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bis iby EM study on plasma-assisted nitriding of aluminium
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TUL Sy ppg Bernhard Wielage, Harry Podlesak
A] 1 roggeg Lehrstuhl fiir Verbundwerkstoffe, Technische Universitit Chemnitz
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{short crack ini. 1 Introduction
are discussed in To improve the surface properties the nitriding of aluminium and its alloys is of great interest.
Onditions for the However, the nitriding process is restricted because of oxide formation at the surface. Plasma-
Gian boundary assisted nitriding applying a d.c. glow discharge is a suitable treatment method, but, more informa-
ent gris § tion about the underlying reaction mechanisms are still necessary. At first, a sputtering process is
soy of the performed to reduce the oxide content at the surface followed immediately by the nitriding process
wk opal [1]. The resulting nitride layer was shown to be nanocrystalline with hexagonal AIN as the main
rate. Under low- phase and cubic face-centred Al as the minor phase [2]. The nitriding behaviour depends on process
vithout chanzing conditions and applied material. To get information about the relation between treatment parameters
yoatlon rate. and the microstructure of the formed nitride layer in-situ examinations of the state of plasma (type,
) intensity and energy distribution of ions) [1,3] were combined with ex-situ examinations of the mi-
crostructure and the chemical composition of samples. A first part of results based on microstruc-
tural and analytical investigations by means of transmission electron microscopy, electron diffrac-
I tion and Auger electron spectroscopy has been published already in [2]. The present paper deals
TS with some effects during sputter cleaning as well as with aspects of topography altering during ni-
oo ie triding with regard in particular to the influence of hydrogen admixture to the plasma atmosphere.
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ed 2 Sample treatment and Investigation methods
Discs of pure aluminium 1050A (Al99.5) and alloy 2024 (AlICuMg2) made by sawing, grinding
(SiC paper) and manual polishing (SiO, suspension) were placed on a grounded cathode [3,4]. After
a. evacuating the vacuum chamber to a pressure of 5x10 Pa the discharge space was heated by sub-
A of the prorty strate heating for several hours at a substrate temperature of 350°C. Then the substrates were sput-
anks are also to tered in an argon d.c. glow discharge (pressure: 20 Pa, applied voltage: 600V, substrate tempera-
le, TU Dresden, ture: 400°C) for a time period from 0.5 to 1 hour, followed by the nitriding process in a nitrogen
atmosphere (pressure: 33-50 Pa, applied voltage: 600V, substrate temperature: 400-460°C). Addi-
tionally, the process atmosphere was varied by the admixture of hydrogen during sputter cleaning as
well as by the admixture of hydrogen or argon respectively during nitriding. After 2 hours nitriding
a nitriding depth of nearly 1 pm has been reached. This scale of layer thickness is suitable for ex-
amination by Auger electron spectroscopy and transmission electron microscopy.
After different steps of treatment the surface of samples has been examined by scanning electron
microscopy (SEM, JEOL JSM840) using both secondary electron imaging (SEI) and backscattered
ence fH electron imaging (BEI). Additionally, the local chemical composition has been examined by an at-
wer. HM. tached system for energy dispersive X-ray spectroscopy (EDXS, EDISON 32). For it, in some cases
the accelerating voltage was reduced to 3 keV to limit the depth of X-ray generation to a scale of
0.1 um as well as to reduce the failure for the determination of the oxygen content. Moreover, the
chemical composition of nitrided samples has been determined by depth profiling using Auger elec-
« Baronean Con- tron spectroscopy (AES, VG ESCALAB MKII) [2]. Selected samples prepared as cross sections have
Co been studied bv transmission electron microscopy (TEM, HITACHI H8100).
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