Views: 360 Author: Lasting Titanium Publish Time: 2026-08-12 Origin: Site
Content Menu
● What Is the Hardness Gradient in a Titanium Rod?
● Why Titanium Rods Need Surface Hardening
● How the Hardness Gradient Forms
>> Nitrogen Diffusion and Surface Phase Formation
>> Oxygen and Mixed-Interstitial Hardening
● Comparison of Surface-Hardening Methods
>> PVD Coatings
>> Thermal Oxidation and Carbo-Oxidation
>> Laser Nitriding and Laser Carbonitriding
● Parameters That Control Hardness Depth
>> Gas Pressure and Atmosphere
>> Rod Diameter, Length, and Fixturing
● How to Measure the Hardness Gradient Correctly
>> Use the Correct Hardness Standard
>> Use Microhardness Rather Than One Bulk Reading
>> Cross-Section Inspection Procedure
>> Define Effective Case Depth
>> Confirm the Metallurgical Structure
● Wear, Fatigue, and Corrosion Considerations
● Practical Specification Guide for Buyers
● Common Failure Modes and Prevention
● Qualification Plan for Surface-Hardened Titanium Rods
>> 3. Characterize the Profile
>> 4. Perform Application Testing
● Selecting the Right Treatment
● How Lasting Advanced Titanium Can Support Your Project
>> 1. What is a hardness gradient in a surface-hardened titanium rod?
>> 2. How hard can nitrided titanium become?
>> 3. How deep is the hardened layer?
>> 4. Is plasma nitriding better than PVD?
>> 5. Does surface hardening improve fatigue strength?
>> 6. Can a hardened titanium rod be machined afterward?
>> 7. What should a supplier provide?
>> 8. Is Grade 5 titanium suitable for surface hardening?
>> 9. Why is core hardness important?
>> 10. Which standard should be used for hardness testing?
Surface-hardened titanium rods combine titanium's low density, corrosion resistance, high strength-to-weight ratio, and biocompatibility with improved surface wear resistance. However, their performance should not be judged by surface hardness alone. The key engineering feature is the hardness gradient—the controlled transition from a hardened outer surface, through a diffusion zone, to a tougher titanium alloy core.
For buyers of titanium bars and titanium rods, this gradient affects wear life, galling, friction, fatigue behavior, dimensional stability, and machining response. A very hard surface with a brittle or poorly supported layer may perform worse than a slightly softer surface supported by a deeper and smoother transition zone.
This article explains how hardness gradients form, how titanium surface-hardening methods compare, how to measure case depth correctly, and how buyers can specify and qualify a reliable surface-hardened titanium rod.
A hardness gradient is the gradual variation in hardness from the treated surface toward the untreated core.
A surface-hardened titanium rod normally contains three functional regions:
1. Compound or hardened surface layer
The outermost region may contain titanium nitrides or another hardened phase. Depending on temperature, nitrogen activity, treatment time, and alloy composition, the compound layer may be TiN-dominant, Ti₂N-dominant, mixed, very thin, or discontinuous.
2. Diffusion or transition zone
Nitrogen, oxygen, or carbon gradually decreases with depth. These interstitial elements strengthen the titanium lattice and create a progressive reduction in hardness. This zone may consist mainly of nitrogen-containing α-titanium, often described as an α-Ti(N) diffusion zone.
3. Titanium alloy core
The core retains the original alloy structure and provides ductility, toughness, and load-bearing capacity.
The ideal profile is not simply the hardest possible surface. It is a balanced profile that provides:
- Wear resistance
- Adequate load support
- Fatigue resistance
- Fracture resistance
- Controlled surface roughness
- Dimensional stability
- Suitable corrosion behavior
A gradual hardness reduction is generally preferable to an abrupt drop because the diffusion zone supports the hard outer layer and reduces the risk of cracking, chipping, or spalling.
Titanium alloys are selected for their low density, excellent corrosion resistance, and high specific strength. However, untreated titanium can show relatively poor resistance to adhesive, abrasive, and fretting wear.
This behavior is related to several characteristics:
- Low elastic modulus: Titanium deforms more readily under contact loading than many steels.
- High chemical affinity: Titanium tends to adhere to opposing surfaces during sliding.
- Galling tendency: Repeated metal-to-metal contact can cause material transfer and seizure.
- Limited surface hardness: Titanium's natural oxide film protects against corrosion but does not always provide sufficient mechanical wear resistance.
- Fretting sensitivity: Small-amplitude oscillating motion can damage the surface under high contact pressure.
As a result, a titanium rod may meet its tensile-strength requirements but still fail at a sliding, contacting, or fretting surface.
Surface hardening modifies only the near-surface region while preserving the useful properties of the core. It can improve resistance to:
- Scratching and indentation.
- Adhesive wear.
- Abrasive wear.
- Galling.
- Fretting.
- Particle erosion.
- Repeated surface deformation.
Typical applications include shafts, pins, guides, actuator components, valve parts, fasteners, sliding elements, and selected medical or aerospace components.
Nitriding is one of the most established methods for hardening titanium rods. During gas, plasma, or ion nitriding, nitrogen is introduced into the titanium surface.
The final structure depends on:
- Treatment temperature.
- Nitrogen activity.
- Gas pressure and composition.
- Treatment time.
- Alloy grade.
- Surface activation.
- Heating and cooling conditions.
Depending on these factors, the surface may develop:
- A continuous TiN-rich compound layer.
- A Ti₂N-rich compound layer.
- A mixed TiN/Ti₂N layer.
- A very thin or discontinuous compound layer.
- No continuous compound layer, with hardening mainly occurring in an α-Ti(N) diffusion zone.
Therefore, TiN and Ti₂N should not be presented as the only possible surface phases. At lower temperatures or lower nitrogen activity, a continuous δ-TiN layer may be limited or absent, while Ti₂N or nitrogen-containing α-titanium may dominate.
Where a compound layer forms, it is usually much harder than the base titanium. Beneath it, nitrogen occupies interstitial sites in the titanium lattice and strengthens the diffusion zone through solid-solution hardening.
Because nitrogen concentration is highest near the surface and decreases toward the core, hardness normally follows the same trend.
Oxygen and carbon can also strengthen titanium surfaces. Controlled oxidation, carbonitriding, and mixed nitrogen-carbon-oxygen treatments may produce deeper or differently structured hardened regions.
However, excessive interstitial absorption can increase brittleness and reduce ductility or fatigue resistance. A successful process therefore aims for a controlled composition and hardness profile, rather than the maximum possible hardness.
The original alloy microstructure strongly affects the final result. Commercially pure titanium, Grade 2, Grade 5 / Ti-6Al-4V, Ti-6Al-7Nb, near-alpha alloys, and beta alloys do not respond identically.
The alloy influences:
- Nitrogen diffusion.
- Phase formation.
- Core hardness.
- Residual stress.
- Fatigue behavior.
- Treatment temperature window.
- Microstructural stability.
A treatment qualified for Grade 5 should not automatically be applied to Grade 2 or a beta titanium alloy.
| Region | Typical characteristic | Hardness behavior |
|---|---|---|
| Compound layer | TiN-, Ti₂N-, or mixed-phase outer layer, where formed | May reach several hundred to more than 1,000 HV |
| Diffusion zone | Nitrogen-, oxygen-, or carbon-strengthened titanium | Hardness gradually decreases with depth |
| Core | Untreated titanium alloy | Retains the original bulk hardness |
| Effective case boundary | Defined end of useful hardening | Must be linked to an agreed criterion |
The following values are representative only. Actual values depend on the titanium grade, treatment, measurement load, and acceptance criteria.
Published plasma-nitriding research on Ti-6Al-4V has reported surface hardness above 800 HV0.1 under selected conditions, with a measurable hardened region extending approximately 80–100 μm into the material. The value must always be linked to the test load, because 800 HV0.05, 800 HV0.1, 800 HV0.3, and 800 HV1 are not equivalent measurements. [mdpi]
For this reason, a supplier should not describe a titanium rod simply as "hardened." The technical specification should identify:
- Surface hardness.
- Hardness scale and test load.
- Effective case depth.
- Compound-layer thickness.
- Core hardness.
- Surface roughness.
- Treatment method.
- Alloy grade.
- Inspection method.
Gas nitriding introduces nitrogen through a controlled atmosphere at elevated temperature.
Advantages:
- Suitable for batch processing.
- Capable of producing a diffusion zone.
- Practical for long rods when furnace loading is controlled.
- Suitable for production after process qualification.
Limitations:
- High temperature may alter the substrate microstructure.
- Poor atmosphere control can cause oxidation or α-case formation.
- Excessive treatment can create a brittle surface.
- Thermal exposure may cause dimensional changes.
Gas nitriding can be economical for larger production volumes, but the process must be qualified for the actual titanium grade, rod diameter, length, and loading configuration.
Plasma nitriding uses an ionized gas environment to activate the titanium surface and promote nitrogen diffusion.
Advantages:
- Good control of pressure and gas chemistry.
- Adjustable bias voltage and plasma conditions.
- Possibility of selective treatment and masking.
- Useful control over compound-layer formation.
Limitations:
- Requires specialized equipment.
- Rod ends and fixture-contact areas may be non-uniform.
- High-temperature processing can affect fatigue properties.
- Surface roughness and residual stress must be evaluated.
Plasma nitriding is attractive when a diffusion-supported hardened layer is required and the customer needs close control of the process window.
Low-temperature nitriding aims to improve the surface while limiting changes to the bulk alloy. It is useful when the titanium rod must retain:
- High fatigue strength.
- Tight dimensional tolerances.
- A specific α-β microstructure.
- Stable core mechanical properties.
However, "low temperature" should not be interpreted too broadly. Low-temperature variants such as active-screen plasma nitriding, rare-earth-assisted treatments, pre-activated surfaces, surface nanostructuring, or long-duration diffusion treatments can produce functional case depths under suitable conditions.
By contrast, conventional direct-current plasma nitriding below approximately 600°C on as-received, mill-annealed Ti-6Al-4V may produce only a limited or marginal diffusion zone unless the surface is activated or the treatment is carefully optimized.
This distinction is important for industrial users. A result obtained with active-screen equipment should not automatically be expected from a conventional direct-current ion-nitriding furnace.
Low-temperature treatment should be evaluated using:
- Surface hardness.
- Hardness-depth profile.
- Compound-layer thickness.
- Surface roughness.
- Residual stress.
- Core microstructure.
- Wear performance.
- Fatigue performance.
Physical vapor deposition can apply coatings such as TiN or CrN to titanium rods or finished components.
Advantages:
- Very high coating hardness.
- Thin and controlled coating thickness.
- Attractive appearance.
- Various coating chemistries are available.
- Limited bulk thermal exposure compared with some diffusion treatments.
Limitations:
- The coating is deposited rather than deeply diffused.
- Adhesion depends on substrate preparation.
- A hard coating on a soft substrate may crack under heavy contact.
- Delamination can occur if the interface is weak.
- Damaged edges and poor surface finish reduce coating life.
PVD is often suitable for moderate loads and precision surfaces. A diffusion layer may be preferable where the surface must withstand high contact stress.
Controlled oxidation and mixed-interstitial processes introduce oxygen, nitrogen, and/or carbon into the near-surface region.
They may be useful for:
- Sliding wear.
- Erosion.
- High-temperature service.
- Specialized corrosion-wear environments.
The process requires control of:
- Oxygen partial pressure.
- Nitrogen activity.
- Treatment temperature.
- Treatment duration.
- Surface chemistry.
- Phase formation.
- Residual stress.
- Final roughness.
Because the process window can be narrow, pilot testing is recommended before production.
Laser treatment provides localized energy and can create a hardened alloyed or nitrided region.
Advantages include:
- Localized hardening.
- Rapid heating and cooling.
- Potentially deeper alloyed zones.
- Flexibility for selected areas.
Potential risks include:
- Surface cracking.
- Porosity.
- Uneven scan overlap.
- Thermal distortion.
- Sensitivity to laser power, scan speed, and beam diameter.
Laser treatment is often more appropriate for localized components than for complete commodity-length titanium bars.
Higher temperature generally accelerates diffusion, but excessive temperature may cause:
- Grain growth.
- α-β microstructural changes.
- Reduced toughness.
- Brittle compound formation.
- Dimensional distortion.
- Fatigue degradation.
Longer treatment time may increase diffusion depth, but excessive time can also produce a thick brittle layer, higher residual stress, roughness changes, and unnecessary cost.
The best process balances surface hardness, effective depth, phase constitution, and core stability.
Gas pressure, nitrogen activity, hydrogen content, plasma density, and bias voltage influence the supply of active nitrogen to the surface.
The process should therefore be described as a complete recipe, not simply as "nitrided at high temperature." Atmosphere control is also essential for minimizing oxygen contamination and α-case formation.
Oil, oxide scale, embedded particles, machining damage, or inconsistent roughness can produce local differences in the hardness gradient.
A typical preparation sequence includes:
1. Controlled turning, grinding, or polishing.
2. Degreasing and cleaning.
3. Removal of loose oxide and contamination.
4. Surface activation where required.
5. Masking of untreated areas.
6. Initial roughness and dimension checks.
7. Verification of straightness.
Long titanium rods may be more difficult to treat uniformly than short laboratory coupons. Important variables include:
- Rod spacing.
- Chamber orientation.
- Fixture-contact points.
- End-to-center temperature variation.
- Gas circulation.
- Shielding effects.
- Rod bowing or sagging.
The final process should be validated using the actual production geometry.
A technical specification should distinguish between macrohardness and microindentation hardness.
- ASTM E92 is commonly used for Vickers and Knoop hardness testing at conventional or macrohardness levels.
- ASTM E384 is the more appropriate reference for microindentation hardness, especially when mapping thin compound layers and diffusion zones across polished cross-sections.
- ISO 6507 provides an internationally recognized reference for Vickers hardness testing.
A suitable specification may state:
> Surface and cross-sectional microhardness shall be measured according to ASTM E384, with Vickers hardness reported at the specified test load. Macrohardness, where applicable, shall reference ASTM E92 or ISO 6507.
Rockwell testing may be suitable for the core but is often unsuitable for a thin hardened layer. The indentation may extend through the surface layer and include softer material below it.
For gradient analysis, laboratories commonly use:
- Vickers microhardness.
- Knoop microhardness.
- Instrumented indentation.
- Cross-sectional hardness mapping.
The load must always be reported. HV0.05, HV0.1, HV0.2, HV0.3, and HV1 are not interchangeable.
Testing should also control:
- Indentation spacing.
- Distance from the specimen edge.
- Cross-section preparation.
- Indenter calibration.
- Measurement uncertainty.
- Indentation visibility.
- Distance from the treated surface.
A practical inspection sequence is:
1. Cut a representative sample from the rod or a witness coupon.
2. Mount the sample so the surface is fully supported.
3. Polish the cross-section without rounding the surface edge.
4. Measure hardness at defined depths.
5. Repeat readings to identify variation.
6. Plot hardness against depth.
7. Calculate effective case depth according to the agreed criterion.
8. Compare the profile with the purchase specification.
Measurements should be closer together near the surface, where hardness changes most rapidly.
"Case depth" may refer to:
- Compound-layer thickness.
- Total visibly modified layer.
- Nitrogen diffusion depth.
- Depth at which hardness falls below a specified value.
- Depth at which hardness returns to a defined percentage of core hardness.
The customer and supplier must agree on the definition before production. Otherwise, different laboratories may report different case depths for the same rod.
Hardness alone is insufficient for high-performance components. Additional tests may include:
- Optical microscopy.
- Scanning electron microscopy.
- Energy-dispersive spectroscopy.
- X-ray diffraction.
- Nitrogen or oxygen depth profiling.
- Surface roughness measurement.
- Residual-stress analysis.
- Wear testing.
- Dimensional inspection.
For aerospace, medical, and safety-critical products, traceability should cover raw material, machining, treatment batch, inspection, and final shipment.
A high surface hardness may improve resistance to indentation and abrasive wear, but wear life also depends on:
- Counterface material.
- Contact pressure.
- Sliding speed.
- Lubrication.
- Surface roughness.
- Compound-layer continuity.
- Residual stress.
- Diffusion-zone support.
- Operating temperature.
- Contaminating particles.
A very hard but brittle layer may fail under impact or cyclic loading. A moderately hard layer supported by a deeper diffusion zone may provide better service life.
Surface hardening can also have either a positive or negative effect on fatigue. Potential benefits include improved resistance to fretting damage and possible compressive residual stress. Potential risks include:
- Brittle compound layers.
- Tensile residual stress.
- Surface roughness growth.
- Microcracks.
- α-case formation caused by oxygen contamination.
- Substrate microstructural changes.
- Reduced near-surface ductility.
α-case is an oxygen-enriched, hard, and relatively brittle region that may become a fatigue-crack initiation site. It should be controlled when titanium is treated at elevated temperature.
Titanium's oxide film provides excellent corrosion resistance in many environments, but surface hardening is not automatically a corrosion solution. For medical, marine, and chemical-processing applications, the customer should evaluate corrosion, cleanliness, surface chemistry, and biocompatibility in addition to hardness.
When requesting a quotation for a surface-hardened titanium rod, specify:
- Titanium grade.
- Diameter and length.
- Straightness tolerance.
- Final dimensional tolerance.
- Surface finish.
- Machining allowance.
- Operating temperature.
- Contact and loading conditions.
- Treatment type.
- Minimum surface hardness.
- Hardness scale and test load.
- Effective case depth.
- Compound-layer thickness, if applicable.
- Maximum surface roughness.
- Masking requirements.
- α-case acceptance criteria, where relevant.
- Post-treatment finishing requirements.
- Core mechanical properties.
- Core hardness.
- Chemical composition.
- Microstructure.
- Hardness-depth chart.
- Metallographic report.
- Surface roughness results.
- Non-destructive testing, where required.
- Batch traceability.
- Certificate of conformity.
- Applicable standard, such as ASTM E384, ASTM E92, or ISO 6507.
A practical specification could state:
> Ti-6Al-4V titanium rod, plasma nitrided after final machining, minimum surface hardness of ___ HV0.1, effective case depth of ___ μm at ___ HV, core hardness of ___ HV, maximum Ra of ___ μm, with a cross-sectional microhardness profile measured according to ASTM E384 and a metallographic report supplied for each treatment batch.
The target values should be established through application testing rather than copied from a generic catalogue.
| Failure mode | Likely cause | Prevention |
|---|---|---|
| Surface cracking | Excessive compound-layer thickness or residual stress | Reduce treatment severity and inspect cross-sections |
| Poor wear life | Case too shallow or insufficiently supported | Specify effective depth, not hardness alone |
| Coating delamination | Weak adhesion or poor cleaning | Improve preparation and consider diffusion support |
| Dimensional variation | High temperature or uneven heating | Validate furnace uniformity and machining allowance |
| Fatigue reduction | Brittle layer, roughness, or residual stress | Control treatment and perform fatigue testing |
| α-case formation | Oxygen contamination at elevated temperature | Control atmosphere and inspect microstructure |
| Inconsistent hardness | Uneven gas flow, loading, or surface condition | Standardize cleaning, fixturing, and batch control |
| Misleading hardness data | Wrong test load or rounded cross-section | Use ASTM E384 microhardness testing |
| Local soft spots | Masking defects or poor plasma distribution | Inspect ends, transitions, and fixture-contact zones |
| Excessive roughness | Over-treatment or surface sputtering | Define Ra limits and validate finishing |
| Failure mode | Likely cause | Prevention |
||||
| Surface cracking | Excessive compound-layer thickness or residual stress | Reduce treatment severity and inspect cross-sections |
| Poor wear life | Case too shallow or insufficiently supported | Specify effective depth, not hardness alone |
| Coating delamination | Weak adhesion or poor cleaning | Improve preparation and consider diffusion support |
| Dimensional variation | High temperature or uneven heating | Validate furnace uniformity and machining allowance |
| Fatigue reduction | Brittle layer, roughness, or residual stress | Control treatment and perform fatigue testing |
| α-case formation | Oxygen contamination at elevated temperature | Control atmosphere and inspect microstructure |
| Inconsistent hardness | Uneven gas flow, loading, or surface condition | Standardize cleaning, fixturing, and batch control |
| Misleading hardness data | Wrong test load or rounded cross-section | Use ASTM E384 microhardness testing |
| Local soft spots | Masking defects or poor plasma distribution | Inspect ends, transitions, and fixture-contact zones |
| Excessive roughness | Over-treatment or surface sputtering | Define Ra limits and validate finishing |
The most common purchasing mistake is specifying only a minimum surface-hardness value. That requirement may permit a thin, brittle layer with insufficient support.
Before full production, a supplier and customer should use a staged qualification program.
Verify the titanium grade, heat number, chemical composition, initial mechanical properties, microstructure, and starting surface condition.
Use coupons or short rod sections to evaluate different temperatures, times, gas compositions, pressures, bias voltages, and surface-activation methods.
For each condition, measure:
- Surface hardness with test load.
- Hardness at multiple depths.
- Compound-layer thickness.
- Effective case depth.
- Surface roughness.
- Metallographic structure.
- Residual stress.
- Oxygen contamination or α-case, where relevant.
Test wear, friction, fretting, fatigue, corrosion, thermal stability, and dimensional stability under representative conditions.
Define the approved process window, sampling frequency, witness coupons, acceptance limits, traceability requirements, and nonconformance procedures.
This process converts surface hardening from a general marketing description into a controlled and verifiable manufacturing process.
The correct treatment should be selected according to the application rather than the treatment name.
Important questions include:
1. Is the rod structural, wear-resistant, or both?
2. Is the contact continuous, intermittent, oscillating, or impact-loaded?
3. What material contacts the titanium?
4. Will the rod be machined after treatment?
5. Which core properties must remain unchanged?
6. Is fatigue performance more important than maximum hardness?
7. What dimensional tolerance is acceptable?
8. Is a hardness-depth chart required?
9. Will the rod operate in saltwater, body fluid, vacuum, or elevated temperature?
10. Are there coating or biocompatibility restrictions?
For a structural titanium bar, aggressive nitriding may create more risk than benefit. For a sliding guide, shaft, pin, or wear-contact component, a controlled diffusion layer may significantly extend service life.
The best solution is usually a qualified process window, including treatment temperature, time, atmosphere, surface condition, hardness profile, roughness, residual stress, oxygen control, and acceptance criteria.
Selecting a surface-hardened titanium rod requires coordination between raw-material quality, machining, treatment, inspection, and application performance.
As a China-based supplier of titanium bars, titanium rods, and customized titanium materials, Lasting Advanced Titanium can support international brand owners, wholesalers, manufacturers, and engineering companies with:
- Titanium grade selection.
- Diameter, length, and tolerance review.
- Surface finish and machining allowance.
- Hardness and case-depth requirements.
- Surface-treatment coordination.
- Inspection documentation.
- Batch traceability.
- Customized export supply.
Before requesting a quotation, prepare the expected load, counterface material, operating environment, final dimensions, hardness target, case-depth definition, and inspection requirements.
Contact Lasting Advanced Titanium to discuss your titanium rod requirements and request a customized technical proposal, hardness-depth inspection plan, and production quotation.
It is the gradual change in hardness from the treated surface through the diffusion zone to the softer titanium core. This transition supports the hard surface and balances wear resistance with toughness.
The achievable hardness depends on the titanium grade, treatment, phase constitution, and test load. Published Ti-6Al-4V plasma-nitriding research has reported surface hardness above 800 HV0.1 under selected conditions. The measurement load must always be included.
The depth varies widely. Some processes produce diffusion zones of several tens of micrometers, while optimized treatments can produce effective hardening approaching or exceeding 100 μm. The result depends on the case-depth definition.
Neither is universally better. Plasma nitriding creates a diffusion-supported modified surface, while PVD produces a thin deposited coating. The correct choice depends on load, wear mode, fatigue requirements, dimensional tolerance, and adhesion requirements.
Not automatically. Brittle layers, α-case formation, surface roughness, or unfavorable residual stress can reduce fatigue performance. Safety-critical components should be fatigue-tested under representative conditions.
Light finishing may be possible, but machining can remove or damage the hardened layer. Final dimensions and surface finish should preferably be achieved before treatment.
Request the alloy grade, treatment method, surface hardness, test load, effective case-depth definition, core hardness, surface roughness, hardness-depth profile, metallographic report, and batch traceability.
Yes. Grade 5 / Ti-6Al-4V is widely studied and commonly treated, but the process must be qualified for the required dimensions, microstructure, fatigue performance, and service environment.
The core supports the hardened layer and provides toughness and load-bearing capacity. A very hard surface over a thermally damaged or unsuitable core may crack, spall, or fail through fatigue.
For thin surface layers and cross-sectional hardness mapping, ASTM E384 is generally the more appropriate microindentation reference. ASTM E92 and ISO 6507 may be used for applicable Vickers or Knoop testing, provided the test load and method are clearly stated.
1. Investigation of Microstructure, Residual Stress, and Hardness of Ti-6Al-4V after Plasma Nitriding Process with Different Times and Temperatures, *Coatings*, MDPI. [Read the study]
2. D.C. Diode Ion Nitriding Behaviour of Titanium, *Surface and Coatings Technology*. This reference concerns earlier plasma or ion-nitriding behavior and should not be described as an active-screen bias-voltage optimization study. [View the source record]
3. Carbonitriding of Ti-6Al-4V Alloy via Laser Irradiation of Pure Graphite Powder in Nitrogen Environment, *ScienceDirect*. This is a research paper on laser carbonitriding, surface hardness, hardening depth, and process parameters. [Read the study]
4. Wear Resistance of Ti–6Al–4V Alloy Ball Heads for Use in Implants, *MDPI*. [Read the study]
5. ASTM E92, Standard Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials. [View ASTM information]
6. ASTM E384, Standard Test Method for Microindentation Hardness of Materials. [View ASTM information]
7. ISO 6507, Metallic Materials—Vickers Hardness Test. [View ISO information]
