pvd-coating

name	pvd-coating
description	Physical vapor deposition (PVD) coating — sputtering (DC magnetron, RF, HiPIMS), evaporation (e-beam, arc), coating types (TiN, TiAlN, CrN, DLC, AlTiN), deposition parameters (substrate temperature, bias voltage, target power, Ar/N₂ partial pressure), coating properties (hardness H [GPa], H/E ratio, residual stress, adhesion Lc [N]), Rockwell HF scratch test, coating thickness (1–10 μm), fatigue and tribological performance, and ASTM B244/B568 coating standards.
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PVD Coating — Complete Skill

PVD Process Types

DC Magnetron Sputtering

Principle: DC power applied to metal target (cathode) in Ar atmosphere; Ar⁺ ions bombard target → eject target atoms → deposit on substrate Magnetic field confines plasma near target → higher ionization density → higher deposition rate than basic sputtering

Process parameters: Ar pressure: 0.1–1.0 Pa; Target power density: 2–20 W/cm²; Substrate bias: -30 to -200 V DC Deposition rate: 0.5–5 nm/s typical; Substrate temperature: 100–500°C (heating by plasma + bias) Reactive sputtering: N₂ or C₂H₂ added to gas mix → form nitride (TiN) or carbide (TiC) coatings

Target poisoning: in reactive sputtering, target surface forms compound layer → rate drops; control by partial pressure (N₂ partial pressure feedback loop)

High Power Impulse Magnetron Sputtering (HiPIMS)

Key advantage: much higher ionization fraction (>80% vs. 1–5% for DC) Peak power: 10–100 kW/cm² in short pulses (50–200 μs); average power same as DC Resulting coating properties: denser microstructure; higher adhesion; smoother surface (Ra 0.05–0.10 μm) Trade-off: lower deposition rate (60–80% of DC at same average power)

Cathodic Arc Evaporation

Principle: High-current arc spot on metal target (Ti, Cr, Al-Ti alloy); intense local heating → material evaporation at very high ionization (>90%) High ion energy → dense, adherent coatings; excellent adhesion to substrate

Macroparticle (droplet) issue: Arc spots eject macroparticles (0.1–10 μm) that embed in coating → rougher finish Mitigation: magnetic duct (filter arc) → macroparticle-free deposition; or post-polish Unfiltered arc: Ra = 0.2–0.5 μm; suitable for cutting tools but not optical coatings

Deposition rate: 2–10 nm/s; substrate temperature: 200–600°C; bias: -50 to -300 V

Electron Beam Evaporation (e-beam PVD)

Principle: High-energy electron beam melts target in water-cooled crucible; evaporated atoms traverse vacuum → deposit on substrate Low ionization (< 1%); requires separately ionized plasma assist (IBAD) for dense coatings

Applications: Thermal barrier coatings (TBC): 7YSZ deposited by EB-PVD → columnar microstructure → strain tolerant → turbine blades Optical coatings: precise thickness control; low substrate temperature (< 100°C) Deposition rate: 1–10 nm/s; substrate temperature: 100–300°C

Coating Systems and Properties

Common Hard Coatings

Coating	H (GPa)	E (GPa)	H/E	T_max (°C)	μ (dry)	Applications
TiN	24	260	0.092	600	0.4–0.6	General purpose; gold color
TiAlN	32	380	0.084	800	0.3–0.5	High-speed machining; thermal stable
AlTiN (Al-rich)	35	370	0.095	900	0.3–0.5	High-temp machining; dry cutting
CrN	20	230	0.087	700	0.3–0.5	Corrosion; plastic injection molds
CrAlN	30	350	0.086	1,000	0.3–0.4	Extreme temperature
TiCN	30	350	0.086	400	0.2–0.4	Machining non-ferrous; smoother
DLC (a-C:H)	15–30	150–200	0.12–0.18	300	0.05–0.15	Ultra-low friction; auto parts
ta-C (tetrahedral)	40–80	400–700	0.12	400	0.02–0.05	Highest hardness DLC; bearings
ZrN	22	260	0.085	550	0.4	Decorative (brass-gold color)

H/E ratio (plasticity index): High H/E → better toughness; resists plastic deformation without cracking H/E > 0.1: "elastic" hard coating; resists cracking under contact H/E < 0.07: brittle; cracks under cyclic loading

Multilayer and Nanocomposite Coatings

Superlattice coatings (TiN/CrN alternating): Bilayer period Λ = 5–30 nm; hardness enhancement by coherency strain and blocking dislocation motion H_multilayer > (H_TiN + H_CrN)/2; typical H = 40–60 GPa peak for optimal Λ

Nanocomposite (nc-TiN/a-Si₃N₄): TiN nanocrystals (3–5 nm) in amorphous Si₃N₄ matrix; H = 40–50 GPa; Veprek design Strong blocking of dislocation motion; thermal stability > 1,000°C

Deposition Quality and Adhesion

Adhesion Testing

Rockwell indentation HF test (HF1–HF6): Diamond Rockwell indenter pressed into coated surface at 60 kgf (HRC test) Inspect crack/delamination pattern around indentation under 20× optical: HF1–HF4: acceptable (minor/no delamination); HF5–HF6: reject (extensive chipping)

Scratch test (Rockwell-style progressive load): Increase load from 0 to 100 N while moving diamond stylus across coated surface Lc₁ = first cracking; Lc₂ = cohesive failure; Lc₃ = adhesive failure (delamination) Good adhesion: Lc₃ > 50 N for cutting tools; > 30 N for forming tools ISO 20502: standardized scratch test; acoustic emission signal identifies Lc

Nanoindentation (H and E measurement): Oliver-Pharr method: load-displacement curve → hardness H = F_max/A_proj; E_r from unloading slope H = F_max / (24.5 × h_c²) [Berkovich indenter; h_c = contact depth corrected for pile-up] Coating properties from nanoindentation: use h_max ≤ t/10 to avoid substrate influence

Residual Stress

Intrinsic compressive stress: PVD coatings typically -1 to -6 GPa compressive (beneficial for fatigue; deleterious for adhesion if excessive) Deposition parameters control stress: higher bias → more compressive; higher temperature → less compressive

Measurement: Stoney equation: σ_f = E_s × t_s² / (6 × (1-ν_s) × t_f × R) − E_s × t_s / (6 × (1-ν_s) × R) R = curvature radius of coated substrate (wafer bow measurement by profilometry or XRD sin²ψ method) XRD (sin²ψ): measure d-spacing at multiple tilt angles; slope gives biaxial stress

Coating Thickness Measurement

Calotest (ball cratering): Rotate ball (D = 10–20 mm) on coated surface with abrasive slurry → reveal coating-substrate interface t_coating = (a² - b²) / (4R_ball) [a, b = outer and inner radii of spherical crater] Quick; destructive; typical accuracy ±0.1 μm

XRF (X-ray fluorescence): Non-destructive; measures characteristic X-rays from coating elements Calibrated to thickness via standard references; good for 0.1–10 μm TiN, CrN, etc. ASTM B568: standard for XRF thickness measurement

Cross-section SEM: Destructive; direct measurement; submicron accuracy; reveals microstructure and columnar vs. equiaxed grain

Process Control and Quality

Target Power and Gas Partial Pressure

Reactive gas control (N₂ partial pressure for TiN): P_N₂ / (P_Ar + P_N₂) = nitrogen flow fraction; typically 10–30% N₂ for stoichiometric TiN Stoichiometric TiN: N/Ti = 1.0 → golden yellow; N/Ti < 1 → darker; N/Ti > 1 → lighter/softer Control loop: emission spectrometry (OES) of target plasma emission as feedback

Substrate bias optimization: V_bias = -50 to -150 V: promotes ion bombardment → denser coating, higher compressive stress V_bias > -200 V: too much stress → delamination; grain structure over-modified Temperature during deposition: T_substrate = 0.2–0.5 × T_melt (substrate material); above 0.3 T_melt → columnar to equiaxed transition

Tool Life Performance

Cutting Tool Coating Selection

Dry machining of steel: AlTiN or CrAlN: oxidation resistance up to 900°C → tool life 2–5× longer than uncoated

Interrupted cut (milling): Need tough coating: CrN or TiAlN multilayer (lower stress; high H/E) DLC: not suitable for steel > 200°C (graphitization and diffusion)

Non-ferrous (aluminum, copper): DLC or TiCN: low affinity with non-ferrous; prevents built-up edge; lower friction

Forming tools: CrN + top TiN or WC/C: release properties; corrosion resistance for polymer injection molds

Standards and References

Standard	Scope
ASTM B244	Measurement of coating thickness by eddy current
ASTM B568	XRF coating thickness measurement
ISO 20502	Fine ceramics — scratch test for coatings
ISO 14707	Nanoscratch testing of coatings
VDI 3198	Adhesion testing of PVD coatings (HF test)
ISO 14577	Nanoindentation testing (Oliver-Pharr)

Output

Provide: substrate material (hardness HRC; surface roughness Ra [μm] pre-coat; geometry constraints), application (cutting/forming/wear/corrosion; operating T [°C]; lubrication), coating selection (compound; thickness t [μm]; H [GPa]; E [GPa]; H/E; T_max [°C]), deposition process (DC magnetron sputtering/HiPIMS/arc/EB-PVD; reason for selection), key parameters (Ar:N₂ ratio; bias V_bias [V]; target power [W/cm²]; T_substrate [°C]), adhesion test (HF1–6 pass/fail; scratch Lc₃ [N]; target), residual stress (compressive [GPa]; Stoney measurement or XRD sin²ψ), thickness measurement method (calotest/XRF/SEM; accuracy [μm]), tool life improvement estimate (× vs. uncoated; data source), surface roughness post-coat Ra [μm], and applicable standard (ASTM B568, VDI 3198, ISO 20502, ISO 14577).