HTS Coatings — machining & grinding

Nickel Chrome

17.5% Cr, 5.5% Al, 2.5% Co, 0.5% Y₂O₃, Ni-balance

  • Arc
  • Flame

Nickel Chrome — a NiCrAlY bond coat with cobalt and a trace of yttria — is the coating that makes the rest of the stack work. It's intentionally soft at 200-300 HV and isn't supposed to win a fight with a rock. Its job is to bond to steel, grow a tenacious alumina/chromia scale at temperature, and give the ceramic topcoat or wear overlay above it a partner that expands and contracts on the same schedule as the steel below.

At HTS we apply Nickel Chrome most often by twin-wire arc spray — fast, cost-effective, and the right tool for furnace panels, stack interiors, ductwork, and large mill housings where you need honest coverage at an honest price. For roll work, shaft repair, and anything going under a ceramic YSZ or Al2O3 topcoat, we shift to flame-spray powder or plasma for a denser, lower-oxide bond layer. Typical thickness is 3-8 mils as a bond coat; 15-30 mils as a standalone mild high-temp corrosion coat. Service temperature is comfortable to ~950°C and the yttria pins the scale so it doesn't spall on the first thermal cycle.

Got a thermal barrier stack to build or a furnace wall scaling itself apart? Send us the drawing — we'll scope the right bond coat for the duty above it.

Technical data

Hardness
200-300 HV typical arc-sprayed NiCrAl(Y) deposits; flame-spray powder deposits run slightly softer; published HVOF/plasma reference values reach 370-490 HV after heat treatment — this is intentionally soft because it is meant to be the bond coat, not the wear coat
Bond strength
Tensile adhesion 4,900-7,900 psi (34-54 MPa) on grit-blasted steel — arc-spray deposits near the low end, flame/plasma near the top end; post-treatment heat cycles can push adhesion above 9,000 psi (62 MPa)
Max service temp
~1740-1800°F (oxidation limit at which the protective Al2O3 / Cr2O3 scale remains stable)
Max service temp
~950-980°C continuous; short excursions to ~1050°C acceptable; Y2O3 addition pins the scale and delays spallation through repeated thermal cycling
As-sprayed porosity
Arc-spray typical 3-8%; flame-spray powder 2-6%; sprayed-to-parameter bond coats generally stay under 5% to keep the alumina-scale pathway intact
Typical thickness
3-8 mils (75-200 microns) as a bond coat under ceramic or wear overlays; 15-30 mils as a standalone mild high-temperature corrosion coat on stacks, ducts, and furnace panels

Where it earns its keep

  • Proven bond-coat chemistry at the foundation of every reputable ceramic thermal-spray stack — YSZ, alumina, and chromia all sit happier on NiCrAlY
  • Self-forming, self-healing Al2O3 / Cr2O3 scale at temperature — the yttria pins the scale and resists spallation across thermal cycles
  • Excellent adherence to grit-blasted carbon and alloy steels; typical tensile adhesion 34-54 MPa is enough to carry a 20-40 mil ceramic or wear topcoat
  • Arc-spray application is fast and cost-effective for large coverage areas — ducts, hearths, furnace panels, stack interiors get protected without the HVOF price tag
  • Ductile enough (Co-modified, <300 HV) to accommodate CTE mismatch between steel substrate and ceramic topcoat without debonding

Where it doesn't

  • Soft — 200-300 HV is NOT a wear coating on its own. If the duty is abrasion, gouging, or hard-particle erosion, pick WC-Co, Stellite, or a Ni-chrome carbide overlay on top of this bond coat
  • Arc-spray deposits run more porous (3-8%) and more oxide-stringered than HVOF or vacuum-plasma equivalents — fine for duct and furnace service, not fine for flight-critical aerospace bond coats
  • For aerospace bond-coat service (turbine blades, vanes, combustor liners on new-build engines), spec proper Amdry 962 / Amdry 963 NiCrAlY applied by HVOF or LPPS — arc-spray NiCrAl is a repair-tier and industrial-tier bond coat, not an OEM aerospace one
  • Yttria content is small but essential — without Y2O3 the alumina scale rumples and spalls within the first few thermal cycles and the TBC stack fails early
  • Thickness discipline matters — under a ceramic topcoat, keep the bond coat in the 3-8 mil window; thicker bond coats generate their own CTE stress and reduce stack life

Typical applications

  • Bond coat under ceramic topcoats (8%Y2O3-stabilized zirconia YSZ, Al2O3, Cr2O3) in thermal barrier and wear stacks
  • Bond coat under thick HVOF or twin-wire-arc wear overlays on steel shafts, pistons, and rolls
  • Standalone corrosion/oxidation coat for mild high-temperature service on carbon-steel substrates
  • Hot-roll and anneal-line mill rolls (sub-layer under YSZ or cermet topcoats in the hot zone)
  • Industrial furnace hardware — hearth plates, radiant tubes, burner tips, charge-car components
  • Chimney, stack, and duct interiors — flue gas and condensate zones where mild scaling protection is wanted over cost-effective coverage areas
  • Boiler fan housings, fire-tube repairs, and economizer casings
  • Salvage and dimensional restoration of worn nickel-alloy and stainless substrates before topcoating
  • Repair layer on gas-turbine and industrial-turbine hot-section components (combustor liners, transition pieces)

Wear modes addressed

  • High-temperature oxidation (primary duty — the alumina/chromia scale is the working surface)
  • Thermal cycling and TGO (thermally grown oxide) spallation at the bond/ceramic interface
  • Mild flue-gas and condensate-acid corrosion in stack and duct service
  • Sulfidation and hot corrosion in fuel-fired furnace atmospheres (Y2O3 helps but NiCrAlY is not a Type-I hot-corrosion coating)
  • Adhesion/delamination stress relief between dissimilar CTEs (metal substrate vs ceramic topcoat)

Industries

  • Steel and iron making (hot-roll mills, anneal lines, galvanizing lines)
  • Industrial heat processing (furnaces, kilns, heat-treat equipment)
  • Power generation (boiler casings, stack interiors, industrial turbines)
  • Pulp and paper (fan housings, duct and stack protection)
  • Chemical process (mild flue and exhaust service)
  • Aerospace and industrial turbine repair (as repair-tier bond coat; see considerations for flight-critical work)

Substrates

  • Carbon and low-alloy steel (A36, 4140, 4340) — the primary arc-spray substrate
  • Stainless steels (304L, 316L, 410, 409 for exhaust and stack work)
  • Cast iron (furnace components, charge hardware)
  • Nickel-base superalloys (Inconel 625, 718, Hastelloy X) for turbine and furnace repair
  • Weldable tool steels and cast steels in salvage/restoration work

Which process, when?

Twin-wire arc spray is the production workhorse for NiCrAl bond coats on large, forgiving geometries — furnace panels, ducts, stack interiors, mill housings. Deposits run 3-8% porosity with typical adhesion in the 34-45 MPa range — plenty for a bond coat, economical on coverage. Flame-spray powder (combustion powder process) gives slightly denser deposits (2-6% porosity) and is the right call on smaller shafts, rolls, and repair parts where a wire feedstock is awkward. Plasma spray (APS) produces denser (2-5%) deposits with tighter oxide control and is the default for ceramic-stack bond coats on rolls and turbine-grade repair parts. HVOF / LPPS NiCrAlY (Amdry 962-class) is the aerospace and OEM-turbine answer — <1% porosity, 50+ MPa adhesion, lowest oxide content — but comes at a price premium that doesn't pencil on a furnace wall. Pick arc-spray for coverage and cost, flame/plasma for shaft and roll work, HVOF when the mission is a flight-qualified bond coat.

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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