Plasma Diffusion Process
Plasma Nitriding Principle| Process Characteristics | Process Advantages | Plasma Nitriding Reactor | Equipments | Salient Features| Manufacturing


Plasma diffusion treatment aims at introducing species like nitrogen, carbon,  boron, e.t.c into the surface of a workpiece by bringing an activated nitrogen, carbon or boron bearing gas into direct contact with the surface, maintained at elevated temperatures. Nitriding, Carburizing and Boriding with positive ions derived from the plasma of an electrical glow discharge is an effective surface treatment to produce wear-resistant, fatigue - resistant,  corrosion - resistant and superficially hard surfaces. 

Plasma Nitriding of ferrous metals like low alloyed steels,high alloyed steels, tool steels,stainless steel, and non-ferrous metals like titanium and chromium have been developed. Technological variants of conventional plasma nitriding process like low pressure nitriding and bias free nitriding have also been developed. Nitrocarburizing and plasma nitriding followed by post oxidation process have been developed for low alloy steels to improve their corrosion resistance. 

Plasma Nitriding Principle :
Plasma Nitriding is a Surface Hardening Process which involves diffusion of nitrogen atoms into the metal surface in presence of a plasma environment. This process is also called Ion nitriding. 

If two electrodes of different potential are placed in a gas at reduced pressure and an increasing voltage is applied, at a minimum voltage a glow is set up around the electrode at low potential. Plasma nitriding is carried out in the region of abnormal glow discharge where the workpiece to be plasma nitrided is completely covered with glow and the voltage and current increases simultaneously.

The workpieces themselves become heated through the transfer of energy associated with the action of ionic bombardment.

As a result nitrogen is transferred to the work pieces, which then penetrates inside by diffusion.

Process Characteristics
  • Reliable and uniform build up of  nitrided cases which are hard but still ductile.
  • Retention of core hardness.
  • No dimensional changes of work piece.
  • Wide range of treatment temperatures.
  • Completely non-toxic and environmentally clean.
  • Low energy consumption and single step operation.
  • Dimensional changes are within small tolerances , thereby eliminating post treatment machining.
  • Components with complex shapes and geometries and different sizes can be nitrided. The process provides excellent dimensional stability with no distortion.
  • Annealing for stress relieving in a protective atmosphere can also be performed in the system.
  • Partial treatment of the components is also possible.
  • Steels sensitive to tempering can be nitrided at comparatively low treatment temperatures.
  • Complete control on white layer formation.
The commercial Plasma Nitriding Reactor has:
  • Two chambers for alternate treatment and cooling operations reducing down time.
  • Dimensions :
    Single Chamber - Diameter 1500 mm   x   Height 1000 mm
    Double Chamber - Diameter 1500 mm   x   Height 2000 mm
  • Maximum work loading capacity - 2 tons
  • Hydraulic operation for lifting and stacking of the two chambers.
  • Roots and Piston combination pumping system having very high pumping rate.


Plasma Nitriding Reactor Hot wall Chamber :
  • Externally heated vacuum chamber.
  • Thermal shields to minimize heat losses.
  • No water cooling is required except for the "o" Rings.
  • Dimensions:
    Diameter : 500 mm
    Height : 510 mm
  • Maximum work load capacity : 25Kgs

The components of a plasma nitriding system  are a vacuum  furnace, an electric power supply with fully automatic process control and a gas supply with a vacuum pump system.

In the furnace, low vacuum can be obtained using roots and piston combination pump. A high voltage is applied between the components and the furnace using pulsed D.C. supply leading to the formation of the plasma. Control on the current and voltage and an appropriate gas composition provides the building up of nitrided cases  with desired properties. Microprocessor control ensures reproducible treatment sequence and guarantees a reliable process performance.
  • Modular System
  • Process Automation using micro-computer
  • Auto/Manual switch-over facility through PLC based control to minimise down-time
  • User friendly menu - driven process software
  • Recipe storage and retrieval facility for reproducibility
  • High frequency pulsed discharge for arc suppression
  • Thermal shields for minimizing heat loss
  • Safety and  process interlocks
  • Voltage measurement and close loop control.
  • Voltage Protection.
  • High output stability.
  • Variable frequency and duty cycle control.
Manufacturing

FCIPT is actively engaged in the manufacture of plasma equipment and has supplied Plasma Nitriding Systems, Power supplies to other organizations on commercial basis. The following are some of the major equipment manufactured:

  • Plasma Nitriding System supplied to M/S Metal Treat, Ahmedabad, India.
  • Research Plasma Nitriding System supplied to National Aerospace Laboratory, Bangalore, India
  • Plasma Nitriding System supplied to IGCAR, Kalpakkam, India.
  • Pulsed Power Supply supplied to Indira Gandhi Centre for Atomic Research, Kalpakkam, India
  • SIDH Modulator supplied to Institute fur Werkstoffkundeund Werstofftechnik, Clausthall, Germany
  • RF Power Supply supplied to Revenshaw College, Orissa

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