What is gas and plasma nitriding ? Why ASPN - Active Screen Plasma Nitriding is the best nitriding technoloy ?

1. ALD France
Gas, and plasma
nitriding
Process and furnace

2. 2
I.Reasons for nitriding
II.Gas nitriding
1. How does gas nitriding work?
2. Structure of nitrided material
3. 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 improvement
4. ALD’s furnace solutions: Plasma
nitriding conception
IV.How to choose between the two technologies
Outline

3. 1) To obtain high surface hardness
(up to 1400 Hv)
1) To increase wear resistance
2) To improve fatigue life
3) To improve corrosion resistance
4) 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
3

4. I.Reasons for nitriding
II.Gas nitriding
1. How does gas nitriding work?
2. Structure of nitrided material
3. 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 improvement
4. ALD’s furnace solutions: Plasma
nitriding conception
IV.How to choose between the two technologies
Outline
4

5. Raising temperature by 40°C
requires
about twice more ammonia flow.
II. 1. How does gas nitriding work?
2NH3 → 3H2 + 2N (dissolved in α-Fe
→ 3H2 + N2 (gas)
5

6. II. 2. Structure of nitrided material
Oxide layer : 1-2 µm
• Corrosion
resistant
White layer : 5-30
µm
• High hardness
• Abrasive resistant
Diffusion zone : 10-
1000 µm
• High compressive
stress
• High fatigue
strength
• Hardness higher
than substrate
α (0-6%
N)
Diffused
Case
Core
 (6-11%
N)
’ (5,6-
6% N)
Fe3O4
X100
X400
ε
6

7. 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
7

8. 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 HV
Tool steels
- (12% Cr)
≈600 HV >1000 HV
8

9. II. 4. How do we control the process?
By controlling the nitriding potential KN
Lehrer Diagram for Nitriding
KN =
1 −
H
0,75
H1,5
KN =
pNH3
(pH2)3
Norm:
AMS 2759/10
requirements for
nitriding using a
process controlled
by the nitriding
potential
H2
sensor
9

10. 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–
520 °C
10h
580 °C
10h
550 °C
10h
600 °C 7h
Nitrogencontent
(at.%)
Nitrogencontent
(at.%)
Nitrogencontent
(at.%)
Nitrogencontent
(at.%)
Depth (µm) Depth (µm)
Depth (µm) Depth (µm)
Norm:
AMS 2750
pyrometric
requirements for
thermal
processing
equipmentFurnace
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
10

11. The thickness of
the diffusion
layer is
proportional to
the square root
of time,
It follows the
Fick Law
Nitriding time,
hours
Effectivecase
depth,µm
Hand Book On Mechanical Maintenance Compiled by: K P Shah
𝐽 𝐷 = −𝐷
𝜕𝑐
𝜕𝑧
II. 4. How do we control the process?
By controlling the time
11

12. 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,
=
=
= =
=
=
=
=
=
=
=
= =
=
=
=
II. 4. How do we control the process?
General rules
12

13. Typical nitriding cycle
13

14. Main constituents of nitriding /
nitrocarburizing installation :
Vacuum Purging Furnace
Control Cabinet
Gas panel
Exhaust Gas Neutralizer
Ammonia Gas Dissociator
H2 and O2 sensor
1
2
3
4
Exhaust
gas
neutrali
zer
Ammonia Gas
Dissociator
5
4
1
2
3
4
5
6
6
II. 5. ALD’s solutions
NiH furnace for Gas nitriding
14

15. I.Reasons for nitriding
II.Gaz nitriding
1. How does gas nitriding work?
2. Structure of nitrided material
3. 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 improvement
4. ALD’s furnace solutions: Plasma
nitriding conception
IV.How to choose between the two technologies
Outline
15

16. 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.
16
III. 1. Plasma nitriding
Introduction

17. Incoming
electron
Ejected
electron
Deviated
incoming
electron
III. 1. Plasma nitriding
Introduction to the physics
E
n
Light
emission
Incoming
electron
Deviated
incoming
electron
Light
emissio
n
Excited
electron
17

18. Low
pressure
H2
H
H+
𝐸𝑐 =
1
2
𝑚𝑉2
Cations
bombardment
s
III. 1. Plasma nitriding
Introduction to the process
18

19. • 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)
Volta
ge
Time
Voltage (-
)
III. 2. Plasma nitriding
process parameters
19

20. • 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
20

21. 1) Vacuum tight furnace
2) Pumping stand with pressure control
(throttle valve)
3) Gas cabinet
4) Power and control cabinet
5) Plasma power supply cabinet
6) Closed‐loop water cooling systems
61
2
3
4
5
III. 4. ALD’s furnace solutions
Plasma nitriding conception
21

22. I.Reasons for nitriding
II.Gaz nitriding
1. How does gas nitriding work?
2. Structure of nitrided material
3. 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 improvement
4. ALD’s furnace solutions: Plasma
nitriding conception
IV.How to choose between the two technologies
Outline
22

23. ■ 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 impact
No harmful discharge released into the atmosphere - 99%
removed
Consumptions and emissions
Plasma 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
23

24. Gas Nitriding Plasma nitriding
Easy loading Etching cleaning
Part with complex shapes Sintered parts
Very thick white layer No or very thin white layer
Kn control> recipe and
metallurgical results independent
of the loaded part amount
Very low gas consumption
No ammonia
Maintain stainless steel properties
Easy installation of the furnace in
a workshop
Easy masking
IV. Performances of:
24

25. Do you want more about
nitriding ?
Contact ALD France
73D Av. Général Mangin
38100 Grenoble, France
 +33 (0) 476 33 64 40
info@ald-france.eu
Sales :  +33 (0) 643 81 99 06 10
sales@ald-france.eu
Visit us
www.ald-france.eu
Nitriding
Lab’
Process definition
Sample analyze
25