90 MXC
23% Cr, 4% Mo, 2% B, 9% Ni, 1% Si, 1% Mn, Fe-balance
- Arc
90 MXC is the iron-based amorphous answer to wear-plus-corrosion — a cored wire engineered to form a glass-like metallic structure as it hits the substrate off a twin-wire arc torch. The chemistry (23% Cr, 4% Mo, 2.3% B, 9% Ni, Fe balance) is a classic glass-forming recipe: metalloid additions (B, Si) and refractory metals (Cr, Mo) frustrate crystallization during the arc-spray quench, locking atoms into an amorphous matrix with embedded nanocrystalline phases.
The reason that structure matters: amorphous coatings have no grain boundaries. Grain boundaries are where corrosion pits start, where fatigue cracks nucleate, and where abrasive particles find soft pockets to scour. Eliminate them and the coating resists slurry erosion, chloride pitting, and cavitation implosion at once — exactly the combination hydroelectric runners, coal-boiler waterwalls, and seawater slurry pumps fight every day.
HTS runs 90 MXC (Polymet PMET 270) as a twin-wire arc feedstock at 20-30 mils for waterwall armor and slurry-pump refurbishment, thinner for hard-chrome replacement on hydraulic rods. At 45-50 HRC with 800-1,100 HV hard phases, 1,600°F service, and 50+ MPa bond strength, it's the cost-effective middle ground between carbon-steel cladding and HVOF tungsten carbide.
Got a hydro runner, boiler section, or slurry pump due for overhaul? Send a photo and erosion map — we'll scope the spray pattern and quote it back.
Technical data
- Hardness
- ~800-1,100 HV typical for the iron-based amorphous/nanocrystalline family; peer Fe-based amorphous TWAS coatings report 807 HV0.1 and HVOF variants reach 898 ± 67 HV as-sprayed climbing to ~1,245 HV after 650°C heat treatment; boride hard phases within the amorphous matrix reach ~23.85 GPa
- Hardness (HRC)
- 45-50 HRC as-sprayed (twin-wire arc); Polymet PMET 270 datasheet lists Rockwell Hardness 45-50 C for the 1/16 in (1.6 mm) arc-spray wire
- Bond strength
- ~7,500 psi (52 MPa) tensile for comparable FeNiCrBSiNbW twin-wire arc amorphous coatings; HVAF/HVOF variants of the same chemistry family report >10,000 psi (>70 MPa) at 0.020 in thickness
- Max service temp
- 1,600°F service environment per Polymet PMET 270 datasheet
- Max service temp
- ~870°C continuous service per Polymet; amorphous-to-nanocrystalline transition begins around 650°C which actually raises hardness rather than degrading it
- As-sprayed porosity
- ~1-3% typical twin-wire arc; 1.2-1.8% reported for peer Fe-based amorphous TWAS coatings; HVAF/HVOF variants of same chemistry reach <1%
- Typical thickness
- 20-30 mils (0.5-0.75 mm) typical arc-spray service thickness for boiler waterwall and slurry protection per Polymet field data; up to 40 mils (1 mm) achievable
- Density
- ~7.5-7.6 (Fe-base with Cr/Mo/Ni/B)
Where it earns its keep
- Glass-forming iron chemistry — the Cr/Mo/B/Si/Ni recipe suppresses crystallization during arc-spray quenching, yielding a partially amorphous matrix with no grain boundaries for corrosion or cracks to travel along
- Combined wear + corrosion + cavitation in one alloy — the typical trade-off between hardness and corrosion resistance is broken by the amorphous structure
- Iron-base cost point — roughly a quarter to a third the cost of nickel-base Colmonoy or cobalt-base Stellite for equivalent coverage
- 9% Ni addition vs. the sister 95 MXC grade — meaningfully better pitting and crevice corrosion performance in seawater and chloride-bearing slurries
- Amorphous-to-nanocrystalline transition at ~650°C actually raises hardness in service (reports of 898 HV climbing to 1,245 HV) — the coating gets better under heat, not worse
- Arc-spray deposition is fast and portable — suits on-site repair of large hydro runners, waterwall panels, and pump bodies where HVOF is impractical
- High chrome-like finish achievable by grinding and lapping — legitimate hard-chrome plating replacement for hydraulic rods
Where it doesn't
- Partially amorphous, not fully amorphous — arc spray's cooling rate (~10^4 K/s) is slower than HVAF/HVOF, so amorphous fraction typically 40-70% vs. 80%+ in detonation or HVAF variants
- Fatigue-sensitive — amorphous coatings are not recommended for high-cycle rotating fatigue service; the coating absorbs energy but doesn't deform ductily
- Bond strength ~7,500 psi (52 MPa) is respectable for arc spray but lower than HVOF/HVAF (>10,000 psi) — thick build-ups need interlayer or process review
- Thickness ceiling ~40 mils before residual stress causes delamination — not a deep build-up alloy
- Surface finish as-sprayed is rough (~500 µin Ra); finishing to sub-10 Ra requires diamond or silicon-carbide grinding
- Arc-spray overspray capture is essential — Fe-Cr-Mo-B dust is a respiratory hazard and requires proper PPE and booth exhaust
Typical applications
- Hydroelectric turbine runners, wicket gates, and draft tubes (Francis, Kaplan, Pelton) — combined cavitation + silt erosion
- Waterwall tubes in pulverized-coal, circulating fluidized bed (CFB), and black liquor recovery boilers (BLRB)
- Slurry pump impellers, casings, shrouds, and wear rings
- Marine components exposed to seawater corrosion plus abrasion (shafts, rudder pintles, pump sleeves)
- Hydraulic cylinders and cylinder rods — hard-chrome replacement with high chrome-like finish
- Anti-skid surfacing for walkways and deck plates
- Mining and mineral-processing chute liners, centrifuge scrolls, dredge pump components
- Coal pulverizer yokes and journals; ash handling pipe elbows
- Pulp and paper screening and refining surfaces
- Concrete pump pistons and delivery cylinder ID protection
Wear modes addressed
- Cavitation erosion — amorphous structure absorbs implosion energy without grain-boundary crack propagation
- Slurry and silt erosion — embedded nanocrystalline borides resist hard-particle impingement
- Chloride and seawater corrosion — Cr 23% + Mo 4% + amorphous passive film resists pitting
- High-temperature oxidation and sulfidation in boiler flue-gas streams to 1,600°F
- Three-body abrasion from coal, ash, ore, and dredge solids
- Combined erosion-corrosion in aggressive aqueous chemistry (the 'hydropower problem')
Industries
- Hydropower and renewable energy (turbine overhaul, impeller refurbishment)
- Power generation (coal, CFB, biomass, black-liquor boilers — waterwall tube armor)
- Marine and offshore (seawater pumps, propulsion shafts, ballast systems)
- Mining and aggregate (slurry transport, dredge pumps, chutes)
- Pulp and paper (black-liquor recovery, screen plates, refiners)
- Oil and gas (downhole tools, sucker rods, wellhead valves in sour service)
- Chemical and petrochemical processing (pump and agitator parts in corrosive slurries)
- Wastewater and desalination (pump and valve internals)
Substrates
- Carbon steels (1018, 1045, A36) — workhorse substrate for boiler tubes and pump bodies
- Low-alloy boiler tube steels (T11, T22, T91) — 1-3 mil white-metal blast + arc-spray interlayer optional
- Stainless steels (304, 316, 410, 420) — direct arc-spray with roughened surface prep
- Cast iron (grey and ductile) — preheat to 150-200°F to avoid thermal shock
- Duplex stainless (2205) in marine and slurry service
- Nickel alloys (Monel, Inconel) in heat-exchanger and high-temperature service
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.
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Polymet Corporation — PMET 270 Iron-Based Amorphous Cored Wire (equivalent to TAFA 90 MXC)
“PMET 270 is a cored wire designed for arc spray systems that produces a partially amorphous, hard, abrasive and corrosion resistant coating, with a service environment up to 1600 degrees F. Composition: Cr 23.0%, Ni 9.0%, Mo 4.0%, B 2.3%, Cu 2.0%, Mn 1.3%, Si 1.0%, Fe balance. Rockwell Hardness 45-50 C. Diameter 1/16 in (1.6 mm). Equivalent to TAFA 90 MXC. The addition of 9% Ni gives it greater corrosion resistance than PMET 273 / 95 MXC for most environments. High chrome-like finishes achievable through grinding and lapping.”
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Polymet Blog — Wire Arc Spray Coatings for the Protection of Boiler Tubes (September 2012)
“FeCrBSi amorphous wire, Polymet's Vecalloy B and PMET 273 are particularly effective coatings for waterwall protection in coal-fired power boilers, circulating fluidized bed boilers (CFBs) and black liquor recovery boilers (BLRBs) in the pulp and paper industry. Typical applied thickness 20-30 mils (0.5-0.75 mm); service life 5-10 years.”
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Journal of Iron and Steel Research International — High-temperature corrosion resistance of Fe–Cr–Mo amorphous coating for water wall protection of USC boiler (2024)
“The excellent high-temperature corrosion resistance of Fe–Cr–Mo amorphous coating is primarily attributed to the stable Fe/Cr oxide film generated by the metastable state of the amorphous structure, which serves as an excellent barrier. Under high-temperature service the amorphous structure gradually transforms into a nanocrystalline structure; the oxide film of the amorphous/nanocrystalline coating has low thermal stress, leading to better adhesion and resistance to cracking and peeling.”
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Journal of Thermal Spray Technology — Microstructure and Corrosion Resistance of Fe-Based Coatings Prepared by Twin Wires Arc Spraying Process
“FeNiCrBSiNbW coating prepared by twin-wire arc spraying consisted of amorphous phase and α-(Fe, Cr) nanocrystalline phase, with porosity of 1.8%, hardness of 807 HV0.1 and tensile bonding strength of 52.1 MPa. The coating had superior corrosion resistance attributed to the amorphous/nanocrystalline structure and the presence of corrosion-resistant element Cr.”
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Journal of Thermal Spray Technology — Cavitation Erosion Resistance of Fe-Based Amorphous/Nanocrystal Coatings Prepared by High-Velocity Arc Spraying
“After 180 min of cavitation erosion, the cumulative weight loss of the FeCrNiBSiNb and FeCrBSiWNb amorphous/nanocrystal coatings was 21.3 and 24.0 mg respectively, whereas the weight loss of a 0Cr18Ni9 stainless coating was 62.6 mg — roughly 2.5-3x better cavitation resistance for the amorphous family.”
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Kermetico — Nanosteel SHS-7574 Iron-Based Amorphous Metallic Glass Coating (HVAF)
“Iron-based amorphous coating with Cr <25%, Mo <20%, W <10%, B <5%, Fe balance. Hardness 65 HRC. Bond strength 70+ MPa at 500 µm thickness. Apparent metallographic porosity <1.0%. Operating temperature up to 700°C (1,300°F). Applications: waterwall tubing in pulverized-coal and fluidized-bed boilers, hydraulic cylinders, wear plates, sealing rings. Outstanding corrosion resistance in high-chlorine, salt fog, and seawater environments; alternative to hard-chromium plating. Not recommended for parts exposed to fatigue.”
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ScienceDirect — Identifying optimal HVOF spray parameters to attain minimum porosity and maximum hardness in iron-based amorphous metallic coatings
“Iron-based amorphous coatings can achieve microhardness values of 898 ± 67 HV as-sprayed, climbing to 1,245 ± 109 HV after post-heat treatment at 650°C. Porosity reduces the hardness value of the coating layer; reducing porosity yields a denser coating with fewer cavities and improved corrosion barrier performance.”
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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