Overview of IVD
Let us help you understand what Ion Vapor Deposited Aluminum is, or I.V.D. as it is commonly known. It was developed by McDonnell Douglas in St. Louis for the Air Force. The intent is to show that this is an effective coating for replacing cadmium for both the aerospace and commercial market. It was developed to solve a number of different problems. Corrosion was the major problem, I.V.D. also avoids hydrogen embrittlement, galvanic corrosion, dissimilar metal problems, solid metal embrittlement (cadmium in contact with titanium), fatigue reduction vs. weight (on aluminum), and has worked in space. The process is the same no matter what size the chamber. The standard procedures are degreasing the parts, aluminum oxide, clean/grit blast, I.V.D., glass bead, and then chromate seal.
IVD Process
The I.V.D. process begins once the parts are clean and put into an I.V.D. Chamber. It is pumped down to a very low vacuum (8 x 10 -5) at which time a power supply is turned on and the chamber is back filled with argon. This is called glow discharge cleaning. Then the chamber is pumped down again and ceramic heat resistant elements called boats are heated. Next, 99.9 high purity aluminum wire is fed into them and vaporized. The I.V.D. process is versatile and adaptable to a wide variety of parts, shapes, and sizes. It is basically a line of sight process with some wrap around. The current military specification for this is Mil-DTL-83488 Revision C. In this specification, there are three classes and two types. The coating thickness is controlled by the class call out:
| Mil-DTL-83488 | Table 1 | Type I Spray Test (hours) | Type II Spray Test (hours) |
|---|---|---|---|
| Class 1 | .001 Minimum | 504 | 672 |
| Class 2 | .0005 Minimum | 336 | 504 |
| Class 3 | .0003 Minimum | 168 | 336 |
Class 1 is used for rack coating parts or wherever good corrosion protection is needed.
Class 2 is used where there might be some close tolerance that needs to be held. The blue print can call out other thicknesses.
Class 3 is basically used for fasteners where the threads cannot stand a large build-up.
The Type 1 call out is for “as coated” or coated and glass beaded. The Type II call out is for glass bead and a chromate conversion coat. The replacements for chromate conversion coating work for I.V.D. the same as they do for other aluminum alloys.
Advantages of IVD
The use of I.V.D. Aluminum has many known advantages. Some of the advantages are.
- It outperforms cadmium in actual service test as well as acidic salt fog.
- It has a 925°F (500°C) continuous service temperature.
- It does not induce hydrogen embrittlement or solid metal embrittlement.
- It helps to relieve dissimilar metal problems and galvanic corrosion.
- There is no fatigue factor for aluminum parts as is caused by anodize.
- It is Conductive.
- It has a wrap around ability to coat but basically considered a line of sight coating.
- It has no sublimation of the coating in a space environment.
I.V.D. Aluminum is the US Government’s choice as a cadmium replacement for all branches of the service: The Army, Navy, Marines and Air Force. Military Handbook 1568 (USAF) Materials and Processes for Corrosion Prevention and Control in Aerospace Systems, identifies I.V.D. Aluminum as an acceptable alternative to cadmium, citing its corrosion protection and non-toxic properties.
IVD Programs
The following is a list of programs using I.V.D.:
| Military | Commercial |
|---|---|
| Aircraft Military | Industrial Turbines |
| Aircraft Commercial | Steam Turbine Blades |
| Helicopters | Fasteners |
| Missile | Neodymium Magnets |
| Misc. Military | Fuel Cell Components |
| Engine Mounts |
