What are the key technological issues relating to the development of new coatings, advanced materials and surface treatments?
TLT Sounding Board September 2011
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As is often the case with technology, some desirable attributes in a product seem to be mutually exclusive. With coatings the conflict appears to be between hardness/durability and low friction. However, TLT readers also noted the need to observe environmental restrictions, an even more important consideration due to the long-lasting attributes of these products. As one reader noted: “All the good stuff lasts forever, which is exactly why it’s an environmental issue and why we can’t use them anymore.” Asked about emerging technologies with surface treatments, nanotechnology and diamond-like carbon topped the list.
Durability, thickness and frictional coefficient variances among surface area.
Environmental restrictions.
Lack of rust.
New coatings should have the hardness of diamond, the lowest friction coefficient among all materials, high resistance to chemical attack by acids or any other strong fluid, extremely smooth surface and processability for surface treatment making the coating hydrophobic or hydrophilic as needed. My colleagues and I have developed such a coating (ultranano-crystalline diamond).
Temperature variations, pressures exerted and surface qualities.
It depends on the end-use result. We have surface treatments that need to be easily washed off before painting but still need to provide protection while parts are in process before paint. Very fine line here between durability and washability.
More durable coatings. Many coatings do not hold up to the tens of millions of RCF cycles typical for rolling bearings, especially at high-Hertzian contact loads.
Cost of use.
I believe there will be many different technological issues depending on how the coatings, materials and surface treatments are used.
Adhesion.
Performance, cost and regulatory compliance.
Lubricant additive compatibility. Traditional additive chemistries may not be effective on new surface coatings.
Need to determine whether they offer a sufficient functional advantage and low enough cost relative to current materials to justify the R&D needed.
Two properties of coatings must be optimized but are often mutually exclusive: hardness/fracture toughness and low friction.
Long lasting, compatible with lubricant, low friction in most applications, economical and relatively easy to apply.
Stability with existing fluids.
Effectiveness vs. cost.
Optimization of coating thickness for minimum friction and wear and for maximum resistance to delamination. Optimization of surface texturing for best tribological performance of various mechanical components.
Titanium nitride.
Surface coatings can substitute lubricants to some extent.
Wear resistance and friction reduction.
Compatibility with PAG-based lubricants is an issue for OEMs, who prefer to use this synthetic technology.
Cost effectiveness, commercialization.
Balancing the need with increasing performance requirements with the regulatory pressures for more green coatings/surface treatments.
In-can stability, VOCs and other environmental factors.
Lubricant capability and stability.
Would you include surface engineering among the top candidates when looking for a solution to improve the tribological performance of a bearing component?
Yes
73%
No
27%
Based on results from some 13,000 TLT readers.
What new technologies have you either seen or heard about relating to advanced materials, coatings and surface treatments?
Advance protective coatings.
DLC coatings have promise to achieve both hardness and low friction.
Solid materials.
Antibacteria-coated, steel, polymer replacement of hex chrome sealers.
Application techniques and surface preparation.
Waiting on a five-year rust preventative for machined parts that is easily washed off.
Magnetron-sputtered coatings. Vacuum sputtering and ion-plating electrophoresis.
Ultra thin coatings.
We are in that business, and you don’t have enough space to address all of the coatings, materials science and surface treatment technologies that are emerging.
Cross-lined polymer.
Diamond-like carbon and microsurface texturing.
Nanoadditives.
Polymer ceramic coatings, molybdenum and boride lubricantless coatings.
New boriding treatments, low-temperature super-carburization treatments for steels, new durable coatings for rolling element bearings.
Nanocomposite metal carbide reinforced amorphous hydrocarbon.
Diamond-like carbon, laser texturing, isotrophic superfinishing.
Nanotechnologies.
Laser surface texturing technology.
Self-lubricating hard coatings, textured surfaces exhibiting microlubrication effect, superlubricity additives, biomimetic coatings, triboconditioning.
Superfinishing to improve efficiency.
Plasma and HVOF.
We are working in physical vapor deposition coatings, plasma electroxidation, nitruration, solgel coatings and laser cladding.
What are the most important criteria for selecting a surface engineering technique?
Hardness/wear resistance
17%
Frictional behavior
15%
Lubricant compatibility
15%
All the above
57%
None of the above
0%
Other
20%
Based on results from some 13,000 TLT readers. Total exceeds 100% because some readers chose more than one answer.
Editor’s Note: Sounding Board is based on an e-mail survey of 13,000 TLT readers. Views expressed are those of the respondents and do not reflect the opinions of the Society of Tribologists and Lubrication Engineers. STLE does not vouch for the technical accuracy of opinions expressed in Sounding Board, nor does inclusion of a comment represent an endorsement of the technology by STLE.