Tailoring of Transition Metal Silicides as Protective Thin Films on Austenitic Stainless Steel
Doktorsavhandling, 2011

The objective of this study is to make use of transition metal silicides in a novel way as protective thin films on engineering metals. It can then be possible to take advantage of the potentially good corrosion resistance of metal silicides while compensating for their brittle nature by the ductile bulk material. Transition metal silicide thin films based on the systems of Ti-Si, Cr-Si, Fe-Si, Ni-Si were fabricated by means of ion-beam co-sputter deposition on 304 stainless steel substrates, with or without subsequent annealing treatment. Thin film characterisation was done by means of X-ray photoelectron and X-ray diffraction analysis. For the films in crystalline form after annealing, the silicides were well-characterised by means of both techniques. The co-sputtered films showed short-range ordered structures, but the possible silicide phases could be depicted from the core-level XPS spectra of the transition metal peaks defined by the crystalline forms. Except for the Cr-Si system, the phase formation sequence during annealing processes was possible to predict by means of Pretorius’ effective heat of formation (EHF) model provided that the initial thin film compositions were determined. The corrosion properties of the as-deposited silicide films and the uncoated stainless steel specimens were assessed by means of polarisation measurements in dilute hydrochloric (HCl) and sulphuric (H2SO4) acid solutions. All silicide-coated specimens showed lower current densities along the measured potentials than the uncoated steel, suggesting their lower reactivity. Among the silicide films, the Ti-Si and Ni-Si based films showed the best corrosion properties and Si content above 60 at.% for all films facilitated high integrity Si-oxide layer development, whereby corrosion properties improved. Further studies conducted on the Ni-Si system showed that composition is a more important design factor than structure. When considering their tribological properties, Rockwell-C adhesion tests and reciprocating sliding wear tests proved the silicide films to be well-adhering on the substrates and to show lower specific wear rate (10e-13 m3/Nm) than that (10e-12 m3/Nm) of the uncoated steel. It is supposed that transition metal silicides can act as protective thin films on stainless steel as well as any other engineering materials as far as good adhesion is guaranteed.

Rockwell-C adhesion test

X-ray diffractrometry (XRD)

Pretorius’ effective heat of formation (EHF) model

Ion-beam sputter deposition (IBSD)

Reciprocating sliding wear test

Corrosion

Stainless steels

Thin films

Tribology

Transition metal silicides

X-ray photoelectron spectroscopy (XPS)

Potentiodynamic polarisation measurements

Lecture Hall HA1, Hörsalsvägen 4, Chalmers University of Technology, Gothenburg
Opponent: Professor Christofer Leygraf

Författare

Eric Tam

Chalmers, Material- och tillverkningsteknik

Sputter deposition and XPS analysis of nickel silicide thin films

Surface and Coatings Technology,; Vol. 203(2009)p. 2886-2890

Artikel i vetenskaplig tidskrift

Corrosion behaviour of amorphous Ni-Si thin films on AISI 304L stainless steel

Materials at High Temperatures,; Vol. 26(2009)p. 177-186

Artikel i vetenskaplig tidskrift

A novel way of making use of transition metal silicides as protective coatings on engineering metals is proposed in this thesis. Transition metal silicide coatings based on the binary systems including Ti-Si, Cr-Si, Fe-Si, Ni-Si were fabricated by means of physical vapour deposition (PVD) technique on 304 stainless steel plates. The corrosion properties of the silicide-coated and the uncoated stainless steel specimens were assessed by means of polarisation measurements in dilute hydrochloric (HCl) and sulphuric (H2SO4) acid solutions. All silicide-coated specimens showed higher corrosion resistivity than the uncoated steel. Among the silicide coatings, the Ti-Si and Ni-Si based films showed better corrosion properties and this can be further improved if the Si content is above 60 at.%. Further studies showed that composition is a more important design factor than structure for this kind of coatings. When considering their tribological properties, the silicide coatings were proved to be well-adhering on the substrates and to show lower specific wear rate than that of the uncoated steel. It is supposed that transition metal silicides can act as protective thin films on stainless steel as well as any other engineering materials as far as good adhesion is guaranteed.

Ämneskategorier

Maskinteknik

Oorganisk kemi

Materialteknik

Fysikalisk kemi

Teknisk mekanik

Analytisk kemi

Bearbetnings-, yt- och fogningsteknik

Den kondenserade materiens fysik

Styrkeområden

Materialvetenskap

ISBN

978-91-7385-560-0

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3241

Lecture Hall HA1, Hörsalsvägen 4, Chalmers University of Technology, Gothenburg

Opponent: Professor Christofer Leygraf