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Amorphous and amorphous-crystalline coatings of stainless steel with addition of refractory metals obtained by magnetron sputtering in vacuum
Vacuum/volume 36/number Printed in Great Britain
0042-207X/86 $3.00+ .OO Pergamon Journals Ltd
1 O/pages 699 to 603/l 986
Amorphous and amorphous-crystalline coatings of stainless steel with addition of refractory metals obtained by magnetron sputtering in vacuum St Grudeva
and M Kanev,
Technical University ‘Angel Kanchev’, Russe 7004, Bulgaria
Amorphous and amorphous-crystalline stainless steel films were obtained with additions of Ti or W. The deposition rate was v = 6-360 nm min - ‘, the thickness h = 50 to 5000 nm and the substrate temperature T, varied from 77 to 293 K. A magnetron compound target was used for sputtering and coatings were deposited on Al, steel, glass-ceramic and Corning glass substrates. Structural data for the coexistence of amorphous and amorphous-crystalline phases in stainless steel films are presented. A study was made of the structure sensitive properties: specific electrical resistivity and magnetic characteristics. Some data were obtained for films Fe + Ti and Fe + W, prepared by the same method. Properties affecting the practical application of such amorphous and amorphous-crystalline metal coatings were also studied.
Introduction This study presents preliminary data on the conditions under which amorphous and amorphous
discs with a thickness of 3 mm. Additional elements were built in mechanically in the form of rods. The number of the rods was determined according to the desired composition of the film. The form of target for films Fe +Ti and Fe + W will be described elsewhere. The quantity of Ti and W obtained in the films was determined by chemical analysis and X-ray microanalysis. Table 1 shows the results for the different kinds of films. Results and discussion Structure. The structure of the films was determined by different methods according to the thickness of the individual specimens. Transmission electron diffraction was used for thin films with a thickness under 50 nm. Electron micrographs obtained by SEM with magnification x 100,000 were prepared for all similar specimens. Figure 2 shows typical results with micrographs (a) and electron diffraction patterns (b) from thin films of stainless steel without additions. The films were 30 nm thick and deposited on NaCl substrates cooled with liquid nitrogen. Results for films deposited on an uncooled substrate are shown in the same figure: (c) micrograph, (d) electron diffraction pattern, both from the same area. Although in the first case phase contrast was not apparent in the micrograph, in the second case grains with a diameter of 500 A were seen. The respective diffraction patterns also confirm the presence of polycrystalline areas in the film. All films with a thickness above 500 a were studied by reflection electron diffraction and those with thickness above 1000 nm by Xray diffraction. Figure 3 shows typical electron diffraction 599
St Grudeva and M Kanev: Amorphous and amorphous-crystalline
coatings of stainless steel with addition of refractory metals
---5 4
u,
<-I. 5kV
,U, =0-60V
o=k”
t
/? cos 0
r
-r
(b)
-
H,O
1
Figure 1. General systems of the experimental equipment for magnetron deposition of amorphous metal films: (a) vacuum and cooling systems (1) N,-trap, (2) vacuum drossel, (3) N,-coolable box, (4) Ti-getter, (5) Ti. (b) Electrical system (1) magnetron, (2) anode ring, (3) quartz monitor, (4) substrate, (5) shutter-shield.
Table 1. Quantity of the additional elements in the films Kind of coating X18H9T+Ti I X18H9T+Ti II X18H9T+ W Fe+Ti Fe+W 600
Content of the elements determined by: Chemical analysis X-ray microanalysis W-18.8
Ti-6 Ti-9
wt% wt%
wt% Ti-23
w-11
patterns for films of stainless steel without additions. A clear difference in the number and width of the diffraction rings is observed in films deposited at 77 K and 293 K, (a) and (b) respectively. Figures 4 and 5 show typical results for thin films of stainless steel with addition of 6 wt% Ti (Figure 4) and 22 wt% W (Figure 5). Highly broadened diffraction rings in the patterns confirm the presence of an amorphous structure in the films obtained. Figure 6(a) shows a typical X-ray diffraction pattern of films which were determined as amorphous by the electron diffraction method. These X-ray diffraction patterns are comparable with the results reported for similar films of stainless steel deposited by triode sputtering’. Diffraction data were collected on a Philips diffractometer with monochromator for Cu Kg-radiation and on a diffractometer (‘Dron 3’). In the X-ray patterns of all the films studied one or two broad lines appear around 28=44” and 28=82.5”. The half width of the diffraction peaks changes considerably depending on the conditions urder which they were obtained in the range 0.8-5”. The films which were determined as amorphous by electron diffraction on their X-ray patterns had only one broad peak with a half width of /?r 3.2”. X-ray data show that the structure of the deposited films, whose composition is stainless steel with addition of Ti below (I) 6%, is very sensitive to the degree of overcooling of the vapours when condensed on a respective specimen. This shows that 6% is a limiting value for stabilizing the amorphous state in the films obtained under above conditions. The appearance of the X-ray diffraction patterns suggest that the film consists of an amorphous matrix in which small crystals are dispersed. For the films of iron with addition of Ti (23%) the X-ray diffraction patterns contain broader and smoother lines which characterize the films as fully amorphous (Figure 6b). By measuring the half peak width of all X-ray patterns the mean crystallite size D was determined using Sherer’s equations:
wt%
wt%
where k is characteristic constant, 2 is the wavelength of the X-ray radiation and 0 is the glancing angle. b is the half width of the peaks. The results are listed in Table 2. It should be noted for comparison that the dimensions of the grains in the amorphous film according to Figure 2 were estimated at D < 50 8, whilst that for the polycrystalline film was 500 w.
Electrical and magnetic properties. It is known that the specific electrical resistivity p of bulk amorphous metals is considerably larger than that of bulk crystal metals of the same composition6 and on crystallization it reduced drastically. Also, slow structural changes of non-equilibrium phases lead to a change in p. Thus stable amorphous films should have a considerably larger p than crystalline films. Moreover, p should not change with time. This was confirmed for films obtained at very low temperature (q = 77 K) and at a sufficiently high deposition rate and suitable composition. Table 3 shows values of p for typical amorphous films obtained by the method described and (in parentheses) the values of p for respective crystalline materials7. The changes of p with time are shown in percentages in the last column. For films with a stable amorphous and microcrystalline structures the changes were not greater than 0.20% in 24 h. For films with an unstable structure the mean change reaches 50% in 24 h. The
St Grudeva and M Kanev: Amorphous and amorphous-crystalline
coatings of stainless steel with addition of refractory metals
(b)
(4
(cl
(d)
Fimre 2. Tvoical results from transmission electron microscoov and electron cooled film: xTS= 77 K; (c) and (d) from uncooled film, T, = 29jSK.
(b) Figure 3. Reflective electron diffraction patterns from stainless steel X 18H9T: (a) T, = 77 K; (b) T, = 293 K.
diffraction
of thin films (366 A) of pure stainless
steel: (a) and (b) from
@I films of pure
Figure 4. Reflective electron diffraction patterns steel X18H9T+6% Ti: (a) T,=77 K; (b) T,=293
from films of stainless K. 601
St Grudeva and M Kanev: Amorphous and amorphous-crystalline
coatings of stainless steel with addition of refractory metals
Table 2. Values of the mean crystalline Kind of film X18H9T X18H9T+6% X18H9T+22% Fe + 23% Ti Fe+71% W
Ti W
size in the films
Dmin (A)
D,,x (A)
D,r c,e rn.,Strirmsj(A)
90 39 32 27 29
240 130 190 120 -
190 70 64 54
Table 3. Specific electrical resistivity of the obtained amorphous films and changes in percentages in 24 h (in parentheses-p for crystal materials) Kind of film
p(@.cm)
WP,
X18H9T X18H9T+Ti FefTi
698 (7.5) 742 (7.5 and 55) 440 (9.7 and 55)
+0.20 +0.15 +0.14
%
-
measurements on 20 films showed that they had a coercive force il the range 7-70 Oe with a rectangularity for B,/B, in the range 0.1 to 0.65. Some of the films had magnetic anisotropy.
(b) Figure 5. : steel X18H9T+22%
W:(a)
T,=77
K; (b) T,=293
K.
50 40
-2 30
2
Corrosion stability. The corrosion resistance of the films was determined by testing them in a humid saline atmosphere at a temperature of 100°C. The substrates used were Al, steel and glass. The test period was 30 days. Amorphous, crystalline and crystallized coating of all compositions which had been annealed as described above were tested. All the amorphous films were resistant on all kinds of substrate. Figure 7 shows micrographs of
‘r 20 IO
00
75
65
70
60
55
50
45
40
35
I 30
2e0
1’ L..
A 50
@I
45
40
(a)
\
0
35
28”
Figure 6. X-ray diffraction patterns of electronographic films: (a) X18H9T+6 wt% Ti; (b) Fe+23 wt% Ti.
ally amorphous
value of p for well crystallized films of all compositions is almost equal to that of bulk crystal materials. The interrelation between Ap/p and certain mechanical properties of the coatings was established. Coatings with high Ap/p always had bad adhesion, while those with a low Ap/p had good adhesion and high microhardness. The magnetic properties of the crystal films were comparable to those of films, obtained in other work’. The results of preliminary
602
(b) Figure 7. Micrographs steel and(b) crystalline x 900.
of: (a) amorphous corroded coating
uncorroded coating Xl 8H9T on X18H9T on steel. Magnification
Sr Grudeva and M Kanev: Amorphous and amorphous-crystalline
coatings of stainless steel with addition of refractory metals
the surfaces of stable amorphous and corroded crystal coatings, (a) and (b) respectively. Adhesion and mechanical
properties. Adhesion was tested by scratching a rod contacting the film rod with a measurable force. The maximum adhesion measured for the films studied was for an amorphous sample X18H9T on steel and had a value of 23 MPa. The microhardness of the prepared films was considerably higher than that of the respective crystal materials. Stainless steel films with crystalline-amorphous and amorphous structures had H, = 85&1050 kg mm-*; films of X18H9T containing 6% Ti, up to 1100 kg mm-* and films of X18H9T with 23% W, up to 1200 kg mm-*. The foregoing results were obtained by a Vickers method adapted for measurement of microhardness of films with a thickness above 2000 A’.
amorphous films at T, = 77 K and in individual cases the 7” may be as high as 293 K. When the Ti or W concentrations are large enough a substrate temperature of 293 K is sufficient to obtain amorphous films also from two-component alloys Fe+Ti and Fe+W. The electric, magnetic and mechanical properties of the prepared films were very sensitive to their structure and structure stability. The coatings we obtained possessed properties which should be further studied with a view to their practical use.
References ’ Ronp. Wang, J Mat Sci Technol, 17, 1142 (1982). * P I Grundy and I H March, J Mat Sci Technol, 13, letters (1978). 3 I L Brimhall. I A Charlot and H E Kissineer. - , J Mat Sci Technol. 17.1149 (1982).
Conclusions
The work reported here shows that it is possible to prepare amorphous stainless steel + Ti (W) and Fe + Ti (W) coatings by magnetron sputtering. Film composition and substrate temperature are determining factors when preparing such films. Films of X18H9T with less than 6% Ti are unstable and to make them amorphous, extreme reduction of temperature during growth is necessary. Increasing the concentration of Ti or W makes it possible to deposit stable
4 M Kanev, St Grudeva, Tz Usunov and J Jordanov, Proc 1st Natn Conf ‘Equipment for Obtaining and Measuring of Vacuum and Technical Applications’, Jambol 1985, Bulgaria, deposited in Central Institute for Scientific and Technical Information (CINTI), Sofia, Bulgaria (1985). ’ H P Klug and L Alexander, X-ray Diffraction Procedures, New York (1954). 6 P Munoz and H Miranda, Thin Solid Films, 88, 211 (1982). ’ I K Kikoin (Ed). Tablitzi Phvsicheskich V&chin. Atomisdat. Moscow (1976). ~ ” . ’ K Roll, R Kukla, M Mayer and W D Miinz, IEEE Trans Magnetics, 20, 63 (1984). ’ B Jonson and S Hogmark, Thin Solid Films, 114, 257 (1984).
603
0042-207X/86 $3.00+ .OO Pergamon Journals Ltd
1 O/pages 699 to 603/l 986
Amorphous and amorphous-crystalline coatings of stainless steel with addition of refractory metals obtained by magnetron sputtering in vacuum St Grudeva
and M Kanev,
Technical University ‘Angel Kanchev’, Russe 7004, Bulgaria
Amorphous and amorphous-crystalline stainless steel films were obtained with additions of Ti or W. The deposition rate was v = 6-360 nm min - ‘, the thickness h = 50 to 5000 nm and the substrate temperature T, varied from 77 to 293 K. A magnetron compound target was used for sputtering and coatings were deposited on Al, steel, glass-ceramic and Corning glass substrates. Structural data for the coexistence of amorphous and amorphous-crystalline phases in stainless steel films are presented. A study was made of the structure sensitive properties: specific electrical resistivity and magnetic characteristics. Some data were obtained for films Fe + Ti and Fe + W, prepared by the same method. Properties affecting the practical application of such amorphous and amorphous-crystalline metal coatings were also studied.
Introduction This study presents preliminary data on the conditions under which amorphous and amorphous
discs with a thickness of 3 mm. Additional elements were built in mechanically in the form of rods. The number of the rods was determined according to the desired composition of the film. The form of target for films Fe +Ti and Fe + W will be described elsewhere. The quantity of Ti and W obtained in the films was determined by chemical analysis and X-ray microanalysis. Table 1 shows the results for the different kinds of films. Results and discussion Structure. The structure of the films was determined by different methods according to the thickness of the individual specimens. Transmission electron diffraction was used for thin films with a thickness under 50 nm. Electron micrographs obtained by SEM with magnification x 100,000 were prepared for all similar specimens. Figure 2 shows typical results with micrographs (a) and electron diffraction patterns (b) from thin films of stainless steel without additions. The films were 30 nm thick and deposited on NaCl substrates cooled with liquid nitrogen. Results for films deposited on an uncooled substrate are shown in the same figure: (c) micrograph, (d) electron diffraction pattern, both from the same area. Although in the first case phase contrast was not apparent in the micrograph, in the second case grains with a diameter of 500 A were seen. The respective diffraction patterns also confirm the presence of polycrystalline areas in the film. All films with a thickness above 500 a were studied by reflection electron diffraction and those with thickness above 1000 nm by Xray diffraction. Figure 3 shows typical electron diffraction 599
St Grudeva and M Kanev: Amorphous and amorphous-crystalline
coatings of stainless steel with addition of refractory metals
---5 4
u,
<-I. 5kV
,U, =0-60V
o=k”
t
/? cos 0
r
-r
(b)
-
H,O
1
Figure 1. General systems of the experimental equipment for magnetron deposition of amorphous metal films: (a) vacuum and cooling systems (1) N,-trap, (2) vacuum drossel, (3) N,-coolable box, (4) Ti-getter, (5) Ti. (b) Electrical system (1) magnetron, (2) anode ring, (3) quartz monitor, (4) substrate, (5) shutter-shield.
Table 1. Quantity of the additional elements in the films Kind of coating X18H9T+Ti I X18H9T+Ti II X18H9T+ W Fe+Ti Fe+W 600
Content of the elements determined by: Chemical analysis X-ray microanalysis W-18.8
Ti-6 Ti-9
wt% wt%
wt% Ti-23
w-11
patterns for films of stainless steel without additions. A clear difference in the number and width of the diffraction rings is observed in films deposited at 77 K and 293 K, (a) and (b) respectively. Figures 4 and 5 show typical results for thin films of stainless steel with addition of 6 wt% Ti (Figure 4) and 22 wt% W (Figure 5). Highly broadened diffraction rings in the patterns confirm the presence of an amorphous structure in the films obtained. Figure 6(a) shows a typical X-ray diffraction pattern of films which were determined as amorphous by the electron diffraction method. These X-ray diffraction patterns are comparable with the results reported for similar films of stainless steel deposited by triode sputtering’. Diffraction data were collected on a Philips diffractometer with monochromator for Cu Kg-radiation and on a diffractometer (‘Dron 3’). In the X-ray patterns of all the films studied one or two broad lines appear around 28=44” and 28=82.5”. The half width of the diffraction peaks changes considerably depending on the conditions urder which they were obtained in the range 0.8-5”. The films which were determined as amorphous by electron diffraction on their X-ray patterns had only one broad peak with a half width of /?r 3.2”. X-ray data show that the structure of the deposited films, whose composition is stainless steel with addition of Ti below (I) 6%, is very sensitive to the degree of overcooling of the vapours when condensed on a respective specimen. This shows that 6% is a limiting value for stabilizing the amorphous state in the films obtained under above conditions. The appearance of the X-ray diffraction patterns suggest that the film consists of an amorphous matrix in which small crystals are dispersed. For the films of iron with addition of Ti (23%) the X-ray diffraction patterns contain broader and smoother lines which characterize the films as fully amorphous (Figure 6b). By measuring the half peak width of all X-ray patterns the mean crystallite size D was determined using Sherer’s equations:
wt%
wt%
where k is characteristic constant, 2 is the wavelength of the X-ray radiation and 0 is the glancing angle. b is the half width of the peaks. The results are listed in Table 2. It should be noted for comparison that the dimensions of the grains in the amorphous film according to Figure 2 were estimated at D < 50 8, whilst that for the polycrystalline film was 500 w.
Electrical and magnetic properties. It is known that the specific electrical resistivity p of bulk amorphous metals is considerably larger than that of bulk crystal metals of the same composition6 and on crystallization it reduced drastically. Also, slow structural changes of non-equilibrium phases lead to a change in p. Thus stable amorphous films should have a considerably larger p than crystalline films. Moreover, p should not change with time. This was confirmed for films obtained at very low temperature (q = 77 K) and at a sufficiently high deposition rate and suitable composition. Table 3 shows values of p for typical amorphous films obtained by the method described and (in parentheses) the values of p for respective crystalline materials7. The changes of p with time are shown in percentages in the last column. For films with a stable amorphous and microcrystalline structures the changes were not greater than 0.20% in 24 h. For films with an unstable structure the mean change reaches 50% in 24 h. The
St Grudeva and M Kanev: Amorphous and amorphous-crystalline
coatings of stainless steel with addition of refractory metals
(b)
(4
(cl
(d)
Fimre 2. Tvoical results from transmission electron microscoov and electron cooled film: xTS= 77 K; (c) and (d) from uncooled film, T, = 29jSK.
(b) Figure 3. Reflective electron diffraction patterns from stainless steel X 18H9T: (a) T, = 77 K; (b) T, = 293 K.
diffraction
of thin films (366 A) of pure stainless
steel: (a) and (b) from
@I films of pure
Figure 4. Reflective electron diffraction patterns steel X18H9T+6% Ti: (a) T,=77 K; (b) T,=293
from films of stainless K. 601
St Grudeva and M Kanev: Amorphous and amorphous-crystalline
coatings of stainless steel with addition of refractory metals
Table 2. Values of the mean crystalline Kind of film X18H9T X18H9T+6% X18H9T+22% Fe + 23% Ti Fe+71% W
Ti W
size in the films
Dmin (A)
D,,x (A)
D,r c,e rn.,Strirmsj(A)
90 39 32 27 29
240 130 190 120 -
190 70 64 54
Table 3. Specific electrical resistivity of the obtained amorphous films and changes in percentages in 24 h (in parentheses-p for crystal materials) Kind of film
p(@.cm)
WP,
X18H9T X18H9T+Ti FefTi
698 (7.5) 742 (7.5 and 55) 440 (9.7 and 55)
+0.20 +0.15 +0.14
%
-
measurements on 20 films showed that they had a coercive force il the range 7-70 Oe with a rectangularity for B,/B, in the range 0.1 to 0.65. Some of the films had magnetic anisotropy.
(b) Figure 5. : steel X18H9T+22%
W:(a)
T,=77
K; (b) T,=293
K.
50 40
-2 30
2
Corrosion stability. The corrosion resistance of the films was determined by testing them in a humid saline atmosphere at a temperature of 100°C. The substrates used were Al, steel and glass. The test period was 30 days. Amorphous, crystalline and crystallized coating of all compositions which had been annealed as described above were tested. All the amorphous films were resistant on all kinds of substrate. Figure 7 shows micrographs of
‘r 20 IO
00
75
65
70
60
55
50
45
40
35
I 30
2e0
1’ L..
A 50
@I
45
40
(a)
\
0
35
28”
Figure 6. X-ray diffraction patterns of electronographic films: (a) X18H9T+6 wt% Ti; (b) Fe+23 wt% Ti.
ally amorphous
value of p for well crystallized films of all compositions is almost equal to that of bulk crystal materials. The interrelation between Ap/p and certain mechanical properties of the coatings was established. Coatings with high Ap/p always had bad adhesion, while those with a low Ap/p had good adhesion and high microhardness. The magnetic properties of the crystal films were comparable to those of films, obtained in other work’. The results of preliminary
602
(b) Figure 7. Micrographs steel and(b) crystalline x 900.
of: (a) amorphous corroded coating
uncorroded coating Xl 8H9T on X18H9T on steel. Magnification
Sr Grudeva and M Kanev: Amorphous and amorphous-crystalline
coatings of stainless steel with addition of refractory metals
the surfaces of stable amorphous and corroded crystal coatings, (a) and (b) respectively. Adhesion and mechanical
properties. Adhesion was tested by scratching a rod contacting the film rod with a measurable force. The maximum adhesion measured for the films studied was for an amorphous sample X18H9T on steel and had a value of 23 MPa. The microhardness of the prepared films was considerably higher than that of the respective crystal materials. Stainless steel films with crystalline-amorphous and amorphous structures had H, = 85&1050 kg mm-*; films of X18H9T containing 6% Ti, up to 1100 kg mm-* and films of X18H9T with 23% W, up to 1200 kg mm-*. The foregoing results were obtained by a Vickers method adapted for measurement of microhardness of films with a thickness above 2000 A’.
amorphous films at T, = 77 K and in individual cases the 7” may be as high as 293 K. When the Ti or W concentrations are large enough a substrate temperature of 293 K is sufficient to obtain amorphous films also from two-component alloys Fe+Ti and Fe+W. The electric, magnetic and mechanical properties of the prepared films were very sensitive to their structure and structure stability. The coatings we obtained possessed properties which should be further studied with a view to their practical use.
References ’ Ronp. Wang, J Mat Sci Technol, 17, 1142 (1982). * P I Grundy and I H March, J Mat Sci Technol, 13, letters (1978). 3 I L Brimhall. I A Charlot and H E Kissineer. - , J Mat Sci Technol. 17.1149 (1982).
Conclusions
The work reported here shows that it is possible to prepare amorphous stainless steel + Ti (W) and Fe + Ti (W) coatings by magnetron sputtering. Film composition and substrate temperature are determining factors when preparing such films. Films of X18H9T with less than 6% Ti are unstable and to make them amorphous, extreme reduction of temperature during growth is necessary. Increasing the concentration of Ti or W makes it possible to deposit stable
4 M Kanev, St Grudeva, Tz Usunov and J Jordanov, Proc 1st Natn Conf ‘Equipment for Obtaining and Measuring of Vacuum and Technical Applications’, Jambol 1985, Bulgaria, deposited in Central Institute for Scientific and Technical Information (CINTI), Sofia, Bulgaria (1985). ’ H P Klug and L Alexander, X-ray Diffraction Procedures, New York (1954). 6 P Munoz and H Miranda, Thin Solid Films, 88, 211 (1982). ’ I K Kikoin (Ed). Tablitzi Phvsicheskich V&chin. Atomisdat. Moscow (1976). ~ ” . ’ K Roll, R Kukla, M Mayer and W D Miinz, IEEE Trans Magnetics, 20, 63 (1984). ’ B Jonson and S Hogmark, Thin Solid Films, 114, 257 (1984).
603