Method and apparatus for altering material using ion beams

Abstract

A method and apparatus for treating material surfaces using a repetitively pulsed ion beam. In particular, a method of treating magnetic material surfaces in order to reduce surface defects, and product amorphous fine grained magnetic material with properties that can be tailored by adjusting treatment parameters of a pulsed ion beam. In addition, to a method of surface treating materials for wear and corrosion resistance using pulsed particle ion beams.

Description

FIELD OF THE INVENTIONThis invention relates generally to material modification, and more specifically to a class of techniques whereby a thin layer of material on the surface of a body can be rapidly heated, followed by a rapid quench as the heat energy is conducted into the body. The invention also relates to other types of surface treatment using ion beams to convey energy to a near-surface region.BACKGROUNDThe mechanical and chemical properties of surfaces are an important factor in almost all materials applications. Numerous techniques have been developed to enhance these properties for particular applications. These techniques range from widely used techniques such as galvanizing and heat treatment of alloys to specialty techniques such as ion implantation and laser glazing which are expensive and not scaleable to common industrial use. The use of surface treatments to improve properties such as surface hardness, wear resistance, corrosion resistance, and fatigue lifetime add ...

AI Technical Summary

Benefits of technology

The present invention provides a system for generating a high energy, pulsed ion beam repetitively over an extended number of operating cycles. In particular, the present invention provides an ion beam generator capable of repetitive operation over an extended operating cycle suitable for thermally treating large surface areas of a material at low cost. This ion beam generator comprises a high voltage, high current pulsed power system and a pulsed ion beam source, both capable of high repetition rates and both having the capability for an extended operating life.

Problems solved by technology

These techniques range from widely used techniques such as galvanizing and heat treatment of alloys to specialty techniques such as ion implantation and laser glazing which are expensive and not scaleable to common industrial use.

Wrought iron is reasonably tough, but is very soft, and hence not well suited to the production of weapons.

It is possible to harden the material by cold-working in the course of shaping, thus producing a work-hardened material, but this material is brittle as well as hard.

However, many other materials, including metals, alloys, semiconductors, ceramics, and other nonmetals are subject to corrosive effects.

A side effect of corrosion mechanisms can be hydrogen embrittlement, in which the hydrogen generated by a corrosive process enters into a metal or alloy, reducing the ductility of the material, which is then weakened, allowing surface flaws to grow under a stress, thus increasing the susceptibility of the material to further corrosion and eventual failure under stress.

Many methods exist to reduce the pernicious effects of corrosion, but it is estimated that some 4% of the gross national product is still lost to corrosive effects.

Wear is occasionally a useful process (e.g., writing with pencil and paper), but more often is deleterious to both the structure and the operation of mechanisms.

Adhesive wear arises from the formation, during sliding, of regions (called junctions) of adhesive bonding on a microscopic scale.

Such particles constitute wear in their formation, and may also add to abrasive wear.

Abrasive wear is produced by a hard object being dragged along a softer one, thereby digging out a groove.

Fatigue wear occurs as cracks form and grow as the result of fatigue, especially in rolling systems.

A crack forms below the surface, and grows to intersect the surface, thereby lifting a large particle out of the surface.

The various forms of wear are often synergistic, resulting in a form of degradation which is nearly universal in any mechanism or device having moving parts.

However, unless the relative velocities of the surfaces is high enough that the surfaces `surf` on a continuous film of lubricant, there will still be contact and adhesive wear will occur.

Third, the shock wave created in the substrate by such ablation produces work-hardening effects far into the material (perhaps several hundred microns) through formation of dislocation structures below the heated surface layer.

There are numerous reasons why previous laboratory-scale attempts to apply such processes failed to be accepted in the market.

Further, unless rapid cycling (>>1 Hz) of the source is possible, the amount of material that can be treated per source unit is too small to have an impact on any but specialty items.

High process efficiency is also required, as otherwise removing the waste heat from the source unit will become a difficult task, as will providing the total power required.

The cost in wasted electricity alone is about $10 million dollars per year of operation.

The low power efficiency of laser systems which provide short enough pulses of sufficient energy to treat large areas of a surface is clearly a problem.

Lasers present other problems when considered for this class of applications.

A pulsed laser system with the required level of power has been developed for antiballistic missile systems, but the physical size and capital cost of each system is enormous.

In addition, the lifetime of certain critical components is quite short (<10.sup.3 pulses), requiring enormous downtime for maintenance in an industrial situation.

Further, the depth of power deposition is limited to an optical skin depth.

This option results in long heating periods, and substantial heating of the material underlying the desired surface heating region.

Such a situation is non-optimal.

Such control in a general industrial manufacturing environment would prove difficult.

Two problems present themselves.

Second, what total dosage is required to melt the affected area?

The use of ion beams for thermally altering the near surface characteristics of a material has been fraught with substantial problems.

Most notable of the limitations with existing ion beam technologies have been: 1) high costs per area treated; 2) the inability to generate a large number of pulses without the costly replacement of ion beam generator components; 3) low repetition rates; 4) low average power; and 5) the inability to reliably produce a uniform ion beam of a single selectable ion species.

Other difficulties arising from flashover include: production of large quantities of neutral gas that makes high repetition rate difficult, generation of debris which can contaminate surfaces being treated, and non-uniformity and irreproducibility of the beam in some cases due to the localized and difficult to control nature of flashover.

Existing ion beam generators cannot be operated at high repetition rates (<<1 Hz) for a number of reasons.

First, existing pulsed power supplies are no able to generate electrical pulses at high repetition rates having the voltage, pulse width (i.e., normal temporal duration), and power required to generate the ion beams needed (i.e., consistent with the discussion above) for the various beneficial applications described herein.

This limitation renders commercial exploitation impractical.

Second, the design of existing ion beam generators does not allow repetitive operation for an extended number of operating cycles (<<10.sup.3) without replacement of major components.

This limitation would require a maintenance time--manufacturing time ratio incompatible with routine manufacturing operations.

Fourth, existing ion beam generators generally operate with electrical efficiencies<5%, thus presenting major challenges to the pulsed power supply and the cooling system of the generator.

These limitations and others have made it impossible to routinely utilize the ion beam technology described above for surface treating materials.

Images