Thin composite wire saw with surface cutting crystals

#A method of sawing or cutting is known in which a metal wire is passed through a suspension containing hard cutting particles. These particles adhere to the metal wire which is brought to the work piece which is to be cut. The metal wire having the cutting particles on its surface is brought into contact with the work piece and suitable pressure applied resulting in a saw-notch being formed in the work piece as a consequence of the effect of the hard particles thereon. This method has been used inter alia for sawing semi-conductor materials; the wire usually consisting of tungsten and the particles usually consisting of diamond or alumina, etc. The advantages of this method are that very thin saw-notches can be obtained by selecting a very thin tungsten wire and a suspension containing fine-grained particles, with consequent minimal loss of material. The disadvantages of the aforesaid described method is that the cutting particles only lightly adhere to the wire and readily are detached therefrom when the cutting wire contacts the workpiece resulting in low product output and increased wear of the wire.

#The present invention provides a cutting wire in which the said cutting particles which in the prior art only lightly adhering to the surface of the wire are replaced by specified crystals which are formed by a chemical reaction and are permanently a part of the surface of the cutting wire. The cutting wire is heated by passing electric current through it. It is passed through a reaction chamber containing gaseous substances which on thermal decomposition form hard crystals on the wire surface. These hard crystals form a cutting surface.

#The present invention therefore provides a composite metal saw having a wire core between about 10 and 500 .mu.m and preferably between 20 and 250 .mu.m thick. The wire core has hard cutting crystals with cutting edges projecting irregularly from the wire core surface. The cutting crystals form a surface layer between 1.5 and 10 and preferably between 5 and 8 .mu.m thick. The composite wire saw preferably also has a layer intermediate between the core and the cutting surface which is formed integral therewith. The intermediate layer is a fine-grained layer between about 1 and 5 and preferably 1.5 and 3 .mu.m thick. The intermediate layer is equal to or thinner than the surface layer. The composite saw wires are prepared by vapor deposition of the cutting surface layer. Vapor deposition coating is well known in the literature. (For example, see Powell, "Vapor-Plating," John Wiley Sons, New York, 1955.)

#In the drawings:

#FIG. 1a is a magnified photograph of a cross-section of a composite saw wire of the present invention;

#FIG. 1b is a diagrammatic depiction of a longitudinal cross-section of a composite saw wire of the present invention;

#The composite saw wire has a core which is of a high tensile strength metal or alloy, such as tungsten, molybdenum, tantalum, osmium, and rhenium, and alloys thereof.

#The cutting surfaces are preferably boron, or borides, nitrides and/or carbides. They are preferably selected from the group consisting of boron, and the borides, nitrides, and carbides of the transition metals and silicon.

#Vapor deposition which is plating from the gaseous phase is usually used in order to provide a surface having special mechanical, chemical, electrical or optical properties. The usual object of this technique of coating in the prior art is to give a closely adherent and smooth coating. In order to obtain the object which is the subject of the present invention, it was necessary to modify the known vapor coating technique and carry it out in a manner counter to that taught by the prior art.