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Potentials of Post-Processing Thermal Spray Coatings for Tribological Applications

Potentials of Post-Processing Thermal Spray Coatings for Tribological Applications. R. Ahmed Heriot-Watt University , United Kingdom. Typical Post-treatments for Thermal Spray Coatings. Annealing/Austempering Laser Remelting Hot Isostatic pressing. Coating material. Substrate material.

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Potentials of Post-Processing Thermal Spray Coatings for Tribological Applications

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  1. Potentials of Post-Processing Thermal Spray Coatings for Tribological Applications R. Ahmed Heriot-Watt University, United Kingdom

  2. Typical Post-treatments for Thermal Spray Coatings • Annealing/Austempering • Laser Remelting • Hot Isostatic pressing

  3. Coating material Substrate material Coating process Target – To Improve or promote Annealing / Austempering Annealing / Austempering 400 ~ 800 oC for 60 minutes (Vacuum annealed) WC-Co and WC-Co-Cr Mild steel JP5000, Jet Kote, Top Gun and Diamond Jet Hardness ,wear resistance, crystalline phase transformation 600, 800, 900 oC for 15 ~ 30 minutes (Annealed) Ni based WC-Co Mild steel Gas thermal spraying Hardness ,wear resistance, metallurgical bonding 900 oC for 10~180 minutes (inert atmosphere) WC-Co - Plasma (Metco 9MB) Hardness ,wear resistance 870 oC for 30 minutes (salt bath) WC-Co in Ni base alloy AISI 5150 Air Plasma Spraying Hardness, wear resistance Post-Treatment • Improved Hardness and Sliding Wear Resistance • Low Cost • Control of Residual Stress • USEFUL FOR LOW STRESS SLIDING WEAR APPLICATIONS • Need for correct Coating Substrate Pair • Marginal Pore Modification and Metallurgical Bonding

  4. Laser Remelting • GOOD FOR CORROSION AND SLIDING WEAR RESISTANCE • Good Depth Control of Treatment • Substrate Material Not Critical • Good for Eliminating Porosity • Promote Metallurgical Bonding • No Control of Residual Stress • Not Good for Lubricated Contacts

  5. Hot Isostatic Pressing • IDEAL FOR HIGH STRESS TRIBOLOGICAL APPLICATIONS • Improves Impact, Delamination,Abrasion and Fatigue Resistance • Ideal for Metallurgical Bonding • Good Control of Residual Stress • Improves Product Cost Effectiveness • Attenuate Coating Anisotropy • Requires a Correct Coating Substrate Pair

  6. POTENTIAL IMPROVEMENTS – Post Treatment • Promotion of the metallurgical bonding at splat/splat and splat/substrate level to improve the adhesive and cohesive strength. • Elimination of porosity and microcracks to avoid stress concentrations within the coating microstructure. • Amorphous to crystalline and other phase transformations. • Generation of uniform compressive stress in the coating by appropriate control of heat transfer for a given coating and substrate material. • Attenuation of the coating anisotropy, to obtain near homogenous material properties. 

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