Tribocorrosion Assessment of Laser Clad Ceramic Reinforced TI6Al4V Surface Composites

Summary

Assessing the wear resistance, microhardness, and corrosion resistance of composites with ceramic reinforcement particles (Zr/TiC and Ti/TiC systems) in conditions relevant to biomedical implants (NaCl/H₂SO₄).

Abstract

This article presents a comprehensive experimental protocol for evaluating the tribocorrosion behavior of additively manufactured TI₆Al₄V based composites reinforced with ceramic phases using laser metal deposition (LMD). This protocol addresses the need to understand the synergistic degradation mechanisms that arise in components exposed to mechanical loading and corrosive environments in biomedical and aerospace applications. The protocol includes controlled laser cladding of TI₆Al₄V with Zr/TiC and Ti/TiC reinforcements, followed by detailed microstructural, mechanical, electrochemical, and tribocorrosion characterization. The procedures cover powder handling, substrate preparation, laser processing, metallographic preparation, microscopy, X–ray diffraction, microhardness testing, electrochemical corrosion measurements, and tribocorrosion testing using a reciprocating ball–on–plate tribometer under electrochemical control in a NaCl/H₂SO₄ electrolyte. This method enables real-time assessment of wear–corrosion interactions, including passive film breakdown and re–passivation under sliding conditions, while accounting for additive manufacturing-induced microstructural features. The protocol serves as a standardized framework for evaluating the effectiveness of ceramic reinforcement strategies in improving the functionality of additively manufactured metallic systems intended for challenging environments.

Introduction

Laser surface modification incorporating ceramic phases is an effective approach to enhance the surface performance of metallic implants, enabling the formation of corrosion–resistant and mechanically reinforced coatings via laser metal deposition (LMD)¹. Titanium alloy TI₆Al₄V is widely used in biomedical implants due to its biocompatibility, high strength–to–weight ratio, and corrosion resistance^2,3. Nevertheless, it remains vulnerable to corrosion and tribocorrosion in aggressive physiological environments, where mechanical wear and electrochemical degradation can compromise implant performance and trigger adverse biological responses^4,5,6,7. LMD improves surface properties through localized remelting, rapid solidification, and incorporation of reinforcing phases, producing dense, metallurgically bonded layers with tailored microstructures. Compared with alternative techniques such as laser nitriding or electron beam processing, LMD offers compositional flexibility, lower operational costs, and broad accessibility^8,9,10. These advantages make it particularly suitable for additively manufactured (AM) implants, where corrosion resistance is critical for long term in vivo performance¹⁰.

The corrosion and tribocorrosion behavior of AM implants is influenced by porosity, surface roughness, residual stresses, and microstructural heterogeneity¹¹. Therefore, evaluation requires electrochemical testing in aggressive electrolytes (e.g., NaCl/H₂SO₄), complemented by microstructural characterization using SEM and EDS. Post-processing strategies, including hot isostatic pressing, surface polishing, and laser remelting, further improve corrosion resistance by reducing defects and refining surface topology.

Reinforced TI₆Al₄V composites containing Zr, Ti, and TiC exhibit improved corrosion resistance due to a combination of enhanced passive layer stability and microstructural refinement. Zirconium stabilizes the passive TiO₂ – ZrO₂ mixed oxide, promoting rapid re–passivation and higher polarization resistance^12,13. TiC and Ti particles provide mechanical reinforcement and act as diffusion barriers to corrosive ions, while well-bonded interfaces minimize microcrevices that can initiate localized corrosion¹⁴. The Table of Materials shows the materials used, including reagents and instruments.

The overall goal of this method is to evaluate tribocorrosion performance of AM TI₆Al₄V composites reinforced with ceramic particles (Zr/TiC and Ti/TiC), capturing synergistic damage mechanisms that occur under simultaneous mechanical wear and electrochemical exposure. Tribocorrosion testing integrates wear and electrochemical measurements, providing real time assessment under dynamic, physiologically relevant conditions^{15,16,17,18,19,20}. The method is appropriate for load-bearing biomedical implants or components exposed to combined mechanical and chemical stresses, simulating worst–case in-vivo scenarios using chloride-containing electrolytes. Optimal performance is achieved by balancing mechanical reinforcement with electrochemical stability, emphasizing the importance of microstructural uniformity and passive film integrity. This protocol provides a reproducible, application-relevant framework for assessing AM TI₆Al₄V composites under tribocorrosion conditions, supporting informed material selection, surface engineering, and implant design.

Protocol

1. Materials, equipment, and starting powders

1. Starting powders
   1. Obtain gas atomized TI₆Al₄V powder (ASTM F136) with a particle size range of 15–53 µm, zirconium (Zr) powder with ≥99.5 wt% purity and particle size of 10–45 µm, and titanium carbide (TiC) powder with ≥99 wt% purity and particle size of 2–10 µm.
   2. Store all powders in sealed containers under a dry argon atmosphere to prevent oxidation and moisture uptake prior to processing.
2. Substrate preparation
   1. Cut TI₆Al₄V substrate plates to dimensions of 50 mm × 50 mm × 5 mm.
   2. Grind the substrate surface sequentially using SiC papers from P320 to P800 grit to remove surface oxides and irregularities.
   3. Ultrasonically clean the substrates in acetone for 10 min, followed by ethanol for 10 min.
   4. Dry the substrates using compressed nitrogen and mount them securely on the laser metal deposition (LMD) build platform.

2. Laser metal deposition of ceramic reinforced surface composites

1. LMD system configuration
   1. Use a laser metal deposition system equipped with a multi–hopper powder feeding unit.
   2. Employ a continuous wave fiber laser with a wavelength of approximately 1070 nm.
   3. Set the laser spot diameter to 1.0–1.5 mm using a coaxial nozzle.
2. Powder feeding and shielding
   1. Load TI₆Al₄V, Zr, and TiC powders into separate hoppers under an argon-filled glove box.
   2. Purge all powder lines and hoppers with high-purity argon for at least 20 min to reduce oxygen levels below 10 ppm.
   3. Calibrate each powder feeder gravimetrically and adjust feed rates to achieve the desired composition, maintaining a total powder feed rate of 5–10 g/min with a deviation within ±2%.
3. Deposition parameters
   1. Set laser power to 800–1200 W.
   2. Set scanning speed to 6–12 mm/s.
   3. Maintain an argon shielding gas flow rate of 10–15 L/min to protect the molten pool from oxidation.
   4. Deposit material using a raster scan strategy with 30–50% overlap between adjacent tracks.
   5. Build coatings layer by layer, allowing controlled cooling intervals between layers to minimize residual stress.
   6. Allow samples to cool to room temperature under an argon atmosphere after deposition.

3. Microstructural and phase characterization

1. Metallographic preparation
   1. Cut the deposited samples perpendicular to the build direction using a precision diamond saw.
   2. Embed the specimens in conductive epoxy and cure as per the manufacturer’s instructions.
   3. Grind with SiC papers (P120 to P1200) and polish with diamond suspensions down to 1 µm.
2. Scanning electron microscopy (SEM): Coat the polished samples with a thin conductive layer before SEM imaging to reduce surface charging. Mount each polished sample on an aluminum SEM stub using conductive carbon tape for proper electrical contact.
   1. Place the mounted samples in a sputter coater and deposit a 5–10 nm thick layer of gold or carbon in an argon atmosphere. Apply a sputtering current of around 20 mA for 45–60 s to ensure a uniform conductive coating. After coating, store the samples in a clean, dust–free container until SEM analysis.
      NOTE: Coat polished samples with a conductive carbon or gold layer (~5–10 nm): To ensure a conductive surface for SEM imaging and accurate EDS elemental analysis, coat polished samples with a thin layer of carbon or gold (~5–10 nm). Use a sputter coater to apply the conductive layer. Secure the samples on aluminum stubs with conductive carbon tape and sputter a 5–10 nm gold layer at 20 mA for 60 s in an argon atmosphere. Materials required for this preparation include polished metallurgical samples, a carbon or gold coating source, a sputter coater or thermal evaporator, a conductive sample stub, adhesive tape, and an ultrasonic bath with ethanol or acetone. The procedure is as follows:
      1. Sample preparation: Ensure the sample surface is smooth and scratch–free. For metallic samples, grind with SiC papers: 320–1200 grit, polish with diamond paste: 6–3–1 µm, clean in ethanol or acetone for 5–10 min, and dry the sample completely using warm air or nitrogen.
      2. Choose the coating material: Carbon is commonly used for EDS applications to minimize interference with elemental peaks, while gold (Au) is suitable for non–conductive or poorly conducting samples due to its high conductivity, although it may obscure nearby elemental peaks in EDS.
      3. Choose a coating technique:
         Sputter coating (preferred for metals and SEM): Place the sample in the sputter coater vacuum chamber, pump down to high vacuum, set the sputtering current and voltage according to the manufacturer's specifications, and sputter-coat for a calibrated time to achieve a ~5–10 nm thickness.
      4. Coating tips for best results
         Rotate the sample during deposition for uniform coverage, avoid overcoating (>10 nm thickness), verify coating thickness with calibration or a profilometer, and ensure the sample is clean post–coating to prevent contamination.
      5. Storage before SEM
         Store coated samples in a dust–free container and avoid touching the coated surface to maintain conductivity and image quality.
      6. Optional: Combination coating
         Apply a thin carbon layer (~5 nm) followed by gold (~5 nm) for balanced elemental analysis accuracy and enhanced image quality, especially for heterogeneous or low–conductivity samples.
   2. Conduct SEM imaging with an accelerating voltage between 10 and 20 kV and a working distance of 8 to 12 mm.
   3. Capture secondary electron images to evaluate clad geometry, porosity, and reinforcement distribution. Place the coated samples in the scanning electron microscope chamber and follow the instrument's procedure to achieve the necessary vacuum level. Capture secondary electron (SE) images using a field–emission scanning electron microscope at 10–15 kV and a working distance of 8–10 mm. Use the secondary electron detector for high–resolution surface images. Take micrographs at different magnifications to analyze clad geometry, porosity, and reinforcement distribution in the laser–cladded layers. Include a scale bar in the bottom right corner of each exported image.
      1. Sample preparation
         Polish the sample flat, grind with 320 to 1200 grit papers, and polish using diamond paste (6, 3, 1 µm). Clean the sample in an ultrasonic bath with ethanol or acetone and coat it with a conductive layer (approximately 5–10 nm of carbon or gold) to prevent charging during imaging.
      2. Sample mounting
         Attach the sample to a conductive stub using carbon tape or conductive adhesive, ensuring it is flat and stable. Insert the stub into the SEM chamber and evacuate to high vacuum.
      3. Mode selection
         In the SEM control software, choose secondary electron (SE) mode and select a detector that captures SE signals. Adjust the accelerating voltage based on the material and features of interest.
      4. Adjusting parameters
         Set the working distance to 5–15 mm for higher resolution; use a small spot size (approximately 1–5 nm) for improved resolution; choose a medium–slow scan speed for better detail; adjust magnification as needed for clad analysis; and balance beam current for brightness and noise control.
      5. Image acquisition
         Start at low magnification and gradually increase to capture finer details. Take multiple images to cover clad geometry, porosity, and reinforcement distribution.
      6. Optional tilt and 3D perspective
         Tilt the sample (5–20°) for enhanced topographical contrast. Observe reinforcement particles protrusion or embedding in the matrix.
      7. Post–imaging steps
         Save images in high–resolution formats and annotate them with scale bars, regions of interest, and particle sizes. Utilize image analysis software for quantification and analysis.
      8. Workflow example for clad metallurgy
         Prepare a TiC – reinforced Ti clad sample, polish, coat with carbon, mount on a conductive stub, insert into SEM, use SE mode at 15 kV, 10 mm working distance, acquire images for clad geometry and reinforcement distribution, save and analyze images.
   4. Perform EDS point analysis and elemental mapping to confirm Zr and TiC distribution.
      Perform elemental analysis using an energy dispersive X–ray spectroscopy (EDS) detector integrated with the SEM system. Operate the SEM at an accelerating voltage of 15–20 kV to ensure sufficient excitation of characteristic X–ray signals. Conduct point analysis on selected regions of interest within the clad layer to identify elemental composition. Acquire spectra with a live acquisition time of approximately 60 s to obtain reliable elemental peaks.
      NOTE: For elemental mapping, scan the selected area of the clad surface while collecting spatially resolved X–ray signals corresponding to the elements of interest. Generate distribution maps to confirm the presence and spatial distribution of zirconium (Zr) and titanium carbide (TiC) reinforcement phases within the titanium matrix. Export the elemental maps with consistent scale bars and panel labels for subsequent image processing.
      1. Sample preparation
         Polish the sample to a mirror finish using SiC papers and diamond paste. Clean the sample in an ultrasonic bath with ethanol or acetone and apply a conductive coating if necessary to prevent charging.
      2. Mount sample and configure SEM
         Mount the sample on a conductive stub with carbon tape, insert it into the SEM chamber, and pump to high vacuum. Select an appropriate accelerating voltage for EDS detection.
      3. EDS detector setup
         Ensure proper cooling and calibration of the EDS detector, calibrate the spectrometer using a standard material, and set live time or counts for optimal signal–to–noise ratio.
      4. EDS point analysis
         ​Navigate to points of interest on the SEM image, acquire EDS spectrum at each point, identify characteristic peaks for Zr, Ti, and C, and record weight % or atomic % using the software.
      5. EDS elemental mapping
         Select the area of interest on the SEM image, activate mapping mode in the EDS software, and start scanning to generate elemental distribution maps.
      6. Cross–check with SEM imaging
         Use BSE imaging for compositional contrast, compare SE images and EDS maps for correlation.
      7. Data saving and analysis
         Save spectra, maps, and annotated SEM images. Utilize software for elemental fraction quantification, particle size measurement, and distribution uniformity calculation.
3. X–ray diffraction (XRD)
   1. Phase characterization
      Perform elemental analysis using an energy dispersive X–ray spectroscopy (EDS) detector integrated with the SEM system. Operate the SEM at an accelerating voltage of 15–20 kV to ensure sufficient excitation of characteristic X–ray signals. Conduct point analysis on selected regions of interest within the clad layer to identify elemental composition. Acquire spectra with a live acquisition time of approximately 60 s to obtain reliable elemental peaks.
      NOTE: For elemental mapping, scan the selected area of the clad surface while collecting spatially resolved X–ray signals corresponding to the elements of interest. Generate distribution maps to confirm the presence and spatial distribution of zirconium (Zr) and titanium carbide (TiC) reinforcement phases within the titanium matrix. Export the elemental maps with consistent scale bars and panel labels for subsequent image processing.

4. Mechanical characterization

1. Vickers microhardness testing
   1. Perform Vickers microhardness measurements on polished cross sections using a load of 100 g and a dwell time of 15 s.
   2. Place indentations at intervals of at least 100 µm to avoid interaction effects.
   3. Calculate average hardness values and standard deviations from at least ten measurements per sample.

5. Electrochemical corrosion testing

1. Electrochemical cell setup
   1. Prepare an electrochemical cell with the sample as the working electrode, a platinum mesh counter electrode, and an Ag/AgCl reference electrode.
   2. Expose a working electrode area of 1 cm² using an insulating lacquer.
   3. Use a NaCl/H₂SO₄ aqueous electrolyte maintained at 25 ± 1 °C.
2. Open circuit potential and polarization
   1. Immerse the sample and allow stabilization at open circuit potential (OCP) for 30 min.
   2. Perform potentiodynamic polarization scans from −0.25 V to +1.5 V vs. Ag/AgCl at a scan rate of 1 mV/s.
   3. Determine corrosion potential (E_corr) and corrosion current density (i_corr) from Tafel extrapolation.

6. Integrated tribocorrosion testing

1. Tribocorrosion-setup
   1. Mount the electrochemical specimen in a reciprocating ball-on-plate tribometer coupled to a potentiostat.
   2. Use an alumina (Al₂O₃) counterbody ball with a diameter of 6 mm.
   3. Apply a normal load of 5 N and a sliding frequency of 1 Hz over a sliding distance of 5 mm.
   4. Conduct tribocorrosion tests in the same NaCl/H₂SO₄ electrolyte under electrochemical control.
2. Test execution and standards
   1. Record coefficient of friction, current response, and potential continuously during sliding.
   2. Perform tribocorrosion testing in accordance with ASTM G119 for evaluating synergistic wear corrosion effects.
   3. After testing, rinse samples with distilled water, dry with nitrogen, and examine wear tracks using SEM.

Results

Powder and substrate characterization
Representative scanning electron microscopy (SEM) micrographs of the starting reinforcement powders ((A) Ti, (B) Zr, and (C) TiC) are shown in Figure 1. The Images illustrate typical particle morphologies obtained from gas atomized and commercially sourced powders. Titanium and zirconium particles predominantly exhibited spherical to near spherical shapes, whereas titanium carbide (TiC) particles displayed more angul...

Discussion

This methods article presents a reproducible protocol for the fabrication, characterization, and tribocorrosion evaluation of additively manufactured TI₆Al₄V based composites reinforced with ceramic phases using laser metal deposition (LMD). The methodology integrates powder characterization, automated in situ mixing, laser cladding, microstructural analysis, electrochemical testing, and coupled tribocorrosion assessment to address the complex degradation mechanisms encountered by titanium ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Raw Materials / Powders
Ti6Al4V Powder			Gas-atomized, 15–53 μm (ASTM F136) Use in Study: Matrix material for laser cladding and substrate.
Zirconium (Zr) Powder			Purity ≥99.5 wt.%, 10–45 μm Use in Study: Composite reinforcement  and stabilizer material.
Titanium Carbide (TiC) Powder			Purity ≥99 wt.%, 2–10 μm Use in Study: Ceramic reinforcement material for composite.
Ti/TiC Powder			Blended composite powder (specific weight ratios) Use in Study: Reinforcement blend for composite.
Zr/TiC Powder			Blended composite powder (specific weight ratios) Use in Study: Reinforcement blend for composite.
Gases & Chemicals
Nitrogen (N2)			Controlled environment/Safety precaution Use in Study: Controlled environment for powder mixing and Laser Metal Deposition (LMD) system.
Argon (Ar)			Purging environment, Carrier/Shielding Gas Use in Study: Powder loading, LMD atmosphere, and coaxial nozzle with carrier gas.
Acetone			Cleaning solvent Use in Study: Cleaning of Ti6Al4V substrate.
Ethanol			Cleaning solvent Use in Study:
Cooling Solution			water Use in Study: Cleaning of Ti6Al4V substrate.
Transparent Epoxy Resin			Mounting material Use in Study: Mounting specimens for electrode or metallographic preparation.
Conductive Epoxy			Mounting material Use in Study: Mounting Specimens for Microscopy (Post-Sectioning)
Emery Paper (SiC)			Various grit sizes Use in Study: Grinding samples (metallographic preparation).
Diamond Paste			Polishing compound Use in Study: Polishing the exposed surfaces of electrodes and cross-sections.
Simulated Body Fluid (SBF)			Electrolyte Use in Study: Electrochemical corrosion testing.
NaCl/H2SO4 Electrolyte			Unspecified concentration Use in Study: Electrochemical corrosion testing.
Equipment & Instrumentation
Scanning Electron Microscope (SEM)			With Energy Dispersive Spectroscopy (EDS) Use in Study: Characterization of powders and substrates, microstructural analysis, reinforcement dispersion, and EDS mapping.