Dare I ask this having recently digested threads about costs and 'cookbook' standards - still, I thought a few might have the inclination to try.
I was wondering if anyone has tried the specialized TiN coatings or the family of such coatings for steam locomotive service - specifically I was thinking of journals, valve gear, running gear, etc. where the wear and thermal protection might be beneficial - of course you'd have to be prepared for what the protection of one component does to another.
http://en.wikipedia.org/wiki/Titanium_nitride

-Sully

Hi Sully,

I happen to be in the PVD business. We do TiN coating work along with molybdenum disulfide (or MoS2 - a dry lubricant) and a few other plasma based surface modification processes. Although I cannot get into the details, we are currently evaluating a steam locomotive application and would certainly welcome other projects in the field. Being a volunteer on a steam locomotive (different than the one under consideration), I have a personal interest in bringing the benefits of PVD coatings to the industry, but I need to be able to justify enough of a market segment for our company to put much effort into pursuing it, so it would be helpful to hear from other folks who might be interested.

TiN produces a hard, corrosion resistant surface. MoS2 is a dry lubricant that was originally developed for space applications and has a very low coefficient of friction (on the order of 0.01 - and that's not a typo). Our firm also has a unique technology called metal ion implantation that has been shown to dramatically improve fatigue life while enhancing corrosion resistance. All these processes take place in a vacuum chamber.

Although I am fairly new to the field (having formerly worked on fuel cells), I will be happy to try to answer any questions. If anyone is seriously interested in discussing an application of these surface engineering products to their locomotive, please contact me via PM.

Regards,

I have seen piston and valve rods and air compressor rods ground and hard chromed - which does seem to reduce wear in packings and corrosion on the rod surface, but i find myself worrying about cracks forming under the coating and growing unseen until reaching the point of failure. Visual inspectons happen daily - NDT very infrequently. Is it possible to see developing problems despite a coating being applied without special tools?

dave

Dave,
That is an interesting question/problem - I bet Wolf or someone else can say for sure. My experience was with tool grinding and repair, from what I remember the coating is so thin, that often you can see through it, and physical defects are usually visible as normal. Basically it is similar to surface of anodized aluminum.
Actually I wonder if NDT like ultrasound would be affected or obstructed?
Most of you have probably seen the coatings on drill bits at the hardware store - but more and more the technology is being applied to internal combustion engine components and high wear or temperature power train components like gear sets.

Dave brings up an interesting question. Let me provide some background while working my way toward an answer to his question. A hard chrome process would tend to yield a thicker coating then would a properly applied PVD coating. Each coating I described in my post has an optimal thickness range...too thin and you don't get the performance, too thick and the residual stress in the coating can lead to flaking. In the case of TiN, you would not want to see a coating much thicker than 3.8 microns for a performance application (as opposed to a decorative one). We have specialized measuring equipment to detect coatings that are that thin. SAE AMS 2444A covering TiN PVD coatings is often specified by our aerospace customers as a standard for us to follow.

By way of example, we shipped out some bearing parts for a client yesterday. They came to us with a near mirror finish after grinding, but due to a poorly designed shipping package some of the parts had very light scuff marks. After coating with TiN to an average thickness of about 1 micron, you could still see the scuff marks through the coating. Similarly, any cracks that may develop should also be readily apparent.

Although I am not an NDT expert, my experience in using the ultrasound machine on our boiler showed that they would bounce back at the macro-discontinuities encountered at plate-to-plate interfaces, but gave good thickness readings through the magnetite layer. As the PVD coatings would have a thickness on the order of or smaller than the magnetite layer, it would stand to reasond that a UT machine would not be affected by PVD coatings.

For components where fatigue cracking is a serious concern, metal ion implantation technology is particularly appropriate as there is a dual benefit: an extremely thin layer of the metal ion species is imbedded in the surface providing corrosion protection (depending on the metal species chosen), plus a dislocation structure is created in the subsurface layer yielding compressive stresses that tend to counter crack growth - much like shot peening, but without the damage to the surface finish.

I hope that address the questions at hand satisfactorily...

Best,