The Core Technology For Surface Modification Of Titanium Alloys: Vacuum Coating Of Titanium Alloys

Titanium alloy vacuum coating is a core technology for surface modification of titanium alloys. Its main purpose is to compensate for the local shortcomings of titanium alloys (such as wear resistance, corrosion resistance, high-temperature oxidation resistance, and friction reduction) while retaining their inherent advantages of high strength and light weight. It is widely used in high-end fields such as aerospace, medical, precision machinery, and automotive industries.

Key Prerequisites for Titanium Alloy Vacuum Coating (First, clarify compatibility)

• Characteristics of titanium alloy substrate: The surface easily forms a natural, dense TiO₂ passivation film (thickness 5-10nm), which provides good corrosion resistance. However, it has low hardness (pure titanium HV150-200, TC4 titanium alloy HV300-350), poor wear resistance, and is prone to oxidation and peeling at high temperatures (>400℃). Vacuum coating requires overcoming the passivation film to ensure strong adhesion between the film and the substrate.
• Core coating requirements: ① Adhesion ≥ 50N (scratch test/tensile test); ② Dense and pore-free film; ③ Compatible with the toughness of the titanium alloy substrate, preventing brittle cracking; ④ Does not affect the mechanical properties of the substrate itself.
• Core advantages: Coating in a vacuum environment (vacuum degree 10⁻³~10⁻⁶Pa) ensures no oxidation or impurity contamination, resulting in good film uniformity and controllable thickness (0.5-50μm). It is suitable for complex-shaped titanium alloy workpieces (such as titanium rods, titanium alloy blades, and medical implants).

Process: Magnetron sputtering coating (the most mainstream method, suitable for medium and low temperature, high-precision applications)

1. Core Principle
In a high-vacuum chamber, electrons are confined by a magnetic field to bombard the target material (metal/ceramic target), causing the target atoms/ions to detach and deposit onto the titanium alloy substrate surface, forming a dense film layer. This process falls under the category of physical vapor deposition (PVD).

2. Dedicated Core Process for Titanium Alloys (Key lies in Substrate Pre-treatment, which determines the bonding strength)
Substrate Pre-treatment (Core step, accounts for 70% of coating quality)
Rough cleaning: Ultrasonic cleaning (acetone + alcohol) to remove oil and dust, followed by drying;
Passivation film removal: Argon ion etching (vacuum degree 10⁻³Pa, argon pressure 0.5-1Pa, bias voltage -100~-300V, time 15-30min) to break down the TiO₂ film, expose a fresh titanium surface, and simultaneously roughen the surface layer (roughness Ra 0.1-0.3μm) to enhance mechanical interlocking;
Preheating: Preheating the titanium alloy substrate to 150-300℃ to reduce the temperature difference stress between the film and the substrate and prevent film cracking.
Coating Process (Two steps: first a base layer, then deposition)
Base layer: First, a transition layer is deposited (Ti layer or Cr layer, thickness 0.1-0.5μm) to eliminate the lattice mismatch between the titanium alloy and the functional film and improve bonding strength. Parameters: target current 2-5A, bias voltage -50~-100V, time 5-10min;
Functional layer deposition: Select target material according to requirements, control film thickness. Core parameters: vacuum degree 10⁻⁴~10⁻⁵Pa, argon flow rate 20-50sccm, target current 3-8A, bias voltage -30~-80V, deposition temperature ≤400℃ (to avoid annealing and softening of the titanium alloy).
Post-treatment: Natural cooling to room temperature after removal from the furnace. High-end parts can undergo low-temperature annealing (150-200℃ × 1h) to eliminate internal stress in the film.

Typical Application Scenarios of Titanium Alloy Vacuum Coating (Corresponding Process Selection)

1. Aerospace field: Titanium alloy blades, connectors → Ion nitriding + TiAlN multi-arc coating; Titanium alloy precision shafts → Magnetron sputtering TiCN coating;
2. Medical field: Titanium alloy joints, bone screws → Magnetron sputtering DLC ​​coating (biocompatible); Titanium alloy implants → Vacuum arc ion plating (non-toxic);
3. Precision machinery field: Titanium alloy tools, molds → TiN/TiCN magnetron sputtering; Titanium alloy sliders → DLC coating;
4. Marine engineering field: Titanium alloy fasteners, pipes → CrN magnetron sputtering (salt spray corrosion resistance);
5. Decorative field: Titanium alloy jewelry → Vacuum evaporation plating Au/TiN (bright coloring).