1. 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. Yadlowsky HY-Tech Research Corporation, Radford, VA 24141
Gail Ludtka M & C Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831

2. 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

3. 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

4. File: SVC paper_all.ppt
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
File: SVC paper_all.ppt

5. Advantages of Boron Deposition Using Cathodic Vacuum Arc Technique
Very high current density ( 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.

6. Coating Material Selection Criterion
Thermodynamic calculations suggest that boron is an excellent candidate for a non-wetting coating for iron-based substrates

7. Illustration of the Thermodynamics - Heats of Formation - for Relevant Alloy Systems
B has a repulsive chemical reaction with aluminum
B is attracted to steel

8. Schematic of Automated “Dipper”
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).

9. Soldering Test Set-up and Die Pin Schematic of Pin for Solder Testing
Automated, molten aluminum testing apparatus
Dimensions are in inches

10. Examples of Soldering Trials Data on Coated vs. Bare H13 Pins
Experimental Data indicating the onset of Soldering
Experimental Data indicating No Soldering

11. 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

12. Boron-coated H13 Steel Pin Exhibits No Soldering After 50 Cycles
Boron-coated H13 Steel Pin Exhibits No Soldering After 50 Cycles* in Molten Aluminum
End view of die casting pin

13. 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.

14. 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.