The core processes for H13 steel ceramic coating mainly include plasma spraying (APS), high-velocity flame spraying (HVOF), and physical vapor deposition (PVD). Each of these three methods has its own emphasis in terms of equipment principles, process parameters, and applicable scenarios, but all require three main stages: substrate pretreatment, spraying/deposition, and post-treatment.
I. General Pretreatment Process (Shared by All Processes)
Regardless of the coating technology used, the H13 steel substrate must undergo rigorous pretreatment to ensure bonding strength:
Degreasing and Cleaning: Remove surface oil using acetone or ultrasonic cleaning.
Sandblasting and Roughening: Sandblast the surface with Al₂O₃ abrasive (60–80 mesh) to improve surface roughness (Ra≥3.2μm) and enhance mechanical adhesion.
Preheating Treatment: Heat the workpiece to 150–200℃ to reduce thermal stress differences during spraying.
II. Detailed Explanation of Three Mainstream Processes
1. Plasma Spraying (APS)
Utilizes a high-temperature plasma arc to melt ceramic powder and spray it at high speed onto the substrate surface.
Process Steps:
1. Plasma Arc Generation: An Ar/N₂/H₂ mixed gas is ionized by an electric arc to form a plasma jet with temperatures up to 15,000–20,000 K.
2. Powder Feeding and Melting: Al₂O₃, ZrO₂, or Al₂O₃-TiO₂ powder is fed into the jet and heated to a molten or semi-molten state.
3. High-Speed Deposition: Powder impacts the substrate at a velocity of 200–600 m/s and rapidly cools to form a coating.
4. Control Parameters: Current 100–600 A, Voltage 30–80 V, Powder Feed Rate 10–30 g/min
5. Features: Can spray various ceramic materials; coating thickness 100–200 μm, porosity approximately 2–5%.
6. High-Voltage Flame Spraying (HVOF): Achieving dense coating deposition by generating a supersonic flame stream through the combustion of fuels (such as kerosene or hydrogen) and high-pressure oxygen.
2. High-Voltage Flame Spraying (HVOF) Process Steps:
Combustion Reaction: Fuel and O₂ burn continuously in the combustion chamber, producing a high-temperature flame of 2900–3000℃.
Gas Acceleration: Gas expands through a Laval nozzle, forming a supersonic jet of 1500–2000 m/s.
Powder Acceleration and Deposition: Ceramic powder (such as WC-Co, Cr₃C₂-NiCr) is heated to a plastic state and impacts the substrate at high speed, forming a high-adhesion coating.
Typical Parameters: Spraying distance 150–300 mm, coating bonding strength can reach over 70 MPa.
Characteristics: Porosity <1%, high bonding strength, suitable for high wear resistance and fatigue resistance conditions.
3. Physical Vapor Deposition (PVD)
In a vacuum environment, the target material is atomized physically and deposited onto the substrate surface to form a film.
Process Steps:
Vacuuming: Evacuate the chamber to above 10⁻³ Pa to ensure a clean environment.
Ion Cleaning: Introduce Ar gas and apply a negative bias to generate argon ions that bombard the workpiece surface, activating and removing oxides.
Film Deposition: Use arc evaporation or magnetron sputtering to vaporize metal targets such as Ti and Cr, which react with N₂ to form hard coatings such as TiN and CrN.
Deposition Control: Temperature 200–500℃, deposition rate 0.1–1 μm/h, film thickness typically 2–5 μm.
Features: Dense, non-porous coating with high surface finish, suitable for precision molds and anti-adhesion applications.
III. Post-treatment and Quality Control
Slow Cooling: Slowly cool to room temperature after spraying to avoid thermal stress cracking.
Surface Finishing: Grinding or polishing as needed to ensure dimensional accuracy.
Testing Methods:
Microhardness Test (HV)
Adhesion Test (ASTM C633 standard)
Metallographic Analysis and SEM Observation of Coating Structure
