Wayne D. Niemeyer
• Senior Research Scientist
• 40+ years of experience
• Scanning Electron Microscopy
• Webinar is being recorded
• Type your questions into the Questions box
The Eight Forms of Corrosion
1. Uniform Attack2. Galvanic (2 metal) Corrosion3. Crevice Corrosion4. Intergranular Corrosion5. Pitting Corrosion6. Selective Leaching7. Erosion Corrosion8. Stress Corrosion
Fontana and Green, Corrosion Engineering, McGraw-Hill, Inc., ©1967, pp28-107
The Eight Forms of Corrosion
1. Uniform Attack2. Galvanic (2 metal) Corrosion3. Crevice Corrosion4. Intergranular Corrosion5. Pitting Corrosion6. Selective Leaching7. Erosion Corrosion8. Stress Corrosion
Case #1Catastrophic Corrosion Failure of
Stainless Steel Rods
Scenario: The steel rods for liquid fills were prematurely breaking while in an assembly line machine, causing the entire line to shut down. We need to determine the mode of failure and identify a potential cause(s) of the failure.
Fracture Face – EDS Data
Element Weight % Weight % SigmaOxygen (O) 13.25 1.01Sodium (Na) 1.99 0.55Silicon (Si) 0.73 0.20Sulfur (S) 0.36 0.15Chlorine (Cl) 0.78 0.17Chromium (Cr) 20.42 0.49Manganese (Mn) 1.15 0.31Iron (Fe) 54.75 0.89Nickel (Ni) 6.57 0.41
Epoxy Mount
Grain boundary corrosion
Polished Cross Section Showing Typical Intergranular Corrosion
SEM BEI Composition Image
Grain boundary corrosion
Polished Cross Section Showing Typical Intergranular Corrosion
SEM BEI Composition Image
Conclusions
• The fracture was caused by intergranular corrosion
• Minor sulfur and trace chlorine in the EDS data indicate sulfate and/or chloride corrosive agents
• The steel rod is very similar to a 304 series stainless steel alloy
• There are apparent chromium carbide precipitates in the grain boundaries, indicating improper heat treatment; thus making the alloy more susceptible to intergranular corrosion attack
Discussions with the Client• Problem #1 – The steel rods are supposed to be 316 alloy stainless steel, but
we determined probable 304 alloy. Their supplier gave them the wrong alloy! The 304 alloy is, in general, much more susceptible to intergranular corrosion than the 316 alloy. Replace any remaining rods with the correct alloy.
• Problem #2 – Apparently the rod is not heat treated properly to minimize chromium carbide precipitation. For future rod purchases specify heat treatment requirement and have the supplier provide certification records with each batch of rods.
• Problem #3 - The client uses an organic acid/strong oxidizer solution to clean the rods and recently increased the concentration. The organic acid is a known cause of intergranular corrosion on stainless steel alloys. Go back to original concentration or replace the cleaner with another solution that does not cause intergranular corrosion on stainless steel.
• We embarked on an in-depth investigation to determine the cause of an
unusual cratering problem on the interior coating of Draw & Iron (D & I)
aluminum beverage cans
• We discovered a surprising set of circumstances that led to a successful
resolution of the problem
Case #2
Acknowledgements
• Frank McDonough – Quaker Chemical,
Conshohocken, PA.
• Mike Shuster – Ball Packaging International,
Westminster, CO
Modern Microscopy, “Microanalysis of Craters in Organic Coating in Aluminum Cans”, February 2006
(https://www.mccrone.com/mm/microanalysis-of-craters-in-organic-coating-of-aluminum-cans/)
Cratering Defined
• The formation of small bowl-shaped depressions in a coating film.
• The depressions frequently have drops or bands of materials at the
center and raised circular edges.
• Common causes are:
– Gel particles
– Dirt
– Fibers
– Undissolved silicone
– Overspray
– Filter aid
– Oil droplets from air lines or machinery
Ref: “Coating Film Defects”, Federation of Societies for Coatings Technology, pp. 14-15, ©1994
SEM Images Aluminum Can Side Wall Crater
Coating
Crater Floor
Bridging + rounded edges = Corrosion!!
EDS - Qualitative Elemental Composition
C,O, Mg, Al, Ca, Mn C,O, Mg, Al, S, Ca, Mn
C,O, Mg, Al, Mn
Crater #1 Crater #2
Crater #3
SIMS Analysis
• Secondary Ion Mass Spectrometry
• Solid sample is bombarded with a beam of particles
(primary ions)
• Ions (secondary ions) are ejected (sputtered) from the
surface
• Secondary ions are collected and mass analyzed (mass
spectrometry)
• Capable of detecting all elements of the Periodic Table
with ppm detection limits
Primary Ion Beam
Secondary Ions,Atoms, Electrons
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Secondary Ions, Atoms, Electrons
SIMS Sputtering Process
SIMS Spectra from Crater Floor and Pit
B
B
Crater floor next to pit: boron ~ 20 counts Crater corrosion pit: boron ~ 2000 counts
Mass (amu) Mass (amu)
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Let’s Piece this Together
• We found Ca, B, Fe in the aluminum can corrosion pits
• Quaker Chemical found abnormally high levels of Ca and Fe in the lubricant/coolant system during the problem time period.
• Production personnel observed sporadic color change in the lubricant/coolant indicative of the dye used in the cooling tower water.
• Borate salts, such as, amine borate are often used as corrosion inhibitors for iron piping in water systems.
• When the production personnel pumped out the lubricant/coolant during the change-over, they replaced a cracked heat exchanger used to circulate the cooling tower water.
• The cooling tower water was highly alkaline (not so corrosive to steel but very corrosive to aluminum).
• THAT’s IT!!! The cooling tower water was leaking into the lubricant/coolant system and causing the severe corrosion on the aluminum cans.
SEM Images from Simulation Tests
Fresh lubricant emulsion Fresh lubricant emulsion with cooling tower water added
Cooling tower water only
Requirements for a Successful Conclusion to this Difficult Problem
• Strong partnership between the vendor and the customer based on open communication, common goals, and mutual trust.
• Teamwork. The “vendor-customer-contract laboratory” team worked closely together with a strong sense of urgency, good project organization, and execution.
Wayne D. NiemeyerSenior Research Scientist
[email protected]• (630) 887-7100
Thank you for joining us. Questions?
UPCOMING WEBINAR
NEW COURSE
• the principles of operation
• basic and advanced imaging modes
• overall capabilities of AFM/SPM
• Hands-on training with a variety of samples
More Than Topography: What Else Can Atomic Force Microscopy Measure?
Tuesday, September 12, 2017 • 1:00 • Dalia Yablon, Ph.D.
Atomic force microscopy (AFM), famous for creating accurate 3D surface maps, is far more powerful than
a mapping tool. AFM can measure nanoscale properties in conjunction with topography – mechanical
properties, magnetic properties, electrical properties and optical properties.
Atomic Force Microscopy/Scanning Probe Microscopy
Wayne D. NiemeyerSenior Research Scientist
[email protected]• (630) 887-7100
Thank you for joining us. Questions?