Ion Nitriding is a process used to impart surface hardening to metals for a wide variety of applications. As the name implies, the process uses IONized nitrogen alone, or in combination with other gases, to react with the work surface. The IONized nitrogen also provides the characteristic purple glow around the work pieces being treated. The process requires a vacuum vessel (to remove possible contaminating gases such as air), a high voltage D.C. power supply (capable of providing at least 800 to 1000 volts, which is needed to strike a glow), a gas distribution system (to provide proper mix ratios, flow rate, and flow distribution across the work load), and a pressure control system (to maintain pressures around 1 to 10 torr, appropriate for supporting a glow within the desired voltage range).
In the CLC PLASVAK system, the D.C. potential is placed across the hearthplate (onto which the work-piece(s) is/are placed) and the vessel itself The hearthplate is at the negative potential (cathode) and the vessel is at the positive potential (anode). When the voltage is applied under process conditions, current will flow in a manner similar to conventional gas or “glow discharge” tube diodes (such as mercury vapor tubes).
Ion Nitriding takes place as current is increased. Current density is uniform around the entire cathode surface which is indicated by a uniform purple glow. Any increase in current, within the region, gives an increase in current density without affecting uniformity. CLC’s PLASVAK ion nitriders are supplied with multiple view-ports (or windows) to allow observation of the work-piece(s) and the glow under process. The effect of pressure on the “glow seam” surrounding the cathode can also be seen. Increasing pressure in the range of 0.5 to 3 torr causes the glow seam to conform more tightly to the cathode. In commercial ion nitriding practice, this phenomenon is useful in causing nitriding through holes in the work-piece (higher pressure or tighter glow seam) or to jump over holes to prevent their being nitrided (lower pressures). For very irregular shaped pieces, it is also possible to control pressure so that all or only selected surfaces are nitrided.
WHY IS IT USED ?
Parts are typically nitrided to impart wear resistance. The advantages of Plasma Ion Nitriding include:
1. The potential for reduced cycle times (33-50% shorter on nitriding steels)
2. Reduced distortion
3. The opportunity to minimize or eliminate finish grinding
4. The opportunity to improve metallurgical properties often with lower cost materials
5. The, opportunity to eliminate copper plate masking through use of simple mechanical masks
6. The ability to impart hard wear resistant surfaces without brittleness or causing of spalling or galling found with conventional nitriding
7. The ability to provide uniform case on complex geometry’s
8. The potential for reducing operating costs (lower labor and lower gas consumption)
9. Elimination of environmental problems (no toxic salts or toxic gases are used in the process)
10. The potential for reduction in scrap through precisely repeatable cycles
These advantages, and others, can make Ion Nitriding superior to conventional nitriding, as well as other surface hardening techniques. These advantages are obtained by controlling the composition of the compound layer. Unlike conventional bath and gas nitriding, it is possible to simply control the crystal structure of the compound layer being formed in the ion nitriding process. This is accomplished by varying the composition of the gas mixture.
COMMERCIAL GAS MIXTURES
1. “NO WHITE LAYER GAS”, a composition of generally less than 5% nitrogen and the balance of inert gas (typically hydrogen or argon). With this composition, no “compound layer” (commonly called “white layer”, due to its appearance after nital etch) of iron nitrides is .formed. The working surface is the diffused case of nitride precipitates of the alloy constituents (chrome, molybdenum, aluminum, vanadium, and/or titanium). This gas composition would typically be used for tool steels.
2. “GAMMA PRIME GAS”, a composition of 15-30% nitrogen and the balance of inert gas. This gas composition has the characteristic of forming a very thin compound layer of predominantly monophase gamma prime crystal structure (Fe4N). The most desirable factor of the gamma prime crystal structure is that this compound layer builds to a very thin layer (0.0001 to 0.0004”) irrespective of the time in the process. Longer process times develop deeper diffused cases and the higher temperatures develop slightly thicker compound layers. Typically, this layer would be used on nitriding steels (Nitralloy 135 or 4140).
3. “EPSILON GAS”™ which is a composition of approximately 60-70% nitrogen, 1-3% methane, and the balance of inert gas. This gas composition tends to form predominantly monophase epsilon crystal structure (Fe2-3N). The longer the work-piece remains in the furnace, the thicker the compound layer formed, as well as the deeper the case. Typically, compound layers of up to 0.0010 to 0.0012” can be formed, although in many applications the epsilon compound layer of only 0.0002 to 0.0006” is sufficient for wear resistant characteristics. Higher furnace temperatures will result in thicker compound layers being formed in shorter periods of time. This gas composition is traditionally used on materials that have no alloy constituents (i.e. chrome, vanadium, molybdenum, aluminum, and/or titanium) for which to form a diffused nitride precipitate case structure.
Crystal structure formations in the compound layer (characteristic of gas nitriding and bath nitriding) can also be obtained. These structures, however, generally yield poor metallurgical properties when compared to properties obtained by monophase crystal structure in 100% compound layer, or no white layer at all. Special gas mixtures may be used to impart unique properties to the surface.
CLC’s PLASVAK ION NITRIDING SYSTEMS
CLC has achieved some of its greatest technical accomplishments in the field of plasma ion nitriding. The PLASVAK line of ion nitriding equipment is the most advanced line surface modification equipment available in the World. CLC manufactures the PLASVAK in a wide variety of loading configurations for laboratory and commercial heat treatment applications. In fact, ETC encourages that you inquire about our PLASVAK retrofit kits which can be added to most conventional heat treatment furnace systems.
CLC Plasvac™ Vacuum Systems
CLC Corp offers the largest variety in Ion Processing Equipment.
CLC's service representatives will help you select the ideal vacuum chamber for your work fixturing, part loading and business environment.
Standard Configurations include:
FLH Series: Front Loading Horizontal
(cylindrical or box style)
TLV Series: Top Loading Vertical chambers
Bell Series: Bell Jar style that lift off the base
CS Series: Clamshell Style opening, front loading chambers
BLE Series: Bottom Loading Elevator system
ILC Series: In Line Continuous for continuous processing of parts in line
RC Series Rotary Continuous for continuous processing rotary style
One or more of these systems will be ideal for you. Please give us a call to discuss with you.
Basic Components of Plasvac™ Systems
(Click for more information)
MULTIPURPOSE IonGlo™ SYSTEMS
FROM CLC
HOT WALL VERSUS COLD WALL
DEDICATED ION NITRIDING SYSTEMS AND MULTIPURPOSE IonGlo™ SYSTEMS
CLC manufactures both types of IonGlo™ Ion Nitriding Systems, just as CLC manufactures a conventional SCR IonGlo™ DC Ion Power Supply, and a pulsed high frequency DC Ion Power Supply.
CLC also manufactures dedicated single purpose single part systems, multipurpose, multi-part systems, and IonGlo™ retrofit packages for existing equipment to allow Ion Nitriding to be added to existing customers equipment, or to other standard products.
Each product has certain advantages and inherently certain limitations. No one chamber configuration is suitable for all applications and all parts.
In the past, a true Hot Wall chamber heated internally only by DC Plasma power was thought to be necessary for the proper application of the Ion Nitriding process. Through time, this has proven to not be true. It is more economic and operator friendly to use auxiliary heating to provide the power to heat the load to the desired operating temperature. This drives off water and oil and makes sputter cleaning faster and easier.
The DC Plasma power required is much less and control of the automatic Arc Detection and Arc Suppression circuits can be much finer.
An externally heated Hot Wall retort vessel is limited to the economic materials of construction of the retort (typically Stainless Steel or Inconel). Potentially corrosive gases used in CVD processes can be used at temperatures within the range of the Inconel or Stainless retorts.
These retort materials then allow processes, which typically use “Retort-Style Vessels” to be combined with a IonGlo™ Ion Processing, for multipurpose processing.
Hot wall retorts can be used for processes ó600ºC and expect a long retort service life. The main disadvantage of a retort is the required exterior insulation which makes the system substantially slower to cool than a conventional cold wall vessel.
The cold wall vessel allows internal heaters and insulation to heat parts to 3000ºC, but traditionally the ferrous metal heat treating falls below 1200ºC, and ferrous metal surface modification below 600ºC.Cold wall vessels allow faster cooling for productivity and metallurgical profile cooling.
At temperatures ó400ºC, vacuum radiation heating is not very good. For processes conducted at those temperatures, a system can be evacuated of air and backfilled with an inert gas to improve heating rates and uniformity by convective heating (this can be done in both a cold wall and hot wall system). The hot wall system will be more thermally efficient as heat will not be transferred into the cooling water as it is in a cold wall vessel.
This thermal efficiency only occurs in the time taken to heat the load to the process temperature (30ºC/minute to 600ºC or only 20 minutes). The system is then evacuated to allow the Sputter Cleaning and Ion Processes to occur (0.5 to 10 torr vacuum).
The insulated retort can also require 12 to 24 hours to cool while the cold wall vessel may take 4 to 8 hours to cool (without fans, blowers or heat exchangers).
The hot wall vessel design requires cooling of the load itself and some method of getting heat out of the insulation surrounding the heating elements attached to the surface of the retort. At a minimum, this requires either :
(1) No thermal Insulation (Thus making the retort also thermally inefficient similar to the cold wall vacuum vessel during the 20 minutes heat-up).
Note : This design requires a perforated stand off skin to prevent the operator from being burned.
(2) Cooling fans on the external heaters and internal load (with optional internal and external fin tube heat exchangers to speed cooling of the chamber shell and load).
Cold wall designs are available in FLH (Front Load Horizontal cylindrical) chambers, FLB (Front Load Box-style) chambers, BLE (Bottom Load Elevator) chambers, TLV (Top Load Vertical) chambers, CS (Clamshell Split Opening) chambers, and BJ (Bell Jar) chambers.
Hot wall retort-style chambers are typical Bell Jar-style chambers with some top load pit and a few bottom load elevators being built.
If the temperature is limited to less than 600ºC, the vacuum level not more than 10-2 torr, and multipurpose CVD, gas nitriding, and oxidation coating multipurpose process capabilities are desired along with IonGlo™ Ion Nitriding capabilities, CLC will construct a Hot Wall Retort-style Bell Jar Vessel and recommend internal Rapicool™ fan cooling and either an uninsulated protected skin vessel or a Plenum, gas cooled vessel.
For multipurpose Processes requiring temperatures higher than 600ºC, CLC recommends a cold wall design with removable internal retort if Plasma CVD processing is desired.
For dedicated IonGlo™ Ion Nitriding systems, CLC will recommend a vessel with loading configuration matching the optimum material handling that can be done in your facility.
Equipment Required for Ion Nitriding without White Layer Formation and Pure Diffused Case
1. Hot Wall or Cold Wall IonGlo™ Ion Nitriding System (with or without auxiliary heating and either a conventional or pulsed IonGlo DC Ion Power Supply).
2. Dedicated “No White Layer” Process Gas Mixture containing approximately 5% Nitrogen.
Note: Use of auxiliary heating and a pulsed DC power supply provide state-of-the-art, user-friendly technology.
Equipment Required for Ion Nitriding with
Epsilon White Layer Formation and Pure Diffused Case
1. Hot Wall or Cold Wall IonGlo™ Ion Nitriding System (with or without auxiliary heating and either a conventional or a pulsed IonGlo DC Ion Power Supply).
2. Dedicated “Epsilon” process gas mixture containing approximately 90% Nitrogen, 5% Methane (CH4) and 5% Hydrogen.
Note: Use of auxilliary heating and a pulsed DC power supply provide state-of-the-art technology which is mostly user-friendly.
EQUIPMENT REQUIRED FOR ION NITRIDING WITH GAMMA PRIME COMPOUND LAYER AND DIFFUSED CASE
1. HOT WALL OR COLD WALL IonGlo™ ION NITRIDING SYSTEM WITH OR WITHOUT AUXILIARY HEATING AND EITHER A CONVENTIONAL OR PULSED DC ION POWER SUPPLY.
2. DEDICATED “GAMMA PRIME” GAS NIXTURE CONTAINING APPROXIMATELY 25% NITROGEN AND 75% HYDROGEN
Note: Use of auxiliary heating and pulsed DC power supply provide state of the art technology which is most user friendly.
EQUIPMENT REQUIRED FOR BLACK OXIDE COROSION RESISTANT COATING OVER ION NITRIDED SURFACES
1. IonGlo™ HOT WALL BELL JAR ION NITRIDING SYSTEM WITH INCONEL RETORT
2. STEAM GENERATOR FOR WATER INJECTION INTO THE RETORT
3. MASSGAS MASS FLOW CONTROLLER WITH OPTIONS FOR CO2, CO, AND O2 GASES TO BE ADDED
EQUIPMENT REQUIRED FOR PLASMA CVD PROCESSING
1. IonGlo™ HOT WALL BELLJAR ION NITRIDING SYSTEM WITH INCONEL RETORT
2. MASSGAS™ MASS FLOW GAS MIXING SYSTEM MODIFIED FOR CVD GASES
• TiCl4 • AlCl3
3. NEUTRAPUMP™ VACUUM PUMPING AND CHEMICAL NEUTRALIZING SYSTEM
4. CHEMICALLY CORROSION RESISTANT VALVES AND GAS MANIFOLD PIPING
ION PROCESSES:
1. ION SPUTTER CLEANING WITH ARGON AND HYDROGEN
2. ION NITRIDING
• GAMMA PRIME
• EPSILON
• NO WHITE LAYER
PLASMA CVD PROCESSES:
• TiN COATING • TiAlN COATING
DUPLEX COATING WITH ION NITRIDED BASED AND CVD SURFACE
ADDITIONAL EQUIPMENT NEEDED FOR DUPLEX ION NITRIDING AND PAPVD COATING
1 CONVENTIONAL IonGlo™ OF SUFFICIENT SIZE TO ACCEPT PAPVD OPTION
1 PULSED BIPOLAR IonGlo™ DC ION POWER SUPPLY
(FOR PAPVD TARGETS)
1 PAPVD DC POWER FEEDTHROUGH
1 DC POWER DISTRIBUTION GRID INTERNAL TO THE CHAMBER
1 PAPVD TARGET GRID
OPTIONS
ROTARY PART FIXTURE TO PROVIDE MORE UNIFORM COATING