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Boriding in a fluidized bed reactor
October 2001
Materials Letters 51 Ž2001. 156–160 www.elsevier.comrlocatermatlet
Boriding in a fluidized bed reactor K.G. Anthymidis a , E. Stergioudis b, D.N. Tsipas a,) a
Laboratory of Physical Metallurgy, Mechanical Engineering Department, Aristotle UniÕersity of Thessaloniki, 54006-Thessaloniki, Greece b Applied Physics Laboratory, Physics Department, Aristotle UniÕersity of Thessaloniki, 54006-Thessaloniki, Greece Received 28 December 2000; accepted 6 January 2001
Abstract Heat treatments of alloys in fluidized bed reactors have been carried out for more than 25 years. Recently, this technology has been used for surface engineering applications in the deposition of hard andror corrosion-resistant layers. In the present paper, we used fluidized bed technology ŽFBT. to deposit boride coatings. The coatings were examined by means of optical microscopy, Vickers microhardness and X-ray diffraction ŽXRD. in terms of coatings thickness and morphology, phase formation and properties. The as-produced coatings are characterized by very good adherence due to its tooth-shape ˚ c s 4.249 A˚ . was morphology and it was found that only one phase belonging to Fe 2 B Žspace group I 4rmcm, a s 5.110 A, formed during the treatment. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Boriding; Fluidized bed coatings
1. Introduction Fluidized bed technology has been successfully used for the formation of different types of coatings, e.g. aluminizing w1–4x, chromizing w1–3x, nitriding w5–7x, carburizing w7x, carbonitriding w7x. On the other hand, very limited information exists on boride coatings obtained using fluidized bed technology, although the method is simple, efficient, environmentally friendly and the boride coatings have been reported to have an excellent combination of properties w8,9,13x. The theory of fluidization is described in great detail elsewhere w10–12x. Briefly, fluidization is a process in which a bed of particles, e.g. Al 2 O 3 , behave like a liquid when a carrier gas is fed
) Corresponding author. Tel.: q30-31-996013; fax: q30-31996069. E-mail address: [email protected] ŽD.N. Tsipas..
through the bed. There are several types of fluidized beds and their main advantages are the high rates for mass and heat transfer. This leads to uniformity of temperature throughout the volume of the reactor and flash mix of all the compounds in it, which results to improved quality of coatings. Some other advantages of this process are the capability of immediate adjustment of the furnace atmosphere for specific requirements, the relatively low capital and operation costs and the fact that it is friendly to the environment. Some of the parameters that affect the quality of fluidization in a fluidized bed reactor are the properties of solids and fluids used, the bed geometry, the gas flow rate, the type of gas distributor and the reactor design. This paper is concerned with the study of boride coatings onto steel, by the fluidized bed process. The boride coatings, which have been prepared using fluidized bed technology, were characterized by optical microscopy and X-ray diffraction measurements.
00167-577Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 1 . 0 0 2 8 3 - X
K.G. Anthymidis et al.r Materials Letters 51 (2001) 156–160
157
2. Experimental procedure
2.2. Coating properties and characterization
2.1. Coating process
The thickness of coatings and their morphology were examined using optical microscopy. Hardness was measured by a Vickers microhardness tester. The phases formed in the coating were identified by X-ray diffraction ŽXRD. measurements, which were performed using monochromatic FeK a radiation. A rough qualitative characterization of the produced coating was also attempted.
Samples were prepared using a typical fluidized bed reactor system, which is shown schematically in Fig. 1. The system consisted of five main parts: Ø Ø Ø Ø Ø
The The The The The
fluidized bed reactor unit, gas preheating and providing system, furnace for heating the reactor, control panels and measuring instruments, trapping of hazardous substances unit.
This experimental set up is simple and flexible and allows to deposit a wide range of single and multi-element coatings. A detailed description of the experimental set up has been given in a previous publication w4x. In the present experiment, boriding was carried out in such a system, on simple 0.5% wt. C steel at temperatures from 8008C to about 10008C. Argon was used as a fluidizing gas, while fluidizing media were composed of B 4 C and halogen-containing compounds.
3. Results and discussion In Fig. 2, a typical morphology of boride coating obtained on 0.5% wt. C steel after 1.5 h of treatment is shown. This coating had average thickness of 80 mm, Vickers microhardness values of 1800–2000 Hv ŽFig. 3. and it is characterized by very good adherence due to its tooth-shape morphology. From X-ray patterns ŽFig. 4., it was concluded that the as-prepared coatings consist of a uniform compound, which was found to belong to Fe 2 B phase. Small traces indicative of an Fe phase are present in the
Fig. 1. The fluidized bed reactor system.
158
K.G. Anthymidis et al.r Materials Letters 51 (2001) 156–160
Fig. 2. Typical tooth-shape morphology of boride coating obtained in a fluidized bed reactor.
thinner than the average coatings. It was also observed that in the case of coating with less than 1 h
of treatment, crystallization proceeds by formation of Fe 2 B crystallites with a preferred orientation. It is
Fig. 3. Measurement of the microhardness of the boride coating.
K.G. Anthymidis et al.r Materials Letters 51 (2001) 156–160
159
Fig. 4. X-ray diffraction ŽXRD. results of the boride coating.
most probably that longer treatment induced secondary recrystallization resulting in improvement of the properties of the coatings. The optimum morphology obtained Žtooth-shape., the type of layer Fe 2 B, coupled with the relatively short boriding time Ž1.5 h. for this type of surface treatment, and the thickness of the coating Ž80 mm. make this process extremely attractive. The compounds used for boriding were only B 4 C, halogen-containing compounds and argon gas. The small amounts of undesirable gases produced during the process were trapped and neutralized, making this boriding process environmentally friendly.
4. Conclusions A simple, environmentally friendly, fast boriding process was carried out in a fluidized bed reactor. Samples of a typical morphology of iron-boride coatings with tooth-shaped adherent and of excellent
quality were produced. Only one phase of ironborides, which was found to belong to Fe 2 B was revealed. Grain size of crystallites and crystallization characteristics depend on the time of treatment.
Acknowledgements We are indebted to J. Tholoulis for his significant help in the experimental procedure.
References w1x F.J. Perez, M.P. Hierro, F. Pedraza, C. Gomez, M.C. Carpi´ ´ enero, Aluminizing and chromizing bed treatment by CVD in a fluidized bed reactor on austenitic stainless steels. Surf. Coat. Technol. 120 Ž1999. 151. w2x S. Kingel, G.N. Angelopoulos, D. Papamantellos, W. Dahl, Feasibility of fluidized bed CVD for the formation of protective coatings. Steel Res. 66 Ž1995. 318. w3x D.N. Tsipas, Y. Flitris, Surface treatment in fluidized bed reactors. J. Mater. Sci. 35 Ž21. Ž2000. 5493.
160
K.G. Anthymidis et al.r Materials Letters 51 (2001) 156–160
w4x N. Voudouris, G.N. Angelopoulos, Formation of aluminide coatings on nickel by a fluidized bed CVD process. 11th International Conference on Surface Modification Technologies SMT11, Paris, 8–10 September, 1997. w5x J.E. Japka, Using the fluidized bed for nitriding-type processes. Met. Prog. Ž1983. 27–33, February. w6x Z. Rogalski, H. Zowczak, Fluidised bed methods of nitriding and oxy-nitriding. 18th International Conference on Heat treatment of Metals. 1980, pp. 181–196. w7x R.W. Reynoldson, Heat Treatment in Fluidized Bed Furnaces. ASM International, 1993. w8x S. Anil Kumar Sinha, Boriding ŽBoronizing., ASM Handbook, vol. 4, pp. 437–447. w9x T. Arai, J. Endo, H. Takeda, Chromizing and boriding by use
w10x w11x w12x w13x
of a fluidized bed. 5th International Conference on Heat Treatment of Materials, 3, Budapest, Hungary. 1986, pp. 1335–1341. J.R. Howard, Fluidized Bed Technology Principles and Applications. Adam Higler, Bristol, 1989. F.A. Zenz, D.F. Othmer, Fluidization and Fluid-Particle Systems. Reinhold Publishing, New York, 1960. C.K. Gupta, D. Sathiyamoothy, Fluid Bed Technology in Materials Processing. CRC Press, Boca Raton, 1999. D.N. Tsipas, G.K. Triantafyllidis, J. Kipkemoi, Y. Flitris, Thermochemical treatments for protection of steel in chemically aggressive atmosphere at high temperature. Mater. Manuf. Processes 14 Ž5. Ž1999. 697–712.
Materials Letters 51 Ž2001. 156–160 www.elsevier.comrlocatermatlet
Boriding in a fluidized bed reactor K.G. Anthymidis a , E. Stergioudis b, D.N. Tsipas a,) a
Laboratory of Physical Metallurgy, Mechanical Engineering Department, Aristotle UniÕersity of Thessaloniki, 54006-Thessaloniki, Greece b Applied Physics Laboratory, Physics Department, Aristotle UniÕersity of Thessaloniki, 54006-Thessaloniki, Greece Received 28 December 2000; accepted 6 January 2001
Abstract Heat treatments of alloys in fluidized bed reactors have been carried out for more than 25 years. Recently, this technology has been used for surface engineering applications in the deposition of hard andror corrosion-resistant layers. In the present paper, we used fluidized bed technology ŽFBT. to deposit boride coatings. The coatings were examined by means of optical microscopy, Vickers microhardness and X-ray diffraction ŽXRD. in terms of coatings thickness and morphology, phase formation and properties. The as-produced coatings are characterized by very good adherence due to its tooth-shape ˚ c s 4.249 A˚ . was morphology and it was found that only one phase belonging to Fe 2 B Žspace group I 4rmcm, a s 5.110 A, formed during the treatment. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Boriding; Fluidized bed coatings
1. Introduction Fluidized bed technology has been successfully used for the formation of different types of coatings, e.g. aluminizing w1–4x, chromizing w1–3x, nitriding w5–7x, carburizing w7x, carbonitriding w7x. On the other hand, very limited information exists on boride coatings obtained using fluidized bed technology, although the method is simple, efficient, environmentally friendly and the boride coatings have been reported to have an excellent combination of properties w8,9,13x. The theory of fluidization is described in great detail elsewhere w10–12x. Briefly, fluidization is a process in which a bed of particles, e.g. Al 2 O 3 , behave like a liquid when a carrier gas is fed
) Corresponding author. Tel.: q30-31-996013; fax: q30-31996069. E-mail address: [email protected] ŽD.N. Tsipas..
through the bed. There are several types of fluidized beds and their main advantages are the high rates for mass and heat transfer. This leads to uniformity of temperature throughout the volume of the reactor and flash mix of all the compounds in it, which results to improved quality of coatings. Some other advantages of this process are the capability of immediate adjustment of the furnace atmosphere for specific requirements, the relatively low capital and operation costs and the fact that it is friendly to the environment. Some of the parameters that affect the quality of fluidization in a fluidized bed reactor are the properties of solids and fluids used, the bed geometry, the gas flow rate, the type of gas distributor and the reactor design. This paper is concerned with the study of boride coatings onto steel, by the fluidized bed process. The boride coatings, which have been prepared using fluidized bed technology, were characterized by optical microscopy and X-ray diffraction measurements.
00167-577Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 1 . 0 0 2 8 3 - X
K.G. Anthymidis et al.r Materials Letters 51 (2001) 156–160
157
2. Experimental procedure
2.2. Coating properties and characterization
2.1. Coating process
The thickness of coatings and their morphology were examined using optical microscopy. Hardness was measured by a Vickers microhardness tester. The phases formed in the coating were identified by X-ray diffraction ŽXRD. measurements, which were performed using monochromatic FeK a radiation. A rough qualitative characterization of the produced coating was also attempted.
Samples were prepared using a typical fluidized bed reactor system, which is shown schematically in Fig. 1. The system consisted of five main parts: Ø Ø Ø Ø Ø
The The The The The
fluidized bed reactor unit, gas preheating and providing system, furnace for heating the reactor, control panels and measuring instruments, trapping of hazardous substances unit.
This experimental set up is simple and flexible and allows to deposit a wide range of single and multi-element coatings. A detailed description of the experimental set up has been given in a previous publication w4x. In the present experiment, boriding was carried out in such a system, on simple 0.5% wt. C steel at temperatures from 8008C to about 10008C. Argon was used as a fluidizing gas, while fluidizing media were composed of B 4 C and halogen-containing compounds.
3. Results and discussion In Fig. 2, a typical morphology of boride coating obtained on 0.5% wt. C steel after 1.5 h of treatment is shown. This coating had average thickness of 80 mm, Vickers microhardness values of 1800–2000 Hv ŽFig. 3. and it is characterized by very good adherence due to its tooth-shape morphology. From X-ray patterns ŽFig. 4., it was concluded that the as-prepared coatings consist of a uniform compound, which was found to belong to Fe 2 B phase. Small traces indicative of an Fe phase are present in the
Fig. 1. The fluidized bed reactor system.
158
K.G. Anthymidis et al.r Materials Letters 51 (2001) 156–160
Fig. 2. Typical tooth-shape morphology of boride coating obtained in a fluidized bed reactor.
thinner than the average coatings. It was also observed that in the case of coating with less than 1 h
of treatment, crystallization proceeds by formation of Fe 2 B crystallites with a preferred orientation. It is
Fig. 3. Measurement of the microhardness of the boride coating.
K.G. Anthymidis et al.r Materials Letters 51 (2001) 156–160
159
Fig. 4. X-ray diffraction ŽXRD. results of the boride coating.
most probably that longer treatment induced secondary recrystallization resulting in improvement of the properties of the coatings. The optimum morphology obtained Žtooth-shape., the type of layer Fe 2 B, coupled with the relatively short boriding time Ž1.5 h. for this type of surface treatment, and the thickness of the coating Ž80 mm. make this process extremely attractive. The compounds used for boriding were only B 4 C, halogen-containing compounds and argon gas. The small amounts of undesirable gases produced during the process were trapped and neutralized, making this boriding process environmentally friendly.
4. Conclusions A simple, environmentally friendly, fast boriding process was carried out in a fluidized bed reactor. Samples of a typical morphology of iron-boride coatings with tooth-shaped adherent and of excellent
quality were produced. Only one phase of ironborides, which was found to belong to Fe 2 B was revealed. Grain size of crystallites and crystallization characteristics depend on the time of treatment.
Acknowledgements We are indebted to J. Tholoulis for his significant help in the experimental procedure.
References w1x F.J. Perez, M.P. Hierro, F. Pedraza, C. Gomez, M.C. Carpi´ ´ enero, Aluminizing and chromizing bed treatment by CVD in a fluidized bed reactor on austenitic stainless steels. Surf. Coat. Technol. 120 Ž1999. 151. w2x S. Kingel, G.N. Angelopoulos, D. Papamantellos, W. Dahl, Feasibility of fluidized bed CVD for the formation of protective coatings. Steel Res. 66 Ž1995. 318. w3x D.N. Tsipas, Y. Flitris, Surface treatment in fluidized bed reactors. J. Mater. Sci. 35 Ž21. Ž2000. 5493.
160
K.G. Anthymidis et al.r Materials Letters 51 (2001) 156–160
w4x N. Voudouris, G.N. Angelopoulos, Formation of aluminide coatings on nickel by a fluidized bed CVD process. 11th International Conference on Surface Modification Technologies SMT11, Paris, 8–10 September, 1997. w5x J.E. Japka, Using the fluidized bed for nitriding-type processes. Met. Prog. Ž1983. 27–33, February. w6x Z. Rogalski, H. Zowczak, Fluidised bed methods of nitriding and oxy-nitriding. 18th International Conference on Heat treatment of Metals. 1980, pp. 181–196. w7x R.W. Reynoldson, Heat Treatment in Fluidized Bed Furnaces. ASM International, 1993. w8x S. Anil Kumar Sinha, Boriding ŽBoronizing., ASM Handbook, vol. 4, pp. 437–447. w9x T. Arai, J. Endo, H. Takeda, Chromizing and boriding by use
w10x w11x w12x w13x
of a fluidized bed. 5th International Conference on Heat Treatment of Materials, 3, Budapest, Hungary. 1986, pp. 1335–1341. J.R. Howard, Fluidized Bed Technology Principles and Applications. Adam Higler, Bristol, 1989. F.A. Zenz, D.F. Othmer, Fluidization and Fluid-Particle Systems. Reinhold Publishing, New York, 1960. C.K. Gupta, D. Sathiyamoothy, Fluid Bed Technology in Materials Processing. CRC Press, Boca Raton, 1999. D.N. Tsipas, G.K. Triantafyllidis, J. Kipkemoi, Y. Flitris, Thermochemical treatments for protection of steel in chemically aggressive atmosphere at high temperature. Mater. Manuf. Processes 14 Ž5. Ž1999. 697–712.