- Email: [email protected]
First experiences on characterization of surface oxide films in powder particles by Glow Discharge Optical Emission Spectroscopy (GD-OES)
Metal Powder Report Volume 00, Number 00 April 2016
metal-powder.net
SPECIAL FEATURE
First experiences on characterization of surface oxide films in powder particles by Glow Discharge Optical Emission Spectroscopy (GD-OES) I. Heikkila¨, C. Eggertson, M. Randelius, S. Caddeo-Johansson and D. Chasoglou The surface characteristics of the powder particles play a key role on the processing of the powders to consolidated products and on the final properties achieved for the material. Characterization of surface oxide films by techniques commonly used such as X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy provide reliable information on the surface films, but they are timeconsuming methods and the analyzed areas are very limited. In this evaluation, the potential of the depth profile analysis by Glow Discharge Optical Emission Spectroscopy (GD-OES) is experimented for loose powder particles for the first time. Hitherto, the lack of a sample preparation technique has hindered the use of this powerful surface analysis technique for loose powder. Introduction Metal powders have a high affinity to oxygen and thus they are very reactive when coming into contact with air or other oxygen containing atmospheres/surroundings. A thin film of metal oxide is formed on the particle surface. Oxidation can occur whenever the material is exposed to oxygen for instance during the manufacturing, processing and handling of the powder. The characteristics of surface oxides are of vital importance in the processing of the powder to a final product as they contribute the properties of the product. Increased knowledge about the surface films is also highly useful for the optimization of the processes such as sintering or additive manufacturing [1,2]. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are commonly used for the characterization of surface oxides in powder materials. In these techniques, the surface of the powder particles is sputtered by energetic particles after which the surface remaining after erosion can be analyzed. The source of sputtering particles can vary from ion source, X-ray source, a plasma, an accelerator or other. The analytical performance such as later and depth resolution can significantly vary depending on the sputtering source. Electron microscopy on crosssections of powder particles is also widely used for the surface characterization. Here, the analytical performance is mainly influenced by the interaction volume of the electron beam with the E-mail address: [email protected].
sample. The main drawbacks of the commonly used surface characterization methods are that they are time-consuming and the analyzed areas are limited to a modest amount of powder particles [1,3]. The analyzing technique making use of glow discharges coupled to optical emission spectrometry (GD-OES) is a well-established method for depth profile analysis of solid materials excluding powder materials. In this technique, a glow discharge is created by applying a voltage between the sample being a cathode and a tubular anode in a low-pressure gas. When the voltage exceeds a certain value, the gas ionizes into plasma and begins conducting electricity. As soon as the plasma is ignited, the surface of the sample material will be subjected to sputtering of the ions of the plasma. The sputtered material from the sample diffuses into the plasma, where it gets excited. The optical emission of the plasma is detected giving indication of the elements present in the sputtered material. The sputtering process is dependent on the properties of the sample, meanwhile the excitation process is essentially independent on the sample material. The fact that the excitation process and optical emission is independent of the sample, is the critical factor for an easy quantification of compositional information as a function of sputtering depth. This technique is called GD-OES depth profiling [3,4]. The technique is a powerful analytical tool for the direct analysis of solid samples. The advantages of it include ease of use, fast sputtering rate, high depth resolution, excellent
0026-0657/ß 2016 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mprp.2016.03.005
1 Please cite this article in press as: I. Heikkila¨, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.03.005
MPRP-587; No of Pages 4 SPECIAL FEATURE
sensitivity for low concentrations, multi-element capability, good quantification and high sample throughput. The aim of this work was to experiment a suitable sample preparation technique for analysis of loose powder by GD-OES and to analyze applicability of the tested method for the analysis of surface oxide films in powder materials [4].
Operational principle of GD-OES depth profiling SPECIAL FEATURE
The glow discharge source commonly used in depth profiling consists of an anode tube and the sample to be analyzed. The source is generally named as Grimm type of glow discharge lamp, see Fig. 1 for an illustration. The flat sample is placed perpendicular to the front of the anode tube, which is kept at ground potential. Electrical power is supplied directly to the sample. A distance of about 0.1–0.2 mm is kept between the sample and anode tube. Sufficient vacuum tightness is achieved by an O-ring, which separates the discharge chamber from air environment [4]. When the plasma is ignited inside the plasma chamber, free electrons and plasma are generated. Both species will move freely in the electrical field controlling the plasma chamber and will influence the electrical field through creation of local charge distributions. Different characteristic areas are formed in the plasma. Two of them are fundamental for the use of the glow discharge for analytical purposes: the negative glow, free of electrical field but showing high charge density for both ions and electrons, and the cathode dark space. The latter attracts positive ions toward the cathode and generates the sample sputtering. The sputtering also sets free secondary electrons, which are accelerated in the electrical field toward the negative glow, where they lose their energy
Metal Powder Report Volume 00, Number 00 April 2016
through collisions. During the collisions the secondary electrons participate in excitation and ionization processes and thus maintain the plasma [4]. The sputtering process depends strongly on the sample material and its surface properties, but once the atoms are sputtered they move as single atoms into the negative glow. There they are diluted in the argon carrier gas. All the elements at the sample surface are sputtered at the same rate as soon as the equilibrium conditions for the plasma are achieved after the plasma ignition. Preferential sputtering of elements does not play a significant role as the sputtering ions have a rather low energy of 100 eV. Mixing of atomic elements during sputtering is very weak. The excitation and ionization process mainly occur in the negative glow. Ionization and excitation yields are independent of the properties of the sample, but however they are strongly element-specific. For emission processes they are even specific to each spectral line. The quantification of GD-OES signals is relative uncomplicated giving quantitative information of the content of several species. GD-OES is able to analyze surfaces varying from a few nanometers to 100 mm. The elemental concentrations range from 0.001% to 100% (mass fraction). The limitation of the technique is that it lacks lateral resolution. The analytical data is averaged over the area defined by the inner diameter of the hollow anode, typically 4 mm. Depending on the application this can be an advantage or disadvantage [4].
Experimental Samples and sample preparation The powder materials of this work included a water atomized Astaloy CrM and a gas atomized 316L material, see Table 1 for ¨ gana¨s AB their nominal chemical composition provided by Ho Sweden and Carpenter Powder Products, respectively. The nominal oxygen content of the tested powders varied between 0.02 and 0.16 wt%. The studied size fraction of both the powders was 25–32 mm. The samples were prepared by compacting powder against a solid metallic substrate in order facilitate the required vacuum tightness and the low distance of 0.1–0.2 mm between the anode and cathode for the Grimm glow discharge source. The adherence of the particles to the substrate was achieved through compaction. The press tool for the compaction had a very fine surface finish and a coating in purpose to prevent the transfer of surface films from the powder to the press tool by adhesive effects, see Fig. 2 for a SEM image displaying the compacted particles. As a final stage in the sample preparation, the compacted particles were coated with a 15 nm thick layer of gold in purpose to assist stabilization of plasma during the start of the measurement. The signals originating from the top coatings can be excluded in the computation of analysis results.
TABLE 1
The nominal chemical composition of Astaloy CrM and 316L powder (wt%).
FIGURE 1
A schematic illustration of Grimm glow discharge source.
Powder
Cr
Mn
Mo
Ni
Si
N
O
Fe
Astaloy CrM 316L
2.96 16.83
0.10 1.42
0.48 2.10
– 10.58
0.03 0.52
– 0.13
0.16 0.02
Bal. Bal.
2 Please cite this article in press as: I. Heikkila¨, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.03.005
MPRP-587; No of Pages 4 SPECIAL FEATURE
SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 April 2016
FIGURE 2
A SEM image by SE-contrast displaying an overview of compacted powder particles (left) and a SEM image by BS-contrast displaying the adhered coating from the press tool (light color) to the particle tops (right).
Instruments GD-OES analysis was performed with LECO GDS 850 equipped with Grimm type of glow discharge source with an anode of 4 mm internal diameter. High purity argon was used as a carrier gas. Calibration of the elements to be analyzed was made with wellestablished reference methods.
Results and discussion GD-OES depth profiling of Astaloy CrM powder As GD-OES provides information of multiple elements, the elements of interest can be specially chosen for each investigation, see Fig. 3 for the depth profile for Astaloy CrM. The most important elements of the surface film of Astaloy CrM are iron and oxygen. Also, some chromium is present in the surface film. In GD-OES the surface active elements such as silicon, magnesium, and sulfur can be displayed at the accuracy of 0.001%. As the used method lacks lateral resolution, it cannot reveal the morphology of the surfaces film. If the morphology of the oxide film is of interest, this can be made for instance by SEM EDS. The depth profile curve in Fig. 3 suggests that the content of oxygen at top layer of the surface films is rather high. Possible explanations for this are the desorbed oxygen molecules and
moisture on the sample surfaces, which will give an increase for the oxygen signal. Also, the stability of the plasma is not reached directly after ignition and therefore it can influence the analysis results even if gold was used a top layer in the specimens. The nominal oxygen content of Astaloy CrM was 0.16 wt%. The repeatability of the measurement results between similar samples is good, see Fig. 4 for comparison between two measurements. The depth of the oxide film in Astaloy CrM is 5 nm in both measurements. The measured area is 12.56 mm2. Thus, the measurement gives an averaged description of the surface film over a very large number of powder particles. In XPS the analyzed areas are generally less than 10% of this area. The total GD-OES analysis time was a few minutes. In XPS the analysis time is generally a few days. No signs of preferential sputtering can be discerned in the sputtered sample, see Fig. 5 for a SEM image. The homogenous sputtering phenomenon is well-established for GD-OES depth profiling.
GD-OES depth profiling of 316L powder The most important metallic elements of the surface oxide of 316L are iron, manganese, chromium, and silicon, see Fig. 6 for the
FIGURE 4 FIGURE 3
Depth profile of the surface film in Astaloy CrM powder.
The repeatability of the GD-OES measurements in two Astaloy CrM powder samples. 3
Please cite this article in press as: I. Heikkila¨, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.03.005
MPRP-587; No of Pages 4 SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 April 2016
SPECIAL FEATURE
FIGURE 7
Small elemental enrichments at the top of surface oxide film in 316L powder. FIGURE 5
The surface of Astaloy CrM powder sample after completed GD-OES analysis.
depth profile graph. The depth of the oxide film is 3 nm. The nominal oxygen content of 316L was 0.02 wt%. The measured lower film thickness in 316L compared to one measured in Astaloy CrM is in line with the measured nominal oxygen contents of the materials, 0.02 wt% in 316L and 0.16 wt% in Astaloy CrM. The nominal oxygen content of steel is also influenced by factors such as inclusion content of the steel. The enrichment of the elements of high surface activity at the top surface layer of 316L powder is displayed in Fig. 7. The content of manganese, silicon and sulfur are low in 316L, but they are enriched at the surface. Also, an indication of the presence of nickel oxides can be seen. It can be concluded that GD-OES is a powerful tool to analyze small elemental enrichments at the surface of powder particles. Hitherto, the amount of testing with powder materials has been very limited and therefore substantially higher amount of evaluations is needed before the GD-OES depth profiling will become a well-established method for powder materials.
Conclusions The conducted experiments show that the chemical composition and thickness of the surface oxides in powder particles can be analyzed by GD-OES with the developed sample preparation technique. The findings of this investigation can be summarized as: - GD-OES displays a thickness of 5 nm for the oxide film of Astaloy CrM powder. The composition of the oxide film is ironrich. Also, some chromium is present in the surface oxide. - The measured thickness of the oxide film of 316L powders is 3 nm. The oxide film is composed of iron, manganese, chromium and silicon. The technique can reveal elemental enrichments at the top of the surface oxide film. - The area measured by the used technique is 12.56 mm2 and analysis time just a few minutes. Thus, the method can become a powerful tool to describe averaged information of the chemistry and thickness of surface films is powder materials. - More investigations are needed before GD-OES depth profiling can fully be established as a surface analysis method for powder materials. References [1] D. Chasoglou, Surface Chemical Characteristics of Chromium-alloyed Steel Powder and the Role of Process Parameters during Sintering, (Ph.D. thesis), Chalmers University of Technology, 2012. [2] Y.N. Zhang, X. Cao, P. Wanjara, M. Medraj, Acta Mater. 61 (2013) 6562–6576. [3] J. Malherbe, H. Martinez, B. Ferna´ndez, C. Pe´cheyran, O.F.X. Donard, Spectrochim. Acta Part B 64 (2009) 155–166. [4] A. Bengtson, T. Nelis, Anal. Bioanal. Chem. 385 (3) (2006) 568–585.
FIGURE 6
Depth profile of the surface film in 316L powder. 4 Please cite this article in press as: I. Heikkila¨, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.03.005
metal-powder.net
SPECIAL FEATURE
First experiences on characterization of surface oxide films in powder particles by Glow Discharge Optical Emission Spectroscopy (GD-OES) I. Heikkila¨, C. Eggertson, M. Randelius, S. Caddeo-Johansson and D. Chasoglou The surface characteristics of the powder particles play a key role on the processing of the powders to consolidated products and on the final properties achieved for the material. Characterization of surface oxide films by techniques commonly used such as X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy provide reliable information on the surface films, but they are timeconsuming methods and the analyzed areas are very limited. In this evaluation, the potential of the depth profile analysis by Glow Discharge Optical Emission Spectroscopy (GD-OES) is experimented for loose powder particles for the first time. Hitherto, the lack of a sample preparation technique has hindered the use of this powerful surface analysis technique for loose powder. Introduction Metal powders have a high affinity to oxygen and thus they are very reactive when coming into contact with air or other oxygen containing atmospheres/surroundings. A thin film of metal oxide is formed on the particle surface. Oxidation can occur whenever the material is exposed to oxygen for instance during the manufacturing, processing and handling of the powder. The characteristics of surface oxides are of vital importance in the processing of the powder to a final product as they contribute the properties of the product. Increased knowledge about the surface films is also highly useful for the optimization of the processes such as sintering or additive manufacturing [1,2]. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are commonly used for the characterization of surface oxides in powder materials. In these techniques, the surface of the powder particles is sputtered by energetic particles after which the surface remaining after erosion can be analyzed. The source of sputtering particles can vary from ion source, X-ray source, a plasma, an accelerator or other. The analytical performance such as later and depth resolution can significantly vary depending on the sputtering source. Electron microscopy on crosssections of powder particles is also widely used for the surface characterization. Here, the analytical performance is mainly influenced by the interaction volume of the electron beam with the E-mail address: [email protected].
sample. The main drawbacks of the commonly used surface characterization methods are that they are time-consuming and the analyzed areas are limited to a modest amount of powder particles [1,3]. The analyzing technique making use of glow discharges coupled to optical emission spectrometry (GD-OES) is a well-established method for depth profile analysis of solid materials excluding powder materials. In this technique, a glow discharge is created by applying a voltage between the sample being a cathode and a tubular anode in a low-pressure gas. When the voltage exceeds a certain value, the gas ionizes into plasma and begins conducting electricity. As soon as the plasma is ignited, the surface of the sample material will be subjected to sputtering of the ions of the plasma. The sputtered material from the sample diffuses into the plasma, where it gets excited. The optical emission of the plasma is detected giving indication of the elements present in the sputtered material. The sputtering process is dependent on the properties of the sample, meanwhile the excitation process is essentially independent on the sample material. The fact that the excitation process and optical emission is independent of the sample, is the critical factor for an easy quantification of compositional information as a function of sputtering depth. This technique is called GD-OES depth profiling [3,4]. The technique is a powerful analytical tool for the direct analysis of solid samples. The advantages of it include ease of use, fast sputtering rate, high depth resolution, excellent
0026-0657/ß 2016 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mprp.2016.03.005
1 Please cite this article in press as: I. Heikkila¨, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.03.005
MPRP-587; No of Pages 4 SPECIAL FEATURE
sensitivity for low concentrations, multi-element capability, good quantification and high sample throughput. The aim of this work was to experiment a suitable sample preparation technique for analysis of loose powder by GD-OES and to analyze applicability of the tested method for the analysis of surface oxide films in powder materials [4].
Operational principle of GD-OES depth profiling SPECIAL FEATURE
The glow discharge source commonly used in depth profiling consists of an anode tube and the sample to be analyzed. The source is generally named as Grimm type of glow discharge lamp, see Fig. 1 for an illustration. The flat sample is placed perpendicular to the front of the anode tube, which is kept at ground potential. Electrical power is supplied directly to the sample. A distance of about 0.1–0.2 mm is kept between the sample and anode tube. Sufficient vacuum tightness is achieved by an O-ring, which separates the discharge chamber from air environment [4]. When the plasma is ignited inside the plasma chamber, free electrons and plasma are generated. Both species will move freely in the electrical field controlling the plasma chamber and will influence the electrical field through creation of local charge distributions. Different characteristic areas are formed in the plasma. Two of them are fundamental for the use of the glow discharge for analytical purposes: the negative glow, free of electrical field but showing high charge density for both ions and electrons, and the cathode dark space. The latter attracts positive ions toward the cathode and generates the sample sputtering. The sputtering also sets free secondary electrons, which are accelerated in the electrical field toward the negative glow, where they lose their energy
Metal Powder Report Volume 00, Number 00 April 2016
through collisions. During the collisions the secondary electrons participate in excitation and ionization processes and thus maintain the plasma [4]. The sputtering process depends strongly on the sample material and its surface properties, but once the atoms are sputtered they move as single atoms into the negative glow. There they are diluted in the argon carrier gas. All the elements at the sample surface are sputtered at the same rate as soon as the equilibrium conditions for the plasma are achieved after the plasma ignition. Preferential sputtering of elements does not play a significant role as the sputtering ions have a rather low energy of 100 eV. Mixing of atomic elements during sputtering is very weak. The excitation and ionization process mainly occur in the negative glow. Ionization and excitation yields are independent of the properties of the sample, but however they are strongly element-specific. For emission processes they are even specific to each spectral line. The quantification of GD-OES signals is relative uncomplicated giving quantitative information of the content of several species. GD-OES is able to analyze surfaces varying from a few nanometers to 100 mm. The elemental concentrations range from 0.001% to 100% (mass fraction). The limitation of the technique is that it lacks lateral resolution. The analytical data is averaged over the area defined by the inner diameter of the hollow anode, typically 4 mm. Depending on the application this can be an advantage or disadvantage [4].
Experimental Samples and sample preparation The powder materials of this work included a water atomized Astaloy CrM and a gas atomized 316L material, see Table 1 for ¨ gana¨s AB their nominal chemical composition provided by Ho Sweden and Carpenter Powder Products, respectively. The nominal oxygen content of the tested powders varied between 0.02 and 0.16 wt%. The studied size fraction of both the powders was 25–32 mm. The samples were prepared by compacting powder against a solid metallic substrate in order facilitate the required vacuum tightness and the low distance of 0.1–0.2 mm between the anode and cathode for the Grimm glow discharge source. The adherence of the particles to the substrate was achieved through compaction. The press tool for the compaction had a very fine surface finish and a coating in purpose to prevent the transfer of surface films from the powder to the press tool by adhesive effects, see Fig. 2 for a SEM image displaying the compacted particles. As a final stage in the sample preparation, the compacted particles were coated with a 15 nm thick layer of gold in purpose to assist stabilization of plasma during the start of the measurement. The signals originating from the top coatings can be excluded in the computation of analysis results.
TABLE 1
The nominal chemical composition of Astaloy CrM and 316L powder (wt%).
FIGURE 1
A schematic illustration of Grimm glow discharge source.
Powder
Cr
Mn
Mo
Ni
Si
N
O
Fe
Astaloy CrM 316L
2.96 16.83
0.10 1.42
0.48 2.10
– 10.58
0.03 0.52
– 0.13
0.16 0.02
Bal. Bal.
2 Please cite this article in press as: I. Heikkila¨, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.03.005
MPRP-587; No of Pages 4 SPECIAL FEATURE
SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 April 2016
FIGURE 2
A SEM image by SE-contrast displaying an overview of compacted powder particles (left) and a SEM image by BS-contrast displaying the adhered coating from the press tool (light color) to the particle tops (right).
Instruments GD-OES analysis was performed with LECO GDS 850 equipped with Grimm type of glow discharge source with an anode of 4 mm internal diameter. High purity argon was used as a carrier gas. Calibration of the elements to be analyzed was made with wellestablished reference methods.
Results and discussion GD-OES depth profiling of Astaloy CrM powder As GD-OES provides information of multiple elements, the elements of interest can be specially chosen for each investigation, see Fig. 3 for the depth profile for Astaloy CrM. The most important elements of the surface film of Astaloy CrM are iron and oxygen. Also, some chromium is present in the surface film. In GD-OES the surface active elements such as silicon, magnesium, and sulfur can be displayed at the accuracy of 0.001%. As the used method lacks lateral resolution, it cannot reveal the morphology of the surfaces film. If the morphology of the oxide film is of interest, this can be made for instance by SEM EDS. The depth profile curve in Fig. 3 suggests that the content of oxygen at top layer of the surface films is rather high. Possible explanations for this are the desorbed oxygen molecules and
moisture on the sample surfaces, which will give an increase for the oxygen signal. Also, the stability of the plasma is not reached directly after ignition and therefore it can influence the analysis results even if gold was used a top layer in the specimens. The nominal oxygen content of Astaloy CrM was 0.16 wt%. The repeatability of the measurement results between similar samples is good, see Fig. 4 for comparison between two measurements. The depth of the oxide film in Astaloy CrM is 5 nm in both measurements. The measured area is 12.56 mm2. Thus, the measurement gives an averaged description of the surface film over a very large number of powder particles. In XPS the analyzed areas are generally less than 10% of this area. The total GD-OES analysis time was a few minutes. In XPS the analysis time is generally a few days. No signs of preferential sputtering can be discerned in the sputtered sample, see Fig. 5 for a SEM image. The homogenous sputtering phenomenon is well-established for GD-OES depth profiling.
GD-OES depth profiling of 316L powder The most important metallic elements of the surface oxide of 316L are iron, manganese, chromium, and silicon, see Fig. 6 for the
FIGURE 4 FIGURE 3
Depth profile of the surface film in Astaloy CrM powder.
The repeatability of the GD-OES measurements in two Astaloy CrM powder samples. 3
Please cite this article in press as: I. Heikkila¨, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.03.005
MPRP-587; No of Pages 4 SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 April 2016
SPECIAL FEATURE
FIGURE 7
Small elemental enrichments at the top of surface oxide film in 316L powder. FIGURE 5
The surface of Astaloy CrM powder sample after completed GD-OES analysis.
depth profile graph. The depth of the oxide film is 3 nm. The nominal oxygen content of 316L was 0.02 wt%. The measured lower film thickness in 316L compared to one measured in Astaloy CrM is in line with the measured nominal oxygen contents of the materials, 0.02 wt% in 316L and 0.16 wt% in Astaloy CrM. The nominal oxygen content of steel is also influenced by factors such as inclusion content of the steel. The enrichment of the elements of high surface activity at the top surface layer of 316L powder is displayed in Fig. 7. The content of manganese, silicon and sulfur are low in 316L, but they are enriched at the surface. Also, an indication of the presence of nickel oxides can be seen. It can be concluded that GD-OES is a powerful tool to analyze small elemental enrichments at the surface of powder particles. Hitherto, the amount of testing with powder materials has been very limited and therefore substantially higher amount of evaluations is needed before the GD-OES depth profiling will become a well-established method for powder materials.
Conclusions The conducted experiments show that the chemical composition and thickness of the surface oxides in powder particles can be analyzed by GD-OES with the developed sample preparation technique. The findings of this investigation can be summarized as: - GD-OES displays a thickness of 5 nm for the oxide film of Astaloy CrM powder. The composition of the oxide film is ironrich. Also, some chromium is present in the surface oxide. - The measured thickness of the oxide film of 316L powders is 3 nm. The oxide film is composed of iron, manganese, chromium and silicon. The technique can reveal elemental enrichments at the top of the surface oxide film. - The area measured by the used technique is 12.56 mm2 and analysis time just a few minutes. Thus, the method can become a powerful tool to describe averaged information of the chemistry and thickness of surface films is powder materials. - More investigations are needed before GD-OES depth profiling can fully be established as a surface analysis method for powder materials. References [1] D. Chasoglou, Surface Chemical Characteristics of Chromium-alloyed Steel Powder and the Role of Process Parameters during Sintering, (Ph.D. thesis), Chalmers University of Technology, 2012. [2] Y.N. Zhang, X. Cao, P. Wanjara, M. Medraj, Acta Mater. 61 (2013) 6562–6576. [3] J. Malherbe, H. Martinez, B. Ferna´ndez, C. Pe´cheyran, O.F.X. Donard, Spectrochim. Acta Part B 64 (2009) 155–166. [4] A. Bengtson, T. Nelis, Anal. Bioanal. Chem. 385 (3) (2006) 568–585.
FIGURE 6
Depth profile of the surface film in 316L powder. 4 Please cite this article in press as: I. Heikkila¨, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.03.005