HTS Coatings — machining & grinding

Metco 314NS

71% Ni, 4% Cr, 4% Al, 21% BN

  • Plasma

Metco 314NS — the NiCrAl/bentonite abradable in Oerlikon Metco DSMTS-0013.5 — is the compressor-shroud seal you reach for above 500°C, where polymer and BN grades fall apart. The chemistry is worth spelling out because it's commonly mistaken: 71% Ni, 4% Cr, 4% Al, 21% calcined bentonite clay (clad powder), NOT a boron-nitride abradable. Bentonite is an aluminosilicate smectite — stable past 815°C, non-gassing, cheap enough to run thick.

The coating is designed to be soft. Target hardness HR15Y 45-55 (Rockwell superficial, not HV — a Vickers indenter punches through the porous structure); porosity 30-50%; density 2.4-3.2 g/cm³. That friability is the product: the blade tip cuts 314NS on first run-in to set its own clearance, and re-cuts on every thermal transient. A 'durable' 314NS coating is a failed one — the blade is wearing instead of the seal.

At HTS we spray this on combustion flame (Metco 6P-II, neutral, 216 mm standoff, 38-45 g/min) over a Metco 450NS NiAl bond coat, 40-120 mils thick on HPC shroud IDs. Continuous service 650°C (1200°F) per DSMTS; peak excursions to 815°C (1500°F) per Pratt & Whitney PMC 5129-1 and Rolls-Royce EMS 56771.

Pick this when the stage runs hot enough to cook a polymer or BN filler. Send us the engine, stage, and fuel — we'll scope bond coat, hardness window, and thickness to OEM.

Technical data

Hardness
Not specified in HV — abradable coatings are characterized in Rockwell superficial 15Y (HR15Y) because HV indenters are too hard/small for a porous, friable seal. Typical specified range HR15Y 30-60 per OEM callout, with 45-55 HR15Y a common as-sprayed window; HR15Y 40 indicates under-fed/cold spray, HR15Y 70+ indicates over-heated/over-melted deposit. Properly sprayed 314NS is deliberately soft — the blade tip must cut it, not the other way around
Bond strength
1,500-3,500 psi (10-24 MPa) typical per ASTM C633 — low by wear-coating standards and intentionally so. Abradable seals rely on a NiAl or Ni-Cr bond coat (Metco 450NS / 443NS) beneath the 314NS working layer; the 314NS-to-bond-coat adhesion is the design concern, not 314NS-to-substrate
Max service temp
Continuous service to ~1200°F (650°C) per Oerlikon Metco DSMTS-0013.5 long-term rating; short-term/peak excursions cited to 1500°F (815°C) in OEM callouts. Above 500°C (930°F) NiCrAl-bentonite is the reference compressor abradable — below 500°C, softer AlSi-polyester (Metco 601NS) or Ni-graphite (Metco 307NS) are preferred
Max service temp
650°C continuous (DSMTS long-term); 815°C peak / short-term per OEM specs. Higher than BN-based abradables because bentonite (aluminosilicate) is stable well above the ~450°C ceiling where hBN begins to oxidize and release N₂
As-sprayed porosity
30-50% typical (intentionally high porosity) — the whole point of an abradable is a friable, open microstructure the blade tip can remove with minimal energy. Literature on NiCrAl-bentonite reports 46-56% porosity ranges with abradability scaling inversely with hardness and directly with porosity
Typical thickness
40-120 mils (1.0-3.0 mm) typical abradable seal thickness — substantially thicker than most wear coatings because the coating is a sacrificial clearance-control layer that gets cut by the blade tip on first run-in and re-cut on every transient. No DSMTS thickness limit cited by the manufacturer
Density
2.4-3.2 (coating density) — lower than the constituent NiCrAl alloy because of the 30-50% porosity and the low-density bentonite phase (bentonite ~2.6 g/cm³ vs. NiCrAl ~7.9 g/cm³)

Where it earns its keep

  • Reference compressor abradable for service above 500°C — higher temperature capability than AlSi-polyester (Metco 601NS, <325°C), Ni-graphite (Metco 307NS, ~480°C), or BN-based abradables (~450°C ceiling due to hBN oxidation)
  • Bentonite is chemically stable to well beyond 815°C and does not gas off nitrogen the way hBN does — makes 314NS the right call for hotter HPC stages and for applications where off-gassing would contaminate downstream hardware
  • Clearance control improves gas-path efficiency: a 1 mil (25 µm) reduction in blade-tip clearance can return ~0.1-0.5% engine efficiency, and that only holds if the seal is cuttable instead of wearing the blade
  • Long service history — NiCrAl/bentonite has accumulated millions of flight-hours in commercial aviation HPC service since the 1980s
  • Qualified under multiple OEM specs (Pratt & Whitney, Rolls-Royce, GE) simplifying MRO drop-in for overhauled engines
  • Flame-spray friendly — runs cleanly on Metco 6P-II combustion guns (the standard abradable gun) as well as atmospheric plasma, making it accessible to a typical aerospace thermal-spray shop without exotic equipment

Where it doesn't

  • IMPORTANT: the chemistry is 71Ni / 4Cr / 4Al / 21 calcined bentonite (aluminosilicate clay), NOT 21% hexagonal boron nitride. Confusing 314NS with a BN-based abradable is a common spec-sheet error — the performance envelopes are different (BN grades top out near 450°C due to hBN oxidation; 314NS runs to 650-815°C because bentonite is stable)
  • Hardness window is narrow and spray-parameter-sensitive — HR15Y 40 means under-fed (too cold, too fragile); HR15Y 70+ means over-melted (too dense, will eat the blade tip); target HR15Y 45-55 with a neutral flame
  • Requires a qualified NiAl or NiCr bond coat underneath — spraying 314NS directly on substrate is a bond-failure risk
  • Post-spray finish matters: per Gordon England forum discussion, hardness readings require light surface preparation (remove loose 'cornflakes' from the top microns) before HR15Y testing to avoid artificially low readings
  • Moisture-sensitive in storage: bentonite clay absorbs water, so powder must be kept sealed/dry and pre-dried before spraying if exposed to humid shop conditions
  • Abradability is the product spec — do not confuse softness/friability with a defect. A 'durable' 314NS coating is a failed 314NS coating
  • Thermal-salt corrosion concern in marine/offshore HPC duty above ~550°C: recent literature (Corrosion Science, 2024) documents accelerated bentonite-phase attack in salt-laden hot atmospheres; for that duty, consider moving to a CoNiCrAlY-BN or NiCrFeAlBN hybrid with better salt resistance

Typical applications

  • Aerospace gas turbine high-pressure compressor (HPC) shrouds — blade-tip abradable seal on rotor path above stage 3-4 where gas-path temperatures exceed 500°C
  • Industrial gas turbine compressor air seals (land-based power gen — GE Frame 7/9, Siemens SGT, Solar Mars/Titan) in HPC stages
  • Steam turbine labyrinth seals in higher-temperature stages
  • Thermal-barrier filler inside honeycomb seal structures (the honeycomb constrains the friable abradable, bentonite phase provides thermal mass)
  • Aeroderivative HPC shrouds (CF6, LM2500, Trent derivatives) in dirty-fuel or industrial-power service
  • Replacement of degraded compressor shrouds during engine overhaul — the abradable is consumed in service and recoated at MRO intervals

Wear modes addressed

  • Blade-tip rub (design intent) — abradable is intentionally cut by the rotating blade during thermal transients, surges, and gear-cycle excursions
  • Thermal-cycling erosion — open-porosity structure progressively loses bentonite phase over thermal cycles, widening clearance
  • Particle erosion from ingested sand, salt, and combustor particulate at blade-tip speeds
  • Hot-salt thermal corrosion of the bentonite phase in marine/offshore service above ~550°C
  • Oxidation of the NiCrAl matrix at the upper end of the service range (above ~700°C long-term)
  • Spallation at the 314NS-to-bond-coat interface under aggressive thermal cycling

Industries

  • Commercial and military aviation (high-pressure compressor sections of turbofan and turboshaft engines)
  • Industrial power generation (land-based gas turbines — GE Frame/7FA, Siemens SGT, Mitsubishi, Solar Turbines)
  • Oil & gas mechanical drive and power-gen turbines (Solar Mars/Titan/Taurus on FPSO, LNG, pipeline service)
  • Marine and naval gas-turbine propulsion
  • Aero-MRO shops rebuilding worn compressor casings and shroud segments during scheduled overhaul

Substrates

  • Ni-base superalloy compressor casings and shroud segments (Inconel 718, Waspaloy, René 41)
  • Fe-base high-temperature stainless compressor housings (Greek Ascoloy, A-286)
  • Hastelloy X and Haynes 230 sheet for combustion / diffuser shrouds
  • Requires a compatible bond coat — typically Metco 450NS (Ni-5Al) or 443NS (Ni-Cr), 3-5 mils, sprayed directly on grit-blasted substrate before the 314NS working layer

Which process, when?

Combustion flame spray (Metco 6P-II Thermospray gun) is the OEM-preferred process for 314NS — neutral oxygen/acetylene flame, 216 mm standoff, 38-45 g/min feed rate, producing the deliberately porous, friable microstructure that defines a compressor abradable. The lower heat input of combustion spray keeps the bentonite phase from over-melting and preserves the open-porosity network. Atmospheric plasma spray (APS) is also qualified for 314NS but requires careful parameter control — too-hot plasma densifies the coating and drives hardness above spec (HR15Y > 65), defeating the abradable function. HVOF is explicitly not used for abradables — the high-velocity, high-density deposit it produces is the opposite of what a seal coating needs. For an aero-MRO or industrial turbine overhaul shop, the decision is straightforward: use a calibrated 6P-II (or equivalent combustion gun) with OEM-spec parameters, verify HR15Y on a witness coupon, bond-coat with Metco 450NS, lay down 40-120 mils of 314NS on the shroud inner diameter, and let the engine cut its own clearance on first start.

Sources

Data points on this page draw on the following published references. Nothing here replaces a material-specific review by our process engineers — but it's the working starting point.

Material data on this page is provided as a general reference and can vary by lot, substrate, and application. Contact HTS to confirm the right material and specification for your specific part.

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