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Microstructural And Corrosion Resistance Study Of Sintered Al-Tin In Sodium Chloride Solution
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 18 (2019) 2881–2886
www.materialstoday.com/proceedings
ICMPC-2019
Microstructural And Corrosion Resistance Study Of Sintered Al-Tin In Sodium Chloride Solution. Samuel Olukayode Akinwamidea*, Neo Tshabalalaa, Oluwasegun Eso Faloduna, Samuel Ranti Okea, Ojo Jeremiah Akinribidea, Bolanle Tolulope Abeb, Peter Apata Olubambia a
Centre for Tribocorrosion and Nanoengineering, University of Johannesburg, Johannesburg 2006 South Africa b Tshwane University of Technology, Pretoria 0001, South Africa
Abstract Aluminium matrix composites were produced by adding 2, 4, 6 and 8 wt. % of titanium nitride (TiN) nanoparticles respectively to aluminium matrix through powder metallurgy technique. The mixed powder was compacted at a pressure of 50 MPa to produce the specimens. The specimens were sintered in nitrogen atmosphere at a sintering temperature of 4000C with sintering time of 2 hours for each. Microstructural and mechanical properties of sintered composites was investigated. Potentiodynamic polarization test was conducted to determine the corrosion behaviour of sintered samples in sodium chloride. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Aluminium; Titanium nitride; Sintering; Open circuit potential; Potentiodynamic polarization.
1. Introduction Aluminum is well known for its light weight and high strength applications. However, there are efforts to improve its properties by making aluminum matrix composites (AMCs). Reinforcing aluminum with hard phases leads to strengthening of the composites[1]. The most widely used reinforcing materials are metal carbides, oxides, nitrides and borides which includes silicon carbide (SiC), aluminium oxide (Al2O3), titanium carbide (TiC) to mention a few[2]. However, the use of SiC as reinforcement in aluminium matrix is limited due to its reaction with aluminium above 720 0C resulting in formation of Al4C3, poor mechanical properties and low corrosion resistance[3]. Aluminium metal matrix composite provides lesser wear resistance when compared to steel and hence it is widely used as a matrix metal. * Corresponding author. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
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Over the years, nanoparticles research has become an area of interest to scientists due to the unexpected results produced by altering the atomic and molecular properties of elements, giving them unique and unparalleled properties. Titanium nitride (TiN), one of these nanoparticles materials is widely used because of the excellent combination of hardware performance properties, aesthetic appearance and contamination safety it possesses, thereby promoting their usage in making surgical tools as well as food contact application[4]. TiN is a high melting point compound with extreme hardness, low electric resistance and good thermal stability. It does not react with aluminium, because of its good stability up to a temperature of 3300 0K[5]. In this study, effects of TiN as reinforcement in the matrix of aluminium produced by spark plasma sintering (SPS) techniques will be investigated. Spark plasma sintering is a material processing technology under powder metallurgy in which powdered materials are consolidated into parts through the combination of pressure and electrical current, it is a novel technique where Direct Current (DC) pulse and uniaxial current are used to obtain fully dense AMCs. Various characterizations including phase analysis and microstructural analysis were performed[6]. 2. Experimental procedure 2.1 Materials In this study pure aluminum powder (99.8% purity) was used as the metal matrix and pure Titanium Nitride powder was used as reinforcement. Pure Titanium nitride from Sigma-Aldrich with nano size range was used as the reinforcements for the experiments at different the chemical composition of TiN powder used is shown in Table 1. Table 1: Composition of TiN powder C Ni Si N
Elements
Fe
TiN
<0.001
0.03
<0.001
<0.003
21.91
Ti 77.83
2.2 Method Pure aluminium powder with different weight percentage (2,4,6 and 8) of TiN were milled together in a high energy ball milling machine comprising of 125 ml steel mixing jar containing 20 steel milling balls of 5 mm diameter. During milling, stearic acid was used as a process control agent (PCA) to prevent the powder from sticking to the balls and walls of the jar. The milling time for Al-TiN composites was 6 hours at 150 rpm, to ensure proper dispersion of the reinforcement material within the aluminium matrix. Sintering of composites was carried out in nitrogen atmosphere at a temperature and pressure of 550 °C and 50 MP respectively, in addition to heating and cooling rate of 100 °C/min and a holding time of 10 minutes. The mixed powders were placed in a cylindrical graphite die of 30mm with the aim of achieving maximum densification for sintered compacts. A graphite foil was placed in between the powder and the die to prevent melting to the inner wall of the die during sintering operation. Microstructural analysis of sectioned samples was carried out using TESCAN Scanning electron microscope (SEM) equipped with Energy dispersive X-ray (EDX). Prior to microstructural investigation, samples cold mounted in epoxy resin were ground to 1200 grits using emery paper, after which they were polished till a mirror like surface was achieved using diamond suspension. Etching was done using Keller’s reagent. Vickers hardness testing of specimen was carried out using an Innovast micro-hardness tester at a load of 100 g. Corrosion properties of samples was investigated in 3.5 wt.% NaCl using potentiodynamic polarization test conducted on a Versastat potentiostat equipped with a three -cell set up consisting of silver/silver reference electrode, graphite counter electrode and a working electrode. 3. Results and Discussion 3.1 Microstructural analysis Figure 1(a-c) shows the dispersion of TiN particles within the matrix of aluminium. Even dispersion of reinforcements can be attributed to longer hours used during milling operation. However, presence of some pores was observed in samples with lesser amount of reinforcements. However, effectiveness of milling process is described by homogeneity of mixed powders and as shown in below Fig 1 (d-e).
S.O. Akinwamide et al. / Materials Today: Proceedings 18 (2019) 2881–2886
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(b)
(a) Pores
(c)
(d) Pores
(e)
TiN
Fig 1. SEM micrographs of sintered (a) pure Aluminium (b) Pure Al + 2 wt. % (c) Pure Al + 4 wt. % (d) Pure Al + 6 wt. % (e) Pure Al + 8 wt. % 3.2 Hardness test Show in Figure 2 is the hardness result for sintered pure aluminium and composites. Lowest hardness value of 40 Hv was observed in pure aluminium, the highest hardness was recorded by composite with 8 wt.% TiN. The trend observed from the figure shows that hardness value in increased upon increase in wt.% of TiN addition. Improved hardness can be ascribed to even distribution of TiN reinforcement within the matrix of aluminium matrix thereby increasing the load bearing capacity and strength of the resulting composites.
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Vickers hardness (Hv0.1)
60 50 40 30 20 10 0 Pure Al
2
4
6
8
Weight % of TiN
Fig. 2. Hardness plot for pure aluminium and aluminium matrix composites. 3,3 Potentiodynamic polarization test The plot of potential against current density for sintered samples in a corrosive medium of sodium chloride is shown in Figure 3. Pure Al was observed to record the lowest corrosion resistance as its cathodic region is seen to have the highest current density. Specimens with titanium nitride reinforcements were observed to have an improved corrosion resistance as they have a lesser corrosion current density. Fluctuations were further observed in the cathodic region of specimens with 6 and 8 % TiN reinforcements. These fluctuations can be attributed to passivation of aluminium surface as a result of oxide film formation in the corrosive media, as no passivation was observed in pure aluminium and specimen with 2 and 4% TiN reinforcements respectively. Similar report was given in a study by Lucas et al [7]. Corrosion resistance of specimens with greater addition of TiN were observed to be improved.
Fig. 3. Potentiodynamic polarization curves for sintered composites in 3.5 wt.% NaCl.
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References [1] [2] [3] [4] [5] [6] [7]
I. Akin and O. Kaya, J. Alloy Compd., 729 (2017) 949-959. K. K. Alaneme, T. M. Adewale, and P. A. Olubambi, J. Mater. Res. Technol. 3 (2014) 9-16. L. F. Xavier and P. Suresh, Scientific World Journal, 2016 (2016). M. E. Maja, O. E. Falodun, B. A. Obadele, S. R. Oke, and P. A. Olubambi, Ceram. Int., 44 (2018) 4419-4425. S. Mohal and S. Mohal, Int. J. Innov. Res. Sci. Technol., 3 (2017) 2349-2510. B. Li, Y. Liu, J. Li, H. Cao, and L. He, J. Mater. Process. Technol.,210 (2010) 91-9. K. A. Lucas, K. A. Lucas, and H. Clarke, Research Studies Pr Ltd, 1993.
ScienceDirect Materials Today: Proceedings 18 (2019) 2881–2886
www.materialstoday.com/proceedings
ICMPC-2019
Microstructural And Corrosion Resistance Study Of Sintered Al-Tin In Sodium Chloride Solution. Samuel Olukayode Akinwamidea*, Neo Tshabalalaa, Oluwasegun Eso Faloduna, Samuel Ranti Okea, Ojo Jeremiah Akinribidea, Bolanle Tolulope Abeb, Peter Apata Olubambia a
Centre for Tribocorrosion and Nanoengineering, University of Johannesburg, Johannesburg 2006 South Africa b Tshwane University of Technology, Pretoria 0001, South Africa
Abstract Aluminium matrix composites were produced by adding 2, 4, 6 and 8 wt. % of titanium nitride (TiN) nanoparticles respectively to aluminium matrix through powder metallurgy technique. The mixed powder was compacted at a pressure of 50 MPa to produce the specimens. The specimens were sintered in nitrogen atmosphere at a sintering temperature of 4000C with sintering time of 2 hours for each. Microstructural and mechanical properties of sintered composites was investigated. Potentiodynamic polarization test was conducted to determine the corrosion behaviour of sintered samples in sodium chloride. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Aluminium; Titanium nitride; Sintering; Open circuit potential; Potentiodynamic polarization.
1. Introduction Aluminum is well known for its light weight and high strength applications. However, there are efforts to improve its properties by making aluminum matrix composites (AMCs). Reinforcing aluminum with hard phases leads to strengthening of the composites[1]. The most widely used reinforcing materials are metal carbides, oxides, nitrides and borides which includes silicon carbide (SiC), aluminium oxide (Al2O3), titanium carbide (TiC) to mention a few[2]. However, the use of SiC as reinforcement in aluminium matrix is limited due to its reaction with aluminium above 720 0C resulting in formation of Al4C3, poor mechanical properties and low corrosion resistance[3]. Aluminium metal matrix composite provides lesser wear resistance when compared to steel and hence it is widely used as a matrix metal. * Corresponding author. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
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S.O. Akinwamide et al. / Materials Today: Proceedings 18 (2019) 2881–2886
Over the years, nanoparticles research has become an area of interest to scientists due to the unexpected results produced by altering the atomic and molecular properties of elements, giving them unique and unparalleled properties. Titanium nitride (TiN), one of these nanoparticles materials is widely used because of the excellent combination of hardware performance properties, aesthetic appearance and contamination safety it possesses, thereby promoting their usage in making surgical tools as well as food contact application[4]. TiN is a high melting point compound with extreme hardness, low electric resistance and good thermal stability. It does not react with aluminium, because of its good stability up to a temperature of 3300 0K[5]. In this study, effects of TiN as reinforcement in the matrix of aluminium produced by spark plasma sintering (SPS) techniques will be investigated. Spark plasma sintering is a material processing technology under powder metallurgy in which powdered materials are consolidated into parts through the combination of pressure and electrical current, it is a novel technique where Direct Current (DC) pulse and uniaxial current are used to obtain fully dense AMCs. Various characterizations including phase analysis and microstructural analysis were performed[6]. 2. Experimental procedure 2.1 Materials In this study pure aluminum powder (99.8% purity) was used as the metal matrix and pure Titanium Nitride powder was used as reinforcement. Pure Titanium nitride from Sigma-Aldrich with nano size range was used as the reinforcements for the experiments at different the chemical composition of TiN powder used is shown in Table 1. Table 1: Composition of TiN powder C Ni Si N
Elements
Fe
TiN
<0.001
0.03
<0.001
<0.003
21.91
Ti 77.83
2.2 Method Pure aluminium powder with different weight percentage (2,4,6 and 8) of TiN were milled together in a high energy ball milling machine comprising of 125 ml steel mixing jar containing 20 steel milling balls of 5 mm diameter. During milling, stearic acid was used as a process control agent (PCA) to prevent the powder from sticking to the balls and walls of the jar. The milling time for Al-TiN composites was 6 hours at 150 rpm, to ensure proper dispersion of the reinforcement material within the aluminium matrix. Sintering of composites was carried out in nitrogen atmosphere at a temperature and pressure of 550 °C and 50 MP respectively, in addition to heating and cooling rate of 100 °C/min and a holding time of 10 minutes. The mixed powders were placed in a cylindrical graphite die of 30mm with the aim of achieving maximum densification for sintered compacts. A graphite foil was placed in between the powder and the die to prevent melting to the inner wall of the die during sintering operation. Microstructural analysis of sectioned samples was carried out using TESCAN Scanning electron microscope (SEM) equipped with Energy dispersive X-ray (EDX). Prior to microstructural investigation, samples cold mounted in epoxy resin were ground to 1200 grits using emery paper, after which they were polished till a mirror like surface was achieved using diamond suspension. Etching was done using Keller’s reagent. Vickers hardness testing of specimen was carried out using an Innovast micro-hardness tester at a load of 100 g. Corrosion properties of samples was investigated in 3.5 wt.% NaCl using potentiodynamic polarization test conducted on a Versastat potentiostat equipped with a three -cell set up consisting of silver/silver reference electrode, graphite counter electrode and a working electrode. 3. Results and Discussion 3.1 Microstructural analysis Figure 1(a-c) shows the dispersion of TiN particles within the matrix of aluminium. Even dispersion of reinforcements can be attributed to longer hours used during milling operation. However, presence of some pores was observed in samples with lesser amount of reinforcements. However, effectiveness of milling process is described by homogeneity of mixed powders and as shown in below Fig 1 (d-e).
S.O. Akinwamide et al. / Materials Today: Proceedings 18 (2019) 2881–2886
2883
(b)
(a) Pores
(c)
(d) Pores
(e)
TiN
Fig 1. SEM micrographs of sintered (a) pure Aluminium (b) Pure Al + 2 wt. % (c) Pure Al + 4 wt. % (d) Pure Al + 6 wt. % (e) Pure Al + 8 wt. % 3.2 Hardness test Show in Figure 2 is the hardness result for sintered pure aluminium and composites. Lowest hardness value of 40 Hv was observed in pure aluminium, the highest hardness was recorded by composite with 8 wt.% TiN. The trend observed from the figure shows that hardness value in increased upon increase in wt.% of TiN addition. Improved hardness can be ascribed to even distribution of TiN reinforcement within the matrix of aluminium matrix thereby increasing the load bearing capacity and strength of the resulting composites.
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S.O. Akinwamide et al. / Materials Today: Proceedings 18 (2019) 2881–2886
Vickers hardness (Hv0.1)
60 50 40 30 20 10 0 Pure Al
2
4
6
8
Weight % of TiN
Fig. 2. Hardness plot for pure aluminium and aluminium matrix composites. 3,3 Potentiodynamic polarization test The plot of potential against current density for sintered samples in a corrosive medium of sodium chloride is shown in Figure 3. Pure Al was observed to record the lowest corrosion resistance as its cathodic region is seen to have the highest current density. Specimens with titanium nitride reinforcements were observed to have an improved corrosion resistance as they have a lesser corrosion current density. Fluctuations were further observed in the cathodic region of specimens with 6 and 8 % TiN reinforcements. These fluctuations can be attributed to passivation of aluminium surface as a result of oxide film formation in the corrosive media, as no passivation was observed in pure aluminium and specimen with 2 and 4% TiN reinforcements respectively. Similar report was given in a study by Lucas et al [7]. Corrosion resistance of specimens with greater addition of TiN were observed to be improved.
Fig. 3. Potentiodynamic polarization curves for sintered composites in 3.5 wt.% NaCl.
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S.O. Akinwamide et al. / Materials Today: Proceedings 18 (2019) 2881–2886
References [1] [2] [3] [4] [5] [6] [7]
I. Akin and O. Kaya, J. Alloy Compd., 729 (2017) 949-959. K. K. Alaneme, T. M. Adewale, and P. A. Olubambi, J. Mater. Res. Technol. 3 (2014) 9-16. L. F. Xavier and P. Suresh, Scientific World Journal, 2016 (2016). M. E. Maja, O. E. Falodun, B. A. Obadele, S. R. Oke, and P. A. Olubambi, Ceram. Int., 44 (2018) 4419-4425. S. Mohal and S. Mohal, Int. J. Innov. Res. Sci. Technol., 3 (2017) 2349-2510. B. Li, Y. Liu, J. Li, H. Cao, and L. He, J. Mater. Process. Technol.,210 (2010) 91-9. K. A. Lucas, K. A. Lucas, and H. Clarke, Research Studies Pr Ltd, 1993.