of microscopic and macroscopic residual stresses, the generation mechanism was discussed.

An ASM Recommended Practice for Modified Layer Removal Method (MLRM) to Evaluate Residual Stress in Thermal Spray Coatings

2000 ◽  
Author(s):  
E.F. Rybicki ◽  
J.R. Shadley ◽  
R.T.R. McGrann ◽  
A.C. Savarimuthu ◽  
D. Graving
Keyword(s):  
Mechanical Properties ◽  
Residual Stress ◽  
Residual Stresses ◽  
Thermal Spray ◽  
Thermal Spray Coatings ◽  
Removal Method ◽  
Layer Removal ◽  
Spray Coatings ◽  
Layer Removal Method ◽  
Modified Layer

Abstract Thermal spray coatings are subjected to mechanical loadings in many applications, and there is a need to evaluate the mechanical properties of these coatings. Mechanical properties of interest in the performance of thermal spray coatings include fatigue life, wear resistance, bond strength. Young's modulus, Poisson's ratio, and residual stresses. One property that has a large effect on the performance of thermal spray coated parts is the residual stress distribution in the thermal spray coating and in the substrate. Thus, it is important to have (1) a fundamentally sound method for evaluating residual stresses and (2) a written recommended procedure for applying the method. ASM International is not a standard writing organization. Yet, the increased use of thermal spray coatings and the need for documentation on methods for evaluating mechanical properties of thermal spray coatings have generated a need to prepare Recommended Practices. To meet this need, the ASM International Thermal Spray Society has formed three subcommittees to prepare Recommended Practices for thermal spray coatings. This paper describes a draft form of a Recommended Practice for evaluating residual stresses in thermal spray coatings. This Recommended Practice is being developed by the Subcommittee on "Evaluating of Mechanical Properties of Thermal Spray Coatings". The method, called the Modified Layer Removal Method, has been presented in several papers and has been used for a variety of different coatings. The paper describes the dimensions of the test specimen, the equipment needed, the procedure for removing layers, and the methods for collecting and interpreting the data to evaluate through thickness residual stresses. The Recommended Practice (RP) is in Draft form, but is presented to let the thermal spray community know about the RP effort and invite comments and volunteers to write other RP's.

Modeling Residual Stress Development in Thermal Spray Coatings: Current Status and Way Forward

2017 ◽  
Vol 26 (6) ◽  
pp. 1115-1145 ◽  
Author(s):  
Abba A. Abubakar ◽  
Abul Fazal M. Arif ◽  
Khaled S. Al-Athel ◽  
S. Sohail Akhtar ◽  
Javad Mostaghimi
Keyword(s):  
Residual Stress ◽  
Thermal Spray ◽  
Thermal Spray Coatings ◽  
Current Status ◽  
Stress Development ◽  
Spray Coatings

Fatigue Life in Bending and Coatings Residual Stress in Tungsten Carbide Thermal Spray Coatings

1997 ◽  
Author(s):  
R.T.R. McGrann ◽  
J.R. Shadley ◽  
E.F. Rybicki ◽  
D.J. Graving ◽  
B.E. Badger ◽  
...  
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Tungsten Carbide ◽  
Thermal Spray ◽  
Thermal Spray Coatings ◽  
Chrome Plating ◽  
Spray Coatings ◽  
Wear Protection ◽  
Carbide Coatings ◽  
Flat Beam

Abstract Tungsten caibide (WC) thermal spray coatings are being used for wear protection on selected components of aircraft. Tungsten carbide coatings are being used on aircraft flap tracks and fan and compressor blade mid-span dampers. However, a larger use of tungsten carbide coatings is being considered for other commercial aircraft applications where it would be used as a replacement for chrome plating. For instance, WC coatings are currently being tested on aircraft landing gear parts. One factor that affects the suitability of WC coatings for these applications is the fatigue life of the coated part. Coatings, whether chrome plating or thermal spray coating, can reduce the fatigue life of the part compared to an uncoated part. This study compares the fatigue life of uncoated 6061 aluminum specimens to the fatigue life of WC thermal sprayed coated 6061 aluminum specimens. The relation between the residual stress level in the coating and the fatigue life of the specimens is also investigated. Fatigue tests were run on cantilever flat beam specimens that were coated on one side. Specimens were cycled in bending so that the coatings experienced tensile fatigue stresses. Residual stress levels for each type of coating were determined using the Modified Layer Removal Method on specimens processed along with the cantilever flat beam specimens. Test results show that the fatigue life of the WC coated specimens is directly related to the level of compressive residual stress in the coating.

Variation in Residual Stress Field During Fatigue Failure of Thermal Spray Coatings

2000 ◽  
Author(s):  
R. Ahmed ◽  
M. Hadfield ◽  
S. Tobe
Keyword(s):  
Residual Stress ◽  
Thermal Spray ◽  
Fatigue Failure ◽  
Contact Stress ◽  
Rolling Direction ◽  
Rolling Contact ◽  
Thermal Spray Coatings ◽  
Residual Stress Field ◽  
Stress Measurements ◽  
Spray Coatings

Abstract A non-destructive experimental approach was adapted to investigate the variations in residual stress fields within thermal spray coatings. WC-Co coatings produced by a HVOF technique were considered for concentrated rolling sliding contacts in this study. These coatings were produced in various thicknesses on various substrates. Residual stress measurements were made using an x-ray diffraction technique, along and across the rolling direction. A modified four-ball machine was used to conduct rolling contact fatigue tests under various tribological conditions of contact stress, lubrication and contact configuration. Residual stress measurements were made before and after the tribological tests. Failed rolling elements were analyzed using scanning electron microscopy, electron probe microscopy and surface interferometry. Results indicate that the magnitude of compressive residual stress attenuates during fatigue failure. The magnitude of attenuated residual stress was dependent upon the type of tribological failure. This attenuation of residual stress was attributed to the microcracking of coating under the influence of contact stress.

Methods of Determination and Control of Residual Stresses in Plasma Spray Coatings

1997 ◽  
Author(s):  
L. Dekhtyar ◽  
A. Kleyman ◽  
V. Andreychuk ◽  
S. Berman
Keyword(s):  
Residual Stresses ◽  
Thermal Spray ◽  
Plasma Spray ◽  
Thermal Spraying ◽  
Thermal Spray Coatings ◽  
Coating Deposition ◽  
Spray Coatings ◽  
Plasma Spray Coatings ◽  
And Control ◽  
Elastic Characteristics

Abstract Residual stresses exert profound influence on the longevity of parts with thermal spray coatings. The distribution and value of the residual stresses depend on method of coating deposition, composition of the applied material, parameters of thermal spraying and methods of post-treatment. Therefore, the study of the influence of the various technological factors on the residual stresses in the plasma spray coatings is very important. Due to heterogeneity of the coating, residual stresses can be determined only by the experimentation by using new methods which take into consideration real values of elastic characteristics and density of elementary layers. Methods and formulas for the calculations of the residual stresses in coatings deposited on bars, rings, discs, cylinders are presented. Experimental results for the various thermal spray coatings are also shown. These results can be used for the optimization of coating deposition and would supplement the existing database.

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