Numerical Modeling of Selected Thermal Spraying Issues

Opis

Thermal spraying is one of the most universal techniques for depositing feedstock materials on a substrate. It allows the production of metallic, ceramic, and composite coatings on both metallic and ceramic substrates. Spray deposition involves ejecting heated or cold particles of feedstock material at high velocity toward the substrate. In the final stage of the process, the substrate and the formed coating are cooled to ambient temperature, resulting in residual stresses due to differences in the thermal, physical, and mechanical properties of the feedstock materials and the substrate. The residual stress state of the coating and substrate has a significant effect on their strength, thermal shock resistance, and fatigue life under cyclically varying thermal loads.

Table of Contents

List of major designations and abbreviations / 9
Preface / 11
Introduction / 15

1. Thermal spraying of layers and coatings / 17
1.1. Methods of depositing layers and coatings / 18
1.2. Arc spraying / 20
1.3. Plasma spraying / 23
1.4. Flame spraying / 26
1.4.1. Flame spraying at subsonic velocities / 26
1.4.2. Flame spraying at supersonic velocities / 28
1.5. Laser spraying / 36
1.6. Cold spraying / 39
1.7. Laser alloying and remelting / 42
1.7.1. Laser alloying / 42
1.7.2. Laser remelting of coatings / 43
1.8. Comparison of thermal spraying methods / 44

2. Selected properties of sprayed coatings / 49
2.1. Coating formation process / 49
2.2. Coating adhesion / 51
2.2.1. Effect of surface preparation / 52
2.2.2. Effect of temperature / 52
2.2.3. Effect of kinetic energy / 53
2.2.4. Effect of the physical and chemical properties of materials / 54
2.3. Residual stresses in surface layers / 55
2.4. Residual stresses due to thermal mismatch / 60

3. Feedstock materials for spraying / 64

4. Testing of thermally deposited coatings by flame and detonation methods / 69
4.1. Preliminary testing of sprayed coatings by flame and detonation methods / 71
4.2. Characterization of feedstock materials / 71
4.3. Stresses in the coating–substrate system / 73
4.4. Construction of an instrument for testing the deflection of a coated substrate after the spraying process / 75
4.5. Spraying titanium coatings on ceramic substrates / 76
4.6. Determination of residual stresses in sprayed coatings / 77
4.6.1. Titanium coatings / 77
4.6.2. Ti+Al₂O₃ composite coatings / 79
4.7. Numerical analysis of residual stresses in titanium and composite coatings / 80
4.8. Temperature field during cooling of the coating–substrate system / 85
4.8.1. Object of study / 86
4.8.2. Assumptions for numerical calculations / 87
4.8.3. Calculation results / 88
4.8.4. Comparative analysis of temperature distribution calculation results / 93
4.9. Stress investigation in Ti and Ti+Al₂O₃ coatings sprayed on Al₂O₃ substrate by detonation gun method (D-gun) / 99
4.9.1. Feedstock materials / 99
4.9.2. Detonation spraying parameters / 100
4.9.3. Measurements of deflection in specimens after detonation spraying / 101
4.9.4. Stresses in the sprayed coating based on the curvature of the specimen / 102
4.10. Conclusions / 106

5. Residual stress modelling in the thermal spraying process / 109
5.1. Introduction – physical modelling of the process and generation of residual stresses / 109
5.2. Methodology adopted for modelling residual stresses in thermally sprayed coatings / 112
5.3. Particle impact modelling using ANSYS-AUTODYN / 115
5.4. Modelling of particle impact on the substrate / 119
5.5. Impact of Ti particles on the Al₂O₃ substrate and particles on the sublayer by detonation spraying / 120
5.6. Thermo-mechanical model of the thermal spraying process / 126
5.6.1. Temperature distributions in the Ti–Al₂O₃ coating–substrate system, detonation spraying / 131
5.6.2. Stress distributions in the Ti–Al₂O₃ coating–substrate system, detonation spraying / 133
5.6.3. The influence of the substrate preheating temperature on the stresses in the Ti–Al₂O₃ coating–substrate system / 136
5.7. The effect of the impact velocity on the residual stresses in the Ti–Al₂O₃ coating–substrate system / 145
5.7.1. Results of dynamic calculations for the impact of a feedstock material particle on a ceramic substrate / 147
5.7.2. Impact of Ti coating particles against the Ti coating sublayer / 152
5.7.3. Results of temperature distribution calculations for different particle impact velocities / 156
5.7.4. Results of specimen deflection and stress distribution calculations for different particle impact velocities / 159
5.7.5. Summary of particle spray velocity effects / 163
5.8. Conclusions / 164

6. Modelling the impact of a single particle on the substrate / 166
6.1. Model description / 166
6.2. Assumptions for the Ti particle model on ceramic and metal substrates / 173
6.2.1. Mode l of spraying Ti particles on Al₂O₃ ceramic substrate (V = 500 m/s) / 174
6.2.2. Model of spraying Ti particles on Al₂O₃ ceramic substrate (V = 800 m/s) / 180
6.3. Comparative analysis of particle impact simulations of ceramic and metallic substrates / 186
6.3.1. Titanium particle / 186
6.3.2. Copper particle / 192
6.3.3. Particle geometry after impact / 199
6.4. Modelling of the impact of a heated Ti particle on a ceramic substrate / 199
6.4.1. Geometric model / 199
6.4.2. Model deformation simulation results / 202
6.4.3. Temperature distribution in the Ti particle–Al₂O₃ substrate system / 206
6.4.4. Distribution of reduced stresses in the Ti particle–Al₂O₃ substrate system / 207
6.5. Conclusions / 211

7. Coating testing and modelling of residual stresses in the thermal spraying process using the HVOF method / 214
7.1. Testing of metal coatings sprayed on Al₂O₃ ceramic substrate / 214
7.2. Test object / 214
7.3. Spraying station / 215
7.4. Structural studies / 219
7.5. Coating wettability tests / 224
7.5.1. Wettability tests in argon / 226
7.5.2. Wettability tests in vacuum / 227
7.5.3. Conclusions / 228
7.6. Residual stress tests in the coating–substrate system / 228
7.6.1. Determination of residual stresses based on the curvature of the specimen / 229
7.6.2. Research on residual stresses in coatings using the X-ray method / 231
7.7. Conclusions / 234
7.8. Numerical and experimental analysis of residual stresses generated in metallic coatings deposited by HVOF on an Al₂O₃ substrate / 235
7.8.1. Impact of Ti particles on the Al₂O₃ substrate / 235
7.8.2. Temperature distributions in the Ti, Cu, Ni coating system / 239
7.8.3. Stress distributions in the Ti (Cu, Ni) coating–Al₂O₃ substrate system / 241
7.8.4. Conclusions / 245

8. Investigation of strains and stresses in sprayed Ti and Cu coatings using grating interferometry / 247
8.1. Grating interferometry method / 247
8.2. Specimen grating technology / 249
8.3. Automatic analysis of fringe images / 250
8.4. Measuring station / 251
8.5. Measurement procedure / 253
8.6. Measurements on a titanium coating sprayed on an Al₂O₃ substrate / 254
8.6.1. Measurement of displacements in the measuring field of 14.3×14.3 mm prior to cutting / 255
8.6.2. Measurement of displacements in the measuring field of 14.3×14.3 mm after cutting / 256
8.6.3. Measurement of displacements in the measuring field of 14.3×14.3 mm after the second cutting / 259
8.6.4. Measurements in a small measuring field (3.7×3.7 mm) / 262
8.7. Measurements on a copper coating sprayed on an Al₂O₃ substrate / 264
8.7.1. Measurement of displacements in the measuring field of 14.3×14.3 mm prior to cutting / 264
8.7.2. Measurement of displacements in the measuring field of 14.3×14.3 mm after cutting / 265
8.7.3. Measurements in a small measuring field (3.7×3.7 mm) after the second cutting / 268
8.8. Strain comparison for Cu and Ti coated specimens / 270
8.9. Modelling of deflection and residual stresses in Cu/Al₂O₃ and Ti/Al₂O₃ systems before and after cutting the plate / 273
8.9.1. Cu–Al₂O₃ coating–substrate model / 274
8.9.2. Ti–Al₂O₃ coating–substrate model / 276
8.10.Comparison of determined residual stresses / 279
8.11. Conclusion / 279

9. Summary and conclusions / 282

Bibliography / 291

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