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Title: Residual Stress Determination in Thermally Sprayed Coatings – A Comparison of Curvature Models and X-Ray Techniques

Abstract

Residual stresses were calculated from the curvature of coating-substrate coupons using three different models: a simple two-beam elastic model; the Tsui-Clyne progressive deposition model; and the Tsui-Clyne progressive deposition model with substrate plasticity. The coatings studied were metallic and prepared by high-velocity oxy-fuel (HVOF) thermal spraying. The calculated stresses were compared to those measured on the same coupons using x-ray diffraction (XRD) techniques. Coating surface stresses calculated using the two-beam elastic model disagreed with those measured using XRD for coupons with significant curvature. Trends in residual stresses (with varying coating and substrate thickness, substrate material, and HVOF spray particle velocity) predicted by the elastic and elastic-plastic versions of the Tsui-Clyne progressive deposition model agreed with the trends measured by XRD. The magnitudes of stresses calculated using the Tsui-Clyne model agreed with the XRD measurements for coatings sprayed at low particle velocities but were significantly more compressive for coatings sprayed at higher velocities. Accounting for substrate plasticity in the Tsui-Clyne model improved the agreement with the XRD results, but only slightly.

Authors:
;
Publication Date:
Research Org.:
Idaho National Laboratory (INL)
Sponsoring Org.:
DOE - FE
OSTI Identifier:
912309
Report Number(s):
INEEL/JOU-04-02333
Journal ID: ISSN 0257-8972; SCTEEJ; TRN: US200801%%747
DOE Contract Number:
DE-AC07-99ID-13727
Resource Type:
Journal Article
Resource Relation:
Journal Name: Surface and Coatings Technology; Journal Volume: 200; Journal Issue: 12-13
Country of Publication:
United States
Language:
English
Subject:
36 - MATERIALS SCIENCE; COATINGS; DEPOSITION; PLASTICITY; RESIDUAL STRESSES; SPRAYED COATINGS; STRESSES; SUBSTRATES; THICKNESS; VELOCITY; X-RAY DIFFRACTION; HVOF; Iron Alloys; Residual Stress; Thermal Spray; X-ray Diffraction

Citation Formats

T.C. Totemeier, and J.K. Wright. Residual Stress Determination in Thermally Sprayed Coatings – A Comparison of Curvature Models and X-Ray Techniques. United States: N. p., 2006. Web. doi:10.1016/j.surfcoat.2005.06.003.
T.C. Totemeier, & J.K. Wright. Residual Stress Determination in Thermally Sprayed Coatings – A Comparison of Curvature Models and X-Ray Techniques. United States. doi:10.1016/j.surfcoat.2005.06.003.
T.C. Totemeier, and J.K. Wright. Wed . "Residual Stress Determination in Thermally Sprayed Coatings – A Comparison of Curvature Models and X-Ray Techniques". United States. doi:10.1016/j.surfcoat.2005.06.003.
@article{osti_912309,
title = {Residual Stress Determination in Thermally Sprayed Coatings – A Comparison of Curvature Models and X-Ray Techniques},
author = {T.C. Totemeier and J.K. Wright},
abstractNote = {Residual stresses were calculated from the curvature of coating-substrate coupons using three different models: a simple two-beam elastic model; the Tsui-Clyne progressive deposition model; and the Tsui-Clyne progressive deposition model with substrate plasticity. The coatings studied were metallic and prepared by high-velocity oxy-fuel (HVOF) thermal spraying. The calculated stresses were compared to those measured on the same coupons using x-ray diffraction (XRD) techniques. Coating surface stresses calculated using the two-beam elastic model disagreed with those measured using XRD for coupons with significant curvature. Trends in residual stresses (with varying coating and substrate thickness, substrate material, and HVOF spray particle velocity) predicted by the elastic and elastic-plastic versions of the Tsui-Clyne progressive deposition model agreed with the trends measured by XRD. The magnitudes of stresses calculated using the Tsui-Clyne model agreed with the XRD measurements for coatings sprayed at low particle velocities but were significantly more compressive for coatings sprayed at higher velocities. Accounting for substrate plasticity in the Tsui-Clyne model improved the agreement with the XRD results, but only slightly.},
doi = {10.1016/j.surfcoat.2005.06.003},
journal = {Surface and Coatings Technology},
number = 12-13,
volume = 200,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2006},
month = {Wed Mar 01 00:00:00 EST 2006}
}
  • Specimens have been produced by plasma spraying of boron carbide coatings about 1 mm in thickness on to titanium alloy substrates about 3 mm thick. The residual stress distributions in these specimens have been calculated using a numerical process model and also estimated from observed changes in curvature on debonding. Good agreement as observed between the two methods, with both suggesting the average substrate stress to be about +20 MPa and the average coating stress to be about [minus]60 MPa. In both constituents, there was a significant positive gradient of stress level through the thickness. These specimens were loaded inmore » four point bending until cracks propagated along the interface between substrate and coating. From the load/displacement plots obtained during this testing, and taking account of the effect of relaxation of the residual stresses during debonding, the critical strain energy release rates of the interfaces, G[sub ic], were estimated to be [approximately] 0.2--0.5 kJ m[sup [minus]2]. Substantial errors would have resulted from neglect of the presence of the residual stresses. Also of significance is the effect of the residual stresses on the mode mixity of interfacial loading, as characterized by the phase angle, [psi], since G[sub ic] has been often observed to vary with [psi]. The value of [psi] for the four point bend test in the absence of residual stress is about 47[degree], whereas for the specimens tested here it was estimated to cover the complete range from 90[degree] (pure shear) to 0[degree] (pure opening) as the applied load was increased. The quoted values of G[sub ic] were obtained in a regime where [psi] [approximately] 30[degree].« less
  • The residual stresses induced from thermal spraying process have been extensively investigated in previous studies. However, most of such works were focused on the elastic deformation range. In this paper, an elastoplastic model for predicting the residual stresses in thermally sprayed coatings was developed, in which two main contributions were considered, namely the deposition induced stress and that due to differential thermal contraction between the substrate and coating during cooling. The deposition induced stress was analyzed based on the assumption that the coating is formed layer-by-layer, and then a misfit strain is accommodated within the multilayer structure after the additionmore » of each layer (plastic deformation is induced consequently). From a knowledge of specimen dimensions, processing temperatures, and material properties, residual stress distributions within the structure can be determined by implementing the model with a simple computer program. A case study for the plasma sprayed NiCoCrAlY on Inconel 718 system was performed finally. Besides some similar phenomena observed from the present study as compared with previous elastic model reported in literature, the elastoplastic model also provides some interesting features for prediction of the residual stresses.« less
  • Low-mobility materials, like transition metal nitrides, usually undergo large residual stress when sputter-deposited as thin films. While the origin of stress development has been an active area of research for high-mobility materials, atomistic processes are less understood for low-mobility systems. In the present work, the contribution of grain boundary to intrinsic stress in reactively magnetron-sputtered ZrN films is evaluated by combining in situ wafer curvature measurements, providing information on the overall biaxial stress, and ex situ x-ray diffraction, giving information on elastic strain (and related stress) inside crystallites. The thermal stress contribution was also determined from the in situ stressmore » evolution during cooling down, after deposition was stopped. The stress data are correlated with variations in film microstructure and growth energetics, in the 0.13-0.42 Pa working pressure range investigated, and discussed based on existing stress models. At low pressure (high energetic bombardment conditions), a large compressive stress is observed due to atomic peening, which induces defects inside crystallites but also promotes incorporation of excess atoms in the grain boundary. Above 0.3-0.4 Pa, the adatom surface mobility is reduced, leading to the build-up of tensile stress resulting from attractive forces between under-dense neighbouring column boundary and possible void formation, while crystallites can still remain under compressive stress.« less
  • Residual stress is an important factor in thermally sprayed deposits which affects both processing and performance. High stress magnitudes and/or concentrations can undermine the structural integrity of sprayed parts and impair their functionality. Therefore, it is important to know the stress state, understand its generation and be able to control it. Results of experimental stress determination in plasma sprayed deposits are presented. Neutron diffraction as a non-destructive and phase-distinctive measurement method was used to determine residual stress profiles in thick NiCrAlY and yttria-stabilized zirconia (YSZ) deposits. Measurements were complemented with calculations based on experimentally determined material properties, which allowed formore » separation of quenching and thermal stress contributions to final residual stress. Since the application of neutron diffraction to plasma sprayed deposits is relatively novel, certain verification measurements were performed. Specimens were prepared at two different deposition temperatures, to determine the effect of temperature on the stresses and relevant deposit properties.« less