HTS Coatings — machining & grinding

B50A919

Cobalt-base chromium-tungsten (proprietary)

B50A919 is a General Electric material specification calling out the L-605 / Haynes 25 chemistry — Co-20Cr-15W-10Ni, UNS R30605 — as a thermal-spray powder feedstock, typically paired with GE process spec P16B-AG11 for application on GE-built aerospace engine hot-section hardware. That chemistry has been flying in combustion chambers and guide vanes since the 1950s: among the strongest fabricable cobalt alloys, useful to roughly 980°C continuous (intermittent to ~1095°C), and resists sulfidation better than nickel-base alternatives in the same window.

For coating duty, the GE-specified deposit sits in the thermal-spray L-605 family — HVOF for dense, sub-2% porosity restorations of combustor liners, transition pieces, and exhaust-nozzle sections; APS plasma for thicker dimensional rebuild on casings and shrouds; VPS/LPPS where the procedure calls for aerospace-grade, oxide-free microstructure on first-stage hardware. Expect ~400-500 HV as-sprayed and bond strengths in the 7,000-10,000 psi band on prepared superalloy substrates.

Honest note: the full text of GE B50A919 and P16B-AG11 is proprietary; exact qualification values live inside the controlled procedure. The L-605 chemistry itself is fully public, which is what lets a qualified shop run the spec with confidence.

Got an engine part tagged for B50A919 / P16B-AG11 rework? Send us the disposition — we'll scope powder lot, process, and post-spray procedure to the GE repair bulletin.

Technical data

Hardness
~200-300 HV wrought/annealed baseline; thermal-sprayed deposits run materially higher due to work-hardening of splats and oxide dispersion — typical HVOF L-605 coatings land in the ~400-500 HV range as-sprayed. Exact values for the GE-specified deposit require the B50A919 / P16B-AG11 qualification document
Bond strength
HVOF L-605 coatings typically 7,000-10,000 psi (48-70 MPa) per ASTM C633 on grit-blasted superalloy substrates; plasma-sprayed deposits 4,500-7,500 psi (31-52 MPa). OEM qualification spec sets the acceptance floor for GE-controlled repair work
Max service temp
~1800°F continuous / ~2000°F intermittent — the L-605 wrought alloy retains useful strength and oxidation resistance through this window; coating duty typically tracks the wrought baseline on hot-section parts
Max service temp
~980°C continuous, with intermittent excursions to ~1095°C. This is the high-temperature strength envelope that makes L-605 chemistry valuable for aero-engine hot-section repair work
As-sprayed porosity
HVOF 0.5-2.0% typical; APS plasma 3-6%; aerospace-qualified repair deposits are held toward the low end of that band to meet OEM acceptance
Typical thickness
5-20 mils HVOF (125-500 µm) for wear/erosion restoration; 10-40 mils plasma spray for dimensional rebuild of worn engine hardware; exact thickness range set by the GE-specified repair procedure for the part in question
Density
9.13-9.24 (L-605 wrought); thermal-spray deposits land within a few percent of wrought depending on porosity

Where it earns its keep

  • Qualified chemistry path for GE-controlled engine repair — using B50A919 / P16B-AG11-class coatings keeps parts inside OEM-blessed disposition scope and preserves airworthiness
  • High-temperature strength envelope rivaled only by true superalloys — L-605 is among the strongest fabricable cobalt alloys, useful to ~980°C continuous and ~1095°C intermittent
  • Good oxidation resistance to 2000°F from the 20% chromium content forming an adherent Cr₂O₃ scale
  • Strong sulfidation resistance — the cobalt base plus chromium content handles sulfur-bearing combustion products better than most nickel-base coatings in the same temperature window
  • Galling and wear resistance at temperature — useful for loaded interfaces in hot-section assemblies where stainless-on-stainless would seize
  • Proven pedigree — L-605 / Haynes 25 has been flying in combustion chambers and guide vanes since the 1950s; the metallurgy is extensively characterized

Where it doesn't

  • **Honest note on the spec:** the full text of GE B50A919 and the P16B-AG11 application procedure is proprietary to General Electric and is not public. Quoted hardness, bond, and porosity values here are derived from the L-605 wrought baseline and the published thermal-spray coating family using the same Co-20Cr-15W-10Ni chemistry — they are indicative, not lifted from the GE document
  • GE-controlled repair work requires GE-approved source qualification for the powder lot, the application equipment, and the operator — this is not an off-the-shelf coating job
  • Cobalt raw-material cost is materially higher than nickel-base alternatives; when GE disposition permits a substitute (e.g., MCrAlY or an Inconel-class coating), there may be cost-effective options
  • Not a substitute for tungsten-carbide coatings where cold-hardness and abrasive wear govern — L-605 chemistry is chosen for its high-temperature strength, not its room-temperature hardness
  • Post-spray heat treatment per GE procedure may be required to homogenize the deposit and achieve qualification-grade oxidation performance
  • Work-hardens rapidly — any post-spray machining must be planned with L-605's cold-work behavior in mind

Typical applications

  • GE-specified aerospace engine hot-section component repair — combustion chamber hardware, combustor liners, transition pieces
  • Exhaust nozzle sections and exhaust-side hot-gas-path hardware on GE aero engines
  • Turbine casing and shroud repair where GE P16B-class coatings are qualified
  • Guide vanes and combustor dome restoration on GE and GE-derivative engines
  • Afterburner and augmentor hardware in military engine repair
  • Industrial and aeroderivative gas turbine hot-section rebuild on GE LM-series and Frame engines following GE repair bulletins
  • Overhaul-depot refurbishment of engine hardware where the OEM disposition calls out B50A919 / P16B-AG11 or an equivalent L-605-chemistry coating

Wear modes addressed

  • High-temperature oxidation in the 800-980°C combustor/exhaust gas stream
  • Sulfidation and hot corrosion where fuel sulfur, salt ingestion, or combustion contaminants drive Type I / Type II attack
  • Thermal fatigue and thermal-cycling stress at start/stop transitions
  • Erosion from combustion particulate and ingested debris
  • Galling and fretting at loaded interfaces in hot-section assemblies
  • Creep and stress-rupture of the underlying superalloy substrate (coating restores dimension but does not arrest substrate creep)

Industries

  • Aerospace engine OEM repair and overhaul (GE Aerospace-controlled repair work)
  • Military aviation depot-level engine maintenance (F110, F404, F414, T700 and derivatives)
  • Commercial aviation engine MRO (CF6, CFM56, GE90, GEnx families under GE repair dispositions)
  • Aeroderivative industrial gas turbines (LM2500, LM6000) where GE controls the repair procedure
  • Power-generation heavy-duty gas turbines (GE Frame 7/9 class) for hot-section rebuild work

Substrates

  • Ni-base superalloys (René N5, Mar-M 247, IN-738, IN-792, CMSX-4) — first-stage hot-section blade and vane parent metal
  • Co-base superalloys (X-40, Mar-M 509) for vane hardware
  • Hastelloy X and Haynes 230 combustion-liner and transition-duct sheet stock
  • L-605 itself as a self-on-self buildup during wrought-part rebuild
  • Precipitation-hardened stainless and Ni-base sheet stock in cooler hot-section zones

Which process, when?

HVOF is the default modern process for L-605-chemistry coatings where density, bond strength, and thin-to-moderate thickness (5-20 mils) are the requirement — dense enough for combustor-liner and transition-duct service, bonded well enough for thermal-cycling hot-gas-path duty. APS (air plasma spray) handles thicker dimensional rebuild (10-40 mils) on worn engine casings and shrouds, accepting somewhat higher porosity in exchange for build rate. VPS/LPPS (vacuum / low-pressure plasma spray) produces the cleanest, oxide-free L-605 deposits with sub-1% porosity — aerospace-grade, the OEM-preferred process for critical first-stage hardware when the GE procedure calls for it. Flame spray is rarely specified for GE hot-section repair. Which process the B50A919 / P16B-AG11 disposition calls for is set by the GE procedure for the specific part; a qualified repair shop runs the spec.

Notes

Thermal-spray hard-coating powder (L-605), GE Specification P16B-AG11.

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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