AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for produc... more AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for producing orthopaedic implants, although they have the limitations of low resistance to wear and fatigue due to low surface hardness. Thus, thermochemical surface treatment methods are used to modify the surface properties. In this research, pack carburising with 60% BaCO 3 , 30% activated carbon and 10% NACl was used on AISI 316L austenitic stainless steel at 450ºC, 550ºC, 650ºC, 700ºC and 750ºC for 24 hours. Pack carburised specimens of tensile and fatigue specimens were analysed with optical microscopy, Vicker's micro hardness tester, scanning electron microscopy and XRD.
The effect of surface hardening by pack carburizing on the mechanical properties of AISI 316L ste... more The effect of surface hardening by pack carburizing on the mechanical properties of AISI 316L steel was studied. Pack carburizing with 60 wt% BaCO 3 , 30 wt% activated carbon, and 10 wt% sodium chloride was carried out at 450, 550, 650, 700, and 750°C for 24 hours and the specimens were furnace-cooled. Tensile, impact, hardness, and fatigue tests were conducted, and SEM and was used to characterize the specimens.
Austenitic stainless steel is widely used structural components, for instance in the chemical and... more Austenitic stainless steel is widely used structural components, for instance in the chemical and petrochemical industry due to their excellent corrosion resistance and good mechanical properties 1 . The type 316L is more resistant to pitting and crevice corrosion due to at least 2-3 wt% Mo and at most 0.04 wt% C and also has good forming characteristics 2 . However, due to its inherent austenitic structure, it has relatively low hardness, as well as poor wear resistance and short fatigue life. Thus, thermochemical surface treatment methods are used to modify the surface properties to improve the fatigue life. Austenitic stainless steel is usually difficult to pack carburise due to the tenacious Cr 2 O 3 layer on the surface. The appropriate case hardening technique is plasma processing were surface hardness is increased at most five times to the asreceived 3 . However, this investigation was undertaken to see the effect of using higher temperature on the mechanical properties without the removal of the Cr 2 O 3 layer from the surface.
AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for produc... more AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for producing orthopaedic implants, although they have the limitations of low resistance to wear and fatigue due to low surface hardness. Thus, thermochemical surface treatment methods are used to modify the surface properties. In this research, pack carburising with 60% BaCO 3 , 30% activated carbon and 10% NACl was used on AISI 316L austenitic stainless steel at 450ºC, 550ºC, 650ºC, 700ºC and 750ºC for 24 hours. Pack carburised specimens of tensile and fatigue specimens were analysed with optical microscopy, Vicker's micro hardness tester, scanning electron microscopy and XRD. Tensile strengths of specimens treated at 450ºC and 550ºC were 709MPa and 722MPa as compared with the as-received specimen of 645MPa. However, microhardness values of the treated specimens were about the same as the as-received specimens. Hence, the increasing trend in the tensile properties could be attributed to the heat treatment and not the carburising process. Specimens tested at 650ºC, 700ºC and 750ºC showed appreciable increases in tensile strength and microhardness, and specimens carburised at 750ºC experienced deformation. This could be attributed to the onset of recrystallization of the AISI 316L at temperatures above 700ºC.
Pt-based alloys for high-temperature applications in aggressive environments have been under deve... more Pt-based alloys for high-temperature applications in aggressive environments have been under development for over 10 years, and are targeted to be used as either as bulk, or as coatings. The alloys comprise Pt, Al, Cr, and Ru, and the microstructure has been improved by composition to a best possible analogue of the nickel-based superalloys, which these alloys could partially replace. This was necessary because the previous best alloy had a strengthening precipitate volume proportion of only approximately 40 vol.%, whereas the nickel-based superalloys have around 70 per cent, and a lower volume would mean that the strength would not be the best that could be obtained. The microstructures were assessed using electron microscopy, and have been related to the alloys' hardness values. The current microstructures are much more like those of NBSAs, with a high proportion of the strengthening ~Pt 3 Al precipitates. Since the samples have to be small (platinum is expensive), hardness has been used as an indication of strength. Nano-indentation studies showed that the hardness and Young's modulus were higher for ~Pt 3 Al than the (Pt) matrix. More extensive oxidation studies have been undertaken on the previous optimum sample, and the effect of cooling rate after heat treatment has also been ascertained. In addition, the samples were studied after different heat treatment times, and cross-sections were made in order to characterize the alumina scale that formed. The oxide scales of Pt-11Al-3Cr-2Ru (at.%) up to 100 h exposure did not spall, and were at least as good as those of the ternary alloys. There was no discernable Al depletion zone in the substrate, although it could have been at a greater depth than thickness of the samples studied.
International Journal of Applied Ceramic Technology, 2014
ABSTRACT The nature and magnitude of stress in the scales formed on Pt-11Al-3Cr-2Ru (at.%) alloy ... more ABSTRACT The nature and magnitude of stress in the scales formed on Pt-11Al-3Cr-2Ru (at.%) alloy oxidized in air at 1250°C, for up to 500 h, were determined. This is to establish their long-term viability during high-temperature applications. Residual stress in the scales was measured using luminescence piezospectroscopy and found to be compressive. It decreased gradually with increased oxidation time, before reaching a constant value. The compressive stress was also found to be lower than those of other Ni- and Fe-based superalloys. Thus, the current alloy has a promising potential for high-temperature applications.
This thesis studies the factors that govern transverse cracking during continuous casting of low ... more This thesis studies the factors that govern transverse cracking during continuous casting of low carbon, niobium microalloyed and boron microalloyed steels. Crack susceptibility in the thick slab, billet and thin slab casting processes are compared by using typical conditions in laboratory hot ductility tests.
Since platinum has a similar chemistry and atomic structure to nickel, platinum-based alloys are ... more Since platinum has a similar chemistry and atomic structure to nickel, platinum-based alloys are possible contenders for partial or complete substitution of nickel-based superalloys. Although the major disadvantages are high price and density, platinum-based alloys have many advantages, including excellent chemical and oxidation resistance and high strength at high temperatures. Since the melting point is higher than nickel, there is potential that Ptbased alloys can exhibit mechanical properties that surpass those of the nickel-based superalloys. Pt-modified coatings are already employed on turbine blades. These can be modified with the addition of different elements and various coating procedures can be used so that the coatings can complement different substrates. This chapter covers the basic properties of a range of Pt-based alloys and describes the different strengthening mechanisms that exist in these alloys, mainly through a structural approach. The oxidation resistance and corrosion resistance are also described. Further, new alloying additions and their effects on the structure and properties are identified. Nickel-based superalloys (NBSAs) have excellent mechanical properties due to precipitation strengthening. The microstructure comprises many small, strained-coherent, particles of the ' phase based on Ni 3 Al, in a softer matrix of the phase, the solid solution (Ni) of nickel . The strengthening originates from dislocations being slowed down as they negotiate the small ordered ' particles. There are several mechanisms whereby a unit dislocation has to split into partial dislocations to pass through the ordered precipitates and then re-associate to pass into the random matrix. Each stage requires energy, thus slowing the dislocation movement and providing strengthening. The strengthening depends on the amount of interfacial boundary between the two phases, and is highest when the amount of boundary to be negotiated is highest. This occurs when there are many small precipitates densely distributed, comprising at least 70 vol. % in the alloy . For NBSAs, these are usually cubic ' precipitates aligned on the {100} planes . Additionally, there is solid solution strengthening in the (Ni) matrix, as other elements are dissolved into the nickel, forming a random solid solution. The (Ni) strengthening depends mainly on the difference in elastic and bulk moduli between the Ni and solute atoms , as well as the size misfit, since each atom varies in size according to its atomic number. There are also bonding effects, all of which make it more difficult for the dislocations to pass.
AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for produc... more AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for producing orthopaedic implants, although they have the limitations of low resistance to wear and fatigue due to low surface hardness. Thus, thermochemical surface treatment methods are used to modify the surface properties. In this research, pack carburising with 60% BaCO 3 , 30% activated carbon and 10% NACl was used on AISI 316L austenitic stainless steel at 450ºC, 550ºC, 650ºC, 700ºC and 750ºC for 24 hours. Pack carburised specimens of tensile and fatigue specimens were analysed with optical microscopy, Vicker's micro hardness tester, scanning electron microscopy and XRD.
Austenitic stainless steel is widely used structural components, for instance in the chemical and... more Austenitic stainless steel is widely used structural components, for instance in the chemical and petrochemical industry due to their excellent corrosion resistance and good mechanical properties 1 . The type 316L is more resistant to pitting and crevice corrosion due to at least 2-3 wt% Mo and at most 0.04 wt% C and also has good forming characteristics 2 . However, due to its inherent austenitic structure, it has relatively low hardness, as well as poor wear resistance and short fatigue life. Thus, thermochemical surface treatment methods are used to modify the surface properties to improve the fatigue life. Austenitic stainless steel is usually difficult to pack carburise due to the tenacious Cr 2 O 3 layer on the surface. The appropriate case hardening technique is plasma processing were surface hardness is increased at most five times to the asreceived 3 . However, this investigation was undertaken to see the effect of using higher temperature on the mechanical properties without the removal of the Cr 2 O 3 layer from the surface.
The high-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)3 and 1,2-hexa... more The high-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)3 and 1,2-hexadecanediol was used to synthesise iron oxide and gold-coated iron oxide nanoparticles. Different surface functionalities, such as sebacic acid (SA) and 1, 10–Decanediol (DD), were introduced on the surface of the particles to investigate the stabilising effect of carboxylic groups (SA) in comparison to the hydroxyl groups (DD). Nanoparticle thermal
Journal of Materials Research and Technology, 2015
ABSTRACT Aluminium hybrid composites are a new generation of metal matrix composites that have th... more ABSTRACT Aluminium hybrid composites are a new generation of metal matrix composites that have the potentials of satisfying the recent demands of advanced engineering applications. These demands are met due to improved mechanical properties, amenability to conventional processing technique and possibility of reducing production cost of aluminium hybrid composites. The performance of these materials is mostly dependent on selecting the right combination of reinforcing materials since some of the processing parameters are associated with the reinforcing particulates. A few combinations of reinforcing particulates have been conceptualized in the design of aluminium hybrid composites. This paper attempts to review the different combination of reinforcing materials used in the processing of hybrid aluminium matrix composites and how it affects the mechanical, corrosion and wear performance of the materials. The major techniques for fabricating these materials are briefly discussed and research areas for further improvement on aluminium hybrid composites are suggested.
International Journal of Applied Ceramic Technology, 2014
ABSTRACT The nature and magnitude of stress in the scales formed on Pt-11Al-3Cr-2Ru (at.%) alloy ... more ABSTRACT The nature and magnitude of stress in the scales formed on Pt-11Al-3Cr-2Ru (at.%) alloy oxidized in air at 1250°C, for up to 500 h, were determined. This is to establish their long-term viability during high-temperature applications. Residual stress in the scales was measured using luminescence piezospectroscopy and found to be compressive. It decreased gradually with increased oxidation time, before reaching a constant value. The compressive stress was also found to be lower than those of other Ni- and Fe-based superalloys. Thus, the current alloy has a promising potential for high-temperature applications.
AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for produc... more AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for producing orthopaedic implants, although they have the limitations of low resistance to wear and fatigue due to low surface hardness. Thus, thermochemical surface treatment methods are used to modify the surface properties. In this research, pack carburising with 60% BaCO 3 , 30% activated carbon and 10% NACl was used on AISI 316L austenitic stainless steel at 450ºC, 550ºC, 650ºC, 700ºC and 750ºC for 24 hours. Pack carburised specimens of tensile and fatigue specimens were analysed with optical microscopy, Vicker's micro hardness tester, scanning electron microscopy and XRD.
The effect of surface hardening by pack carburizing on the mechanical properties of AISI 316L ste... more The effect of surface hardening by pack carburizing on the mechanical properties of AISI 316L steel was studied. Pack carburizing with 60 wt% BaCO 3 , 30 wt% activated carbon, and 10 wt% sodium chloride was carried out at 450, 550, 650, 700, and 750°C for 24 hours and the specimens were furnace-cooled. Tensile, impact, hardness, and fatigue tests were conducted, and SEM and was used to characterize the specimens.
Austenitic stainless steel is widely used structural components, for instance in the chemical and... more Austenitic stainless steel is widely used structural components, for instance in the chemical and petrochemical industry due to their excellent corrosion resistance and good mechanical properties 1 . The type 316L is more resistant to pitting and crevice corrosion due to at least 2-3 wt% Mo and at most 0.04 wt% C and also has good forming characteristics 2 . However, due to its inherent austenitic structure, it has relatively low hardness, as well as poor wear resistance and short fatigue life. Thus, thermochemical surface treatment methods are used to modify the surface properties to improve the fatigue life. Austenitic stainless steel is usually difficult to pack carburise due to the tenacious Cr 2 O 3 layer on the surface. The appropriate case hardening technique is plasma processing were surface hardness is increased at most five times to the asreceived 3 . However, this investigation was undertaken to see the effect of using higher temperature on the mechanical properties without the removal of the Cr 2 O 3 layer from the surface.
AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for produc... more AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for producing orthopaedic implants, although they have the limitations of low resistance to wear and fatigue due to low surface hardness. Thus, thermochemical surface treatment methods are used to modify the surface properties. In this research, pack carburising with 60% BaCO 3 , 30% activated carbon and 10% NACl was used on AISI 316L austenitic stainless steel at 450ºC, 550ºC, 650ºC, 700ºC and 750ºC for 24 hours. Pack carburised specimens of tensile and fatigue specimens were analysed with optical microscopy, Vicker's micro hardness tester, scanning electron microscopy and XRD. Tensile strengths of specimens treated at 450ºC and 550ºC were 709MPa and 722MPa as compared with the as-received specimen of 645MPa. However, microhardness values of the treated specimens were about the same as the as-received specimens. Hence, the increasing trend in the tensile properties could be attributed to the heat treatment and not the carburising process. Specimens tested at 650ºC, 700ºC and 750ºC showed appreciable increases in tensile strength and microhardness, and specimens carburised at 750ºC experienced deformation. This could be attributed to the onset of recrystallization of the AISI 316L at temperatures above 700ºC.
Pt-based alloys for high-temperature applications in aggressive environments have been under deve... more Pt-based alloys for high-temperature applications in aggressive environments have been under development for over 10 years, and are targeted to be used as either as bulk, or as coatings. The alloys comprise Pt, Al, Cr, and Ru, and the microstructure has been improved by composition to a best possible analogue of the nickel-based superalloys, which these alloys could partially replace. This was necessary because the previous best alloy had a strengthening precipitate volume proportion of only approximately 40 vol.%, whereas the nickel-based superalloys have around 70 per cent, and a lower volume would mean that the strength would not be the best that could be obtained. The microstructures were assessed using electron microscopy, and have been related to the alloys' hardness values. The current microstructures are much more like those of NBSAs, with a high proportion of the strengthening ~Pt 3 Al precipitates. Since the samples have to be small (platinum is expensive), hardness has been used as an indication of strength. Nano-indentation studies showed that the hardness and Young's modulus were higher for ~Pt 3 Al than the (Pt) matrix. More extensive oxidation studies have been undertaken on the previous optimum sample, and the effect of cooling rate after heat treatment has also been ascertained. In addition, the samples were studied after different heat treatment times, and cross-sections were made in order to characterize the alumina scale that formed. The oxide scales of Pt-11Al-3Cr-2Ru (at.%) up to 100 h exposure did not spall, and were at least as good as those of the ternary alloys. There was no discernable Al depletion zone in the substrate, although it could have been at a greater depth than thickness of the samples studied.
International Journal of Applied Ceramic Technology, 2014
ABSTRACT The nature and magnitude of stress in the scales formed on Pt-11Al-3Cr-2Ru (at.%) alloy ... more ABSTRACT The nature and magnitude of stress in the scales formed on Pt-11Al-3Cr-2Ru (at.%) alloy oxidized in air at 1250°C, for up to 500 h, were determined. This is to establish their long-term viability during high-temperature applications. Residual stress in the scales was measured using luminescence piezospectroscopy and found to be compressive. It decreased gradually with increased oxidation time, before reaching a constant value. The compressive stress was also found to be lower than those of other Ni- and Fe-based superalloys. Thus, the current alloy has a promising potential for high-temperature applications.
This thesis studies the factors that govern transverse cracking during continuous casting of low ... more This thesis studies the factors that govern transverse cracking during continuous casting of low carbon, niobium microalloyed and boron microalloyed steels. Crack susceptibility in the thick slab, billet and thin slab casting processes are compared by using typical conditions in laboratory hot ductility tests.
Since platinum has a similar chemistry and atomic structure to nickel, platinum-based alloys are ... more Since platinum has a similar chemistry and atomic structure to nickel, platinum-based alloys are possible contenders for partial or complete substitution of nickel-based superalloys. Although the major disadvantages are high price and density, platinum-based alloys have many advantages, including excellent chemical and oxidation resistance and high strength at high temperatures. Since the melting point is higher than nickel, there is potential that Ptbased alloys can exhibit mechanical properties that surpass those of the nickel-based superalloys. Pt-modified coatings are already employed on turbine blades. These can be modified with the addition of different elements and various coating procedures can be used so that the coatings can complement different substrates. This chapter covers the basic properties of a range of Pt-based alloys and describes the different strengthening mechanisms that exist in these alloys, mainly through a structural approach. The oxidation resistance and corrosion resistance are also described. Further, new alloying additions and their effects on the structure and properties are identified. Nickel-based superalloys (NBSAs) have excellent mechanical properties due to precipitation strengthening. The microstructure comprises many small, strained-coherent, particles of the ' phase based on Ni 3 Al, in a softer matrix of the phase, the solid solution (Ni) of nickel . The strengthening originates from dislocations being slowed down as they negotiate the small ordered ' particles. There are several mechanisms whereby a unit dislocation has to split into partial dislocations to pass through the ordered precipitates and then re-associate to pass into the random matrix. Each stage requires energy, thus slowing the dislocation movement and providing strengthening. The strengthening depends on the amount of interfacial boundary between the two phases, and is highest when the amount of boundary to be negotiated is highest. This occurs when there are many small precipitates densely distributed, comprising at least 70 vol. % in the alloy . For NBSAs, these are usually cubic ' precipitates aligned on the {100} planes . Additionally, there is solid solution strengthening in the (Ni) matrix, as other elements are dissolved into the nickel, forming a random solid solution. The (Ni) strengthening depends mainly on the difference in elastic and bulk moduli between the Ni and solute atoms , as well as the size misfit, since each atom varies in size according to its atomic number. There are also bonding effects, all of which make it more difficult for the dislocations to pass.
AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for produc... more AISI 316L austenitic stainless steels are one of the most common biomaterials utilized for producing orthopaedic implants, although they have the limitations of low resistance to wear and fatigue due to low surface hardness. Thus, thermochemical surface treatment methods are used to modify the surface properties. In this research, pack carburising with 60% BaCO 3 , 30% activated carbon and 10% NACl was used on AISI 316L austenitic stainless steel at 450ºC, 550ºC, 650ºC, 700ºC and 750ºC for 24 hours. Pack carburised specimens of tensile and fatigue specimens were analysed with optical microscopy, Vicker's micro hardness tester, scanning electron microscopy and XRD.
Austenitic stainless steel is widely used structural components, for instance in the chemical and... more Austenitic stainless steel is widely used structural components, for instance in the chemical and petrochemical industry due to their excellent corrosion resistance and good mechanical properties 1 . The type 316L is more resistant to pitting and crevice corrosion due to at least 2-3 wt% Mo and at most 0.04 wt% C and also has good forming characteristics 2 . However, due to its inherent austenitic structure, it has relatively low hardness, as well as poor wear resistance and short fatigue life. Thus, thermochemical surface treatment methods are used to modify the surface properties to improve the fatigue life. Austenitic stainless steel is usually difficult to pack carburise due to the tenacious Cr 2 O 3 layer on the surface. The appropriate case hardening technique is plasma processing were surface hardness is increased at most five times to the asreceived 3 . However, this investigation was undertaken to see the effect of using higher temperature on the mechanical properties without the removal of the Cr 2 O 3 layer from the surface.
The high-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)3 and 1,2-hexa... more The high-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)3 and 1,2-hexadecanediol was used to synthesise iron oxide and gold-coated iron oxide nanoparticles. Different surface functionalities, such as sebacic acid (SA) and 1, 10–Decanediol (DD), were introduced on the surface of the particles to investigate the stabilising effect of carboxylic groups (SA) in comparison to the hydroxyl groups (DD). Nanoparticle thermal
Journal of Materials Research and Technology, 2015
ABSTRACT Aluminium hybrid composites are a new generation of metal matrix composites that have th... more ABSTRACT Aluminium hybrid composites are a new generation of metal matrix composites that have the potentials of satisfying the recent demands of advanced engineering applications. These demands are met due to improved mechanical properties, amenability to conventional processing technique and possibility of reducing production cost of aluminium hybrid composites. The performance of these materials is mostly dependent on selecting the right combination of reinforcing materials since some of the processing parameters are associated with the reinforcing particulates. A few combinations of reinforcing particulates have been conceptualized in the design of aluminium hybrid composites. This paper attempts to review the different combination of reinforcing materials used in the processing of hybrid aluminium matrix composites and how it affects the mechanical, corrosion and wear performance of the materials. The major techniques for fabricating these materials are briefly discussed and research areas for further improvement on aluminium hybrid composites are suggested.
International Journal of Applied Ceramic Technology, 2014
ABSTRACT The nature and magnitude of stress in the scales formed on Pt-11Al-3Cr-2Ru (at.%) alloy ... more ABSTRACT The nature and magnitude of stress in the scales formed on Pt-11Al-3Cr-2Ru (at.%) alloy oxidized in air at 1250°C, for up to 500 h, were determined. This is to establish their long-term viability during high-temperature applications. Residual stress in the scales was measured using luminescence piezospectroscopy and found to be compressive. It decreased gradually with increased oxidation time, before reaching a constant value. The compressive stress was also found to be lower than those of other Ni- and Fe-based superalloys. Thus, the current alloy has a promising potential for high-temperature applications.
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Papers by Lesley Chown