HTS Coatings — machining & grinding

95 MXC

27–29% Cr, 1.5–2% Mn, 1–2% Si, 3–4% B, Fe-balance

  • Arc

95 MXC is the high-chromium step in the iron-cored arc-spray wire family — TAFA 95 MXC / Polymet PMET 273 / Armacor M — the alloy HTS reaches for when the damage mechanism is hot, oxidizing, or ash-laden. Chemistry runs Cr 27-29%, B 3.7%, Mn 1.5-1.7%, Si 1.4-4.6%, Fe balance. Hardness is 55-60 HRC as-sprayed, bond strength 6,000 psi on prepped carbon steel, service ceiling 1,700°F. The partially amorphous microstructure carries Cr borides and carbides that hold up under combined abrasion and oxidation. Typical thickness is 10-40 mils for erosion-corrosion duty; arc-spray porosity runs 2-8% — plan a sealer for aqueous immersion.

Step up to 95 MXC when the chemistry is the issue. 90 MXC (PMET 270) leans on Ni-Mo-Cu alongside 23% Cr for reducing-environment corrosion; 95 MXC drops the nickel and bumps chromium six points — the right call on boiler waterwalls, superheater tubes, fan blades, yankee dryer rolls, hydro-turbine runners in silty water, marine shafts, and pumps handling acidic slurries. HTS runs 95 MXC on twin-wire arc for large-area fireside reconditioning. Got a tube panel that keeps scaling off, or a turbine runner eating through itself? Send the photos and service conditions — we'll tell you whether 95 MXC is the right call.

Technical data

Hardness
~595-700 HV equivalent (HRC 55-60 conversion) — partially amorphous microstructure with Cr borides and carbides dispersed in an Fe-Cr matrix
Hardness (HRC)
55-60 HRC as-sprayed across TAFA 95 MXC / Polymet PMET 273 / Armacor M datasheets — the high-chromium step in the iron-cored-wire family; published test work on 95 MXC on 304 stainless measured 45.98 HRC after sandblast prep, exceeding a 43 HRC spec floor, which is consistent with the 55-60 HRC wire average once process parameters are dialed
Bond strength
6,000 psi typical on grit-blasted carbon steel per Polymet PMET 273 datasheet; independent testing on 95MXC reports ~5,772 psi — both consistent with arc-spray FeCrBSi on properly prepared substrate (SSPC-SP10 / Sa 2.5 angular profile, NiAl or 75B bond coat optional on hot or heavy-cycle duty)
Max service temp
~1,700°F continuous oxidation service per TAFA / Polymet / HAI datasheets — the Cr borides and carbides plus the amorphous matrix hold structure where lower-Cr arc-spray wires scale off
Max service temp
~925°C continuous
As-sprayed porosity
2-8% typical arc-spray porosity on 95 MXC; practitioner forum reports note arc-spray never produces truly pore-free coatings — published comparative TWAS study measured ~7.1% porosity on 95MXC; porosity drops with higher wire feed rate, shorter standoff, and optimized air-cap selection; seal-coat over the top for aqueous or acid service
Typical thickness
10-40 mils (0.25-1.0 mm) typical arc-spray deposit for erosion-corrosion protection; field applications on boiler tubes commonly run 15-25 mils, with 80 mils (2 mm) reported on heavier build-ups; keep individual passes thin (~20 microns) to control porosity and residual stress
Melting range
Arc-spray wire — no fuse cycle; droplet melt temperatures during twin-wire arc run well above 3,000°F in the arc column, but the coating is mechanically bonded splat structure, not a fused layer
Density
~7.3-7.5 typical for FeCrBSi arc-spray deposits (supplier datasheets do not publish exact coating density; pure wire density trends with Fe-Cr-B-Si chemistry and partial amorphous fraction)

Where it earns its keep

  • Highest chromium in the iron-cored-wire arc-spray family (27-29% Cr) — step up from 90 MXC when oxidation and hot-end corrosion dominate the damage mechanism
  • Partially amorphous microstructure — the rapid solidification of arc-spray droplets locks in disordered structure that resists both abrasion and corrosion propagation along grain boundaries
  • 1,700°F continuous service — 100°F higher than 90 MXC's 1,600°F ceiling, which matters on superheater tubes and hot ID fans
  • Good machinability despite 55-60 HRC hardness — grinds and laps to a high-chrome-like finish for sealing surfaces, dryer rolls, and precision restoration
  • Iron-base chemistry — significantly cheaper per pound than nickel- or cobalt-base options for large-area fireside coverage
  • Runs on standard twin-wire arc equipment (TAFA 8830 / 9000-class, Oerlikon Metco SmartArc, Praxair ArcJet) at ~10 lb/hr per 100 A at 70% efficiency — productive for the large surface areas typical of waterwall reconditioning
  • 6,000 psi bond strength on grit-blasted carbon steel — strong enough for thermally cycled boiler service with proper substrate prep

Where it doesn't

  • Positioned vs. 90 MXC: 90 MXC (PMET 270) carries Ni-Mo-Cu alongside 23% Cr, which favors general aqueous corrosion in reducing environments; 95 MXC bumps Cr to 27-29% without Ni/Mo, which favors oxidation and chromate-passivation in hot and oxidizing service. Pick 95 MXC when the chemistry is hot, ash-laden, or oxidizing; stay with 90 MXC when the chemistry is reducing or chloride-heavy
  • Arc-sprayed coatings are never pore-free — practitioner experience and published research confirm 2-8% porosity is normal; for aqueous or acid immersion, plan on a sealer (epoxy, silicone, or polymer) to block through-porosity
  • Not a fused deposit — bond is mechanical plus partial metallurgical diffusion, not a fusion weld; substrate prep (grit blast profile, NiAl or 75B bond coat where cycling is severe) is non-negotiable
  • Continuous service above 1,700°F will degrade the amorphous fraction and accelerate oxidation; keep peak metal temperature below that ceiling
  • Keep individual spray passes thin (~20 microns) to manage residual stress and porosity on thick builds; heavy single-pass deposits crack and spall
  • Finishing to a sealing-surface tolerance requires grinding with SiC or diamond wheel — the Cr borides and carbides are hard on conventional abrasive media

Typical applications

  • Boiler tube erosion-corrosion protection — waterwalls, superheaters, economizers, and tube shields in coal, biomass, and waste-to-energy plants (the flagship 95 MXC application)
  • Hydro turbine components exposed to corrosive or silt-laden water — runner blades, wicket gates, and wear rings where chromium chemistry resists both oxidation and aqueous attack
  • Marine shafts, sleeves, and propulsion hardware requiring combined hardness and corrosion tolerance in saline service
  • Pump wear rings, sleeves, and impellers in acidic slurries, mine-water, and process streams
  • Yankee dryer rolls in paper mills — hard, grindable surface that holds a Cr-like finish
  • Fan blades and ID-fan housings exposed to fly ash and combustion-gas abrasion
  • Drill collars and tool joints where abrasion and mild corrosion run in parallel
  • Anti-skid deck plate and walkway surfacing on platforms and marine vessels
  • Kiln, dryer, and calciner components in cement and minerals processing
  • Chemical and petrochemical process piping wear sleeves, cyclones, and separators

Wear modes addressed

  • High-temperature erosion-corrosion (fly ash, fireside attack on boiler tubes)
  • Oxidation resistance to ~1,700°F from the high-chromium matrix
  • Three-body abrasion from silt, ash, slurry particulate
  • Aqueous corrosion in mildly acidic, saline, and silt-laden water (chromium-rich surface layer)
  • Cavitation and solid-particle erosion on hydro-turbine surfaces
  • Combined wear-plus-oxidation duty where lower-Cr arc-spray wires scale off

Industries

  • Power generation — coal, biomass, waste-to-energy, circulating fluidized bed (CFB) boilers
  • Hydroelectric generation (runners, wicket gates, wear rings in silty or corrosive rivers)
  • Marine (shafts, sleeves, deck surfacing, pump internals)
  • Pulp and paper (yankee dryer rolls, process rolls)
  • Oil and gas (drill collars, tool joints, pipe wear sleeves)
  • Mining and minerals (slurry pumps, cyclones, fan housings)
  • Cement and aggregate (kiln and calciner components, ID-fan blades)
  • Chemical and petrochemical process

Substrates

  • Carbon steel boiler tube alloys (SA-178, SA-192, SA-210, T11, T22) — the dominant substrate for fireside protection
  • Low-alloy and alloy steels (4140, 4340) for shafts and pump components
  • Martensitic stainless (410, 420) on hydro-turbine and pump hardware
  • Austenitic stainless (304, 316) — confirmed in independent TWAS research
  • Cast iron with standard grit-blast prep
  • Duplex and super-duplex stainless on marine service components

Which process, when?

Twin-wire arc spray (TWAS) is the only deposition method for 95 MXC — it is sold exclusively as a 1/16" (1.6 mm) cored wire, with some suppliers offering 2.0 mm and 3.17 mm for high-deposition field work. Arc spray is the right pick here because the application set rewards high deposition rate over precision: boiler waterwalls, fan blades, and tube shields are big surfaces that need to be coated fast and economically. Compared to HVOF tungsten-carbide on the same duty, arc-sprayed 95 MXC is coarser and more porous but 3-5x cheaper per square foot and runs with portable field equipment — often the right call on large reconditioning scopes. Compared to flame-sprayed nickel-chrome, 95 MXC runs hotter and harder. Compared to plasma-sprayed oxides, 95 MXC is tougher and less brittle on thermally cycled components. For high-temp fireside and hydro service where the coating must cover hundreds of square feet quickly and stand up to combined abrasion and oxidation, arc-sprayed 95 MXC is the workhorse.

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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