ALD FranceGas, and plasma

nitridingProcess and furnace

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I. Reasons for nitridingII. Gas nitriding

1. How does gas nitriding work?2. Structure of nitrided material3. What kind of material can be nitrided?4. How the gas process is controlled?5. ALD’s solutions : NiH furnace for Gas nitriding

III.Plasma nitriding 1. Plasma physics 2. How the plasma process is controlled?3. Plasma nitriding technology improvement4. ALD’s furnace solutions: Plasma nitriding

conception

IV.How to choose between the two technologies

Outline

1) To obtain high surface hardness (up to 1400 Hv)

2) To increase wear resistance

3) To improve fatigue life

4) To improve corrosion resistance

5) To obtain a surface that is resistant to the softening effect of heat at temperatures up to the nitriding temperature (500 °C)

I. 5 reasons to nitride parts

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I. Reasons for nitridingII. Gas nitriding

1. How does gas nitriding work?2. Structure of nitrided material3. What kind of material can be nitrided?4. How the gas process is controlled?5. ALD’s solutions : NiH furnace for Gas nitriding

III.Plasma nitriding 1. Plasma physics 2. How the plasma process is controlled?3. Plasma nitriding technology improvement4. ALD’s furnace solutions: Plasma nitriding

conception

IV.How to choose between the two technologies

Outline

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Raising temperature by 40°C requiresabout twice more ammonia flow.

II. 1. How does gas nitriding work?

2NH3 → 3H2 + 2N (dissolved in α-Fe

→ 3H2 + N2 (gas)

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II. 2. Structure of nitrided materialOxide layer : 1-2 µm• Corrosion resistant

White layer : 5-30 µm• High hardness• Abrasive resistantDiffusion zone : 10-1000 µm• High compressive

stress• High fatigue strength• Hardness higher than

substrate

α (0-6% N)

DiffusedCase

Core

(6-11% N)

’ (5,6-6% N)

Fe3O4

X100

X400

ε

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II. 3.What kind of material can be nitrided?

Effect of alloying element additions on hardness after nitriding. Base composition is 0,25% C, 0,30% Si, 0,70% Mn

Useful alloying elements for nitriding: Cr, Va, Mo, Al, Ti,…

Me + nN => MeNn

Me: Metal

N: nitrogen

The Effects of Alloying Elements on Steels Mehran Maalekian October 2007

Hardness Hv

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Tables: ASM Handbook Volume 4A 2013 Nitriding

II. 3. Hardness improvement

Material Hardness prior to Nitriding

Hardness obtained by Nitriding

Iron ≈120 HV ≈250 HV

Low alloyed carbon steels - i.e. AlSi 1045 ≈180 HV ≈350 HV

Medium-carbon, chromium-containing low alloy steels - 1.1% Cr (AlSi 4140) - 2.5% Cr (AlSi 4340)

≈240 HV≈240HV

≈600 HV≈750 HV

Nitriding steels - (Cr and Al) ≈240 HV ≈1000 HVTool steels - (12% Cr) ≈600 HV >1000 HV

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II. 4. How do we control the process?By controlling the nitriding potential KN

Lehrer Diagram for Nitriding

K N=1−( H0,75 )H 1,5

K N=pNH 3

√( pH 2)3

Norm:AMS 2759/10 requirements for nitriding using a process controlled by the nitriding potential

H2 sensor

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S.S. Hosmani, R.E. Schacherl, and E.J. Mittemeijer, Kinetics of Nitriding Fe- 2 wt% V Alloy: Mobile and Immobile Excess Nitrogen, Metall. Mater. Trans. A , Vol 38, 2007, p 7–16

520 °C 10h

580 °C 10h

550 °C 10h

600 °C 7h

Nitro

gen

cont

ent (

at.%

)

Nitro

gen

cont

ent (

at.%

)

Nitro

gen

cont

ent (

at.%

)

Nitro

gen

cont

ent (

at.%

)Depth (µm) Depth (µm)

Depth (µm) Depth (µm)

Norm:AMS 2750 pyrometric requirements for thermal processing equipment

Furnace class

Temperature uniformity range (°C)

1 ± 3

2 ± 6

3 ±8

4 ±10

II. 4. How do we control the process?By controlling the temperature

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The thickness of the diffusion layer is proportional to the square root of time,It follows the Fick Law

Nitriding time, hours

Effec

tive

case

dep

th,

µm

Hand Book On Mechanical Maintenance Compiled by: K P Shah

𝐽𝐷=−𝐷 𝜕𝑐𝜕 𝑧

II. 4. How do we control the process?By controlling the time

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Parameters influencing nitrided layer formation (acc. to Spies and Bergner)

Compound layer

thickness

Case (surface) hardness

Effective case depth

Case hardness

depth

Nitriding conditions : - Higher temperature

- Longer soak time

- Higher KN

     

Material composition : - Higher Cr concentration

- Higher Al concentration

- Higher C concentration

       

Material structure : - Normalized

- Hardened, increasing tempering temperature

       

=

== =

===

=

=

=

=

= =

=

==

II. 4. How do we control the process?General rules

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Typical nitriding cycle

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Main constituents of nitriding / nitrocarburizing installation :Vacuum Purging FurnaceControl CabinetGas panelExhaust Gas NeutralizerAmmonia Gas DissociatorH2 and O2 sensor

1

2

3

4

Exhaust gas neutralizer

Ammonia GasDissociator

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123456

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II. 5. ALD’s solutionsNiH furnace for Gas nitriding

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I. Reasons for nitridingII. Gaz nitriding

1. How does gas nitriding work?2. Structure of nitrided material3. What kind of material can be nitrided?4. How the gas process is controlled?5. ALD’s solutions : NiH furnace for Gas nitriding

III.Plasma nitriding 1. Plasma physics 2. How the plasma process is controlled?3. Plasma nitriding technology improvement4. ALD’s furnace solutions: Plasma nitriding

conception

IV.How to choose between the two technologies

Outline

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Plasma nitriding, known also as ion nitriding, is a form of case hardening process. It is an extension of conventional gas nitriding process, utilizing plasma discharge physic to diffuse nitrogen into the surface of a ferrous alloy.

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III. 1. Plasma nitridingIntroduction

Incoming electron

Ejected electron

Deviated incoming electron

III. 1. Plasma nitridingIntroduction to the physics

En

Light emission

Incoming electron

Deviated incoming electron

Light emission

Excited electron

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Low pressure

H2

H

H+

𝐸𝑐=12𝑚𝑉 2

Cations bombardments

III. 1. Plasma nitridingIntroduction to the process

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• Temperature (400 to 600°C)• Pressure (0.5 to 10 mbar)• Gas composition (Nitrogen, Hydrogen, Methane,

Oxygen, Argon …)• Time (1 - 120 hrs depending on case depth)• Voltage• Current• Power• Pulse duration (tON)• Pause duration (tOFF)

Voltage

Time

Voltage (-)

III. 2. Plasma nitridingprocess parameters

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• Hollow cathode effect• Edge effect• Bad Temperature uniformity• Arcs

Direct Current Plasma Nitriding DCPN

Active Screen Plasma Nitriding ASPN

The ASPN technology is covered by the ION2-cloud® patent owned by ALD

III. 3. Plasma nitriding technologies

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1) Vacuum tight furnace2) Pumping stand with pressure control (throttle

valve)3) Gas cabinet4) Power and control cabinet5) Plasma power supply cabinet6) Closed‐loop water cooling systems

61

2

3

4

5

III. 4. ALD’s furnace solutionsPlasma nitriding conception

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I. Reasons for nitridingII. Gaz nitriding

1. How does gas nitriding work?2. Structure of nitrided material3. What kind of material can be nitrided?4. How the gas process is controlled?5. ALD’s solutions : NiH furnace for Gas nitriding

III.Plasma nitriding 1. Plasma physics 2. How the plasma process is controlled?3. Plasma nitriding technology improvement4. ALD’s furnace solutions: Plasma nitriding

conception

IV.How to choose between the two technologies

Outline

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■ Plasma is a low gas consumption process The amounts of gas used are about 90% lower than for

gas nitriding

■Plasma has a low environmental impactNo harmful discharge released into the atmosphere - 99%

removed

Consumptions and emissionsPlasma nitriding / Nitrocarburizing GAS PLASMA (%)

REDUCTION Gas amount used m3/h 6.0 0.6 90.00

Total carbon emission via CO / CO2 mg/m3 137 253 504 99.63

Total amount of NOx gases mg/m3 664 1.2 99.82

Rejection of residual C carrier gas mg/h 823 518 302 99.96

Residual gas release NOx mg/h 3 984 0.72 99.98

Sources: Jean Georges, Jean-Paul Lebrun

IV. How to choose between the two technologies

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Gas Nitriding Plasma nitridingEasy loading Etching cleaningPart with complex shapes Sintered partsVery thick white layer No or very thin white layer Kn control> recipe and metallurgical results independent of the loaded part amount

Very low gas consumptionNo ammoniaMaintain stainless steel propertiesEasy installation of the furnace in a workshopEasy masking

IV. Performances of:

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Do you want more about nitriding ?

Standard nitriding furnaces

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TrainingsNitriding process

Nitriding furnace

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Sales : +33 (0) 643 81 99 06 10sales@ald-france.eu

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Nitriding Lab’Process definitionSample analyze

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