This article describes a surface treatment process that can significantly improve the life of components that may fail by wear, fatigue or corrosion due to the existence of surface flaws.

Fig. 1 Schematic representation of ion beam surface treatment process. The beam system consists of a pulsed power source that produces an ion beam that heats and melts the surface of the material. Melt depth is set by the material being processed and by varying the energy of the ion beam.

As the cost of materials processing increases, customers are demanding improved product lifetime and performance, longer warranties, and reduced cost of ownership. Critical component failures caused by wear, fatigue, and corrosion of surfaces often initiate premature failure of entire systems. The result is lost revenues that may far exceed the cost of the failed component itself.

There are numerous technologies available to improve the wear, corrosion and fatigue resistance of finished products. These include surface treatment technologies such as carburizing and nitriding (atmospheric or plasma), ion implantation, and mechanical polishing.

A few years ago, another technology was introduced by researchers at Sandia National Laboratories and commercialized by Quantum Manufacturing Technologies, Albuquerque, NM under an exclusive licensing agreement with Sandia. This technology, known as IBESTT (ion beam surface treatment technology) uses a pulsed ion beam process to modify and improve the surface qualities of a material by rapidly melting and resolidifying the surface of the material to a depth of 1 to 10 microns without affecting the underlying material. The process is said to improve surface finish, increase corrosion and wear resistance, remove hard, thin coatings and burrs, and seal surface microcracks and pores, thus improving the mechanical properties of the surface.

Applications of this process include aerospace, automotive, medical, and tool and die. The benefits realized in these applications include healing of microcracks, improved hardness, improved corrosion and wear resistance, smoother surface finishes, more refined grain structures, and extended service life.

Process Description
This thermal process uses a pulsed, high energy (0.1 - 1 MeV) ion beam to deposit energy into the top 1 to 10 microns of a 50 sq. cm area of the surface, rapidly heating it to the melting temperature (Fig. 1). The depth of treatment is dependent upon the material being treated and is controllable by varying the ion energy and species.

The surface is molten for only a few seconds and cools rapidly at a rate of about 109ÝC/second by conduction into the bulk material at the end of the input pulse. The resulting surface microstructure is more homogeneous with a uniform, equiaxed grain size. Grain diameters of less than 100 nm are typical. At sufficiently high energies, the process can remove coatings such as oxides and nitrides.

The processing equipment consists of a repetitive high energy pulsed power (RHEPP) system, an ion beam chamber, and a parts processing chamber. The RHEPP system provides short, high power electrical pulses to the ion beam system and consists of three subsystems: a microsecond pulse compression system; a fast pulse section; and a linear induction adder. The ion beam is a magnetically-confined anode plasma (MAP) system that converts the RHEPP pulses into high intensity beams of ions. The ions are directed onto a material surface to be treated.

The parts to be treated are placed into the treatment chamber by an automated material handling system. Operating at 400 keV and 150 nanosecond pulse lengths with adjustable treatment energies from 0.1-8 J/cm^2, material processing is typically very fast covering 50 cm^2 per pulse.



Fig. 2 Surface of a wire EDM cut edge on a 400 series stainless steel. (a) As-machined surface. (b) Surface after ion beam treatment. (500X)

Fig. 3 Die blade surfaces. (a) As-machined cutting edge. (b) Cutting edge after ion beam surface treatment. The cutting edge is smoothed, deburred, and sealed, increasing the die life while retaining dimensional tolerances.

Fig. 4 Surface of a ground Ni-Ti dental drill. (a) As-machined surface. (b) After ion beam surface treatment showing a much smoother surface that is deburred and having less surface defects than the as-machined surface.

Case Studies and Results
Figures 2 through 4 show the macrostructures of surfaces prepared using the ion beam surface treatment process. Images denoted "a" show the as-finished cut surfaces of products made from various materials for the tool & die, and medical industries. The rough surface finish of these parts is readily apparent and is the result of porosity and/or a rough machining process. Images denoted "b" show the material surfaces after being finished by the ion beam process. The reformed, recast surfaces are clearly smoother and more homogeneous.

The thermal process has been applied to many products in the tool and die industry. Results from five large domestic manufacturers are shown below.

1) Company A
Type of tools treated and tested:
Six uncoated three-flute solid carbide drills measuring 14 mm, 17 mm, 21 mm
Application:
Dry cutting gray cast iron
Type of Drilling, Depth of Holes, and Surface Feet:
Jamming, 25 to 80 mm deep, 240 SFM
RPM/Feed Rates:
14 mm) 1820 RPM, 0.3 mm/rev. feed rate;
17 mm) 1455 RPM, 0.044 mm/rev. feed rate;
21 mm) 1213 RPM, 0.05 mm/rev. feed rate.
Normal Lifetime of these drills:
3 days
Lifetime improvement after ion beam processing:
5 to 6 days (60% improvement)

2) Company B
Type of tools treated and tested:
Soft Steel two-flute carbide tipped drill, 0.75" diam.
Application:
Wet cutting 6262 T4 aluminum (sulferized oil)
Type of Drilling, Depth of Holes, and Surface Feet:
Solid cutting to 0.75"
RPM/Feed Rates:
1528 RPM, 350 SFM, 0.005"/rev. feed rate
Normal Lifetime of these drills:
22 hours
Lifetime improvement after ion beam processing:
132 hours (600% improvement)

3) Company C
Type of tool treated and tested:
Uncoated four-flute solid carbide end mill, 0.75" diam.
Cutting application:
Dry cutting gray cast iron
RPM, Surface Feet, Feed Rate:
1100 RPM, 216 SFM, 7"/min. feed rate
Normal Lifetime of these drills:
10-12 hours
Lifetime improvement after ion beam processing:
up to 40 hrs (Factor of 4x improvement)

4) Company D
Type of tools treated and tested:
Ten triangular uncoated indexable solid carbide inserts
Cutting Application:
Dry cutting gray cast iron
Cutting Speed, Feed Rate, Lead Angle:
350 ft/min.; 0.010"/rev. feed rate; 15 degrees lead angle
Normal Lifetime of these drills:
11.9 minutes
Lifetime improvement after ion beam processing:
19.1 minutes (60% improvement)



CONCLUSION

It is well known that improving the surface finish of a part can lead longer life in certain applications. Parts that are subject to wear, corrosion, and fatigue failure often undergo surface treatments to reduce the number of surface flaws that can lead to premature failure.

The ion beam surface treatment process described here has been shown to improve by as much as 60% the service lives of various products in the machine tool industry. These improvements may also been seen in the medical, aerospace, and automotive industries depending upon the application. IH

For further information on the IBEST process, contact QM Technologies, 3701 Hawkins St. NE, Albuquerque, NM 87109. Phone: 505.342.2851; Fax: 505.342.2852; website: www.qminc.com.