J. Plasma Fusion Res. SERIES, Vol. 5 (2002) 242-244

Fabrication of Al-Pt Goating on Ni-Based Superalloys bySputtering-lon Beam Technique under Argon Plasma
PARCHAMY ARAGHY Homaira, GHORANNEVISS Mahmood, SEDGHI Arman and SHOKOHI Ali
Plasma Physics Research Center, Islamic Azad University, Iran(Received: ll December 2OOl I Accepted:20 June 2002)

Abstract
Protective coatings are applied on the engineering materials to improve their physical, thermo
chemical and mechanical properties. These coatings are used in various fields of industrial applications
specially gas turbine blades, and in this respect, many research projects have been conducted to improvetheir properties. In the present study, the formation of Al-Pt (Aluminum/Platinum) alloy coatings on
Nickel-based superalloys has been investigated. Sputtering ion beam technique under Argon plasma,pack cementation and subsequent heat treatment has been used to fabricate these coatings.
The main goal of this paper is to change the method for fabrication of platinum layer and investigate
about effect of this variation on the morphology of coating. The results of this study confirm well withthe results of other investigations, and it's related to slow diffusion ofplatinum through coating. Thismethod can produce uniform coatings faster and promise to be industrial technique for the fabrication ofsuch coatings.

Keywords:
coating, sputtering, plasma, pack cementation, aluminides, platinum

1. Introduction

electroplating have Platinum and diffusion of Aluminum
through Platinum by pack cementation is been used forthe production of Al-Pt compounds commercially. In
this paper, fabrication of Platinum on superalloys by Ion
beam sputtering and effect of this method on themorphology of resulted platinum aluminide coatings has

In the most of turbine components failures occur
through oxidation and corrosion, hence protection ofthese components is necessary. The use of coatings
permits the separation of surface and substrate. Thus,
such components have been coated with specificmaterials in order to improve their service lives. Someof these materials are Aluminum alloy and Aluminum
intermetallic compounds, and Al-Pt compounds which
the latter is known to be a very effective oxidation
protection coating. These compounds have been used forthe protection of superalloy turbine blades for several
years, and have improved their lifetime [-3].

been investigated. For comparison of this coating
method with electroplating method for fabrication ofplatinum layer, the same aluminum layer fabrication anddiffusion process [1,4,5] applied on our research.

2. Experimental Procedures
Inconel 738 has been used as a substrate in ourexperiments. Substrate samples are 30 mm length, 20mm wide and 3 mm thickness. After cleaning thesubstrate surface, it is fixed in the sputtering chamber.

Coating materials are designed to provide corrosion
or oxidation protection at high temperature applications

so that they are applied to high strength superalloy
substrates. In this respect, some methods such as@2002 by The Japan Society of Plasma
Science and Nuclear Fusion ResearchC o r re sp onding author' s e - mail : h 4arc hami @ y ahoo. c omall

Parchamy A.H. et al., Fabication of Al-Pt Coating on Ni-Based Superalloys by Sputtering-Ion Beam Technique under Argon Plasma

Pure platinum plate is used as atarget pure Argon gas

Ion beam has been used in this experiment. During
electrical discharge, Argon gas is converted to plasma
Ion beam, collide to target atoms, take them to plasma
and then push them to deposit from plasma to substratesurface.

The coating parameters for sputtering were asfollows: Vacuum gas pressure was l0-3 torr,
Accelerating voltage was 28 kV, Beam current was 12mA, Distance between target and substrate Ws 3 cm,angle between the beam and the target was 45o and time
taken for sputtering was about an hour.
The specimens are coated with Platinum layer by
ion beam sputtering and then coated with aluminum bypack cementation. In the pack cementation method thepack consists of Al2O3, Al and NH4CI compounds.
Samples coated by platinum covered in by the pack andgoes to inert gas furnace in order to heat-treated. The
coating was deposited using an aluminizing packFig. 1 Microstructure of ft layer deposited by lon beam
sputtering on Ni-base superalloys substrate.

containing 2O wt%o Aluminum at 900 'C, and was heattreated for 4 h and then at 845 "C for 24h.
The morphology of coated samples is investigatedby Scanning Electron Microscopy (LEO 440i) equippedwith EDS (energy dispersive spectroscopy) equipmentand Jobin yvon GDS (Glow discharge spectroscopy).

3. Results and Discussion
3.1 Platinum Coating
In this study an Ion beam sputtering techniqueunder Argon plasma was applied to deposit the Pt layeron the Nickel-based substrate. A sample has beenstudied by SEM, which is shown in Fig. 1. This figure
shows surface morphology of the Pt layer, which has acauliflower type appearance with a uniform and spongy
surface [2]. If sample surface pretreatment wasinsufficient and deposition process conducted so fast thecoated layer fully cracked and separated from substrate.

i I Shrllt#-E ,'Fig. 2 Microstructure of Platinum-aluminide coatings
treated by lon beam sputtering and pack cementa-

3.2 Aluminum Goating and Diffusion Processes
In this study, the pack cementation and heat
treatment method was applied for fabrication anddiffusion of aluminum layer. The cross sectional

characterized at Fig. 3. The inter diffusion zone has

microstructure of fabricated samples is shown in Fig. 2.
In the Fig. 2 three areas appears: substrate, intermediate

columnar like structure. EDS analysis revealed that thisarea contain more nickel and aluminum and according

area and diffusion coating area. In the diffusion coating

to previous results [3-5] its mainly nickel alumindearea the voids and two phases appear. EDS analysis
exposed that these phases are mainly contain aluminumand platinum (may be as platinum aluminides) whichsimilar to previous studies [1,3,5]. This structure fully

compounds.

tion.

These results confirmed by chemical composition
variation of nickel, aluminum, platinum, chromium andcobalt through thickness of coating, which is been
discovered by GDS. Analysis results are collected inmatured after long-term heat treatment and it better243

Parchamy A.H. et al., Fabrication of Al-Pt Coating on Ni-Based Superalloys by Sputtering-Ion Beam Technique under Argon Plasma

diagram at Fig. 4. In this diagram the variation ofaluminum through platinum and substrate produced

platinum in the coating layer. Because of the same result
concentration of cobalt and nickel through thickness arealso greater than platinum. Then fabrication of platinum
layer by sputtering technique is not change the coating

nickel aluminide and platinum aluminide coating Thissituation made by faster diffusion of aluminum thanchemical morphology.

4. Gonclusion
1. Microstructure and chemical composition of PcAl alloy coating on Inconel 738 superalloy revealed that theapplication of such coatings by Ion beam sputtering isfeasible.

2. The microstructure of samples discovered that they
are mainly uniform, stable and adhere to surface. How-ever, their properties can be improved by controllingsome of the parameters involved.
3. Combination of SEM micrographs, EDS analysis ofcoating cross section and through thickness GDS analysis are very appropriate methods for fabrication ofthesecoatings.

4. Because of slower diffusion characteristics of platinum atoms, morphology of fabricated coatings is sameas the coatings produced by electroplating. But because

Fig. 3 Microstructure of platinum-aluminide coatings
treated by lon beam sputtering, pack cementationand final heat treatment (845 'C tor 24 hl.

sputtered coatings are made faster and more uniform
than others, this method may improve adherence andquality of the coatings, and reduce the cost of coatingprocess.
1.4

Acknowledgments

1.3

17

The authors thank Kh. Rahmany and R. Masoody
for their technical assistance in specimen fabrication.

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