In the Nichrome matrix chromium can be completely dissolved in nickel. The dissolution is highest at 47% in the eutectic temperature and reduces at concentration of 30% at room temperature. Various nickel-chrome alloys are based on this solution that offers superior resistance to elevated temperature oxidation and diverse corrosive media as well as excellent wear resistance.

Oxidation resistance

The addition of chromium in nickel significantly increases the sensitivity of nichrome to oxidation. It is due to increased diffusion rate of oxygen. This process reverses with increasing content % of chromium up to 30%. An increase in content more than this limit may alter the process again. The oxidation resistance offered by nichrome alloy can be enhanced by increasing the content of other elements like silicon, cerium,  calcium and zirconium. Now the oxide layer produced is a combination of nickel and chromium oxides and nickel chromite.

Heating Alloys

The nichrome heating alloy offers significant enhancement in electric resistivity by adding more chromium. Addition of 20% chromium offers adequate electric resistance for heating systems. The nichrome alloys offer excellent electrical features with high strength and ductility that make it fit for wire drawing. The industrially used nickel-chrome alloys include Nichrome and Brightray. Minor alterations in chemical composition can be optimal for specific operations.

By adding suitable concentration of reactive elements, the properties of Nichrome alloy can be improved. The application conditions completely depend on its chemical composition. The following table shows the suitable chemical composition for heating elements

The composition doesn’t have significant effect on mechanical properties of Nichrome grades. The large concentrations of reactive constituents avoid scale flaking while cyclic heating and quenching. It hardly causes troubles while continuous use of heating metals therefore the additional elements can be present nominally.

Thermocoupling

The Nickel Ni80Cr20 heating wire is widely used in thermocoupling and it offers highest service temperature up to 1100oC.The thermocouple is prone to drift in the area of temperature 1000oC because of oxidation after long term use. This effect can be overcome by adding silicon.The industrially used nichrome alloy includes Nicrosil and Nisil. 

Corrosion resistance at high temperature

The Nichrome Ni80Cr20 resistance wire is utilized for wrought and cast components in the elevated temperature operations since it offers much higher resistance to oxidation and corrosion as compare to FeCrAl alloys. The nichrome alloy is best suited in operations that are conducted in oxidation conditions.

In sulfur conditions, chromium sulfide is produced. The creation of nickel sulfide is preferred over chromium sulfide because it offers resistance to production of nickel-nickel sulfide eutectics that has lower melting temperature. Ultimately in the presence of sulfur, nickel reacts with sulfur to produce low melting temperature eutectic solutions that cause liquid phase degradation.

The alloys that go through this degradation get wart growth on their upper layer. This attack can be restricted by the production of chromium sulfides with high content of chromium. 

Nickel-Chrome Ni60Cr15 heating wire has double phase structure that consists of alpha chromium and gamma nickel. The chromium phase is brittle so the alloy loses its ductility when content of chromium is increased. The variable tensile properties of nichrome alloy by varying Cr content are shown in the following table:

By adding 1.5% niobium, the strength and ductility of nichrome alloy can be enhanced however simultaneously decreased embrittlement subsequent to elevated temperature introduces contaminants like carbon, nitrogen and silicon. 

The Nichrome alloy having content of chromium up to 35% is best for hot processing. Beyond this %, it becomes suitable for casting. The ductility can be increased by adding zirconium or titanium. Inconel 671 that consists of 48% chromium,0.35 % titanium is utilized in duplex tubing operations for coal fired super heat tubing.

Wear resistance

The alloy wear process is complicated, high toughness and corrosion resistance increase the wear resistance. The nichrome alloys offer affordable alternative on welded cobalt chrome materials with inclusion of carbon and tungsten that are utilized in wear resistant operations. For instance Nichrome alloy having 8-12% chromium,0.3-1.0% Carbon, 3-4% silicon, 1.5-2.5% Boron, 1-4% Ferrous and the remaining Ni. The coating of this alloy accumulated by inert gas shield arc methods offer 40-50 Rc hardness.