Colaux, Julie

Dauwe, C.

De Baerdemaeker, J.

Terwagne, Guy

Nitrided 304L stainless-steel coatings were deposited on low carbon steel substrates by dc-magnetron sputtering in a reactive atmosphere of argon and nitrogen. The nitrogen partial mass flow (pN2) was varied linearly from 0% to 100% resulting in a nitriding of the stainless-steel coatings with nitrogen concentrations up to 46 at%. Positron annihilation spectroscopy is used to characterize the defect structure of the coatings. The remarkable evolution of the defect structure with increasing pN2 is discussed

Repository of the University of Namur

RESEARCH OUTPUTS / RÉSULTATS DE RECHERCHEAuthor(s) - Auteur(s) :Publication date - Date de publication :Permanent link - Permalien :Rights / License - Licence de droit d’auteur :Bibliothèque Universitaire Moretus PlantinInstitutional Repository - Research PortalDépôt Institutionnel - Portail de la Rechercheresearchportal.unamur.beInvestigation of nitrided 304L stainless steel coatings by positron annihilationspectroscopyDe Baerdemaeker, J.; Colaux, Julie; Terwagne, Guy; Dauwe, C.Published in:Radiation Physics and ChemistryPublication date:2003Document VersionPeer reviewed versionLink to publicationCitation for pulished version (HARVARD):De Baerdemaeker, J, Colaux, J, Terwagne, G & Dauwe, C 2003, 'Investigation of nitrided 304L stainless steelcoatings by positron annihilation spectroscopy' Radiation Physics and Chemistry, vol. 68, pp. 605-608.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 21. May. 2019Radiation Physics and Chemistry 68 (2003) 605–608Investigation of nitrided 304L stainless-steel coatings bypositron annihilation spectroscopyJ. De Baerdemaekera,*, J. Colauxb, G. Terwagneb, C. DauweaaNUMAT, Department of Subatomic and Radiation Physics, Ghent University, Proeftuinstraat 86, B-9000 Ghent, BelgiumbLARN, Facult!es Universitaire Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, BelgiumAbstractNitrided 304L stainless-steel coatings were deposited on low carbon steel substrates by dc-magnetron sputtering in areactive atmosphere of argon and nitrogen. The nitrogen partial mass ﬂow (pN2) was varied linearly from 0% to 100%resulting in a nitriding of the stainless-steel coatings with nitrogen concentrations up to 46 at%. Positron annihilationspectroscopy is used to characterize the defect structure of the coatings. The remarkable evolution of the defectstructure with increasing pN2 is discussed.r 2003 Elsevier Science Ltd. All rights reserved.Keywords: Positron annihilation; Steel; Nitriding; Magnetron sputtering1. IntroductionThe understanding of the addition of nitrogen to ironto improve the surface hardness and tribological proper-ties, goes back to early 1900s (Fry, 1923). Nitriding ofstainless steels is an excellent method to improve theirwear resistance without compromising their well-knowncorrosion resistance performance. Several modern tech-niques are used for nitriding such as conventional ionimplantation, pulsed plasma nitriding, plasma immer-sion ion implantation (PI3), laser nitriding and reactivemagnetron sputtering. Sputter-deposited ﬁlms typicallyexhibit a wide range of defects. The purpose of this workis to investigate the microstructure and in particular tocharacterize the evolution of the defect structure of thesesputtered ﬁlms and how this could be inﬂuenced by thenitriding process.2. Experimental details2.1. Sample preparationSamples of a low carbon steel sheet with a thickness of0.5mm were cut into 20 20mm2 squares. The sampleswere mechanically polished with sandpapers of differentgrain sizes and ﬁnally to a mirror ﬁnish with diamondpaste down to 1 mm. Prior to deposition they werecleaned with pentane. The coatings were deposited usingan unbalanced dc-magnetron sputtering system. A50-mm diameter AISI-304L stainless steel (compositionin wt%: Fe 70%, Cr 18%, Ni 10%, Mn 2%) disktarget was placed just above the magnets with a goodthermal contact and was cooled during deposition. Achimney was placed between the target and the sampleholder to avoid contamination of the sputter chamber.The magnetron power was set to 200W during deposi-tion of the samples. Although the substrate washeated by electron and ion bombardment, the tempera-ture was below 373K during deposition. The coatingswere reactively deposited for 20min with various Ar/N2gas mixtures up to a thickness of 325 nm. Duringdeposition the total gas ﬂow rate remained constant at35 sccm.ARTICLE IN PRESS*Corresponding author. Tel.: +32-9-264-65-70; fax: +32-9-264-66-97.E-mail address: jeremie.debaerdemaeker@rug.ac.be(J. De Baerdemaeker).0969-806X/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S0969-806X(03)00240-82.2. Experimental techniquesThe defect structure of the layers was investigated bypositron annihilation spectroscopy. The Ghent variableenergy positron beam was used to perform depthselective analysis of the Doppler broadening of theannihilation radiation (DBAR). The energy of themagnetically guided positron beam is variable between0.1 and 30 keV. The annihilation radiation is detected byan HPGe detector with a 25% efﬁciency and aresolution of 1.17 keV at 514 keV. Using a 15mCi22Na source moderated by a 1 mm tungsten singlecrystalline moderator we measure a count rate of103 s1 in the photo-peak at 1 cm behind the sample.For each measurement there were at least 106 countsrecorded in the photo-peak. The Doppler broadened511 keV annihilation line is commonly characterized bythe well-known ‘‘Shape’’ parameter S and a ‘‘Wing’’parameter W : These parameters represent, respectively,the fraction of the surface of a central part and thefraction of the surface of the outer parts under theannihilation line to the total surface under the annihila-tion line. From the deﬁnition of the S and W parameterit is clear that S is dominated by the annihilation ofpositrons with low energetic electrons as valenceelectrons and W by the annihilation with higherenergetic core electrons. A raising of the S and loweringof the W parameter measured for a same type ofmaterial could therefore indicate the presence of (bigger)open volume defects because a reduced fraction of thepositrons trapped in the defects will annihilate with coreelectrons in favor of the annihilation with valenceelectrons. The areas used for the characterization werechosen in order to give S ¼ 0:5 (51170.72 keV) andW ¼ 0:05 (2.1 keV ojEg  511 keVjo6:4 keV) for ap-type Si (1 0 0) wafer.The characterization of the layers was performed atLARN by nuclear elemental analyses with the ALTA.IS2MV Tandetron accelerator. The thickness and ele-mental composition of the coatings were measured byRutherford backscattering spectroscopy (RBS) andparticle induced X-ray emission (PIXE). Nuclear reac-tion analysis (NRA) was used to measure the nitrogenconcentration using 14N(a,p)17O at 5.3MeV.3. Results and discussionThe results of the NRA and RBS measurements aresummarized in Table 1. The total amount of nitrogenincorporated in the ﬁlm was found to be proportional tothe nitrogen ﬂow up to a partial nitrogen ﬂow (pN2) of55%. For higher partial ﬂows of nitrogen a saturation ofthe concentration of the nitrogen in the ﬁlm is reachedwith a mean concentration of 46 at%. The PIXEmeasurements conﬁrmed that the relative amount ofFe, Cr, Ni and Mn in the nitrogen-containing coatingsstays within the speciﬁcations of the AISI 304L sputtertarget. For pN2>20% the deposition rate decreasedlinearly which is reﬂected in the thickness of thecoatings.Conversion electron M .ossbauer spectroscopy(CEMS) and grazing incidence X-ray diffraction(GXRD) measurements (Colaux, 2002) showed thatfor nitrogen concentrations up to 17 at% (pN2 20%) thenitrogen atoms are in solid solution in the iron matrix. Itis well known from literature that this nitrogen-super-saturated or expanded fcc phase has an improved wearresistance and a higher corrosion resistance (Dahm,2000). For higher nitrogen ﬂows the nitrogen forms bothiron and chromium nitrides which typically induce wearresistance.Defects such as vacancies, dislocations or impurityatoms introduced during the growth of a ﬁlm can reducedislocation mobility and can in this way also increasehardness. Magnetron sputtered ﬁlms typically have avery high dislocation density. Positron annihilationspectroscopy is an excellent probe of vacancy-typedefects. Only a small selection of the total amount ofsamples was investigated with depth selective DBAR.The results of the S parameter analyses are shown inFig. 1. The surfaces of the samples show the highest Sparameters. For incident positron energies from 2 keVthe inﬂuence of the surfaces on the S becomes negligibleand the S parameters observed up to 7.5 keV (dependingon the thickness of the coating) are dominated by the Sparameters of the stainless-steel coatings. For higherenergies the S parameters evolve to the value of the lowcarbon steel substrate reaching this value from 25 keV.These spectra were analyzed using VEPFIT (Schut,1990). The results are summarized in Table 1. It is clearthat as soon as nitrogen is added to the sputteratmosphere a drastic reduction of the S parameter isobserved compared to coatings sputtered under pure Ar.This reduction in S parameter continues up to a pN2 of50%, for higher pN2 the S parameter increases again butnever reaching the high value of the Ar sputteredARTICLE IN PRESSTable 1Characteristics of the reactive sputter deposited 304L coatingsas measured with NRA, RBS and DBARpN2 (%) [N] (at%) Thickness (nm) (S; W )0 0 325 (0.457, 0.095)9 9.0 325 (0.432, 0.110)11 11.2 325 (0.426, 0.114)15 13.5 325 (0.423, 0.116)35 30.4 290 (0.419, 0.117)50 42.3 265 (0.420, 0.116)90 55.3 190 (0.423, 0.112)100 35.7 305 (0.436, 0.098)J. De Baerdemaeker et al. / Radiation Physics and Chemistry 68 (2003) 605–608606coating. Additional information can be gained if we mapthe depth selective DBAR measurements in an S  Wplot (Mantl, 1978; Liszkay, 1994) because every kind ofpositron annihilation site is characterized by a typical(S; W ) couple. The results are presented in Fig. 2. Forclarity only the cluster points for most of the differentcoatings and for the substrate are presented. Thesecluster points represent successive energies for whichconstant (S; W ) coordinates are measured implying adistinct characteristic (S; W ) for the layer or substrate.From Fig. 2 it is clear that the cluster points forcoatings sputtered with pN2 up to 15% are laying on astrait line. Because of the linearity property of S and Wthis implies that the observed evolution can beeffectively described as trapping of the positrons takingplace at two distinct annihilation sites. These annihila-tion sites are characterized as one having a high S andlow W value and another with a low S and high Wvalue. This behavior could indicate that with increasingnitrogen introduction the fraction of relatively big openvolume defects decreases in favor of relatively smallopen volume defects. It is also worth stating that the lineshape parameters evolve in a strait line from the clusterpoint of the coating to the substrate.For the coatings sputtered with pN2>15% anevolution to another not yet identiﬁed defect site isobserved. Also the cluster points of these coatings donot evolve linearly to the substrate but seem to passthrough an interface zone. These effects could becorrelated on the one hand to the reduced depositionrate which is a consequence of a different sputterdeposition mode or on the other hand to the formationof the nitrides which are observed by CEMS andGXRD.4. ConclusionsReactively sputtered nitrided coatings were investi-gated using depth selective DBAR. The coatings showedan interesting evolution of the defect structure. Futureinvestigations as depth selective positron annihilationlifetime spectroscopy should be performed in order toquantify the defect structures of the reactively sputterednitrided coatings and to try to determine whether theimproved wear resistance of those coatings is solely dueto the formation of interstitial nitrogen and nitrides ordue to the combination with the observed defectmodiﬁcation.AcknowledgementsThis research was ﬁnancially supported by the Belgian‘‘Interuniversity Attraction Poles’’ program No. P4/10,granted by the Ofﬁce of Scientiﬁc, Technical andCultural Affairs and by the Fund for Scientiﬁc ResearchFlanders (Belgium) [G-006.69].ReferencesColaux, J., Terwagne, G., 2002. unpublished data.Dahm, K.L., Dearnley, P.A., 2000. On the nature, propertiesand wear response of s-phase (nitrogen-alloyed stainlesssteel) coatings on AISI 316L. Proc. Inst. Mech. Eng. Part L-J. Mater.-Des. Appl. 214 (L4), 181–198.Fry, A., 1923. Stahl Eisen, 43, 1271.Liszkay, L., Corbel, C., Baroux, L., Hautojarvi, P., Bayhan,M., Brinkman, A.W., Taterenko, S., 1994. PositronARTICLE IN PRESSFig. 2. S W plot of the cluster points of 304L coatingsreactively sputtered in Ar/N2 atmospheres with different partialpressures of nitrogen. For pN2>35% the evolution from thecluster point of the coating to the substrate is shown.Fig. 1. S parameter plotted as a function of incident positronenergy of 304L coatings reactively sputtered in Ar/N2 atmo-spheres with different partial pressures of nitrogen (pN2).J. De Baerdemaeker et al. / Radiation Physics and Chemistry 68 (2003) 605–608 607trapping at divacancies in thin polycrystalline CDTE-ﬁlmsdeposited on glass. Appl. Phys. Lett. 64 (11), 1380–1382.Mantl, S., Triftsha .user, W., 1978. Defect annealing studies ofmetals by positron-annihilation and electrical resistivitymeasurements. Phys. Rev. B 17 (4), 1645–1652.Schut, H., van Veen, A., de Vries, J., Hakvoort, R.A., IJpma,M.R., 1990. In: Schultz, P.J., Massoumi, G.R., Simpson,P.J. (Eds.), Proceedings of the Fourth International Work-shop on Slow-Positron Beam Techniques for Solids andSurfaces. AIP, New York.ARTICLE IN PRESSJ. De Baerdemaeker et al. / Radiation Physics and Chemistry 68 (2003) 605–608608

Investigation of nitrided 304L stainless steel coatings by positron annihilation spectroscopy

RESEARCH OUTPUTS / RÉSULTATS DE RECHERCHEAuthor(s) - Auteur(s) :Publication date - Date de publication :Permanent link - Permalien :Rights / License - Licence de droit d’auteur :Bibliothèque Universitaire Moretus PlantinInstitutional Repository - Research PortalDépôt Institutionnel - Portail de la Rechercheresearchportal.unamur.beInvestigation of nitrided 304L stainless steel coatings by positron annihilationspectroscopyDe Baerdemaeker, J.; Colaux, Julie; Terwagne, Guy; Dauwe, C.Published in:Radiation Physics and ChemistryPublication date:2003Document VersionPeer reviewed versionLink to publicationCitation for pulished version (HARVARD):De Baerdemaeker, J, Colaux, J, Terwagne, G & Dauwe, C 2003, 'Investigation of nitrided 304L stainless steelcoatings by positron annihilation spectroscopy', Radiation Physics and Chemistry, vol. 68, pp. 605-608.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Download date: 13. Nov. 2019Radiation Physics and Chemistry 68 (2003) 605–608Investigation of nitrided 304L stainless-steel coatings bypositron annihilation spectroscopyJ. De Baerdemaekera,*, J. Colauxb, G. Terwagneb, C. DauweaaNUMAT, Department of Subatomic and Radiation Physics, Ghent University, Proeftuinstraat 86, B-9000 Ghent, BelgiumbLARN, Facult!es Universitaire Notre-Dame de la Paix, 61 rue de Bruxelles, B-5000 Namur, BelgiumAbstractNitrided 304L stainless-steel coatings were deposited on low carbon steel substrates by dc-magnetron sputtering in areactive atmosphere of argon and nitrogen. The nitrogen partial mass ﬂow (pN2) was varied linearly from 0% to 100%resulting in a nitriding of the stainless-steel coatings with nitrogen concentrations up to 46 at%. Positron annihilationspectroscopy is used to characterize the defect structure of the coatings. The remarkable evolution of the defectstructure with increasing pN2 is discussed.r 2003 Elsevier Science Ltd. All rights reserved.Keywords: Positron annihilation; Steel; Nitriding; Magnetron sputtering1. IntroductionThe understanding of the addition of nitrogen to ironto improve the surface hardness and tribological proper-ties, goes back to early 1900s (Fry, 1923). Nitriding ofstainless steels is an excellent method to improve theirwear resistance without compromising their well-knowncorrosion resistance performance. Several modern tech-niques are used for nitriding such as conventional ionimplantation, pulsed plasma nitriding, plasma immer-sion ion implantation (PI3), laser nitriding and reactivemagnetron sputtering. Sputter-deposited ﬁlms typicallyexhibit a wide range of defects. The purpose of this workis to investigate the microstructure and in particular tocharacterize the evolution of the defect structure of thesesputtered ﬁlms and how this could be inﬂuenced by thenitriding process.2. Experimental details2.1. Sample preparationSamples of a low carbon steel sheet with a thickness of0.5mm were cut into 20 20mm2 squares. The sampleswere mechanically polished with sandpapers of differentgrain sizes and ﬁnally to a mirror ﬁnish with diamondpaste down to 1 mm. Prior to deposition they werecleaned with pentane. The coatings were deposited usingan unbalanced dc-magnetron sputtering system. A50-mm diameter AISI-304L stainless steel (compositionin wt%: Fe 70%, Cr 18%, Ni 10%, Mn 2%) disktarget was placed just above the magnets with a goodthermal contact and was cooled during deposition. Achimney was placed between the target and the sampleholder to avoid contamination of the sputter chamber.The magnetron power was set to 200W during deposi-tion of the samples. Although the substrate washeated by electron and ion bombardment, the tempera-ture was below 373K during deposition. The coatingswere reactively deposited for 20min with various Ar/N2gas mixtures up to a thickness of 325 nm. Duringdeposition the total gas ﬂow rate remained constant at35 sccm.ARTICLE IN PRESS*Corresponding author. Tel.: +32-9-264-65-70; fax: +32-9-264-66-97.E-mail address: jeremie.debaerdemaeker@rug.ac.be(J. De Baerdemaeker).0969-806X/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S0969-806X(03)00240-82.2. Experimental techniquesThe defect structure of the layers was investigated bypositron annihilation spectroscopy. The Ghent variableenergy positron beam was used to perform depthselective analysis of the Doppler broadening of theannihilation radiation (DBAR). The energy of themagnetically guided positron beam is variable between0.1 and 30 keV. The annihilation radiation is detected byan HPGe detector with a 25% efﬁciency and aresolution of 1.17 keV at 514 keV. Using a 15mCi22Na source moderated by a 1 mm tungsten singlecrystalline moderator we measure a count rate of103 s1 in the photo-peak at 1 cm behind the sample.For each measurement there were at least 106 countsrecorded in the photo-peak. The Doppler broadened511 keV annihilation line is commonly characterized bythe well-known ‘‘Shape’’ parameter S and a ‘‘Wing’’parameter W : These parameters represent, respectively,the fraction of the surface of a central part and thefraction of the surface of the outer parts under theannihilation line to the total surface under the annihila-tion line. From the deﬁnition of the S and W parameterit is clear that S is dominated by the annihilation ofpositrons with low energetic electrons as valenceelectrons and W by the annihilation with higherenergetic core electrons. A raising of the S and loweringof the W parameter measured for a same type ofmaterial could therefore indicate the presence of (bigger)open volume defects because a reduced fraction of thepositrons trapped in the defects will annihilate with coreelectrons in favor of the annihilation with valenceelectrons. The areas used for the characterization werechosen in order to give S ¼ 0:5 (51170.72 keV) andW ¼ 0:05 (2.1 keV ojEg  511 keVjo6:4 keV) for ap-type Si (1 0 0) wafer.The characterization of the layers was performed atLARN by nuclear elemental analyses with the ALTA.IS2MV Tandetron accelerator. The thickness and ele-mental composition of the coatings were measured byRutherford backscattering spectroscopy (RBS) andparticle induced X-ray emission (PIXE). Nuclear reac-tion analysis (NRA) was used to measure the nitrogenconcentration using 14N(a,p)17O at 5.3MeV.3. Results and discussionThe results of the NRA and RBS measurements aresummarized in Table 1. The total amount of nitrogenincorporated in the ﬁlm was found to be proportional tothe nitrogen ﬂow up to a partial nitrogen ﬂow (pN2) of55%. For higher partial ﬂows of nitrogen a saturation ofthe concentration of the nitrogen in the ﬁlm is reachedwith a mean concentration of 46 at%. The PIXEmeasurements conﬁrmed that the relative amount ofFe, Cr, Ni and Mn in the nitrogen-containing coatingsstays within the speciﬁcations of the AISI 304L sputtertarget. For pN2>20% the deposition rate decreasedlinearly which is reﬂected in the thickness of thecoatings.Conversion electron M .ossbauer spectroscopy(CEMS) and grazing incidence X-ray diffraction(GXRD) measurements (Colaux, 2002) showed thatfor nitrogen concentrations up to 17 at% (pN2 20%) thenitrogen atoms are in solid solution in the iron matrix. Itis well known from literature that this nitrogen-super-saturated or expanded fcc phase has an improved wearresistance and a higher corrosion resistance (Dahm,2000). For higher nitrogen ﬂows the nitrogen forms bothiron and chromium nitrides which typically induce wearresistance.Defects such as vacancies, dislocations or impurityatoms introduced during the growth of a ﬁlm can reducedislocation mobility and can in this way also increasehardness. Magnetron sputtered ﬁlms typically have avery high dislocation density. Positron annihilationspectroscopy is an excellent probe of vacancy-typedefects. Only a small selection of the total amount ofsamples was investigated with depth selective DBAR.The results of the S parameter analyses are shown inFig. 1. The surfaces of the samples show the highest Sparameters. For incident positron energies from 2 keVthe inﬂuence of the surfaces on the S becomes negligibleand the S parameters observed up to 7.5 keV (dependingon the thickness of the coating) are dominated by the Sparameters of the stainless-steel coatings. For higherenergies the S parameters evolve to the value of the lowcarbon steel substrate reaching this value from 25 keV.These spectra were analyzed using VEPFIT (Schut,1990). The results are summarized in Table 1. It is clearthat as soon as nitrogen is added to the sputteratmosphere a drastic reduction of the S parameter isobserved compared to coatings sputtered under pure Ar.This reduction in S parameter continues up to a pN2 of50%, for higher pN2 the S parameter increases again butnever reaching the high value of the Ar sputteredARTICLE IN PRESSTable 1Characteristics of the reactive sputter deposited 304L coatingsas measured with NRA, RBS and DBARpN2 (%) [N] (at%) Thickness (nm) (S; W )0 0 325 (0.457, 0.095)9 9.0 325 (0.432, 0.110)11 11.2 325 (0.426, 0.114)15 13.5 325 (0.423, 0.116)35 30.4 290 (0.419, 0.117)50 42.3 265 (0.420, 0.116)90 55.3 190 (0.423, 0.112)100 35.7 305 (0.436, 0.098)J. De Baerdemaeker et al. / Radiation Physics and Chemistry 68 (2003) 605–608606coating. Additional information can be gained if we mapthe depth selective DBAR measurements in an S  Wplot (Mantl, 1978; Liszkay, 1994) because every kind ofpositron annihilation site is characterized by a typical(S; W ) couple. The results are presented in Fig. 2. Forclarity only the cluster points for most of the differentcoatings and for the substrate are presented. Thesecluster points represent successive energies for whichconstant (S; W ) coordinates are measured implying adistinct characteristic (S; W ) for the layer or substrate.From Fig. 2 it is clear that the cluster points forcoatings sputtered with pN2 up to 15% are laying on astrait line. Because of the linearity property of S and Wthis implies that the observed evolution can beeffectively described as trapping of the positrons takingplace at two distinct annihilation sites. These annihila-tion sites are characterized as one having a high S andlow W value and another with a low S and high Wvalue. This behavior could indicate that with increasingnitrogen introduction the fraction of relatively big openvolume defects decreases in favor of relatively smallopen volume defects. It is also worth stating that the lineshape parameters evolve in a strait line from the clusterpoint of the coating to the substrate.For the coatings sputtered with pN2>15% anevolution to another not yet identiﬁed defect site isobserved. Also the cluster points of these coatings donot evolve linearly to the substrate but seem to passthrough an interface zone. These effects could becorrelated on the one hand to the reduced depositionrate which is a consequence of a different sputterdeposition mode or on the other hand to the formationof the nitrides which are observed by CEMS andGXRD.4. ConclusionsReactively sputtered nitrided coatings were investi-gated using depth selective DBAR. The coatings showedan interesting evolution of the defect structure. Futureinvestigations as depth selective positron annihilationlifetime spectroscopy should be performed in order toquantify the defect structures of the reactively sputterednitrided coatings and to try to determine whether theimproved wear resistance of those coatings is solely dueto the formation of interstitial nitrogen and nitrides ordue to the combination with the observed defectmodiﬁcation.AcknowledgementsThis research was ﬁnancially supported by the Belgian‘‘Interuniversity Attraction Poles’’ program No. P4/10,granted by the Ofﬁce of Scientiﬁc, Technical andCultural Affairs and by the Fund for Scientiﬁc ResearchFlanders (Belgium) [G-006.69].ReferencesColaux, J., Terwagne, G., 2002. unpublished data.Dahm, K.L., Dearnley, P.A., 2000. On the nature, propertiesand wear response of s-phase (nitrogen-alloyed stainlesssteel) coatings on AISI 316L. Proc. Inst. Mech. Eng. Part L-J. Mater.-Des. Appl. 214 (L4), 181–198.Fry, A., 1923. Stahl Eisen, 43, 1271.Liszkay, L., Corbel, C., Baroux, L., Hautojarvi, P., Bayhan,M., Brinkman, A.W., Taterenko, S., 1994. PositronARTICLE IN PRESSFig. 2. S W plot of the cluster points of 304L coatingsreactively sputtered in Ar/N2 atmospheres with different partialpressures of nitrogen. For pN2>35% the evolution from thecluster point of the coating to the substrate is shown.Fig. 1. S parameter plotted as a function of incident positronenergy of 304L coatings reactively sputtered in Ar/N2 atmo-spheres with different partial pressures of nitrogen (pN2).J. De Baerdemaeker et al. / Radiation Physics and Chemistry 68 (2003) 605–608 607trapping at divacancies in thin polycrystalline CDTE-ﬁlmsdeposited on glass. Appl. Phys. Lett. 64 (11), 1380–1382.Mantl, S., Triftsha .user, W., 1978. Defect annealing studies ofmetals by positron-annihilation and electrical resistivitymeasurements. Phys. Rev. B 17 (4), 1645–1652.Schut, H., van Veen, A., de Vries, J., Hakvoort, R.A., IJpma,M.R., 1990. In: Schultz, P.J., Massoumi, G.R., Simpson,P.J. (Eds.), Proceedings of the Fourth International Work-shop on Slow-Positron Beam Techniques for Solids andSurfaces. AIP, New York.ARTICLE IN PRESSJ. De Baerdemaeker et al. / Radiation Physics and Chemistry 68 (2003) 605–608608

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Investigation of nitrided 304L stainless steel coatings by positron annihilation spectroscopy

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