Chromium nitride CrN

spore: profile
id: chromium-nitride
spore_version: 0.2
family: carbide-nitride-boride-ceramics
name: Chromium nitride
abbreviation: CrN
role: hard, silver-grey nitride coating for tools, sliding parts and piston rings
category: ceramics
type: nitrides
summary: |
  Chromium nitride is a rock-salt ceramic that is very hard, wear-resistant and resistant to corrosion. A coating supplier gives a density of 5.9 g/cm3, a hardness of 22 GPa and a Young's modulus of 200 GPa. A Danish Technological Institute datasheet gives a micro hardness of 1800 HV for three CrN grades and 2100 HV for the denser HiPIMS grade, and a maximum application temperature of 700 °C for most grades (300 °C for the Super Slip grade). The supplier says oxidation in air begins at 700 °C. An Uppsala CVD study (Adams et al., 2026) measured a room-temperature resistivity of 119 mΩ·cm for a rock-salt film about 110 nm thick.
best_for: Hard, wear-resistant PVD coatings on sliding parts, piston rings and cutting or forming tools, where service stays below about 700 °C in air
weakest_at: Oxidation in air from about 700 °C, and micro-cracking or peeling of the coating under load (patent background)
identity:
  formula: CrN
  cas: 24094-93-7
  crystal_system: cubic
  source: pubchem-crn
  where: Formula and CAS from the PubChem record for CID 90362 (Names and Identifiers); cubic crystal system from the BryCoat physical properties table (Crystal Structure row)
tags:
  environments: []
  stresses:
    - extreme-heat
  applications:
    - mechanisms
    - structures
properties:
  - benchmark: density
    value: 5.9
    unit: g/cm3
    scope: material
    conditions:
      basis: stated in a supplier table without temperature or test method
    method: Supplier datasheet value for the PVD coating
    status: ground
    source: brycoat-crn
    where: Physical properties table, Density row
  - benchmark: vickers_hardness
    label: Micro hardness, CrN-LT, CrN-SS and CrN-SD coatings
    value: 1800
    unit: HV
    scope: material
    conditions:
      grades: CrN-LT, CrN-SS and CrN-SD (PVD)
      load: not stated
    method: Micro hardness stated in the datasheet product table
    status: ground
    source: dti-crn
    where: Product variations table, Micro hardness [HV] row (first three columns)
  - benchmark: vickers_hardness
    label: Micro hardness, CrN-HP (HiPIMS) coating
    value: 2100
    unit: HV
    scope: material
    conditions:
      grade: CrN-HP, HiPIMS process
      load: not stated
    method: Micro hardness stated in the datasheet product table
    status: ground
    source: dti-crn
    where: Product variations table, Micro hardness [HV] row, CrN-HP column
  - benchmark: hardness
    label: Hardness quoted by a coating supplier
    value: 22
    unit: GPa
    scope: material
    conditions:
      basis: stated beside a Knoop or Vickers microhardness statement, without load or test method
    method: Supplier datasheet value
    status: ground
    source: brycoat-crn
    where: Physical properties table, Hardness row
  - benchmark: elastic_modulus
    label: Young's modulus, supplier datasheet
    value: 200
    unit: GPa
    scope: material
    conditions:
      basis: stated without temperature, film orientation or test method
    method: Supplier datasheet value
    status: ground
    source: brycoat-crn
    where: Physical properties table, Young's Modulus row
  - benchmark: poissons_ratio
    value: 0.2
    unit: '-'
    scope: material
    conditions:
      basis: stated without test method
    method: Supplier datasheet value
    status: ground
    source: brycoat-crn
    where: Physical properties table, Poisson's Ratio row
  - benchmark: residual_compressive_stress
    label: Residual compressive stress in the supplier coating
    value: 5.5
    unit: GPa
    scope: material
    conditions:
      basis: stated for the supplier coating without deposition details
    method: Supplier datasheet value; a stress in the coating, not a material constant
    status: ground
    source: brycoat-crn
    where: Physical properties table, Residual Compressive Stress row
  - benchmark: melting_point
    value: 1500
    unit: °C
    scope: material
    conditions:
      basis: supplier table; the same row says CrN decomposes to Cr2N at 1050 °C, which then melts at 1500 °C
    method: Supplier statement, no measurement method given
    status: ground
    note: The supplier wording is ambiguous about which phase melts. Wikipedia gives a different melting value for chromium nitride, marked as decomposition; that value is not used here.
    source: brycoat-crn
    where: Physical properties table, Melting Temperature row
  - benchmark: decomposition_temperature
    label: Decomposition of CrN to Cr2N
    value: 1050
    unit: °C
    scope: material
    conditions:
      basis: supplier statement of decomposition to Cr2N
    method: Supplier statement, no method given
    status: ground
    source: brycoat-crn
    where: Physical properties table, Melting Temperature row (decomposition note)
  - benchmark: max_service_temp
    label: Maximum application temperature, CrN-LT, CrN-SD and CrN-HP
    value: 700
    unit: °C
    scope: material
    conditions:
      grades: CrN-LT, CrN-SD and CrN-HP (PVD and HiPIMS)
      atmosphere: not stated in the datasheet; the supplier says oxidation begins at 700 °C in air
    method: Maximum application temperature from the datasheet product table
    status: ground
    source: dti-crn
    where: Product variations table, Application temperature, max. row (first, third and fourth columns)
  - benchmark: max_service_temp
    label: Maximum application temperature, CrN-SS (Super Slip)
    value: 300
    unit: °C
    scope: material
    conditions:
      grade: CrN-SS, PVD plus a second process step (FGC layer)
    method: Maximum application temperature from the datasheet product table
    status: ground
    source: dti-crn
    where: Product variations table, Application temperature, max. row, CrN-SS column
  - benchmark: deposition_temperature
    label: Deposition temperature range, PVD
    value: 200
    value_high: 450
    bound: range
    unit: °C
    scope: material
    conditions:
      process: PVD vacuum deposition; the supplier's standard process is 400 °C
    method: Range stated by a coating supplier
    status: ground
    source: brycoat-crn
    where: Physical properties table, Deposition Temperature row
  - benchmark: friction_coefficient
    label: Friction coefficient against steel, CrN-LT and CrN-SS
    value: 0.5
    unit: '-'
    scope: material
    conditions:
      counter_material: steel
      grades: CrN-LT and CrN-SS
      test: not stated
    method: Friction coefficient from the datasheet product table; a system property, not a material constant
    status: ground
    source: dti-crn
    where: Product variations table, Friction coefficient against steel row (first and second columns)
  - benchmark: friction_coefficient
    label: Typical friction coefficient, CrN against steel (supplier)
    value: 0.4
    unit: '-'
    scope: material
    conditions:
      counter_material: steel
      basis: typical value quoted by the supplier; published range 0.05 to 0.90
    method: Supplier statement; the supplier says friction depends on the whole system
    status: ground
    source: brycoat-crn
    where: Physical properties table, Coefficient of Friction row
  - benchmark: electrical_resistivity
    label: Electrical resistivity, CVD-grown epitaxial CrN film
    value: 119
    unit: mΩ·cm
    scope: material
    conditions:
      film: single-phase epitaxial CrN, about 110 nm, on c-plane sapphire, grown by thermal CVD
      measurement: four-point probe, room temperature
      spread: plus or minus 30 mΩ·cm
    method: Measured by the authors and stated in the results
    status: ground
    source: adams2026
    where: Results, electrical transport paragraph (room-temperature resistivity)
  - benchmark: electrical_resistivity
    label: Electrical resistivity, supplier statement
    value: 300
    bound: lower
    unit: µOhm-cm
    scope: material
    conditions:
      basis: supplier statement; the supplier says literature values range widely
    method: Supplier statement
    status: ground
    source: brycoat-crn
    where: Physical properties table, Electrical Resistivity row
  - benchmark: seebeck_coefficient
    label: Seebeck coefficient, CVD CrN film (n-type)
    value: -36
    unit: µV/K
    scope: material
    conditions:
      film: same CVD CrN film as the resistivity result, about 110 nm
      measurement: ambient conditions
    method: Measured by the authors in the electrical transport section
    status: ground
    source: adams2026
    where: Results, electrical transport paragraph (Seebeck coefficient)
  - benchmark: heat_of_formation
    label: Heat of formation, supplier table
    value: 29800
    unit: Cal/mole
    scope: material
    conditions:
      basis: stated in a supplier table without state or temperature
    method: Supplier datasheet value
    status: ground
    source: brycoat-crn
    where: Physical properties table, Heat of Formation row
corrosion:
  - environment: Static or flowing air at high temperature
    headline: CrN begins to oxidize in air at about 700 °C, and it is more resistant in an inert atmosphere.
    effect: The supplier says the coating begins to oxidize at 700 °C in air and is more resistant in an inert atmosphere. The source gives no exposure time, film thickness or test method.
    rating: moderate
    conditions:
      atmosphere: air
      exposure: no time or test method given
    source: brycoat-crn
    where: Physical properties table, Temperature Resistance row
  - environment: Acids, bases, solvents and caustic solutions
    headline: The supplier calls CrN highly inert to acids, bases, solvents and caustic solutions.
    effect: No test is described. The statement gives no concentrations, times or temperatures, so it is a supplier claim rather than a measured result.
    rating: low
    conditions:
      basis: supplier statement, no test conditions
    source: brycoat-crn
    where: Physical properties table, Chemical Resistance row
  - environment: Passive oxidation after or during deposition of thin films
    headline: Thin CrN films can contain about 4 at.% oxygen after growth.
    effect: In a CVD-grown epitaxial CrN film about 110 nm thick, the authors estimated about 4 at.% oxygen. They compare this with 1 to 4 at.% in high-vacuum PVD films and link it to passive oxidation or the growth environment.
    rating: low
    conditions:
      film: thermal CVD CrN, about 110 nm, on sapphire
      measurement: ToF-ERDA composition analysis, as described by the authors
    source: adams2026
    where: Results, composition paragraph (oxygen content)
risks:
  hazards:
    - text: PubChem lists chromium nitride as not classified under GHS. The record reports that it does not meet GHS hazard criteria for 100% (3 of 3) of company reports.
      ghs: []
      source: pubchem-crn
      where: Safety and Hazards, GHS Classification (CID 90362 record)
    - text: PubChem's Haz-Map summary describes it as an irritant that may cause skin and respiratory sensitization after prolonged contact.
      ghs: []
      source: pubchem-crn
      where: Safety and Hazards, Hazards Summary (CID 90362 record)
  failure_risks:
    - mode: Oxidation of the coating surface in hot air
      trigger: Heating in air above about 700 °C
      consequence: The coating begins to oxidize, which limits its use in air; the supplier says it is more resistant in an inert atmosphere.
      severity: moderate
      source: brycoat-crn
      where: Physical properties table, Temperature Resistance row
    - mode: Micro-cracking and loss of coating pieces under load
      trigger: Sliding or stress on a CrN coating, as described in the patent background for CrN in general
      consequence: The patent says micro-cracks form on the CrN surface, propagate, and cause loss of small pieces of the coating.
      severity: moderate
      source: us7891669
      where: Background section
  side_effects:
    - text: PubChem's chromium nitride record notes that trivalent chromium is not very toxic, but "may be oxidized to hexavalent chromium, a known carcinogen".
      affects: Workers handling heated or oxidized material
      source: pubchem-crn
      where: Toxicity, Health Effects (CID 90362 record)
    - text: Nitrogen vacancies in the CVD film make it behave more like a metal, lowering its resistivity relative to pure stoichiometric CrN, according to the authors.
      affects: Electrical resistivity and thermoelectric behaviour of the film
      source: adams2026
      where: Results, electrical transport paragraph
  handling:
    - text: The PEL is 0.5 mg/m3 and the TLV is 0.003 mg/m3 as Cr(III), for inhalable particulate. Keep powder out of the air.
      source: pubchem-crn
      where: Exposure Control and Personal Protection (CID 90362 record)
    - text: PubChem gives no handling or storage advice for chromium nitride in the sections read in this run. Check the supplier's safety data sheet for powder, target or coating stock.
      source: pubchem-crn
      where: Safety and Hazards (CID 90362 record)
  mitigations:
    - text: Deposit at 400 °C, the supplier's standard process, which the supplier says gives the toughest coating.
      source: brycoat-crn
      where: Physical properties table, Deposition Temperature row
    - text: The datasheet recommends the dense CrN-SD and HiPIMS CrN-HP grades for heavily loaded work; CrN-HP is described for critical applications in corrosive environments.
      source: dti-crn
      where: Product descriptions (CrN-SD and CrN-HP paragraphs)
uses:
  - application: mechanisms
    device: Piston rings for internal combustion engines (PVD coating on the sliding surface)
    example: The patent claims a piston ring whose sliding surface carries a chromium nitride coating deposited by physical vapor deposition, and it says the coating gives high wear resistance for this component.
    source: us7891669
    where: Claims; Background
  - application: mechanisms
    device: Wear parts, machinery components and injection moulds
    example: The Danish Technological Institute Tribology Centre says CrN suits tools, wear parts and machinery components, and that the coating does not need grinding after it is applied.
    source: dti-crn
    where: Opening section (CrN product family)
  - application: structures
    device: Cutting and forming tools (metal forming)
    example: The datasheet recommends CrN in cutting and forming to prevent soft metals such as aluminium, copper and zinc alloys from sticking.
    source: dti-crn
    where: Cutting and forming of metal paragraph
supply:
  - subject: Chromium (the metal in CrN; nitrogen is not covered by this source)
    producers:
      - country: South Africa
        share_percent: 45.1
        year: 2025
      - country: Turkey
        share_percent: 17.6
        year: 2025
      - country: Kazakhstan
        share_percent: 13.7
        year: 2025
      - country: India
        share_percent: 5.9
        year: 2025
    critical_lists:
      - list: 'USGS 2025 List of Critical Minerals (page prints: Chromium, used in stainless steel)'
        listed: true
    recycling: 'USGS: recycled chromium in reported stainless-steel scrap receipts accounted for 21% of US apparent consumption in 2025.'
    substitutes:
      - 'USGS: chromium has no substitute in stainless steel or in superalloys, the two leading end uses.'
    source: usgs-mcs2026-chromium
    where: 'World Mine Production and Reserves table, 2025e (chromium content in thousand t; world total 51,000 rounded; shares calculated by Space Mushroom against that total); Salient Statistics and Recycling; Substitutes. Critical list: USGS 2025 critical minerals page (usgs-crit2025).'
gaps:
  - 'Thermal conductivity not found: the supplier table has a placeholder (''xxx'') and the open CVD paper does not report it.'
  - 'Coefficient of thermal expansion not found: the supplier table has a placeholder (''xxx'').'
  - 'Band gap not found: the supplier table has a placeholder (''xxx'').'
  - Density is a supplier value; no open paper gave a density for CrN in this run. The search snippet for a theoretical density came from a patent that was not opened and is not used.
  - Oxidation onset in air measured by thermogravimetry for dense CrN not found in an open source; the only onset value is the supplier's 700 °C. The MDPI pages returned access denied.
  - Space exposure, vacuum, atomic oxygen and radiation results for CrN not found in this run.
  - Piston-ring field life and fatigue data not found in an open paper; the piston-ring use rests on a patent's claims and background.
  - The Wikipedia melting value for chromium nitride is not used; Wikipedia is limited here to composition and history. The supplier's melting value is ambiguous about the decomposition step.
  - 'Friction: the datasheet prints 0,3 (decimal comma) for CrN-SD and CrN-HP; those two values are left out to avoid decimal commas.'
  - Hardness method and load are not stated for the supplier's 22 GPa; the datasheet micro-hardness load is also not stated.
  - 'Property names not in spores/property-canon.yaml: vickers_hardness, residual_compressive_stress, decomposition_temperature, deposition_temperature, seebeck_coefficient, heat_of_formation, friction_coefficient.'
  - Nitrogen supply and abundance not sourced in this run; supply covers chromium only.
  - 'EU critical raw materials list: the Commission page read in this run does not name chromium, and the annex list was not opened, so no EU listing is recorded.'
  - Atomic weights of chromium and nitrogen were not read in a fetched page, so the recipe parts have no atomic_weight.
  - Cr3C2 (chromium carbide) is mentioned in the story only; no values for it are given.
  - No media images were added.
sources:
  pubchem-crn:
    title: 'PubChem compound record CID 90362, chromium nitride (CrN): names, GHS classification, toxicity and food-contact entries'
    id: CID 90362; CAS 24094-93-7
    url: https://pubchem.ncbi.nlm.nih.gov/compound/90362
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-mcs2026-chromium:
    title: Mineral Commodity Summaries 2026, Chromium
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS, final list of 60 minerals)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  brycoat-crn:
    title: BryCoat, Chromium Nitride (CrN) PVD Coating Physical Properties (supplier datasheet page)
    url: https://brycoat.com/surface-engineering/brycoat-pvd-coating-solutions/chromium-nitride-crn-pvd-coating/chromium-nitride-crn-pvd-coating/
    kind: web
    license: supplier page (cited, not reproduced)
  dti-crn:
    title: 'CrN product family: Chromium Nitride datasheet (Danish Technological Institute, Tribology Centre)'
    id: DTI Tribology Centre
    url: https://www.dti.dk/_/media/88696_CrN_EN.pdf
    kind: datasheet
    license: datasheet (cited, not reproduced)
  adams2026:
    title: Chemical Vapor Deposition of Epitaxial Chromium Nitride Thin Films (Adams, Baserga, Souqui, Sadek, von Fieandt, Eklund)
    id: arXiv:2603.04154
    url: https://arxiv.org/pdf/2603.04154
    year: 2026
    kind: paper
    license: arXiv preprint (author license as listed on arXiv)
  us7891669:
    title: Piston ring with chromium nitride coating for internal combustion engines (US patent 7891669)
    url: https://patents.google.com/patent/US7891669
    kind: web
    license: patent document (cited, not reproduced)
  wikipedia-crn:
    title: Wikipedia, Chromium nitride (composition, rock-salt structure and history only)
    url: https://en.wikipedia.org/wiki/Chromium_nitride
    kind: web
    license: CC BY-SA
documents:
  - title: 'PubChem: Chromium nitride (CID 90362), GHS and toxicity sections'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/90362
    year: 2026
  - title: Mineral Commodity Summaries 2026, Chromium
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
  - title: CrN product family datasheet (Danish Technological Institute, Tribology Centre)
    type: datasheet
    url: https://www.dti.dk/_/media/88696_CrN_EN.pdf
  - title: Chemical Vapor Deposition of Epitaxial Chromium Nitride Thin Films (arXiv:2603.04154)
    type: paper
    url: https://arxiv.org/pdf/2603.04154
    year: 2026
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 18
  unreachable: 2
  caveats: 3
  note: 'Written by an AI assistant on 2026-10-26 from pages read in this run. Unreachable: MDPI Materials 17(17) 4328 (access denied) and the Justia patent page (Cloudflare check). Most values are supplier or datasheet figures; the resistivity and Seebeck values come from an open paper.'
story:
  recipe:
    line: Chromium nitride is one chromium atom bonded to one nitrogen atom in a rock-salt crystal. The nitrogen sits in the octahedral holes of the chromium lattice, so the compound is an interstitial nitride rather than a chromium(III) salt. Thin films are grown mainly by physical vapour deposition, by cathodic arc and magnetron sputtering, and by thermal CVD in a 2026 Uppsala study.
    parts:
      - name: Chromium
        symbol: Cr
        role: The metal that gives the coating its hardness and wear resistance.
      - name: Nitrogen
        symbol: 'N'
        role: Occupies the octahedral holes of the chromium lattice, giving the rock-salt structure.
  risk_groups:
    - title: For people
      level: 0
      verdict: Not classified hazardous in PubChem reports
      lead: PubChem lists chromium nitride as not classified under GHS in its company reports. An older summary describes it as an irritant that may cause sensitization after prolonged contact.
      points:
        - label: The notifications
          line: PubChem records 3 of 3 company reports as not meeting GHS hazard criteria, with no hazard statements.
        - label: Exposure limits
          line: The PEL is 0.5 mg/m3 and the TLV is 0.003 mg/m3 as Cr(III), for inhalable particulate.
    - title: If the coating is heated in air
      lead: These results come from supplier statements and laboratory work, not from field incidents.
      points:
        - label: Oxidation
          line: The coating begins to oxidize at 700 °C in air, according to the supplier. It is more resistant in an inert atmosphere.
    - title: Handling
      points:
        - label: Dust
          line: PubChem gives no handling advice for chromium nitride. Check the supplier's safety data sheet for powder or target stock.
  why: Chromium nitride (CrN) is a hard ceramic coating with a rock-salt structure. It is silver-grey and is applied as a thin film, usually by PVD. Its hardness, wear resistance and resistance to corrosion explain its use on tools and sliding parts. Its main limit is oxidation that starts at about 700 °C in air. CrN is related to dichromium nitride (Cr2N), which the supplier says CrN decomposes to, and to chromium carbide (Cr3C2), a different chromium ceramic that is listed beside CrN in the chromium compounds table. This profile gives no carbide values.
  uses:
    - where: Piston rings
      line: A patent describes a piston ring for combustion engines with a CrN coating deposited by physical vapour deposition on its sliding surface.
    - where: Wear parts and tools
      line: The Danish Technological Institute says CrN suits tools, wear parts and machinery components. It recommends CrN for cutting and forming, where it stops soft metals such as aluminium and copper from sticking.
    - where: Injection moulds
      line: The same datasheet says the CrN-SD and CrN-HP grades have superior release properties against a variety of plastic types.
  can_do:
    - label: Hardness
      benchmark: vickers_hardness
      value: 1800 HV
      line: The datasheet gives a micro hardness of 1800 HV for three CrN grades and 2100 HV for the denser HiPIMS grade. A coating supplier gives 22 GPa.
    - label: Stiffness
      benchmark: elastic_modulus
      value: 200 GPa
      line: A coating supplier gives a Young's modulus of 200 GPa and a Poisson's ratio of 0.2, without a test method.
    - label: Melting and decomposition
      benchmark: melting_point
      value: 1500 °C
      line: A supplier table gives a melting temperature of 1500 °C and says CrN decomposes to Cr2N at 1050 °C. The source does not say how these were measured.
    - label: Air limit
      benchmark: max_service_temp
      value: 700 °C
      line: The datasheet gives a maximum application temperature of 700 °C for three grades and 300 °C for the Super Slip grade.
    - label: Electrical resistivity
      benchmark: electrical_resistivity
      value: 119 mΩ·cm
      line: A CVD film about 110 nm thick measured 119 mΩ·cm at room temperature, with a spread of plus or minus 30 mΩ·cm.
  compare: Chromium nitride sits in the hard-ceramic group. Its micro hardness of 1800 to 2100 HV in the datasheet is high, but it begins to oxidize in air at about 700 °C, which is its main limit. The supplier figure of 700 °C is higher than the oxidation onset of titanium nitride in this collection, but the two figures come from different sources and tests, so they are not directly comparable. CrN's advantage is its use on sliding and forming parts, not its performance in hot air.
  compare_rows:
    - label: Vickers hardness (datasheet)
      benchmark: vickers_hardness
    - label: Melting point (supplier)
      benchmark: melting_point
    - label: Maximum application temperature
      benchmark: max_service_temp
  handling:
    - The PEL is 0.5 mg/m3 and the TLV is 0.003 mg/m3 as Cr(III). Keep powder out of the air.
    - Keep heating in air below about 700 °C if the coating must stay CrN.
    - PubChem warns that trivalent chromium may be oxidized to hexavalent chromium, a known carcinogen, so avoid heating that oxidizes the material.
    - Check the supplier's safety data sheet for powder, target or coating stock, since PubChem gives no handling advice.
  good_for:
    - Hardness and wear. The datasheet gives 1800 HV for three grades and 2100 HV for the HiPIMS grade.
    - Release from plastic moulds. The datasheet says CrN-SD and CrN-HP release plastics well.
    - Piston rings. A patent describes CrN as giving high wear resistance for this component.
  watch_out:
    - Oxidation in air. The supplier says oxidation starts at 700 °C in air.
    - Micro-cracks and peeling. A patent background says micro-cracks on CrN can grow and lose small pieces of coating.
    - Friction depends on the system. The supplier gives 0.4 typical against steel, and the published range runs from 0.05 to 0.90.
    - Resistivity varies widely. The supplier gives more than 300 µOhm-cm, while one CVD film measured 119 mΩ·cm.
  verdict: Chromium nitride is a hard, wear-resistant coating for tools, sliding parts and piston rings. It should not be used in hot air above about 700 °C, and micro-cracking under load needs a test on the actual part before use.