HTS Coatings — machining & grinding

MCrAlY (Cobalt-base)

32% Ni, 21% Cr, 8% Al, 0.5% Y, Co-balance

  • Plasma
  • HVOF

MCrAlY Cobalt-base — the CoNiCrAlY / NiCoCrAlY family typified by Oerlikon Metco Amdry 995 and Höganäs AMPERIT 415 — is the coating you reach for when sulfur is in the fuel. Composition is deliberate: Co balance, 32% Ni, 21% Cr, 8% Al, 0.5% Y. The high chromium carries the Type II hot-corrosion load (Na₂SO₄ salt attack at 600-800°C, the killer on offshore and heavy-fuel land turbines). Aluminum grows a dense, adherent Al₂O₃ scale for Type I sulfidation resistance up to 950°C. Yttrium anchors that scale against thermal-cycling spallation.

At HTS we spray this alloy two ways. APS at 5-10 mils is the economical bond coat under YSZ top coats on industrial gas turbine blades, vanes, and combustion liners — the Siemens / GE / Solar standard. HVOF at 3-6 mils goes down as a standalone hot-corrosion barrier on marine and offshore hot-section parts, or on restoration work. Expect 450-550 HV HVOF, 48-75 MPa bond strength, and 850-950°C continuous service (up to 1050°C shielded under YSZ).

Pick this when sulfur is in the fuel. For clean natural-gas turbines, Ni-MCrAlY is cheaper and just as good. Running dirty distillate, sour gas, or salt-air duty? Send us the part and the fuel spec — we'll scope the bond coat, post-spray vacuum anneal, and thickness to OEM.

Technical data

Hardness
350-500 HV as-sprayed APS (bond-coat condition); 450-550 HV HVOF; heat-treated/vacuum-annealed deposits densify and harden modestly. Literature cites 486 HV HVOF vs. 422 HV APS for MCrAlY-class powders on the same substrate
Bond strength
7,000-11,000 psi (48-75 MPa) HVOF per ASTM C633; APS typically 4,500-7,000 psi (31-48 MPa); VPS/LPPS routinely exceeds HVOF due to oxide-free splat contact. Used as the adhesion anchor for YSZ top coats, so bond quality is the design driver
Max service temp
~1560-1740°F continuous (850-950°C) for standalone hot-corrosion duty; ~1920°F (1050°C) as a TBC bond coat beneath YSZ, where the ceramic top coat shields the metallic from peak gas-path temperature
Max service temp
850-950°C standalone; up to ~1050°C as YSZ bond coat (Oerlikon Metco Amdry 995 series rating)
As-sprayed porosity
HVOF 0.5-2.0% (typ. 1.5%); APS 3-8%; VPS/LPPS <1%. Porosity is deliberately minimized in bond-coat service — through-porosity lets oxygen reach the bond-coat/substrate interface and shortens TBC life
Typical thickness
3-15 mils (75-375 µm) typical — 3-6 mils standalone hot-corrosion barrier, 5-10 mils as YSZ bond coat, up to 15 mils for rebuild/restoration of worn hot-section parts
Density
7.7-7.9 (Co-base MCrAlY deposits)

Where it earns its keep

  • Best-in-class Type II hot-corrosion resistance among MCrAlY family — the 21% Cr + 32% Ni + Co balance is tuned to resist Na₂SO₄ salt attack that eats lower-Cr bond coats in sulfur fuels
  • Strong Type I sulfidation resistance from high Al (8%) forming adherent Al₂O₃ scale, anchored by yttrium against spallation
  • Qualified bond coat under YSZ for all major industrial gas turbine OEMs (Siemens, GE, Solar, Mitsubishi, Rolls-Royce) — proven in 25+ years of field service
  • Balanced ductility for thermal-cycling duty — CTE matches superalloy substrates better than pure Ni-MCrAlY, reducing TBC spallation
  • Multiple spray-process compatibility: HVOF for dense standalone barriers, APS for thicker bond coats, VPS/LPPS for oxide-free aerospace-grade deposits
  • Vacuum-anneal post-treatment (typ. 1080°C / 4 hr / argon or vacuum) homogenizes the microstructure and seals porosity for extended TBC life

Where it doesn't

  • Pick this when sulfur is in the fuel — for clean natural-gas turbines where oxidation (not hot corrosion) is the design driver, Ni-MCrAlY is simpler, cheaper, and just as durable
  • Cobalt raw-material cost is materially higher than nickel; Co-base MCrAlY powders run 20-40% more per pound than Ni-MCrAlY equivalents
  • Bond coat for YSZ typically requires post-spray vacuum or argon-atmosphere anneal per OEM spec — not a spray-and-ship operation
  • HVOF gives the densest deposit but introduces some oxide stringers; VPS/LPPS produces cleaner splats at materially higher process cost
  • Thickness must be controlled within OEM spec — too thin and the TGO consumes the Al reservoir fast; too thick and thermal-cycling stress spalls the YSZ

Typical applications

  • Bond coat beneath YSZ thermal barrier coatings on land-based industrial gas turbine hot-section parts — blades, vanes, combustion liners, transition ducts
  • Standalone oxidation/hot-corrosion coating on first- and second-stage turbine airfoils in sulfur-burning engines
  • Marine and offshore gas turbine hot sections exposed to salt ingestion + sulfur-containing fuels (FPSO, platform power gen, naval propulsion)
  • Combustion chamber liners and transition pieces in industrial turbines burning sour natural gas, syngas, or heavy distillate
  • Restoration/rebuild of worn superalloy turbine parts prior to YSZ reapplication
  • Aeroderivative turbine hot-section parts in dirty-fuel or coastal service where chlorides + sulfates drive Type II hot corrosion
  • Power-gen turbines running on sour or heavy fuel oils with unburned sulfur (legacy heavy-duty frame units)

Wear modes addressed

  • Type II hot corrosion (Na₂SO₄ salt attack, 600-800°C) — the primary design driver for choosing Co-base over Ni-base MCrAlY
  • Type I hot corrosion / sulfidation (800-950°C molten-sulfate attack)
  • High-temperature oxidation (Al₂O₃/Cr₂O₃ scale formation and spallation)
  • Thermal fatigue and TGO (thermally grown oxide) cracking at the bond-coat/YSZ interface
  • Interdiffusion with the superalloy substrate (topologically close-packed phase formation with long service)
  • Erosion by ingested salt, sand, and combustion-particulate in gas-path duty

Industries

  • Industrial power generation (land-based gas turbines — Siemens SGT, GE Frame/7FA, Mitsubishi)
  • Oil & gas (mechanical-drive and power-gen turbines on offshore platforms, FPSOs, LNG plants — Solar Turbines, GE LM series)
  • Marine propulsion (naval and commercial gas turbines)
  • Aerospace / aeroderivative (CF6, LM2500, Trent derivatives in dirty-fuel service)
  • Petrochemical and refining (mechanical-drive turbines on sour-gas compression)

Substrates

  • Ni-base superalloys (IN-738, IN-792, CMSX-4, René N5, Mar-M 247) — primary turbine blade/vane parent metal
  • Co-base superalloys (X-40, MAR-M 509) for vanes
  • Hastelloy X and Haynes 230 combustion-liner sheet
  • Precipitation-hardened stainless for lower-temperature turbine hardware

Which process, when?

HVOF delivers the densest as-sprayed MCrAlY deposit — 0.5-2% porosity, 48-75 MPa bond strength, and 450-550 HV hardness — which is the right call for standalone hot-corrosion barriers in marine/offshore turbine hot sections. APS (Atmospheric Plasma Spray) is the workhorse for bond-coat-under-YSZ: 3-8% porosity is acceptable because the ceramic top coat carries the gas-path duty, and APS lays down the 5-10 mil bond-coat thickness economically at scale. VPS/LPPS (Vacuum/Low-Pressure Plasma Spray) produces the cleanest, oxide-free deposits with <1% porosity and bond strengths that can exceed 90 MPa — aerospace-grade and the OEM-preferred process for first-stage turbine blade bond coats, but materially more expensive. Cold spray is emerging for heat-sensitive repair where you want zero thermal input and minimal oxidation during deposition. For an industrial gas turbine shop, the decision tree is: HVOF for standalone hot-corrosion duty, APS for YSZ bond coat in land-based service, VPS/LPPS when the OEM spec demands it.

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.

Thinking about MCrAlY (Cobalt-base) for a part?

Send us the spec or a photo. We'll tell you whether this fits, or point you at a better material for the job.

Ask about this material