UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Aluminum Soldering Performance Testing of H13 Steel as Boron Coated by the

Cathodic Arc Technique

James M. Williams, C.C. Klepper, R.C. Hazelton and E.J. YadlowskyHY-Tech Research Corporation, Radford, VA 24141

Gail LudtkaM & C Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Background for this Study• Preliminary deposition studies

demonstrate that boron can be used for the corrosion protection of steel

• Thermodynamic calculations indicate that boron has a negative affinity for aluminum

• This presentation describes the experimental results of a set of dip tests of B coated H13 pins in molten aluminum

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Cathodic Arc Vacuum Technology

Benefits– A fully ionized plasma is

produced out of solid feedstock

– Deposition rates exceed other plasma-discharge methods

– Fully ionized plasma stream allows:

• Substrate biasing to guide ions to coat irregular geometries

• The potential to control of the energy with which ions impinge onto the substrate

Challenges / Drawbacks– Macro-particles require

filtering – Vacuum coatings require a

higher cost than some sprayed and fused cermet coatings

File: SVC paper_all.ppt UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Illustration of Typical Cathodic (Vacuum) Arc Deposition with 90o Bend Magnetic Duct to Filter

out Debris from Solid Cathode

A curved solenoid help prevent debris/ macro-particles from depositing on the substrate

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Advantages of Boron Deposition Using Advantages of Boron Deposition Using Cathodic Vacuum Arc TechniqueCathodic Vacuum Arc Technique

• Very high current density (10-100 MA/cm2) where the arc contacts the cathode results in a non-stationary hot spot that efficiently vaporizes and ionizes materials such as boron, which have very high boiling points (>2000 C).

• Plume is fully ionized and can be guided with the aid of a magnetic solenoid.

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Coating Material Selection Criterion

• Thermodynamic calculations suggest that boron is an excellent candidate for a non-wetting coating for iron-based substrates

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Illustration of the Thermodynamics - Heats of Formation - for Relevant Alloy Systems

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Fraction of Boron or Aluminum

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tha

lpy

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/g-a

tom

) B in Al

B in Fe

Al in FeB is attracted to steel

B has a repulsive chemical reaction with aluminum

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Schematic of Automated “Dipper”* Testing Set-up to Simulate Die Casting Conditions

*A variant of the dunk tester including programmable, computer controls thus enabling control of the dipping cycle and process cycle parameters (i.e., temperature of molten aluminum and of the lubricant, the dipping time in aluminum, in the lubricant, and in the air spray).

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Soldering Test Set-up and Die Pin Schematic of Pin for Solder Testing

0.1875

Thermocouple

2.0000

0.2500

0.5000

0.7500 0.0625

0.03125

Automated, molten aluminum testing apparatus Dimensions are in inches

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Examples of Soldering Trials Data on Coated vs. Bare H13 Pins

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DB103501 Hy-Tech H13

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DB103501 Hy-Tech H13-B28-4

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DB103501 Hy-Tech H13-B28-3

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Experimental Data indicating the onset of Soldering

Experimental Data indicating No Soldering

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

H13 without coating after 16 cycles exhibits soldering

The experimental conditions are as follows,

(1)     Temperature of melt aluminum (Tmelt): 700oC

(2)     Temperature of lubricant (Tlubricant): 21oC(3)     Dipping time in aluminum(t1):10 s(4)     Time in lubricant(t2):3 s(5)     Time in air spray(t3):5 s

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Boron-coated H13 Steel Pin Exhibits

No Soldering After 50 Cycles* in Molten Aluminum

End view of die casting pin

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Boron Concentration as a Function of Depth derived from original RBS Data

All the B has reacted/diffused inward to yield a 0.5 micron thick reaction layer.

UT-BATTELLE

Oak Ridge National LaboratoryU.S. Department of Energy

Summary• Experimental results support the primary hypothesis that,

based on thermodynamic based predictions, cathodic arc deposited boron coatings resist aluminum wetting.

• These coatings strongly adhere to the steel substrate, while resisting wetting by aluminum as predicted by thermodynamic calculations.

• Macroparticle management is the biggest challenge for this technology, but preliminary conceptual equipment designs indicate that this is solvable.

• Boron shows promise as a life-extension coating for aluminum casting steel dies.

• Further R&D would provide an industrially robust coating solution for the prevention of soldering and thermal fatigue of aluminum die casting dies.