Various elements are added to braze filler metals. The purpose and behavior of these alloying elements are listed below.
Nickel (Ni) Provides desirable high temperature chemical and physical properties. Very compatible with other alloying elements.
Cobalt (Co) Has physical behavior that is very similar to nickel and can be freely substituted for a major portion of the nickel in any specific formulation. When added to nickel, it provides increased solubility, higher service temperature and increased matrix strength.
Manganese (Mn) Functions as a melting temperature suppressant.
Boron (B) Acts as a temperature suppressant, aids wetting through self-fluxing of oxides and contributes to high temperature strength and oxidation resistance. As an effective deoxidizer, boron provides additional joint strength and corrosion resistance. Can be readily diffused from the braze deposit.
Silicon (Si) Behaves in much the same manner as boron. Primary duty is as a self-fluxing temperature suppressant. Secondary role is as a grain refiner affording strength, oxidation resistance and corrosion resistance to the joint at elevated temperatures. Cannot be readily diffused.
Iron (Fe) Appears to promote flow of the molten alloy and tends to make a sounder, tougher joint. Acts as a barrier to the migration of base metal elements into the braze joint.
Chromium (Cr) Enhances both joint strength and high temperature oxidation resistance.
Tungsten (W) Improves matrix strength and corrosion resistance. Through matrix solid solutioning, it aids in resisting deformation under high temperature stressing.
Aluminum (Al) Is both a grain refiner and oxidation resistant additive.
Copper (Cu) Improves wetting and molten metal flow characteristics, benefiting corrosion resistance.
Molybdenum (Mo) Can combine with carbon to form complex carbides that enhance joint strength and effectively controls rapid grain growth. Also stiffens the matrix against plastic deformation.
Carbon (C) This element is included in the generally accepted impurities and minor constituents of the alloying elements. Therefore, its inclusion is kept to a minimum. Carbon acts to lower the melting range.
Titanium (Ti) and Niobium (Nb) Appear to form carbides in the presence of excess carbon, providing added high temperature strength without noticeable side effects. In solid solutions, they increase the corrosion resistance of the matrix.
Germanium (Ge) Has the ability to lower the melting temperature and toughen the joint. It is often recognized microscopically as a finely distributed nodular phase.
Rare Earths of Lanthanum (La), Yttrium (Y), Neodymium (Nd), Praseodymium (Pr) and Cerium (Ce) are normally added to the melt as misch metal to promote outgassing. In the alloy, they enhance oxidation resistance, promote grain refinement, increase fluidity and increase joint ductility.
Typical brazing temperature ranges for various
filler metals
