Titanium Carbide (TiC) Plates vs Pure Titanium: Hardness & Wear Resistance

Titanium carbide basics

Titanium carbide (TiC) is an interstitial compound of titanium and carbon with the chemical formula TiC. It has a rock salt (NaCl-type) face-centered cubic crystal structure, with carbon atoms occupying the octahedral interstices of the titanium FCC lattice.

Key properties of TiC

The standout numbers: 2,800-3,200 HV hardness is in the range of the hardest carbides (along with tungsten carbide, chromium carbide, and boron carbide). The melting point of 3,160°C is among the highest of any material, ceramic or metal.

The critical limitation: K_IC of 3-5 MPa·m^0.5 is very low — about 1/20 of titanium alloy. TiC is brittle and cannot deform plastically to absorb impact or redistribute stress.

Hardness and mechanical property comparison

The hardness comparison tells the story:

TiC is 10-20x harder than even the hardest titanium alloy. This translates to dramatically better wear resistance in abrasive and erosive service.

Other mechanical property comparison

The trade is clear: TiC is 10x harder but 20x more brittle than Ti-6Al-4V. The cermet (TiC with metal binder) provides a middle ground — harder than Ti alloys but tougher than monolithic TiC.

Wear resistance comparison

The wear resistance advantage of TiC over pure Ti is dramatic. Test data from standardized wear tests:

For abrasive wear (sand, slurry, particulates), TiC coating on titanium provides ~50x improvement over uncoated titanium. Bulk TiC ceramic provides ~150x improvement. For erosion (high-velocity particle impact), the advantage is even larger because TiC's high hardness resists the cutting action of impacting particles.

The toughness trade-off

TiC's brittleness is its fundamental limitation. A few key consequences:

Impact resistance

Pure titanium absorbs impact by plastic deformation. A 1 kg steel ball dropped 1 m onto a 10 mm Ti plate deforms the plate (creating a dent) but does not fracture it. The same impact on bulk TiC ceramic causes catastrophic fracture — the plate cracks through, possibly shattering.

Thermal shock

TiC has lower thermal expansion coefficient than Ti, which is good for thermal stress. But its low thermal conductivity (compared to metals) and brittleness make it susceptible to thermal shock failure. Rapid heating or cooling can crack TiC.

Geometry limitations

Bulk TiC is typically used as:

• Thin coatings on tougher substrates (5-15 μm TiC on Ti substrate)

• Cermet (TiC + 10-30% metal binder) — tougher than monolithic TiC

• Bulk ceramic in simple, compression-loaded geometries (inserts, dies)

Bulk TiC plate for structural applications (replacing structural Ti) is uncommon due to the brittleness limitation.

Applications for TiC vs pure Ti

The pattern is clear: TiC wins where wear is the primary concern; pure Ti wins where corrosion, toughness, or fatigue is the primary concern.

TiC coating by CVD

Chemical Vapor Deposition (CVD) is the dominant method for applying TiC coating to titanium or other metal substrates.

CVD process

1. Substrate preparation: surface cleaning, often final polishing for critical applications

2. Loading: substrate placed in CVD reactor (typically a hot-wall reactor)

3. Heating: reactor heated to 900-1,100°C in hydrogen atmosphere

4. Precursor introduction: titanium tetrachloride (TiCl₄) and methane (CH₄) introduced with hydrogen carrier gas

5. Reaction: TiCl₄ + CH₄ + H₂ → TiC + 4 HCl + ... at substrate surface

6. Coating growth: TiC layer grows at rate of 1-3 μm/hour

7. Cooling: controlled cooling to room temperature

8. Post-treatment: optional surface finish (polish, grind)

CVD TiC coating characteristics

CVD process limitations for titanium substrates

The 900-1,100°C process temperature is at or above the beta transus of most titanium alloys (~995°C for Ti-6Al-4V). For Ti substrates, this means:

• Microstructure changes during coating (alpha → beta → alpha on cooling)

• Strength reduction compared to original mill condition

• Possible grain growth (especially in alpha alloys)

For titanium substrates, post-coating heat treatment may be required to restore strength. For pure CP Ti substrates, the strength loss is minimal. For Ti-6Al-4V substrates, post-coating solution treat + age is typical.

TiC cermet

TiC cermet (ceramic-metal composite) addresses TiC's brittleness by adding a metal binder phase. The metal binder absorbs impact, redistributes stress, and provides some ductility while the TiC provides hardness.

Common cermet compositions

More binder = lower hardness but higher toughness. The trade-off is balanced for each application.

Cermet manufacturing

1. Powder preparation: TiC powder (1-10 μm) + binder metal powder mixed

2. Compaction: cold pressing in die or isostatic pressing to form green body

3. Sintering: heated to 1,400-1,600°C in vacuum or inert atmosphere

4. Optional HIP: 1,400-1,500°C, 100 MPa pressure for porosity elimination

5. Finishing: grinding, EDM, polishing to final dimensions

Cermet applications

• Cutting tool inserts for steel machining (competing with WC-Co)

• Wear parts in pumps and valves

• Drawing dies for wire and tube

• Seal rings and bearing sleeves

• Armor applications (TiC-Ni cermet for ballistic protection)

Selection framework

Decision tree for TiC vs pure Ti selection:

1. Is wear the primary design constraint?

• Yes → Continue to question 2

• No → Pure Ti (based on other criteria — corrosion, strength, cost)

2. Is impact loading present?

• Yes (impacts > 5 J) → TiC cermet (with binder) or TiC-coated Ti with thick substrate

• No → Continue to question 3

3. Is corrosion also a requirement?

• Yes → TiC-coated Ti (CVD or PVD) — combines both

• No → Bulk TiC or TiC cermet (no need for corrosion resistance)

4. Is dimensional complexity required?

• Yes (thin walls, sharp corners, complex shape) → Pure Ti or thin TiC coating on Ti substrate

• No (simple, compression-loaded geometry) → Bulk TiC or TiC cermet

5. Is cost the primary driver?

• Yes → Pure Ti (cheaper, acceptable wear life for moderate service)

• No → TiC-coated Ti (longest wear life in corrosion-wear combination service)

A real TiC wear case

Scenario

A chemical plant was experiencing premature failure of pump impellers in a slurry service. The pumps handled a 10% solids slurry of abrasive mineral particles (silica + alumina) in sulfuric acid solution at 60°C. The pump impellers were originally specified as Ti-6Al-4V (Grade 5) for corrosion resistance.

The problem

Initial impeller life was 6-8 weeks before the vanes were worn through by the abrasive slurry. The cost per impeller replacement was approximately $8,000 (part + labor + downtime), and the plant was replacing 8 impellers per year. Total annual cost: $64,000.

The solution

The plant evaluated three options:

1. Continue Ti-6Al-4V: 6-8 week life, $64,000/year

2. Upgrade to solid TiC cermet: Estimated 6-9 month life, $15,000/impeller, $30,000/year

3. TiC CVD coating on Ti-6Al-4V substrate: Estimated 4-6 month life, $4,500/impeller, $12,000/year

The plant selected Option 3 (TiC CVD coating on Ti-6Al-4V). The coating provided:

• Corrosion resistance from the Ti-6Al-4V substrate (where coating was damaged)

• Wear resistance from the 10 μm TiC coating on the surfaces exposed to slurry

• Toughness from the substrate to handle impact and pressure fluctuations

The outcome

After 12 months of operation:

• Zero impeller failures

• Two impellers still in service from the original installation

• Annual impeller cost: $0 (no replacements needed)

• Payback period for the upgrade decision: 2 months

The TiC coating extended impeller life from ~7 weeks to over 12 months — a 7x improvement. The ROI was immediate.

Frequently asked questions

What is titanium carbide (TiC)?

Titanium carbide (TiC) is an extremely hard ceramic compound with the chemical formula TiC and a rock salt (NaCl-type) crystal structure. It has a Vickers hardness of 2,800-3,200 HV — among the hardest of the carbide ceramics. TiC is typically used as a wear-resistant coating or as the hard phase in cermet (ceramic-metal composite) materials. It is most commonly produced by sintering TiC powder with a metal binder (typically nickel or molybdenum) to form a cermet, or deposited as a coating by CVD or PVD on a metal substrate.

How does TiC compare to pure titanium in wear resistance?

Pure titanium has Vickers hardness of 160-350 HV depending on grade and condition — soft compared to most metals and very soft compared to ceramics. TiC has hardness of 2,800-3,200 HV — roughly 10-20x harder than pure titanium. In abrasive wear testing, TiC shows wear rates 50-200x lower than pure titanium. For wear-critical applications (cutting tools, pump components, wear plates), TiC coatings or cermets dramatically extend service life compared to pure titanium. The trade-off is brittleness — TiC has fracture toughness 1/10 to 1/20 of titanium and cannot deform plastically to absorb impact.

How is TiC coating applied to titanium?

TiC coating on titanium is typically applied by Chemical Vapor Deposition (CVD) at 900-1,100°C using titanium tetrachloride (TiCl4) and methane (CH4) as precursors in a hydrogen atmosphere. The high temperature produces a metallurgically bonded TiC layer 5-15 μm thick on the titanium surface. Alternative methods: PVD (Physical Vapor Deposition) at lower temperatures (400-600°C) for thinner coatings (1-5 μm), plasma-assisted CVD for moderate temperatures, and pack cementation for diffusion coating. CVD TiC is the most common for cutting tool applications; PVD TiC is used where lower process temperature is required (e.g., to avoid base metal softening).

Is TiC the same as titanium?

No. Titanium (Ti) is a metallic element. Titanium carbide (TiC) is a ceramic compound of titanium and carbon. They have completely different properties: Ti is ductile metal with hardness ~200-400 HV and fracture toughness ~70-100 MPa.m^0.5. TiC is a brittle ceramic with hardness 2,800-3,200 HV and fracture toughness 3-5 MPa.m^0.5. TiC is used where wear resistance is critical; Ti is used where corrosion, toughness, and formability are needed.

What is TiC cermet?

TiC cermet is a ceramic-metal composite consisting of TiC particles in a metal binder matrix (typically nickel, molybdenum, or Ni-Mo combination). The TiC provides hardness (1,000-1,800 HV depending on binder content) while the metal binder provides toughness (K_IC 8-18 MPa.m^0.5). Common compositions: TiC-15%Ni for cutting tool inserts, TiC-30%(Ni+Mo) for impact-resistant wear parts. Cermet is sintered from powder at 1,400-1,600°C in vacuum, often followed by HIP for full density.

How much does TiC coating cost?

CVD TiC coating typically costs $200-500 per batch for small parts (in a commercial CVD service) or $50-200 per square meter of coated area. PVD TiC coating is similar or slightly higher. For a typical pump impeller (0.05 m² coated area), the CVD coating cost is $10-25 per part. This small incremental cost is easily justified when the coating extends part life by 5-10x in wear service.