Nickel Brazing Alloys

Nickel brazing alloys or filler metals are mainly known for their special corrosion and heat resistance. These alloys are specially used for brazing stainless steel, nickel alloys, as in industrial and aerospace applications.


Nickel
Nickel is a transition element that shows a mixture of nonferrous and ferrous metallic properties having atomic number 28 and the symbol Ni. It is siderophile (associated with iron) as well as chalcophile (associated with sulfur).

Physical Properties
Phase	Solid
Density	8.908 g-cm-3
Liquid density at mp.	7.81 g-cm-3
Melting point	1728 K (1455 °C, 2651 °F)
Boiling point	3186 K (2913 °C, 5275 °F)
Heat of vaporization	377.5 KJ-mol-1
Heat capacity	(25 °C) 26.07 J-mol-1-K-1
Heat of fusion	17.48 KJ-mol-1

Chemical Properties
Oxidation states	2, 3
Electro-negativity	1.91 (Pauling scale)
Atomic radius	135 pm
Ionization Energies	1st: 737.1 KJ-mol-1 2nd: 1753.0 KJ-mol-1 3rd: 3395 KJ-mol-1

Nickel Alloys

• Nichrome
  Nichrome is a non-magnetic alloy of nickel and chromium. The common alloy is made up of 80% nickel and 20% chromium. But to accommodate various applications there are many other variations of this alloy with varying constituent percentage.
  
  
• German Silver/ Nickel Silver
  It is a metal alloy of copper with nickel, and it is named for its silvery appearance however don't contain silver. Some formulations include zinc, antimony, tin, lead or cadmium.
  
  
• Hastelloy
  Hastelloy is the registered trademark name of Haynes International Inc. The dominant ingredient in this alloy is the transition metal nickel. Other alloying ingredients include varying percentages of the elements chromium, cobalt, molybdenum, iron, copper, manganese, tungsten, zirconium, aluminum, carbon, and titanium.
  
  
• Nicrosil
  It is a nickel alloy consisting of mainly nickel, chromium, silicon, and magnesium.
  
  
• Chromel
  It is an alloy made of 90% nickel (approx) and 10% chromium.
  
  
• Nisil
  This is an alloy of nickel and silicon. The main constituent is nickel with 4.4% silicon only.
  
  
• Cupronickel
  It is an alloy of nickel and copper. With some strengthening impurities, such as manganese and iron.
  
  
• Monel Metal
  This alloy is a trademark of Special Metals Corporation, for a number of stainless metal alloys, which is mainly composed of nickel (up to 67%) and copper along with some amount of iron.
  
  

Classification of Nickel Brazing Alloys
Nickel and its alloys can be categorized in the following classes:

• Commercially Pure Nickel
• Nickel-Copper Alloys
• Nickel-Chromium-Iron Alloys
• Nickel-Chromium-Molybdenum Alloys
• Thorium Dispersed Nickel Alloys

Pure nickel and Ni-Cu alloys are mainly used for those applications where corrosion resistance is important and purity of the product is to be maintained essentially. Other three also have good corrosion resistance, oxidation resistance at higher temperatures, and high strength.

Nickel and its alloys are altered by sulfur and other low melting metals present in filler metals, like lead, zinc, antimony, and bismuth. Prior to brazing, the base metals surfaces must be cleaned thoroughly to remove any substances which may contain these elements. Sulfur and sulfur compounds should be removed from the brazing atmosphere.

Nickel Brazing Filler Forms
Nickel brazing alloys are found in many forms suitable for various brazing requirements.

• Brazing Powder
• Brazing Rod
• Brazing Paste
• Transfer Tape and Sheet

Applications
Nickel brazing alloys are used in different industries for a number of applications. Some of the main applications are:

• Automotive
• Power generation
• Aerospace
• Electronics
• Telecommunications
• Semi-conductor
• Vacuum power tube
• Medical