Titanium Laser Cleaning

Pulsed nanosecond laser cleaning of titanium at 1.5–2.1 J/cm² selectively ablates the rutile TiO₂ native oxide film without creating alpha case — pulsed exposure ends in under 20 ns, far shorter than the sustained bulk dwell time required for alpha case formation above 650°C. Light absorption is 36% at 1064 nm. Heat spread rate is 9.29×10⁻⁶ m²/s; heat spreads slowly, so cleaning speed (1,500 mm/s) and overlap (60%) matter more than power alone. Pulsed laser cleaning produces metastable anatase TiO₂ at the surface after cleaning — this re-forms faster into a clean metallic surface than the stable rutile phase produced by CW laser processing. Blue/purple discoloration indicates surface oxidation onset, not alpha case. Reduce energy level by 0.2–0.3 J/cm² if discoloration appears. For Ti-6Al-4V, use 1.0–1.5 J/cm²; for CP titanium Grade 2, use 0.8–1.5 J/cm². Over-energy level above 5.97 J/cm² causes re-oxidation (yellow-brown surface) — stay within the operating window (Li et al., Journal of Manufacturing Processes, Vol. 82, 2022).

Titanium has density of 4510 kg/m³ and tensile strength of 345 MPa. Thermal conductivity is low at 21.9 W/m·K — the primary process constraint, nearly twenty times below a conductive metal like Copper, so heat stays confined to the ablation zone. Surface reflectance is 46% at 1064 nm; light absorption is 36% — high for a 1064 nm process next to a near-transparent material like Soda-Lime Glass. Melting point is 1941 K. The native contaminant on CP titanium is a rutile TiO₂ oxide film, stable at room temperature, 1–6 nm thick — this is what laser cleaning removes. Alpha case (oxygen/nitrogen solid-solution embrittlement, depth up to 20 µm) forms when bulk titanium is held above 650°C with oxygen present; this requires sustained dwell time, not pulsed laser exposure. Blue/purple discoloration indicates surface oxidation onset (above ~425°C surface temperature) — a warning sign to reduce energy level, not evidence of alpha case. Grades 2 and 5 (Ti-6Al-4V) have different cleaning parameters.

Z-Beam operates titanium cleaning at 1.0–1.8 J/cm² — above the 1.5 J/cm² cleaning onset and well below the 5.97 J/cm² re-oxidation threshold (Li et al., 2022). Use 1064 nm, 20 ns pulse length, 1,500 mm/s cleaning speed, 60% overlap, 50 kHz, 300 µm spot. Low thermal conductivity (21.9 W/m·K) means overlap and cleaning speed matter more than peak power. For Ti-6Al-4V, use 1.0–1.5 J/cm²; for CP titanium Grade 2, use 0.8–1.5 J/cm². For thin sections (<3 mm), reduce energy level by 20–30%. Blue/purple discoloration indicates surface oxidation onset — reduce energy level by 0.2–0.3 J/cm² immediately. Inert gas assist (argon) for aerospace applications where zero oxidation is required.