Influence of parameters in the magnetron sputtering process (HiPIMS) on the mechanical and antibacterial properties of silver-doped DLC coatings
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-05-20 |
| Journal | Archives of Civil and Mechanical Engineering |
| Authors | Artur Albert Kozera, Z. SĆomka, Joanna KacprzyĆska-GoĆacka, RafaĆ ChoduĆ, Daniel PaÄko |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the optimization of silver-doped Diamond-Like Carbon (DLC) coatings (Cr-CrN-DLC(Ag)) deposited on 316L steel using High-Power Impulse Magnetron Sputtering (HiPIMS) for enhanced mechanical and antibacterial performance.
- Core Achievement: Successfully controlled the silver concentration in the DLC matrix (0.3% to 16%) by varying the Ag target magnetron pulse frequency (200 Hz to 800 Hz).
- Antibacterial Efficacy: All silver-doped coatings demonstrated 100% bactericidal activity against both Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) under static contact conditions.
- Structural Impact: Increased silver content led to a decrease in the sp3/sp2 hybridization ratio of the carbon matrix, resulting in structural disorder and the formation of soft metallic phases.
- Mechanical Trade-off: Hardness decreased significantly with increasing silver content (from ~15 GPa for pure DLC to ~4 GPa for 800 Hz Ag-doped).
- Optimal Formulation: The DLC(Ag)-200 Hz coating (0.3% Ag) provided the best balance, retaining high mechanical properties (Hardness ~12 GPa) while ensuring complete bactericidal activity.
- Process Stability: HiPIMS provided stable deposition, protecting the targets from poisoning and ensuring a compact microstructure with good adhesion.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | 316L | Steel | Base material |
| Deposition Method | HiPIMS | N/A | High-Power Impulse Magnetron Sputtering |
| Deposition Temperature | Below 200 | °C | Process temperature |
| Ag Target Pulse Frequency Range | 200 to 800 | Hz | Controlled variable for Ag content |
| Ag Content (200 Hz) | 0.3 | % | Lowest concentration, optimal coating |
| Ag Content (800 Hz) | 16 | % | Highest concentration |
| Hardness (Pure DLC) | ~15 | GPa | Reference coating |
| Hardness (DLC(Ag)-200 Hz) | ~12 | GPa | Best mechanical properties among doped samples |
| Hardness (DLC(Ag)-800 Hz) | ~4 | GPa | Lowest hardness |
| Youngâs Modulus Range | 150-220 | GPa | Range for all doped coatings |
| Adhesion Critical Load Fc2 (DLC(Ag)-200 Hz) | 15 | N | First adhesive defects (latest appearance) |
| Adhesion Critical Load Fc3 (DLC(Ag)-200 Hz) | 24 | N | Total delamination (earliest occurrence) |
| Graphite Target Power P1 | 9.24 | kW | Constant power supply |
| Silver Target Power P2 | 0.36 | kW | Constant power supply |
| Graphite Target Pulse Duration t1 | 60 | ”s | Constant parameter |
| Silver Target Pulse Duration t2 | 30 | ”s | Constant parameter |
| Bactericidal Efficacy | 100 | % | Against E. coli and S. aureus for all Ag-doped samples |
Key Methodologies
Section titled âKey MethodologiesâThe multilayer Cr-CrN-DLC(Ag) coatings were deposited using a custom-built HiPIMS system featuring three circular magnetrons (Chromium, Graphite, Silver).
- Substrate Preparation: 316L steel substrates were heated to 200 °C and subjected to ion-etching using Cr+ plasma to ensure surface cleanliness and enhance adhesion.
- Interlayer Deposition: Cr and CrN layers were deposited sequentially to serve as adhesion-promoting interlayers between the steel substrate and the DLC top layer.
- DLC Matrix Deposition: The graphite target magnetron was operated at constant parameters: 9.24 kW power, 60 ”s pulse duration, and 1000 Hz frequency.
- Silver Doping Control: The silver target magnetron was operated at a constant power of 0.36 kW and a pulse duration of 30 ”s. The silver content was precisely modulated by varying the voltage pulse frequency (200, 400, 600, and 800 Hz), which controlled the number of Ag ions reaching the substrate.
- Morphological Analysis: Surface morphology was analyzed using Light Microscopy (Keyence VHX1000E) and Scanning Electron Microscopy (HITACHI TM3000).
- Compositional Analysis: Elemental analysis (Ag concentration) was performed using Energy Dispersive Spectroscopy (EDS). Phase composition (sp3/sp2 ratio) was determined via Raman spectroscopy (JASCO NRSâ5100).
- Mechanical Testing: Hardness and Youngâs modulus were measured using nanoindentation, ensuring indentation depth did not exceed 10% of the total coating thickness. Adhesion was assessed via the scratch test (REVETEST CSM) to determine critical loads (Fc1, Fc2, Fc3).
- Antibacterial Testing: Bactericidal activity was measured using the static contact method against E. coli and S. aureus over 24 hours, simulating conditions conducive to biofilm formation.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of mechanically robust, fully bactericidal DLC coatings is highly relevant for industries requiring durable, hygienic surfaces.
- Medical and Healthcare:
- Surgical Implants: Coating 316L stainless steel orthopedic implants (e.g., screws, pins, joint replacements) to prevent bacterial colonization and reduce the risk of antimicrobial-resistant infections.
- Medical Instruments: Application on reusable surgical tools and diagnostic equipment to maintain sterility and high wear resistance during repeated sterilization cycles.
- Consumer Goods and Public Spaces:
- High-Touch Surfaces: Coating handles, railings, and public transport components where frequent contact necessitates continuous antimicrobial protection combined with scratch resistance.
- Industrial and Manufacturing:
- Food and Beverage Processing: Coating machinery and contact surfaces in food production lines to meet stringent hygiene standards and resist chemical cleaning agents.
- Fluid Handling: Application on pump components, valves, and seals in water treatment or chemical processing where both antiwear properties and resistance to biofouling are required.
- Aerospace and Automotive:
- Engine Components: Use in high-wear environments where DLC is traditionally applied, with the added benefit of preventing microbial growth in fuel or fluid systems.
View Original Abstract
Abstract In the present work, DLC coatings, well known for their antiwear properties, were modified by introducing to the structure an additive metal with antibacterial propertiesâsilver. Diamond-like coatings doped with silver were deposited on Cr-CrN layers created on steel 316L. To create the coatings, high-power impulse magnetron sputtering (HiPIMS) was used. The work carried out was divided into doping of DLC layers with silver and obtaining coatings with different contents of this metal by modifying the frequency of the voltage pulses applied to the silver target magnetron and investigating of the surface morphology, chemical and phase composition, mechanical properties and antibacterial activity. Light microscopy was used to analyse the surface morphology. The mechanical properties of the coatings were investigated using nanoindentation and the scratch method. Analysis of the antibacterial properties was carried out using two bacterial strains: Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). The results showed that silver-doped DLC at a magnetron pulse frequency of 200 Hz had the best mechanical properties compared to other silver-doped coatings and possessed bactericidal activity.