Method for laser/plasma surface alloying

Details Method for laser/plasma surface alloying Method for laser/plasma surface alloying

1999-10-13

2001-05-08

Hoang, Tu Ba (Department: 3742)

Electric heating

Metal heating

By arc

C219S121600

Reexamination Certificate

active

06229111

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed toward a method for plasma assisted laser surface alloying. Specifically, the present invention is directed toward a method for surface alloying using a laser beam having a rectangular cross sectional area and a plasma arc, in order to produce an alloyed substrate on the surface of the material.
2. Description of the Prior Art
Laser beams have been used to irradiate the surface of a material coated with preselected alloying elements in order to produce a substrate having enhanced physical and/or metallurgical characteristics. The speed with which the surface of a material may be processed by laser alloying is a function of the thermal energy input produced by the laser. Greater processing speeds require more powerful and more expensive lasers.
The processing speed with which a material can be laser alloyed is also a function of the width of the laser beam used for alloying. Producing a laser beam having a greater cross sectional area, while maintaining a constant power density requires a larger and more expensive laser.
Plasma arcs have been used in the field of laser welding to provide increased energy input to the weld area without the power expenditure needed to produce an equivalent increase in energy input using only a laser. Prior art plasma assisted welding techniques have used a laser beam having a circular cross sectional area.
The present invention provides a plasma arc assisted method of laser alloying in which a plasma arc is used in conjunction with a laser beam having a rectangular cross sectional area. The plasma arc provides additional energy input resulting in an increase in processing speed, without the corresponding increase in cost that would result from using a more powerful laser to produce the increased energy input. Additionally, the plasma arc results in additional heating to the zone surrounding the melt region, thereby reducing the thermal gradient between the melt region and the adjacent regions of the material that is being processed. This reduced thermal gradient results in a reduced cooling rate which is regarded as advantageous.
SUMMARY OF THE INVENTION
The present invention is directed toward a method for laser/plasma surface alloying. This method comprises applying a precursor layer comprising a binder and a ceramic or metallic powder comprising chromium or silicon carbide to the surface of a metal substrate. The invention further comprises irradiating the surface of a substrate with a laser beam having a rectangular cross sectional area. The irradiation takes place at a sufficient energy level and for a sufficient time to melt a portion of the substrate such that it forms an alloy with the precursor.
The invention further comprises directing an uncollimated plasma arc to the surface of the substrate at the same time and location as the irradiating with the laser beam. While the irradiation takes place, the substrate is moved relative to the laser beam and the plasma arc.


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