Metco 31C is Oerlikon's workhorse blend for jobs that need tungsten-carbide wear resistance on a thick build with a metallurgical bond — not the 3-mil HVOF layer, but a 15-to-40-mil deposit fused to the substrate. Chemistry: 65% nickel self-fluxing matrix (Ni-17.5Cr-4Fe-4Si-4B-0.5C) cut with 35% WC-12Co hard phase. The NiCrBSi matrix handles the bond and the mild corrosion; the tungsten carbide carries the abrasive load.

We run it two ways. Spray-and-fuse is the primary route: powder flame gun lays down the porous deposit, then a torch, induction coil, or furnace fuses the layer to roughly 1,050°C. Boron and silicon scavenge oxides during the fuse cycle — that's what self-fluxing means — and the result is sub-1% porosity, 58-62 HRC, metallurgically bonded. HVOF is the alternative for thinner denser as-sprayed layers when a fuse cycle isn't feasible.

Fits: oil-field stabilizers and mud-motor parts, mining slurry pumps, ag tillage and soil-working tools, glass-mold plungers, pump sleeves, screw-conveyor flights. Limits: ~950°F service ceiling (matrix-limited) and not for sour gas or strong acids — that's WC-10Co-4Cr or Hastelloy territory.

When the wear mode is abrasion plus mild corrosion and you need a thick layer on the cheap versus straight WC-Co, 31C is the answer.

Technical data

Hardness: ~730-900 HV0.2 typical for 30-40% WC-12Co loading in NiCrBSi (Jasik et al. report 730 HV at 30% WC-12Co, 838 HV at 40%); matrix NiCrBSi phase ~570 HV, undissolved WC cores ~2,500 HV
Hardness (HRC): 58-62 HRC after fuse cycle — Oerlikon Metco cites 62 HRC fused; comparable NiCrBSi + WC-12Co blends run 56-62 HRC depending on WC fraction and fuse completeness
Bond strength: Metallurgically bonded after fuse cycle — substrate-limited, not coating-limited; unfused flame-sprayed deposit is mechanical bond only and must be fused before service. Research on fused NiCrBSi self-fluxing deposits reports >80 MPa (~11,600 psi) pull strength
Max service temp: ~950°F continuous (matrix-limited)
Max service temp: ~500°C continuous (matrix-limited; WC decarburization and NiCrBSi matrix softening set the ceiling)
As-sprayed porosity: Flame-sprayed unfused 3-8%; after fuse cycle <1% and virtually pore-free per Oerlikon Metco
Typical thickness: Flame spray + fuse 15-40 (380 µm-1 mm); HVOF as-sprayed 5-20; thick build-up via successive spray-and-fuse passes

Where it earns its keep

Balances WC hardness with NiCrBSi matrix — 35% WC-12Co hard phase delivers carbide-level wear resistance while the self-fluxing Ni matrix handles mild corrosion and gives you the fuse-cycle metallurgical bond
Self-fluxing — boron and silicon scavenge oxides during the fuse cycle, so flame-sprayed Metco 31C finishes metallurgically bonded and <1% porosity with no separate flux step
Cheaper per pound than straight WC-12Co on thick builds — the NiCrBSi matrix dilutes expensive WC-Co content without giving up the hard-phase wear floor
Thick-build capable — spray-and-fuse can lay down 15-40 mil protective layers in a single cycle, where HVOF straight WC-Co is typically 3-15 mil
Good abrasion and fretting resistance per Oerlikon DSMTS — the WC hard phase carries the abrasive load while the ductile matrix absorbs incidental shock
Dual process path — flame spray + fuse for thick protective layers, HVOF for thinner denser as-sprayed deposits when a fuse step is not feasible
Grindable and machinable with carbide tooling after fuse; finish-grindable to print tolerances on sleeves, plungers, and shafts

Where it doesn't

Intermediate hardness — sits between pure WC-12Co (1050-1350 HV) and plain Colmonoy 6 (620-720 HV); if the service is pure high-stress abrasion and the part tolerates thin coatings, straight WC-12Co HVOF still wins on wear rate
Matrix-limited service temperature — ~500°C / 950°F ceiling set by NiCrBSi softening and WC decarburization; for hotter service specify Cr₃C₂-NiCr or cobalt-base Tribaloy/Stellite
Spray parameters matter for uniform WC distribution — the hard-phase particles are larger and denser than the matrix, so feeder settings, flame stoichiometry, and gun traverse speed all affect carbide segregation in the deposit
Must be fused before service — as-sprayed flame-spray deposit is porous and mechanically bonded only; skipping the fuse step leaves performance on the table
Fuse cycle heat input matters — too little and porosity stays, too much and WC dissolves into the matrix and loses the hard-phase advantage; torch, induction, or furnace fuse each have tuning requirements
Corrosion limit tracks the Ni matrix — fine for neutral and mildly acidic service, not for sour gas, wet chlorides, or strong mineral acids where Hastelloy or WC-10Co-4Cr is the right answer

Which process, when?

Flame spray + fuse is the primary route — powder flame gun lays down a 15-40 mil porous deposit, then oxyacetylene torch, induction coil, or furnace fuses the layer to ~1,050°C to scavenge oxides and bond metallurgically to the substrate. HVOF applies Metco 31C as-sprayed where a fuse cycle is not feasible (heat-sensitive substrate, tight geometry, thinner layer) — denser as-sprayed but mechanically bonded only, so expect shorter life than a fused deposit. For thick wear build-up on oil-field rotors and glass-mold plungers, spray-and-fuse is the standard.

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.

Oerlikon myMetco — Metco 31C-NS Thermal Spray Powder
“Metco 31C-NS is a self-fluxing alloy with 65% (Ni 17.5Cr 4Fe 4Si 4B 0.5C) and 35% (WC 12Co), agglomerated blend, -125/+45 µm, designed for post-coat fuse to produce dense, virtually porosity-free, metallurgically bonded coatings.”
Oerlikon Metco DSM-0265.2 — Nickel-Based Self-Fluxing Alloys with Hard Phase
“Self-fluxing alloys blended with a hard-phase constituent of tungsten carbide in a gas-atomized nickel matrix; coatings are resistant to abrasive grains, hard surfaces, fretting and particle erosion; matrix hardness is comparable to standard self-fluxing materials while the carbide phase adds wear resistance.”
Oerlikon Metco DSMTS-0077.4 — Nickel-Based Self-Fluxing Alloys with Hard Phase (Technical Bulletin)
“Metco 31C-NS fused-coating hardness 62 HRC; two-stage process — material is first applied by thermal spray and then fused to develop a dense coating with minimal porosity and oxides that is metallurgically bonded to the substrate.”
HTS Coatings — Coating Materials (Metco 31C entry)
“Metco 31C: 65% (Ni, 17.5% Cr, 4% Fe, 4% Si, 4% B, 0.5% C) + 35% (WC, 12% Co); applied by flame spray or HVOF; composite coating blending nickel-chromium binder with tungsten carbide reinforcement for enhanced wear resistance with reasonable toughness.”
Jasik et al. — Tribological Properties of Laser-Cladded NiCrBSi/WC-12Co Metal Matrix Composite Coatings (Materials, 2022)
“Average hardness 573 HV0.2 for pure NiCrBSi, 730 HV0.2 at 30 wt.% WC-12Co, 838 HV0.2 at 40 wt.%, 1067 HV0.2 at 50 wt.%; wear rate dropped 4.7× at 30% WC-12Co and 5.9× at 40% compared with pure NiCrBSi.”
Szymanski et al. — Cavitation Erosion and Corrosion Behavior of Flame-Sprayed NiCrBSi/WC-12Co Composite Coatings (Materials, 2022)
“Flame-sprayed NiCrBSi reinforced with 15% and 30% WC-12Co demonstrates microhardness increase and lower cavitation erosion rate (6.35 ± 0.2 × 10⁻³ mg/min at 15% WC-12Co) versus base NiCrBSi; applicable to steel rolls, sink rolls, exhaust fans, pump housings, conveyor screws and rod couplings up to 500°C.”
EP0377452B1 — Thermal Spray Method for Producing Glass Mold Plungers
“Powder blend for glass-mold plunger coating: self-fluxing alloy particles (Ni/Co-Cr-B-Si) plus carbide particles at 30-70% of the blend weight, with sub-5 µm tungsten carbide in a cobalt matrix; applied by spray-and-fuse.”
Surface & Coatings Technology — Microstructure and Mechanical Characterization of NiCrBSi and NiCrBSi-WC Flame-Sprayed Coatings
“Flame-sprayed and simultaneously fused NiCrBSi-WC coatings showed the highest measured microhardness among tested coatings; WC reinforcement of self-fluxing NiCrBSi matrix produces dense metallurgically bonded layers after the fuse cycle.”

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.

Metco 31C

Technical data

Where it earns its keep

Where it doesn't

Typical applications

Wear modes addressed

Industries

Substrates

Which process, when?

Sources

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