Laser Toughens Metal Without Polluting

By Michael A. Riley and James G. Mitchell

Buyers of military hardware compromise between performance and cost. In many systems, survival in harsh combat environments usually means the selection of expensive materials for corrosion protection, wear and erosion resistance, or thermal management.

This dilemma has fostered the broad and complex field of coatings technology. From advanced polymers to high temperature ceramics, coatings of all types have been developed to improve the surface properties of structures. However, most techniques for metal systems involve coatings that can only adhere mechanically to their substrate metal. In addition, many of today's solutions involve materials that are, or create, toxic and hazardous by-products.

A Tennessee-based firm, meanwhile, has developed a new technology for improved metal surfaces that is environmentally friendly. Surface Treatment Technologies Inc. (ST2) recently licensed a laser surface alloying process and is adapting it to military needs.

The laser process is known as Laser Induced Surface Improvement, or LISIsm. It is the result of efforts by scientists at the University of Tennessee Space Institute. ST2 won five Phase I Small Business Innovative Research (SBIR) contracts from the Defense Department.

In conventional coating processes, a coating is placed on top of a substrate, and adheres via mechanical bonding. While this may be acceptable for many applications, many military applications exceed the strength limits of conventional coatings. LISIsm re-alloys a base metal by using laser energy to rapidly melt the top 1-millimeter of the surface. In this brief molten state, metal or ceramic powders are rapidly melted into the surface, resulting in a new alloy chemistry, a highly refined grain size, and a surface that is metallurgically bound to its substrate, much like a weld.

It is as though the new surface has emerged from the base alloy by virtue of the controlled addition of the master alloying components.

In other processes that offer this metallurgical bond, there often is a high degree of heat put into the part, resulting in what is termed a heat-affected-zone. These zones weaken structures and are detrimental in critical components. Because of the rapid interaction time of the laser with the metal, LISIsm parts produce narrow heat-affected zones in base alloys.

An SBIR project funded by the Naval Air Systems Command, Patuxent, Maryland, is focusing on the ability of LISIsm to provide non-cadmium, alternative surfaces to act as sacrificial anodes for flight-critical hardware. The Environmental Protection Agency is seeking ways to apply the technology to existing commercial applications that require significant use of hard chromium plating.

A recent independent analysis of the LISIsm process shows it has potential to satisfy advanced and basic materials needs. Concurrent Technologies Corporation, a non-profit research and development organization promoting the use of "intelligent, agile, and green processing and manufacturing," is considering LISItm for various manufacturing technology efforts.

Potential military applications for LISIsm surfaces include:

Future applications involve surfaces for ships, cost-effective surface modifications to replace conventional paints, and non-skid surfaces for ship decking.

Experts predict the technology could be applied to the surface modification of those hard to reach places, such as inner diameters of tube structures, hydraulic systems, or blind corners and crevices. Researchers have developed LISIsm fiber-optic heads, known as end-effectors capable of accessing inside 1-inch diameter tubes.

This capability could work for both cadmium and chrome replacement in military hardware, from power trains to hydraulics and weapon systems.

ST2 plans to offer LISIsm production systems to both government and contractor facilities for in-plant operation. This will involve sub-licensing for specific needs, design, assembly, and installation of laser hardware.

Michael A. Riley is president and James G. Mitchell is chief executive officer of Surface Treatment Technologies, Tullahoma, Tennessee.

Topics: Emerging Technologies

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