Minimox™ Alloy Surface Treatment
Alloys designed for high-temperature applications contain certain additions. Research at Material Interface has shown if those addition elements are instead applied as a superficial self-protective alloy treatment to the surface of a more basic alloy, the same high-temperature surface oxidation properties can be achieved.
Why put it IN the alloy when you can put it ON the alloy?
Minimox™ alloy surface treatment is the result of the research. The product is:
- Single component process
- Can be applied in the field without special equipment (spray, brush, dip)
- Can be applied in and on complicated geometries
- No volatile hydrocarbons
- Pennies/sq foot
The surface treatment nucleates alloy self-protection.
What is self-protection?
In alloys that are "self-protected," the composition of the ultimate protective coating is primarily a function of alloy, not the coating material. After treatment with Minimox™ nanoparticle solution, resulting thermal oxides have:
1. Better chemistry, and
|Surface Cr/FE ratio improvement
Bulk 410 Cr/FE ~ 0.14
Untreated & oxidized 410, Cr/Fe = 0.03
Treated & oxidized 410, Cr/Fe = 5.7
The surface oxide after Minimox™ treatment
and suitable oxidation is CR-MN-O spinel,
even though there is no Cr or Mn in the solution.
The enhanced chromium at the surface is due to a change in the surface chemistry of the alloy - there is no chromium in Minimox™ solution. The alloy protects itself.
2. Better structure
Fewer voids and protrusions in the Minimox™-treated and oxidized surface result in fewer nucleation sites for crevice corrosion.
The reduction of oxide scale growth at elevated temperatures is demonstrated on these samples of coated vs. uncoated 410 stainless steel oxidized at 850°C.
|Minimox™- coated and Oxidized
In cross section, these samples show the uncoated sample had a 450µm oxide while the coated sample had a minimal oxide layer.
|Minimox™- coated and Oxidized, 10X
This reduction of oxide scale growth at elevated temperatures occurs after Minimox™-treatment on a wide variety of stainless, aluminum, nickel and superalloys. All of the alloys shown below were dipped in Minimox™ and heated to 850°C (1560°F) for 24 hours.
This is a 304 stainless bowl heated to 927°C (1520°F), for 3 hours/cycle, 3 cycles. The left side (golden) was coated with Minimox™ nanocrystalline surface treatment; the right side was uncoated and shows spalling and excessive oxidation.
One application for the technology lies in a heat-treating pretreatment for martensitic stainless steels. The sample below shows a section of 410 stainless that was heat treated 1037°C (1900°F) 1 hour followed by tempering at 760°C (1400°F) for 4 hours.
Untreated Treated with Minimox™
- Reduction of metal dusting
- Hot salt exposure
- Stress corrosion cracking
- Room temperature electrochemical testing
- Aluminum corrosion
Details of all of these experiments, and more, are included at www.Minimox.com