a stranded form having a large surface to volume ratio this general form consists of a plurality of fine wires having the desired cross sectional area which may be twisted or braided to produce the preform application_number US 8151579 A description it is desirable to produce nickel boron braze alloys in wire form by boriding the surface layer of the wire to provide the desired boron level after the ductile boron free alloy has been drawn to wire the borided surface layer however is extremely brittle and spallation of the brittle surface layer is encountered when the braze wire is bent or otherwise shaped spallation is an increasingly serious problem as the wire diameter increases this spallation problem is related to two factors the first and most important factor is that relatively thicker borided surface layers are required on larger wires to achieve the same overall boron content as that achieved on small wires the required thickness of the surface layer is related to the surface to volume ratio the second factor which contributes to the problem is that the strain at the surface of the wire during bending increases with increasing wire size assuming a consistent bend radius for a wire of circular cross section the ratio of surface area to volume is given by the relation table i shows the ratio of surface area to volume and the cross sectional area for several sizes of circular and square wires it can be seen that the ratio of surface area to volume decreases.