Plasma Chromium Oxide
Quick Spec Summary
| Spec | Value |
| Composition | Chromium oxide, 98% purity |
| Macrohardness | Rc65–72 |
| Cross-sectional hardness | 900–1200 DPH300 |
| Bond strength | 4000 psi (low carbon steel) |
| Service temperature | ≤540°C (1000°F) dry wear; 177–205°C (350–400°F) sealed/corrosive |
| Surface finish achievable | 15–35 µin aa ground; metallographic polish lapped |
| Substrates | Carbon/alloy steels, stainless, nickel alloys, cast iron |
| Industries | Pumps & valves, chemical processing, textiles, industrial wear parts |
| QA / Spec | AS9100 & ISO 9001 certified, NADCAP-compliant, full lab cert on request |
A Ceramic That Takes Punishment
Chromium oxide is the hardest ceramic in our plasma spray lineup. When abrasive grain, slurry, or a hard counterface is chewing through your part, this material is built to slow that down. It also self-mates, which matters when two coated surfaces run against each other under load.
Hard and chemically stable, yes. But it will not flex. That trait decides where it fits and where it does not.
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Hardness
Rc65 to Rc72 on the macro scale. 900 to 1200 DPH300 across the cross section. Those numbers put chromium oxide in the same range as some hardfacing alloys, but with the chemical stability of a ceramic.
What does that mean on the floor? Abrasive grain cuts like a tiny blade. The harder the surface, the slower that blade dulls. On a slurry pump or a wear plate, that difference shows up as months of extra service.
Service Temperature
Two ceilings apply. One for heat. One for chemicals.
Heat. Wear resistance holds below 540°C (1000°F). Above that line, performance shifts. If your part runs hot, tell us before you spec this material. We will say yes or no.
Chemicals. Chromium oxide does not dissolve in acids, alkalis, or alcohol. Sealed properly, it works in corrosive chemical service up to 177 to 205°C (350 to 400°F). The sealer is what makes that range possible. Without it, porosity gives chemicals a path to the base metal.
Bond Strength
Bond strength on low carbon steel is 4000 psi. That 4000 psi bond holds up under thermal cycling and mechanical load when the surface is prepped correctly.
Coating Data
| As-sprayed texture | 350 to 550 microinches RMS |
| Ground finish | 15 to 35 microinches aa |
| Macrohardness | Rc65 to Rc72 |
| Cross-sectional hardness | 900 to 1200 DPH300 |
| Density | 4.9 g/cc |
| Coating weight | 0.027 lb/ft² per 0.001 inch |
Composition
| Composition | Chromium oxide, 98% |
| Size range | -170 mesh +15 microns |
| Melting point | 2435°C (4415°F) approximate |
The 98% purity keeps the chemistry predictable from one run to the next. The size range is tuned for plasma spray, where the powder has to melt fully in the arc and still feed clean through the system.
How the Coating Locks On
The coating does not glue onto the part. It builds there. Particles arrive molten, flatten on impact, and grip the surface profile. That profile is the whole reason prep matters. A smooth face has nothing for the particles to grab.
We treat prep as part of the job, not a warm up. Oil, scale, and residue all have to go before the torch ever fires. Miss that step and the coating can separate in service. On a part that spins or slides, separation means scrap.
The other variable is heat. Chromium oxide is dense, and dense ceramics hold stress. We build the coating in layers with controlled cooling between passes. Rush that cycle and the coating can crack from the inside, long before it ever sees the job site.
Stress and Shape
Geometry changes how thick the coating can go. On a one inch mild steel shaft, we have run chromium oxide past 0.8mm (0.030 inch) on the outside diameter with no spalling and no delamination.
Flats and inside diameters are tighter. Keep those under 0.6mm (0.025 inch). A flat face or a bore gives built up stress nowhere to go. Curved surfaces spread that stress along the curve. That is the whole reason the limit changes with the shape.
Substrates
Grouped by family:
- Carbon and alloy steels: Low carbon steel, alloy steels. The workhorses for rebuild and wear protection.
- Stainless steels: Good for parts that see moisture or mild chemical exposure.
- Nickel based alloys: For high temperature and corrosive service.
- Cast iron: Common in pump housings and older equipment.
Prep comes down to one thing. The coating needs something to hold onto. That means a blasted surface, free of oil, scale, and residue. Skip it and the coating can separate in service. On a part that spins or slides, separation means scrap.
Surface Finish Achievable
As-sprayed, chromium oxide is rough. We can take it smoother three ways.
| As-sprayed | 330 to 500 RMS |
| Brushed, 2 to 5 min | 220 to 290 RMS |
| Brushed, 5 to 10 min | 150 to 200 RMS |
| Brushed, 10 to 15 min | 140 to 160 RMS |
| Ground, 150 grit diamond | 15 to 35 microinches aa |
| Lapped | Standard metallographic polish |
Ground finishes use a 150 grit diamond wheel with the feeds and speeds recommended for flame sprayed ceramic coatings. We can share those settings on request. Lapped finishes follow standard metallographic polishing methods for ceramics.
Industries
Pumps and valves. Particle erosion and cavitation tear up pump internals. Chromium oxide resists both, and its anti-galling property helps with close tolerance fits.
Think about a slurry pump impeller. Grit and sand move through it all day, and the leading edges wear back fast. A chromium oxide coating gives those edges a hard face that stands up to the grit. The impeller keeps its shape, flow stays steady, and the pump stays on line.
Chemical processing. Sealed coatings protect parts in corrosive service up to 177 to 205°C (350 to 400°F). Pumps, valves, and mixer components are common candidates.
Picture a mixer shaft turning in a bath that would eat plain steel over time. Sealed chromium oxide keeps the chemicals off the base metal while the hard surface resists wear from the mixer blades.
Textiles. Machine elements that touch fiber or thread get a coarse, brush finished surface that is hard, wear resistant, and corrosion resistant. Guides, rollers, and contact points last longer and keep thread quality steady.
Industrial wear parts. Seal rings, wear plates, and sleeves are typical when abrasive grain or hard surfaces cause the wear. If your part meets grit, sand, or a hard counterface every day, this material is worth a look.
Against Titanium Dioxide
Titanium dioxide is the other plasma sprayed ceramic we run. It is softer at Rc53, and it wins on one point. Finish. Titania grinds to 6 to 8 microinches aa. Chromium oxide stops at 15 to 35.
So the choice comes down to the threat. If abrasive grain and heat drive the job, chromium oxide takes it. If the part needs the smoothest possible surface and heat stays moderate, titania is the better pick. Hardness or finish. That is the trade.
Sealers
On dry wear jobs, porosity rarely matters. On chemical or wet service, a sealer closes the surface and keeps media away from the base metal. Tell us the service conditions and we will name a sealer that fits. Skip this step in a corrosive job and the base metal can suffer even when the coating itself holds up.
QA / Spec
AS9100 and ISO 9001 certified. NADCAP requirements met. Our lab checks thickness, bond strength, hardness, and microstructure before parts ship. Customer specs welcome, with certification paperwork supplied on request.
Ready to Talk?
Call 888-725-0150 or send your part details through our quote form. Same business day reply.
Where to Go Next
This is one of the materials we run on a plasma spray line. For the full picture, see the thermal spray coating processes page. It covers HVOF, metalizing, plasma spray, and spray and fuse hardfacing, with guidance on how to pick between them.
