- Email: [email protected]
Surface morphology of nitrogen-alloyed steels using high intensity pulsed plasma beams
July 1997
EISEVIER
Materials Letters 32 (1997) 49-53
Surface morphology of nitrogen-alloyed steels using high intensity pulsed plasma beams J. Piekoszewski
a**, L. Walis’ ‘, J. Langner b
a Institute of Nuclear Chemistry and Technology, ul. Dorodna 16, 03-145 Warszawa, Poland b Soltan Institute for Nuclear Studies, M-400 Otwock / iwierk, Poland
Received 5 December 1996; accepted 12 December 1996
Abstract Samples of single phase (AISI 321) steel and two-constituent (AISI 1045) steel were irradiated with intense nitrogen plasma pulses. The action of each pulse resulted in melting of the near surface layer and introducing the dose of about 10” N atoms/cm’. For initially smooth surfaces, in AISI 321 the main morphological changes occur after the first pulse, whereas in AISI 1045 the roughness increases with the number of pulses. For initially rough AISI 1045 (i.e. R, > 0.5 @rn> the pulse processing results in a decrease of R, and a significant increase (by a factor of about 2) of microhardness HV,, . Practical conclusions are drawn from these results. Keywords: Surface; Nitrogen-alloyed steels; Pulsed plasma beams
1. Introduction High intensity pulse or plasma irradiation has recently received growing interest as a potential tool in surface engineering. Likewise in the laser or electron beam case, ions from pulsed beam rapidly heat the surface of irradiated material. The surface remains at a high teimperature (up to the melting point or higher) for a period in nanosecond to microsecond range, and then rapidly cools through conduction into the hulk at rates of the order of lo’-10” K/s. Obviously, the details of heat evolution in the substrate depend on its thermal properties and dimensions as well as on the beam parameters. Heat induced processes result in several nonequilib-
* Corresponding
author.
00167-577X/97/$17.00 Copyright PII SO167-577X(96)00303-5
rium phenomena such as realization of mixing of metallic overlayers on various (even hardly miscible) substrates, formation of metastable crystalline alloys and so on. Excellent examples of such experiments can be found, e.g., in Refs. [l-4]. In each case, for a given power versus time transient and a pulse duration, to achieve the desired surface modification it is necessary to select the energy density so as to cause melting of the near surface layer of the substrate but not to cause the violent mass ablation from its surface. Using ion or plasma beams, beside purely thermal effects, as in the references cited above, it is also possible, under appropriate conditions, to modify the surface properties of solids via thermal effects in conjunction with mass transport. For example, in our previous reports, e.g. Ref. [51, it was shown that it is possible to introduce high doses (up to 10”
0 1997 Elsevier Science B.V. All rights reserved.
50
.I. Piekoszewski
et d/Materials
atoms/cm2 per pulse) of nitrogen into various kinds of steel and thereby to alter their near surface properties. However, even if the desirable structural characteristics are attained by pulse processing, the range of technological applications of this technique will depend to a considerable extent on the final roughness of the processed surface. For instance, the roughness should be less than 2 pm R, for cutting tools, 1 pm R, for punching tools and less then 0.1 pm for cold forming tools [6]. On the other hand, it is known [7] that the transient processing in which melting of near surface layer occurs always results in some roughening of the surface. Until now, the available information in the literature concerning this issue is rather sparse. In this paper, we report the results of a study of the surface morphology of two kinds of steel samples subjected to nitrogen alloying with the use of high intensity pulsed plasma beams. Emphasis has been placed upon the influence of the initial constituents of the substrate, i.e., as to whether it consists of a single phase or of heterogeneous mixture of more than one phase, and on the initial roughness of the surface.
2. Experimental details
2.1. Samples and characterization Two kinds of materials were used in the experiments: (1) Medium/high carbon steel 45, composed of 0.42-0.59 wt% C, OS-O.8 wt% Mn, 0.17-0.37 wt% Si (equivalent to AISI 1045 steel). (2) Stainless steel lH18N9T, composed of max. 0.12 wt% C, max. 2 wt.% Mn, 0.8 wt% Si, 0.035 wt% P, 0.03 wt% S, 17-19 wt% Cr, 8-10 wt% Ni and min. 5 X C wt% Ti (equivalent to AISI 321 steel). The microstructure constituents of these materials are ferrite and perlite in approximately equal proportions in (11, and single phase austenite in (2). Samples were prepared in the form of 2 mm thick discs of 18 to 30 mm diameter. The surfaces of samples were finished to various roughnesses by grinding on the rotating grinding plate. In the case of 45 steel, eight grades of the surface roughness were intentionally procured with R, ranging from 0.16 to 1.95 pm.
Letters 32 (1997) 49-53
All samples of lH18N9T were finished to the roughness of 0.04-0.05 pm R,. Average values of R, for each sample were derived from the surface profiles taken randomly along the traverse direction perpendicular to the visible grinding grooves, using Homme1 tester T-2000. The morphologies were examined by scanning electron microscopy @EM). In addition, the microhardness VH,,, was measured before and after pulsed plasma processing, using Hanemann-type tester. 2.2. Nitrogen plasma pulse processing High intensity nitrogen plasma pulses were produced in IBIS rod plasma injector (RPI) type generator which was described elsewhere [5,8]. Here, for the sake of completeness we shall outline only the most important characteristics of this device. Plasma pulses are formed in a low-pressure, high-current plasma discharge initiated between two concentric cylindrical sets of rods allowing for a free passage of particles through the electrode region. A fast electromagnetic valve introduces a portion of the working gas into the interelectrode region. After some delay r (150-250 ps) from the moment of valve opening, a voltage from the charged condenser bank is applied to the electrodes. Depending on the value of rn, two modes of operation are possible. In the first one, referred to as pulse implantation doping @‘ID), ho is sufficiently long to allow the injected working gas to fill the whole interelectrode space. Under such conditions, a short intense pulse is generated containing exclusively the ions of the working gas. In the second mode, referred to as deposition by pulsed erosion (DPE), delay rn is relatively short and the working gas expanding from the valve does not reach the electrode ends. Under such conditions, arc-evaporation of the electrode material occurs, and as a result, the plasma becomes enriched with the ions of the electrode material. This allows one to make extremely well adhering coatings of variety of metals on any kind of the solid substrate. In the present paper, the PID mode with nitrogen as a working gas was used to generate nitrogen plasma pulses. The power versus time transients of these pulses consist of two distinct phases. In the first one, there is a sharp peak, lasting about 1 ps, the mean energy of ions being several keV. In the second
J. Piekoszewski
51
et al. / Materials Letters 32 (1997) 49-53
3. Results and discussion
phase, there is a long tail, lasting several microseconds with ion energy of order of tens eV. For processing, samples were located at the distance of 20 cm from the plasma source and were irradiated with varying number of pulses. The energy density of pulses was kept constant at 7 J/cm’, as measured by a set of calorimeters placed nearby the sample.
Fig. la shows the dependence of R, of lH18N9T, and 45 steel samples processed by varying number n of nitrogen plasma pulses, i.e., n = 1, 5 and 15 pulses which, according to our previous calibration [lo], introduce the retained doses of nitrogen of
a 0.8
.._--..__ __--.- ..__-_--....... ~_.._._.__._._ -.-......- _..______._
0.7
_.__._.._._ .._.._____-.._._.__._____ . .._______________
0.6 0.5 r 3 LF
0.4 0.3
. - _._____
0.2 0.1 0 0
1
5
number of pulses b
5 5
1
steel
15
number of pulses Fig. 1. (a) Average plasma pulses.
of roughness
R, and (b) nonuniformity
rR,/E,,
of lH18N9T
and 45 steels processed
with various numbers of
52
J. Piekoszewski
et al. /Materials
about 0.3 X lOI7 N/cm’, 1.7 X lOI N/cm’ and 4.4 X 1017 N/cm2 respectively. In Fig. lb the nonuniformities in R, are depicted, being expressed by ((+R,/R,, where aR, is the standard deviation and R, is the mean value of R, in 10 measurements. The following observations can be made from these data. In the case of lH18N9T, the main changes in R, occur after the first pulse. Subsequent pulses practically do not affect R, values, although the increase of aR,/R, with n is evident for both materials. By contrast, the pulses have cumulative effect in the case of 45 steel. Here, both, iR, and aR,/R,, increases significantly with the number of pulses. Our interpretation of these facts is as follows. The lH18N9T steel is composed of the grains of a single fee (y) phase. According to the conclusion drawn in Ref. [lo], in the pulse processed samples nitrogen dissolves in austenitic lattice occupying interstitial positions and forming thereby the local configurations of Fe-N atoms, referred to as yN phase [9]. However, macroscopically it remains still homogeneous single phase system, so the pulse induced melting-solidification process occurs in the same way during each subsequent pulse. Therefore, no cumulation of the pulse induced morphological features is observed. The situation is quite different in the case of two constituent (ferrite, perlite) 45 steel. Here, due to the differences in the physical properties of these constituents, like: melting point, possibly also sensitivity to the ablation, surface tension in the liquid state etc., their response to the pulse melting is different. The homogenization of the planar distribution of alloying components over the regions as large as the grain dimensions cannot be expected for two reasons. First, a diameter of the plasma beam is much larger than the sample size, so there is practically no radial gradient of the temperature to cause the convection flow of the liquid metal, as it is observed in the spot (e.g. laser) melting case [7]. Secondly, since the diffusion coefficients of alloying elements in the liquid metal are of the order of 10-4-10-5 cm*/s, and the liquid state lasts about 7 ks during the single pulse, the diffusion distance does not exceeds 0.5 bm. Therefore, the homogenization by diffusion only cannot be achieved even in the series of 15 pulses. An another aspect explored here was a relation between the initial and final state of the surface morphology of the pulse-processed
Letters 32 (1997) 49-53
Q____
i&P
_O_--
0
I
Fig. 2. Dependence of the normalized roughness R of 45 steel processed with 1, 5 and 15 pulses on the value of its initial roughness R,.
material. Fig. 2 shows the dependence of the normalized roughness R after processing on the initial R, for 45 steel samples irradiated with 1, 5 and 15 pulses. An R value is simply the ratio of the averaged R, after processing to corresponding R, before processing of the same sample. As it could have been predicted, when the initial surface is fairly smooth, the pulse processing deteriorates its smoothness. In contrast, when the initial surface is very rough, the pulse processing smooths this surface. Both, the roughing and smoothing are more pronounced for greater number of pulses. The demarcation point between deterioration and improvement regions lies in our case at about 0.5 pm R, of the initial roughness. The evolutions of the morphology induced by the pulse processing with 0, 1, 5 and 15 pulses are visualized by SEM images in Fig. 3, taken for initially smooth, i.e. 0.16 pm R, and initially rough, i.e. 1.98 Km R, surfaces. As seen in Fig. 3, in the case of smooth sample (top), the grinding scars disappear already after one pulse, being replaced by a large number of neighboring craters. The densities of craters are smaller but on average their size is greater after 5 and 1.5 pulses. In the case of the rough samples (bottom), a gradual disappearance of the grinding scars with the number of pulses occurs. The rounding of the sharp rims and formation of small craters are observed. Our measurements of microhardness performed on six samples of 45
J. Piekoszewski
Fig. 3. SEM images of 45 steel surfaces processed initial roughness 1.98 pm R,.
et al. /Materials
-
1OOpm
-
1OOpm
Letters 32 (1997) 49-53
53
with 0, 1, 5 and 15 nitrogen plasma pulses. Top: initial roughness
steel show that on average, the values of HV,,, , increase by a factor of 1.9, 2.1 and 2.3 after 1, 5 and 15 pulses respectivel:y. Confronting these data with those of Fig. 2, the following conclusion can be drawn as regards the potential application of pulse plasma processing for practical purposes. If for some reason, it would be beneficial to increase the microhardness of a given workpiece and its roughness can be R, > 0.5km, then a single pulse is sufficient to achieve this modification. If in other case, it would be desirable to improve both, the microhardness and roughness of initially rough material (R,> 1 mm), especially as regards the rounding the sharp grinding rims, then several pulses should be applied.
Acknowledgements The authors are grateful to Mr. J. Kominek for his kind collaboration. They also wish to thank to Mrs. B. Sartowska for SEbI pictures, to Mr. J. Krdlik for performing the pulse processing and to Mr. J. Bialosk6rski for his assistance in preparation of manuscript. This work was partially supported by
Foundation for 117/94 grant.
Polish
Science
0.16 pm R,. Bottom:
under
SEZAM/
References [ll J. Gyulai, R. Fastow, K. Kavenagh, M.O. Thompson, C.J. Palmstrom, C.A. Hewett and J.W. Mayer, Mater. Res. Sot. Symp. 13 (1983) 455. [2] R. Fastow and J.M. Mayer, J. Appl. Phys. 61 (1987) 175. [3] A.D. Pogrebnjak, G.E. Remnev, LB. Kurakin and A.E. Ligachev, Nucl. Instr. Methods B 36 (1989) 286. 141 D. Popp, A. Mehling, R. Wilzbach and H. Langhoff, Appl. Phys. A 55 (1992) 561. [5] J. Piekoszewski, J. Langner, J. Bialosk&ski, B. Kozlowska, C. Pochrybniak, Z. Werner, M. Kopcewicz, L. WaliS and A. Ciurapibski, Nucl. Instr. Methods B80/81 (1993) 344. [6] J. Vogel, in: Wear and corrosionresistant coatings by CVD and PVD, ed. H.K. Pulker (Ellis Horwood Publishers, Chichester, 1989) p. 165. [71 T.R. Anthony and H.E. Cline, J. Appl. Phys. 48 (1977) 3888. [8] J. Piekoszewski and J. Langner, Nucl. Instr. Methods B 53 (1991) 148. See also Nukleonika 39 (1994) 3. [9] D.L. Williamson, Li Wang, R. Wei and P.J. Wilbur, Mater. Letters 9 (1990) 302. [lo] J. Piekoszewski, L. WaliS, J. Langner, Z Werner, J. BialoskQski, L. Nowicki, M. Kopcewicz and A. Grabias, Nucl. Instr. Methods, in press.
EISEVIER
Materials Letters 32 (1997) 49-53
Surface morphology of nitrogen-alloyed steels using high intensity pulsed plasma beams J. Piekoszewski
a**, L. Walis’ ‘, J. Langner b
a Institute of Nuclear Chemistry and Technology, ul. Dorodna 16, 03-145 Warszawa, Poland b Soltan Institute for Nuclear Studies, M-400 Otwock / iwierk, Poland
Received 5 December 1996; accepted 12 December 1996
Abstract Samples of single phase (AISI 321) steel and two-constituent (AISI 1045) steel were irradiated with intense nitrogen plasma pulses. The action of each pulse resulted in melting of the near surface layer and introducing the dose of about 10” N atoms/cm’. For initially smooth surfaces, in AISI 321 the main morphological changes occur after the first pulse, whereas in AISI 1045 the roughness increases with the number of pulses. For initially rough AISI 1045 (i.e. R, > 0.5 @rn> the pulse processing results in a decrease of R, and a significant increase (by a factor of about 2) of microhardness HV,, . Practical conclusions are drawn from these results. Keywords: Surface; Nitrogen-alloyed steels; Pulsed plasma beams
1. Introduction High intensity pulse or plasma irradiation has recently received growing interest as a potential tool in surface engineering. Likewise in the laser or electron beam case, ions from pulsed beam rapidly heat the surface of irradiated material. The surface remains at a high teimperature (up to the melting point or higher) for a period in nanosecond to microsecond range, and then rapidly cools through conduction into the hulk at rates of the order of lo’-10” K/s. Obviously, the details of heat evolution in the substrate depend on its thermal properties and dimensions as well as on the beam parameters. Heat induced processes result in several nonequilib-
* Corresponding
author.
00167-577X/97/$17.00 Copyright PII SO167-577X(96)00303-5
rium phenomena such as realization of mixing of metallic overlayers on various (even hardly miscible) substrates, formation of metastable crystalline alloys and so on. Excellent examples of such experiments can be found, e.g., in Refs. [l-4]. In each case, for a given power versus time transient and a pulse duration, to achieve the desired surface modification it is necessary to select the energy density so as to cause melting of the near surface layer of the substrate but not to cause the violent mass ablation from its surface. Using ion or plasma beams, beside purely thermal effects, as in the references cited above, it is also possible, under appropriate conditions, to modify the surface properties of solids via thermal effects in conjunction with mass transport. For example, in our previous reports, e.g. Ref. [51, it was shown that it is possible to introduce high doses (up to 10”
0 1997 Elsevier Science B.V. All rights reserved.
50
.I. Piekoszewski
et d/Materials
atoms/cm2 per pulse) of nitrogen into various kinds of steel and thereby to alter their near surface properties. However, even if the desirable structural characteristics are attained by pulse processing, the range of technological applications of this technique will depend to a considerable extent on the final roughness of the processed surface. For instance, the roughness should be less than 2 pm R, for cutting tools, 1 pm R, for punching tools and less then 0.1 pm for cold forming tools [6]. On the other hand, it is known [7] that the transient processing in which melting of near surface layer occurs always results in some roughening of the surface. Until now, the available information in the literature concerning this issue is rather sparse. In this paper, we report the results of a study of the surface morphology of two kinds of steel samples subjected to nitrogen alloying with the use of high intensity pulsed plasma beams. Emphasis has been placed upon the influence of the initial constituents of the substrate, i.e., as to whether it consists of a single phase or of heterogeneous mixture of more than one phase, and on the initial roughness of the surface.
2. Experimental details
2.1. Samples and characterization Two kinds of materials were used in the experiments: (1) Medium/high carbon steel 45, composed of 0.42-0.59 wt% C, OS-O.8 wt% Mn, 0.17-0.37 wt% Si (equivalent to AISI 1045 steel). (2) Stainless steel lH18N9T, composed of max. 0.12 wt% C, max. 2 wt.% Mn, 0.8 wt% Si, 0.035 wt% P, 0.03 wt% S, 17-19 wt% Cr, 8-10 wt% Ni and min. 5 X C wt% Ti (equivalent to AISI 321 steel). The microstructure constituents of these materials are ferrite and perlite in approximately equal proportions in (11, and single phase austenite in (2). Samples were prepared in the form of 2 mm thick discs of 18 to 30 mm diameter. The surfaces of samples were finished to various roughnesses by grinding on the rotating grinding plate. In the case of 45 steel, eight grades of the surface roughness were intentionally procured with R, ranging from 0.16 to 1.95 pm.
Letters 32 (1997) 49-53
All samples of lH18N9T were finished to the roughness of 0.04-0.05 pm R,. Average values of R, for each sample were derived from the surface profiles taken randomly along the traverse direction perpendicular to the visible grinding grooves, using Homme1 tester T-2000. The morphologies were examined by scanning electron microscopy @EM). In addition, the microhardness VH,,, was measured before and after pulsed plasma processing, using Hanemann-type tester. 2.2. Nitrogen plasma pulse processing High intensity nitrogen plasma pulses were produced in IBIS rod plasma injector (RPI) type generator which was described elsewhere [5,8]. Here, for the sake of completeness we shall outline only the most important characteristics of this device. Plasma pulses are formed in a low-pressure, high-current plasma discharge initiated between two concentric cylindrical sets of rods allowing for a free passage of particles through the electrode region. A fast electromagnetic valve introduces a portion of the working gas into the interelectrode region. After some delay r (150-250 ps) from the moment of valve opening, a voltage from the charged condenser bank is applied to the electrodes. Depending on the value of rn, two modes of operation are possible. In the first one, referred to as pulse implantation doping @‘ID), ho is sufficiently long to allow the injected working gas to fill the whole interelectrode space. Under such conditions, a short intense pulse is generated containing exclusively the ions of the working gas. In the second mode, referred to as deposition by pulsed erosion (DPE), delay rn is relatively short and the working gas expanding from the valve does not reach the electrode ends. Under such conditions, arc-evaporation of the electrode material occurs, and as a result, the plasma becomes enriched with the ions of the electrode material. This allows one to make extremely well adhering coatings of variety of metals on any kind of the solid substrate. In the present paper, the PID mode with nitrogen as a working gas was used to generate nitrogen plasma pulses. The power versus time transients of these pulses consist of two distinct phases. In the first one, there is a sharp peak, lasting about 1 ps, the mean energy of ions being several keV. In the second
J. Piekoszewski
51
et al. / Materials Letters 32 (1997) 49-53
3. Results and discussion
phase, there is a long tail, lasting several microseconds with ion energy of order of tens eV. For processing, samples were located at the distance of 20 cm from the plasma source and were irradiated with varying number of pulses. The energy density of pulses was kept constant at 7 J/cm’, as measured by a set of calorimeters placed nearby the sample.
Fig. la shows the dependence of R, of lH18N9T, and 45 steel samples processed by varying number n of nitrogen plasma pulses, i.e., n = 1, 5 and 15 pulses which, according to our previous calibration [lo], introduce the retained doses of nitrogen of
a 0.8
.._--..__ __--.- ..__-_--....... ~_.._._.__._._ -.-......- _..______._
0.7
_.__._.._._ .._.._____-.._._.__._____ . .._______________
0.6 0.5 r 3 LF
0.4 0.3
. - _._____
0.2 0.1 0 0
1
5
number of pulses b
5 5
1
steel
15
number of pulses Fig. 1. (a) Average plasma pulses.
of roughness
R, and (b) nonuniformity
rR,/E,,
of lH18N9T
and 45 steels processed
with various numbers of
52
J. Piekoszewski
et al. /Materials
about 0.3 X lOI7 N/cm’, 1.7 X lOI N/cm’ and 4.4 X 1017 N/cm2 respectively. In Fig. lb the nonuniformities in R, are depicted, being expressed by ((+R,/R,, where aR, is the standard deviation and R, is the mean value of R, in 10 measurements. The following observations can be made from these data. In the case of lH18N9T, the main changes in R, occur after the first pulse. Subsequent pulses practically do not affect R, values, although the increase of aR,/R, with n is evident for both materials. By contrast, the pulses have cumulative effect in the case of 45 steel. Here, both, iR, and aR,/R,, increases significantly with the number of pulses. Our interpretation of these facts is as follows. The lH18N9T steel is composed of the grains of a single fee (y) phase. According to the conclusion drawn in Ref. [lo], in the pulse processed samples nitrogen dissolves in austenitic lattice occupying interstitial positions and forming thereby the local configurations of Fe-N atoms, referred to as yN phase [9]. However, macroscopically it remains still homogeneous single phase system, so the pulse induced melting-solidification process occurs in the same way during each subsequent pulse. Therefore, no cumulation of the pulse induced morphological features is observed. The situation is quite different in the case of two constituent (ferrite, perlite) 45 steel. Here, due to the differences in the physical properties of these constituents, like: melting point, possibly also sensitivity to the ablation, surface tension in the liquid state etc., their response to the pulse melting is different. The homogenization of the planar distribution of alloying components over the regions as large as the grain dimensions cannot be expected for two reasons. First, a diameter of the plasma beam is much larger than the sample size, so there is practically no radial gradient of the temperature to cause the convection flow of the liquid metal, as it is observed in the spot (e.g. laser) melting case [7]. Secondly, since the diffusion coefficients of alloying elements in the liquid metal are of the order of 10-4-10-5 cm*/s, and the liquid state lasts about 7 ks during the single pulse, the diffusion distance does not exceeds 0.5 bm. Therefore, the homogenization by diffusion only cannot be achieved even in the series of 15 pulses. An another aspect explored here was a relation between the initial and final state of the surface morphology of the pulse-processed
Letters 32 (1997) 49-53
Q____
i&P
_O_--
0
I
Fig. 2. Dependence of the normalized roughness R of 45 steel processed with 1, 5 and 15 pulses on the value of its initial roughness R,.
material. Fig. 2 shows the dependence of the normalized roughness R after processing on the initial R, for 45 steel samples irradiated with 1, 5 and 15 pulses. An R value is simply the ratio of the averaged R, after processing to corresponding R, before processing of the same sample. As it could have been predicted, when the initial surface is fairly smooth, the pulse processing deteriorates its smoothness. In contrast, when the initial surface is very rough, the pulse processing smooths this surface. Both, the roughing and smoothing are more pronounced for greater number of pulses. The demarcation point between deterioration and improvement regions lies in our case at about 0.5 pm R, of the initial roughness. The evolutions of the morphology induced by the pulse processing with 0, 1, 5 and 15 pulses are visualized by SEM images in Fig. 3, taken for initially smooth, i.e. 0.16 pm R, and initially rough, i.e. 1.98 Km R, surfaces. As seen in Fig. 3, in the case of smooth sample (top), the grinding scars disappear already after one pulse, being replaced by a large number of neighboring craters. The densities of craters are smaller but on average their size is greater after 5 and 1.5 pulses. In the case of the rough samples (bottom), a gradual disappearance of the grinding scars with the number of pulses occurs. The rounding of the sharp rims and formation of small craters are observed. Our measurements of microhardness performed on six samples of 45
J. Piekoszewski
Fig. 3. SEM images of 45 steel surfaces processed initial roughness 1.98 pm R,.
et al. /Materials
-
1OOpm
-
1OOpm
Letters 32 (1997) 49-53
53
with 0, 1, 5 and 15 nitrogen plasma pulses. Top: initial roughness
steel show that on average, the values of HV,,, , increase by a factor of 1.9, 2.1 and 2.3 after 1, 5 and 15 pulses respectivel:y. Confronting these data with those of Fig. 2, the following conclusion can be drawn as regards the potential application of pulse plasma processing for practical purposes. If for some reason, it would be beneficial to increase the microhardness of a given workpiece and its roughness can be R, > 0.5km, then a single pulse is sufficient to achieve this modification. If in other case, it would be desirable to improve both, the microhardness and roughness of initially rough material (R,> 1 mm), especially as regards the rounding the sharp grinding rims, then several pulses should be applied.
Acknowledgements The authors are grateful to Mr. J. Kominek for his kind collaboration. They also wish to thank to Mrs. B. Sartowska for SEbI pictures, to Mr. J. Krdlik for performing the pulse processing and to Mr. J. Bialosk6rski for his assistance in preparation of manuscript. This work was partially supported by
Foundation for 117/94 grant.
Polish
Science
0.16 pm R,. Bottom:
under
SEZAM/
References [ll J. Gyulai, R. Fastow, K. Kavenagh, M.O. Thompson, C.J. Palmstrom, C.A. Hewett and J.W. Mayer, Mater. Res. Sot. Symp. 13 (1983) 455. [2] R. Fastow and J.M. Mayer, J. Appl. Phys. 61 (1987) 175. [3] A.D. Pogrebnjak, G.E. Remnev, LB. Kurakin and A.E. Ligachev, Nucl. Instr. Methods B 36 (1989) 286. 141 D. Popp, A. Mehling, R. Wilzbach and H. Langhoff, Appl. Phys. A 55 (1992) 561. [5] J. Piekoszewski, J. Langner, J. Bialosk&ski, B. Kozlowska, C. Pochrybniak, Z. Werner, M. Kopcewicz, L. WaliS and A. Ciurapibski, Nucl. Instr. Methods B80/81 (1993) 344. [6] J. Vogel, in: Wear and corrosionresistant coatings by CVD and PVD, ed. H.K. Pulker (Ellis Horwood Publishers, Chichester, 1989) p. 165. [71 T.R. Anthony and H.E. Cline, J. Appl. Phys. 48 (1977) 3888. [8] J. Piekoszewski and J. Langner, Nucl. Instr. Methods B 53 (1991) 148. See also Nukleonika 39 (1994) 3. [9] D.L. Williamson, Li Wang, R. Wei and P.J. Wilbur, Mater. Letters 9 (1990) 302. [lo] J. Piekoszewski, L. WaliS, J. Langner, Z Werner, J. BialoskQski, L. Nowicki, M. Kopcewicz and A. Grabias, Nucl. Instr. Methods, in press.