Tribaloy T-800 is the hot-corrosion Tribaloy — the Laves-phase cobalt-molybdenum alloy you reach for when T-400's galling immunity is still needed, but the duty adds sustained 700°C+ heat and an oxidizing or corrosive atmosphere that would eat plain Stellite alive. Bump chromium from T-400's ~8% up to 17.5%, keep the 28.5% molybdenum and 3.4% silicon that build the Laves phase, and you get the highest Laves-phase fraction (~60 vol%) of any commercial Tribaloy — 54-62 HRC, roughly 600-700 HV bulk, with 300 HV still on the Vickers at 760°C and validated oxidation stability through 1,000°C.

At HTS we run T-800 across Plasma, HVOF, and PTA. HVOF is the dense-coating default for pump seals, extrusion screw tips running glass-filled polymers, and mechanical seal faces. PTA weld overlay handles thick, fully fused deposits on high-temperature valve seats and hot-work die inserts — with the preheat, interpass, and slow-cool discipline T-800 demands. The trade is brittleness: more Laves means more crack sensitivity on weld, and T-800 is the most crack-sensitive Tribaloy in routine service. Pick T-400 for corrosion plus galling without hot service; pick T-800 when sustained elevated-temperature operation and hot corrosion are both on the spec.

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Technical data

Hardness: ~600-700 HV bulk deposit equivalent; Laves-phase constituent itself measures 1,000-1,200 HV
Hardness (HRC): 54-62 HRC as-deposited (Kennametal nominal range); typical plasma/HVOF/PTA deposits land 55-60 HRC
Bond strength: ~8,000-10,000 psi (55-70 MPa) HVOF on steel substrates typical for Laves-phase cobalt alloys; PTA weld overlay metallurgically bonded (substrate-limited)
Max service temp: ~1,290-1,470°F continuous service; hot hardness ~300 HV retained at 1,400°F (760°C); oxidation-stable through 1,830°F (1,000°C) in long-term isothermal tests; Laves structure believed stable to ~2,240°F (1,230°C)
Max service temp: ~700-800°C sustained service with useful hot hardness; oxidation resistance validated to 1,000°C; step up from T-400's ~650°C envelope
As-sprayed porosity: <1% HVOF (typ. 0.5-1.0%); 2-5% plasma spray; PTA weld overlay essentially fully dense
Typical thickness: Plasma 5-20; HVOF 5-20; PTA weld overlay 40-120 (1-3 mm)
Melting range: 2,350-2,465°F
Density: 8.6

Where it earns its keep

The hot-corrosion Tribaloy — extra 6% chromium over T-400 (17.5% vs 8%) delivers materially better oxidation and hot-corrosion resistance at sustained 700°C+ service
Highest Laves-phase fraction (~60 vol%) of any commercial Tribaloy means maximum hot hardness and galling immunity — 300 HV retained at 760°C where Stellite 6 would already be soft
Laves-phase self-mated galling immunity — runs against itself, stainless, or Inconel without cold-welding in dry or starved-lube contact
Useful continuous service to ~700-800°C with validated oxidation stability to 1,000°C
High molybdenum (28.5%) delivers pitting-corrosion resistance in chlorides and seawater that plain Stellites don't match
Three-process deposition flexibility — Plasma, HVOF, and PTA all work with proper parameter control
Covers the use case where T-400 won't hold up: hot corrosive valve trim, oxidizing hot gas service, and extrusion screws cooking glass-filled polymers

Where it doesn't

Even more brittle than T-400 — the higher Laves-phase volume that buys the hot hardness also makes the deposit crack-sensitive; Kennametal and valve OEMs both note T-800 weld overlays are "very difficult" to lay crack-free
Weld and fusion deposits require aggressive preheat (typically 400-650°C), strict interpass control, and slow-cool/post-weld heat treatment; thick sections on hardenable substrates need isothermal anneal
Cobalt raw-material cost is volatile and high; Mo content pushes price above Stellite 6/12 per pound
Machining is difficult — carbide or CBN tooling required, finishing almost always by grind
Low impact toughness — not the pick for heavy pounding or impact-loaded service
For corrosion-plus-galling without sustained hot service, T-400 (lower Cr, less brittle) is the better-economic pick; reserve T-800 for the elevated-temperature duty that justifies the trade
Modern T-400C variant offers improved weldability and oxidation performance — worth considering for new-build USC valve programs where T-800 cracking has been the historical failure mode

Which process, when?

Plasma spray lays down 5-20 mil coatings on valve faces, piston rings, and turbine shrouds where a thin, hot-hard surface is needed without the brittleness risk of a thick weld deposit; porosity 2-5% and a mechanical bond. HVOF is the dense-coating default for T-800 — <1% porosity, 55-70 MPa bond, and deposits that retain the fine Laves microstructure that drives the hot-hardness story; used on pump components, mechanical seals, and extrusion screw tips. PTA weld overlay is the answer when 40-120 mils of thick, fully fused hardfacing is needed on valve seats, hot-work die inserts, or galvanizing line rolls — but preheat, interpass, and slow-cool discipline are non-negotiable because T-800's Laves volume makes it the most crack-sensitive cobalt alloy in routine service. Pick plasma for thin-and-hot, HVOF for dense-and-precise, PTA for thick-and-fused (with crack discipline).

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.

Kennametal Stellite Tribaloy T-800 Alloy Technical Data
“Nominal composition Cr 17.5%, Mo 28.5%, Si 3.4%, C <0.08%, Ni + Fe, Co balance; hardness 54-62 HRC; density 8.6 g/cm³ (0.312 lb/in³); melting range 1,288-1,352°C (2,350-2,465°F); hard intermetallic (Laves) phase dispersed in a softer matrix; applications include aircraft engine wear surfaces, galvanizing roll bushings, cams and retainer rings, diesel piston rings, mechanical seals and bearing seats, valve trim and pump components.”
Valve Magazine — Hardfacing Alloys and Processes for Advanced Ultra-Supercritical
“Tribaloy T-800 (Co-17.5%Cr-28.5%Mo-3.4%Si) is believed to be stable up to 2,240°F (1,230°C); at approximately 1,400°F (760°C), T-800 achieves hardness around 300 HV — equivalent to Stellite 6's hardness at considerably lower temperatures (800-1,000°F); however, T-800 is extremely brittle and the welding of T-800 hardfacing overlays is very difficult, which has driven industry interest in the improved T-400C variant.”
The Tribaloy T-800 Coatings Deposited by Laser Engineered Net Shaping (LENS) — Materials, MDPI/PMC
“Tribaloy T-800 composition Co balance, Mo 27-30 wt%, Cr 16.5-18.5 wt%, Si 3-3.8 wt%, Fe + Ni max 3 wt%; two-phase dendritic microstructure with Laves intermetallic phase (Co3Mo2Si, C-14 type) comprising ~60 vol% — the highest Laves-phase fraction of any commercial Tribaloy; Laves constituent hardness 1,000-1,200 HV; LENS-deposited coating 800-900 HV0.1; powder hardness 1,180 HV0.1; high sensitivity to brittle fracture requires substrate pre-heating to manage thermal stresses.”
MFG Shop — Comprehensive Guide to Tribaloy T-800: Composition, Properties, and Uses
“Tribaloy T-800 was designed to resist high-temperature wear and abrasion with exceptional oxidation and corrosion resistance due to its high chromium content; exhibits the highest content of Laves phase of all commercial Tribaloy alloys; high molybdenum content increases resistance to pitting corrosion in seawater service; features high resistance to erosion, corrosion and galling; applied via HVOF and plasma spraying to form dense, adherent coatings.”
High-temperature wear behavior of Tribaloy T400 and T800 coatings prepared by ethanol-fueled HVOF — Surface & Coatings Technology
“T400 and T800 Tribaloy coatings successfully prepared via ethanol-fueled HVOF; under room-temperature sliding wear conditions, the T800 coating demonstrated better wear resistance compared to T400; at 800°C T800 coating exhibited oxidative wear as the dominant mechanism, confirming oxidation-dominated high-temperature wear regime for the high-Cr Tribaloy.”
Microstructure and mechanical properties of Tribaloy coatings deposited by high-velocity oxygen fuel — Journal of Materials Science
“HVOF-deposited Tribaloy coatings retain the fine Laves-phase microstructure responsible for high-temperature hardness and galling resistance; coating density, bond strength, and retained hardness validated for valve and pump component service.”

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.

Tribaloy T-800

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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