Leandro Bolzoni - Academia.edu (original) (raw)

Papers by Leandro Bolzoni

Materials Characterization, 2013

ABSTRACT This study addresses the processing of near-net-shape, chemically homogeneous and fine-g... more ABSTRACT This study addresses the processing of near-net-shape, chemically homogeneous and fine-grained Ti–3Al–2.5V components using vacuum hot-pressing. Two Ti–3Al–2.5V starting powders were considered. On one side, hydride–dehydride (HDH) elemental titanium was blended with an HDH Ti–6Al–4V prealloyed powder. On the other side, an Al:V master alloy was added to the HDH elemental titanium powder. The powders were processed applying a uniaxial pressure of 30 MPa. The sintering temperatures studied varied between 900 °C and 1300 °C. The relative density of the samples increased with processing temperature and almost fully dense materials were obtained. The increase of the sintering temperature led also to a strong reaction between the titanium powders and the processing tools. This phenomenon occurred particularly with boron nitride (BN) coating, which was used to prevent the direct contact between titanium and graphite tools. The flexural properties of the Ti–3Al–2.5V samples increased with vacuum hot-pressing temperature and are comparable to those specified for wrought titanium medical devices. Therefore, the produced materials are promising candidates for load bearing applications as implant materials.

En primer lugar me gustaría dar las gracias a todos los miembros del departamento de Ciencia e In... more En primer lugar me gustaría dar las gracias a todos los miembros del departamento de Ciencia e Ingeniería de Materiales e Ingeniería Química (profesores, técnicos y secretarias) ya que cada uno, con su particular actitud, me ha motivado para afrontar y terminar el reto de la tesis doctoral.

Key Engineering Materials, 2016

El desarrollo de las nuevas tecnologías de extracción de titanio, que producen titanio elemental ... more El desarrollo de las nuevas tecnologías de extracción de titanio, que producen titanio elemental directamente en forma de polvo, sitúan a la pulvimetalurgia en un puesto estratégico para la fabricación de componentes de titanio. La disminución de coste del material base, junto a la economía de los procesos pulvimetalúrgicos, hacen más viable la diversificación de la industria del titanio, lo que permitiría alcanzar volúmenes de producción capaces de popularizar el metal y estabilizar su precio. En este trabajo se muestran algunas de las técnicas pulvimetalúrgicas empleadas para la fabricación de componentes de titanio a partir de los dos enfoques clásicos de mezcla de polvos elementales y el uso de polvos prealeados. Se describen entre otras las técnicas de prensado y sinterización convencional o compactación isostática en frío y caliente, que tratan de competir con las técnicas de procesado convencional, y se muestran algunas aplicaciones actuales y potenciales.

The applicability of irregular prealloyed Ti-6Al-4V powder for the fabrication of titanium produc... more The applicability of irregular prealloyed Ti-6Al-4V powder for the fabrication of titanium products by pressing and sintering and its employment as a master alloy to obtain the Ti-3Al-2.5V alloy was studied. To this end, the starting powders were characterised by dilatometry, differential thermal analysis and XRD. Green samples were obtained by cold uniaxial pressing, and the evolution of the microstructure over the sintering temperature range 900-1400°C was studied. The variation of the final density and mechanical properties with the sintering temperature was considered. Based on the study carried out, it can be stated that more reliable powders are needed to open the titanium market to new applications. A relative density of 95% and diverse microstructural features and mechanical properties equivalent to those of biomedical devices can be obtained by the pressing and sintering route.

Materials Chemistry and Physics

Cast Al alloys are important structural materials for the lightweighting of cars and, consequentl... more Cast Al alloys are important structural materials for the lightweighting of cars and, consequently, reduction of greenhouse gases emission and pollution. The microstructure and properties of cast Al alloys could be further improved by means of grain refinement, practise which cannot efficiently be performed with common Al-Ti-B grain refiners used for wrought Al alloys. In this work we proposed the employment of Nb+B inoculation as an alternative for the refinement of the primary α-Al dendrites of cast Al-Si alloy by studying the grain refinement induced by the Nb+B inoculants as a function of key aspects such as cooling rate, fading behaviour and simulated recyclability tests. It is found that the grain size of the Nb+B inoculated material is noticeably less sensitive to the cooling rate. Nb+B inoculants are still present and promote the refinement of the Al-12Si alloy even after few hours of contact time, although some fading is detected. Furthermore, Nb+B inoculants are also still...

Journal of Materials Processing Technology

This study deals with the grain refinement of the LM25 alloy by means of the addition of a 96Al-2... more This study deals with the grain refinement of the LM25 alloy by means of the addition of a 96Al-2Nb-2B master alloy. Nb-based intermetallics contained in the master alloy act as potent heterogeneous nucleation substrate for the nucleation of primary Al dendrites. The addition of the 96Al-2Nb-2B master alloy to the LM25 alloy permits to significantly refine its microstructural features and the refinement is achieved in a great range of cooling rates. The formation of columnar grains at slow cooling rates is prevented.

Metal Powder Report, 2008

Materials science & engineering. C, Materials for biological applications, 2015

Titanium and its alloys are characterized by an exceptional combination of properties like high s... more Titanium and its alloys are characterized by an exceptional combination of properties like high strength, good corrosion resistance and biocompatibility which makes them suitable materials for biomedical prosthesis and devices. The wrought Ti-6Al-4V alloy is generally favored in comparison to other metallic biomaterials due to its relatively low elastic modulus and it has been long used to obtain products for biomedical applications. In this work an alternative route to fabricate biomedical implants made out of the Ti-6Al-4V alloy is investigated. Specifically, the feasibility of the conventional powder metallurgy route of cold uniaxial pressing and sintering is addressed by considering two types of powders (i.e. blended elemental and prealloyed). The characterization of physical properties, chemical analysis, mechanical behavior and microstructural analysis is carried out in-depth and the properties are correlated among them. On the base of the results found, the produced alloys ar...

Materials and Design

A comparison between the properties achievable by processing the Ti–6Al–4V alloys by means of two... more A comparison between the properties achievable by processing the Ti–6Al–4V alloys by means of two powder metallurgy approaches, precisely prealloyed and master alloy addition, was carried out. Prealloyed and master alloy addition hydride–dehydride powders characterised by an irregular morphology were shaped by means of cold uniaxial pressing and high vacuum sintered considering the effect of the variation of the sintering temperature and of the dwell time. Generally, the higher the temperature and the longer the dwell time, the higher the relative density and, consequently, the better the mechanical performances. Nevertheless, a higher processing temperature or a longer time leads also to some interstitials pick-up, especially oxygen, which affects the mechanical behaviour and, in particular, lowers the ductility. Although some residual porosity is left by the pressing and sintering route, mechanical properties, thermal conductivity and electrical resistivity values comparable to th...

Materials Chemistry and Physics

This study addresses the processing of near-net-shape, chemically homogeneous and fine-grained Ti... more This study addresses the processing of near-net-shape, chemically homogeneous and fine-grained Ti–3Al–2.5V components using vacuum hot-pressing. Two Ti–3Al–2.5V starting powders were considered. On one side, hydride–dehydride (HDH) elemental titanium was blended with an HDH Ti–6Al–4V prealloyed powder. On the other side, an Al:V master alloy was added to the HDH elemental titanium powder. The powders were processed applying a uniaxial pressure of 30 MPa. The sintering temperatures studied varied between 900 °C and 1300 °C. The relative density of the samples increased with processing temperature and almost fully dense materials were obtained. The increase of the sintering temperature led also to a strong reaction between the titanium powders and the processing tools. This phenomenon occurred particularly with boron nitride (BN) coating, which was used to prevent the direct contact between titanium and graphite tools. The flexural properties of the Ti–3Al–2.5V samples increased with ...

Revista de Metalurgia, 2011

El desarrollo de las nuevas tecnologías de extracción de titanio, que producen titanio elemental ... more El desarrollo de las nuevas tecnologías de extracción de titanio, que producen titanio elemental directamente en forma de polvo, sitúan a la pulvimetalurgia en un puesto estratégico para la fabricación de componentes de titanio. La disminución de coste del material base, junto a la economía de los procesos pulvimetalúrgicos, hacen más viable la diversificación de la industria del titanio, lo que permitiría alcanzar volúmenes de producción capaces de popularizar el metal y estabilizar su precio. En este trabajo se muestran algunas de las técnicas pulvimetalúrgicas empleadas para la fabricación de componentes de titanio a partir de los dos enfoques clásicos de mezcla de polvos elementales y el uso de polvos prealeados. Se describen entre otras las técnicas de prensado y sinterización convencional o compactación isostática en frío y caliente, que tratan de competir con las técnicas de procesado convencional, y se muestran algunas aplicaciones actuales y potenciales.

Materials & Design, 2014

Titanium is characterised by two contrasting aspects: outstanding combination of properties and h... more Titanium is characterised by two contrasting aspects: outstanding combination of properties and high production costs which confine its application to high demanding sectors. The employment of powder metallurgy (P/M) techniques is one creative alternative to lower the final costs of titanium products due to some intrinsic advantages of P/M such as high yield of material and limited machining requirement. In this work the performances of Hydride-DeHydride (HDH) and sponge elemental titanium products obtained by cold uniaxial pressing and sintering are compared. It is found that the two materials achieved similar relative density values but HDH shows much better mechanical performances.

Materials Science Forum, 2013

ABSTRACT Titanium is characterised by an outstanding combination of properties like high strength... more ABSTRACT Titanium is characterised by an outstanding combination of properties like high strength, low density, good corrosion resistance and biocompatibility. Nonetheless, widespread employment of titanium at the industrial level, especially in the automotive industry, has not been achieved yet because of its high extraction and production costs. Consequently, titanium finds applications mainly in high demanding sectors, such as the aerospace industry or to produce biomedical devices, where the final high cost is not the principal issue. The processing of titanium and its alloys by means of powder metallurgy (PM) techniques is claimed to be a suitable way to reduce the fabrication cost of titanium products as well as offering the possibility to design new alloys which are difficult to obtain using the conventional metallurgical route, for example due to segregation of heavy alloying elements. This work deals with the processing of hydride-dehydride elemental titanium powder by means of different PM methods and aims at investigating the processing of near net-shape, chemically-homogeneous and fine-grained titanium-based components. In particular, properties achievable (i.e. relative density, microstructure and mechanical properties) and problems related to the processing of elemental titanium, by both the conventional PM route of pressing and sintering and the advanced PM method of hot-pressing, are presented.

Key Engineering Materials, 2012

Powder metallurgy (PM) permits to obtain titanium alloys with properties and microstructures clos... more Powder metallurgy (PM) permits to obtain titanium alloys with properties and microstructures close to ingot metallurgy products. However, residual porosity is normally present in the products produced by the PM route of powder pressing and sintering (P&S)\, and this needs to be reduced by using post-sintering process step such as hot isostatic pressing (HIP) and forging. In this study, the microstructural and mechanical property changes caused by HIP of samples of two alloys, near-α Ti-3Al-2.5V alloy and α+β Ti-6Al-4V, produced by P&S route were investigated. Two types of powders were utilised: prealloyed powders and blend of elemental titanium powder and master alloy powder. Four conditions defined by HIP temperature, pressure and time were used to HIP the sintered samples with two geometries. The results show that, independent of the HIP conditions used, HIP increased the relative density of the samples to approximately 97.5% and their hardness by 30-50 HV depending on the HIP condition. However, HIP at 1000ºC changes the fracture mode of the sintered samples from ductile to brittle.

Sadler/Light, 2013

ABSTRACT Over the last few decades the grain refinement practice using Ti based chemical addition... more ABSTRACT Over the last few decades the grain refinement practice using Ti based chemical additions (Al-Ti-B) is well established for wrought Al alloys, however in the case of Al-Si casting alloys, the practice of adding grain refiners and the impact on castability is not well established in industries, due primarily to chemical instability of conventionally known Ti based grain refiner with Si element in the melt. Research at Brunel University has identified a novel chemical composition that can effectively refine grain structure of Al-Si castings alloys. First, the effect of addition of grain refiner, in the form of powder addition, on micro structural and mechanical properties of LM6 (A423) and LM25 (A356) alloys was investigated. Afterwards, a suitable method to produce the novel grain refiner in the form of master alloy was developed and the effect of addition of master alloy on grain refinement of the previously mentioned Al-Si alloys was studied.

The development of low-cost Titanium alloys can be tackled by reducing the cost of the raw materi... more The development of low-cost Titanium alloys can be tackled by reducing the cost of the raw materials a nd/or reducing processing costs. Material savings can be performed replacing V by additions of other beta-phase stabi lizers as Fe and Cr, while reducing processing costs are possible du e to the use of near-net-shape techniques as Powder Metallurgy. Both aspects have

Powder Metallurgy, 2011

ABSTRACT This work studies a set of low cost beta alloys with the composition Ti?7Fe, processed b... more ABSTRACT This work studies a set of low cost beta alloys with the composition Ti?7Fe, processed by conventional powder metallurgy (PM). The materials were prepared by conventional blending of elemental Ti hydride?dehydride powder with three different Fe powder additions: water atomised Fe, Fe carbonyl and master alloy Fe?25Ti. The optimal sintering behaviour and the best mechanical properties were attained with the use of Fe carbonyl powder, which reached a sintered density of up to 93% of the theoretical density, with UTS values of 800 MPa in the ?as sintered? condition. Coarse water atomised powder particles promoted reactive sintering, and coarse porosity was found due to the coalescence of Kirkendall porosity and by the pores generated during the exothermic reaction between Ti and Fe. The addition of Fe?25Ti produced brittle materials, as its low purity (91?5%) was found to be unsuitable for formulating Ti alloys.

Powder Metallurgy, 2011

ABSTRACT The use and development of titanium and titanium alloys have been strongly correlated to... more ABSTRACT The use and development of titanium and titanium alloys have been strongly correlated to high technology industries where costs are not the most important aspect. Titanium could see its market grow by the application of lower cost and more efficient processing methods such as powder metallurgy. This work deals with the characterisation of two types of powders: commercial prealloyed powder and powder produced from master alloy combining mechanical milling and conventional blending to adjust the particle size. The characteristics of the powders, sintering behaviour and final properties of the parts indicate that the master alloy approach leads to better compressibility than the prealloyed powders and, therefore, to lower dimensional change during sintering. The most important result is that it is possible to obtain Ti alloys with properties similar to or better than alloys from prealloyed powders and to obtain homogeneous microstructures, which allows the composition to be adjusted to requirements.

Materials Characterization, 2013

ABSTRACT This study addresses the processing of near-net-shape, chemically homogeneous and fine-g... more ABSTRACT This study addresses the processing of near-net-shape, chemically homogeneous and fine-grained Ti–3Al–2.5V components using vacuum hot-pressing. Two Ti–3Al–2.5V starting powders were considered. On one side, hydride–dehydride (HDH) elemental titanium was blended with an HDH Ti–6Al–4V prealloyed powder. On the other side, an Al:V master alloy was added to the HDH elemental titanium powder. The powders were processed applying a uniaxial pressure of 30 MPa. The sintering temperatures studied varied between 900 °C and 1300 °C. The relative density of the samples increased with processing temperature and almost fully dense materials were obtained. The increase of the sintering temperature led also to a strong reaction between the titanium powders and the processing tools. This phenomenon occurred particularly with boron nitride (BN) coating, which was used to prevent the direct contact between titanium and graphite tools. The flexural properties of the Ti–3Al–2.5V samples increased with vacuum hot-pressing temperature and are comparable to those specified for wrought titanium medical devices. Therefore, the produced materials are promising candidates for load bearing applications as implant materials.

En primer lugar me gustaría dar las gracias a todos los miembros del departamento de Ciencia e In... more En primer lugar me gustaría dar las gracias a todos los miembros del departamento de Ciencia e Ingeniería de Materiales e Ingeniería Química (profesores, técnicos y secretarias) ya que cada uno, con su particular actitud, me ha motivado para afrontar y terminar el reto de la tesis doctoral.

Key Engineering Materials, 2016

El desarrollo de las nuevas tecnologías de extracción de titanio, que producen titanio elemental ... more El desarrollo de las nuevas tecnologías de extracción de titanio, que producen titanio elemental directamente en forma de polvo, sitúan a la pulvimetalurgia en un puesto estratégico para la fabricación de componentes de titanio. La disminución de coste del material base, junto a la economía de los procesos pulvimetalúrgicos, hacen más viable la diversificación de la industria del titanio, lo que permitiría alcanzar volúmenes de producción capaces de popularizar el metal y estabilizar su precio. En este trabajo se muestran algunas de las técnicas pulvimetalúrgicas empleadas para la fabricación de componentes de titanio a partir de los dos enfoques clásicos de mezcla de polvos elementales y el uso de polvos prealeados. Se describen entre otras las técnicas de prensado y sinterización convencional o compactación isostática en frío y caliente, que tratan de competir con las técnicas de procesado convencional, y se muestran algunas aplicaciones actuales y potenciales.

The applicability of irregular prealloyed Ti-6Al-4V powder for the fabrication of titanium produc... more The applicability of irregular prealloyed Ti-6Al-4V powder for the fabrication of titanium products by pressing and sintering and its employment as a master alloy to obtain the Ti-3Al-2.5V alloy was studied. To this end, the starting powders were characterised by dilatometry, differential thermal analysis and XRD. Green samples were obtained by cold uniaxial pressing, and the evolution of the microstructure over the sintering temperature range 900-1400°C was studied. The variation of the final density and mechanical properties with the sintering temperature was considered. Based on the study carried out, it can be stated that more reliable powders are needed to open the titanium market to new applications. A relative density of 95% and diverse microstructural features and mechanical properties equivalent to those of biomedical devices can be obtained by the pressing and sintering route.

Materials Chemistry and Physics

Cast Al alloys are important structural materials for the lightweighting of cars and, consequentl... more Cast Al alloys are important structural materials for the lightweighting of cars and, consequently, reduction of greenhouse gases emission and pollution. The microstructure and properties of cast Al alloys could be further improved by means of grain refinement, practise which cannot efficiently be performed with common Al-Ti-B grain refiners used for wrought Al alloys. In this work we proposed the employment of Nb+B inoculation as an alternative for the refinement of the primary α-Al dendrites of cast Al-Si alloy by studying the grain refinement induced by the Nb+B inoculants as a function of key aspects such as cooling rate, fading behaviour and simulated recyclability tests. It is found that the grain size of the Nb+B inoculated material is noticeably less sensitive to the cooling rate. Nb+B inoculants are still present and promote the refinement of the Al-12Si alloy even after few hours of contact time, although some fading is detected. Furthermore, Nb+B inoculants are also still...

Journal of Materials Processing Technology

This study deals with the grain refinement of the LM25 alloy by means of the addition of a 96Al-2... more This study deals with the grain refinement of the LM25 alloy by means of the addition of a 96Al-2Nb-2B master alloy. Nb-based intermetallics contained in the master alloy act as potent heterogeneous nucleation substrate for the nucleation of primary Al dendrites. The addition of the 96Al-2Nb-2B master alloy to the LM25 alloy permits to significantly refine its microstructural features and the refinement is achieved in a great range of cooling rates. The formation of columnar grains at slow cooling rates is prevented.

Metal Powder Report, 2008

Materials science & engineering. C, Materials for biological applications, 2015

Titanium and its alloys are characterized by an exceptional combination of properties like high s... more Titanium and its alloys are characterized by an exceptional combination of properties like high strength, good corrosion resistance and biocompatibility which makes them suitable materials for biomedical prosthesis and devices. The wrought Ti-6Al-4V alloy is generally favored in comparison to other metallic biomaterials due to its relatively low elastic modulus and it has been long used to obtain products for biomedical applications. In this work an alternative route to fabricate biomedical implants made out of the Ti-6Al-4V alloy is investigated. Specifically, the feasibility of the conventional powder metallurgy route of cold uniaxial pressing and sintering is addressed by considering two types of powders (i.e. blended elemental and prealloyed). The characterization of physical properties, chemical analysis, mechanical behavior and microstructural analysis is carried out in-depth and the properties are correlated among them. On the base of the results found, the produced alloys ar...

Materials and Design

A comparison between the properties achievable by processing the Ti–6Al–4V alloys by means of two... more A comparison between the properties achievable by processing the Ti–6Al–4V alloys by means of two powder metallurgy approaches, precisely prealloyed and master alloy addition, was carried out. Prealloyed and master alloy addition hydride–dehydride powders characterised by an irregular morphology were shaped by means of cold uniaxial pressing and high vacuum sintered considering the effect of the variation of the sintering temperature and of the dwell time. Generally, the higher the temperature and the longer the dwell time, the higher the relative density and, consequently, the better the mechanical performances. Nevertheless, a higher processing temperature or a longer time leads also to some interstitials pick-up, especially oxygen, which affects the mechanical behaviour and, in particular, lowers the ductility. Although some residual porosity is left by the pressing and sintering route, mechanical properties, thermal conductivity and electrical resistivity values comparable to th...

Materials Chemistry and Physics

This study addresses the processing of near-net-shape, chemically homogeneous and fine-grained Ti... more This study addresses the processing of near-net-shape, chemically homogeneous and fine-grained Ti–3Al–2.5V components using vacuum hot-pressing. Two Ti–3Al–2.5V starting powders were considered. On one side, hydride–dehydride (HDH) elemental titanium was blended with an HDH Ti–6Al–4V prealloyed powder. On the other side, an Al:V master alloy was added to the HDH elemental titanium powder. The powders were processed applying a uniaxial pressure of 30 MPa. The sintering temperatures studied varied between 900 °C and 1300 °C. The relative density of the samples increased with processing temperature and almost fully dense materials were obtained. The increase of the sintering temperature led also to a strong reaction between the titanium powders and the processing tools. This phenomenon occurred particularly with boron nitride (BN) coating, which was used to prevent the direct contact between titanium and graphite tools. The flexural properties of the Ti–3Al–2.5V samples increased with ...

Revista de Metalurgia, 2011

El desarrollo de las nuevas tecnologías de extracción de titanio, que producen titanio elemental ... more El desarrollo de las nuevas tecnologías de extracción de titanio, que producen titanio elemental directamente en forma de polvo, sitúan a la pulvimetalurgia en un puesto estratégico para la fabricación de componentes de titanio. La disminución de coste del material base, junto a la economía de los procesos pulvimetalúrgicos, hacen más viable la diversificación de la industria del titanio, lo que permitiría alcanzar volúmenes de producción capaces de popularizar el metal y estabilizar su precio. En este trabajo se muestran algunas de las técnicas pulvimetalúrgicas empleadas para la fabricación de componentes de titanio a partir de los dos enfoques clásicos de mezcla de polvos elementales y el uso de polvos prealeados. Se describen entre otras las técnicas de prensado y sinterización convencional o compactación isostática en frío y caliente, que tratan de competir con las técnicas de procesado convencional, y se muestran algunas aplicaciones actuales y potenciales.

Materials & Design, 2014

Titanium is characterised by two contrasting aspects: outstanding combination of properties and h... more Titanium is characterised by two contrasting aspects: outstanding combination of properties and high production costs which confine its application to high demanding sectors. The employment of powder metallurgy (P/M) techniques is one creative alternative to lower the final costs of titanium products due to some intrinsic advantages of P/M such as high yield of material and limited machining requirement. In this work the performances of Hydride-DeHydride (HDH) and sponge elemental titanium products obtained by cold uniaxial pressing and sintering are compared. It is found that the two materials achieved similar relative density values but HDH shows much better mechanical performances.

Materials Science Forum, 2013

ABSTRACT Titanium is characterised by an outstanding combination of properties like high strength... more ABSTRACT Titanium is characterised by an outstanding combination of properties like high strength, low density, good corrosion resistance and biocompatibility. Nonetheless, widespread employment of titanium at the industrial level, especially in the automotive industry, has not been achieved yet because of its high extraction and production costs. Consequently, titanium finds applications mainly in high demanding sectors, such as the aerospace industry or to produce biomedical devices, where the final high cost is not the principal issue. The processing of titanium and its alloys by means of powder metallurgy (PM) techniques is claimed to be a suitable way to reduce the fabrication cost of titanium products as well as offering the possibility to design new alloys which are difficult to obtain using the conventional metallurgical route, for example due to segregation of heavy alloying elements. This work deals with the processing of hydride-dehydride elemental titanium powder by means of different PM methods and aims at investigating the processing of near net-shape, chemically-homogeneous and fine-grained titanium-based components. In particular, properties achievable (i.e. relative density, microstructure and mechanical properties) and problems related to the processing of elemental titanium, by both the conventional PM route of pressing and sintering and the advanced PM method of hot-pressing, are presented.

Key Engineering Materials, 2012

Powder metallurgy (PM) permits to obtain titanium alloys with properties and microstructures clos... more Powder metallurgy (PM) permits to obtain titanium alloys with properties and microstructures close to ingot metallurgy products. However, residual porosity is normally present in the products produced by the PM route of powder pressing and sintering (P&S)\, and this needs to be reduced by using post-sintering process step such as hot isostatic pressing (HIP) and forging. In this study, the microstructural and mechanical property changes caused by HIP of samples of two alloys, near-α Ti-3Al-2.5V alloy and α+β Ti-6Al-4V, produced by P&S route were investigated. Two types of powders were utilised: prealloyed powders and blend of elemental titanium powder and master alloy powder. Four conditions defined by HIP temperature, pressure and time were used to HIP the sintered samples with two geometries. The results show that, independent of the HIP conditions used, HIP increased the relative density of the samples to approximately 97.5% and their hardness by 30-50 HV depending on the HIP condition. However, HIP at 1000ºC changes the fracture mode of the sintered samples from ductile to brittle.

Sadler/Light, 2013

ABSTRACT Over the last few decades the grain refinement practice using Ti based chemical addition... more ABSTRACT Over the last few decades the grain refinement practice using Ti based chemical additions (Al-Ti-B) is well established for wrought Al alloys, however in the case of Al-Si casting alloys, the practice of adding grain refiners and the impact on castability is not well established in industries, due primarily to chemical instability of conventionally known Ti based grain refiner with Si element in the melt. Research at Brunel University has identified a novel chemical composition that can effectively refine grain structure of Al-Si castings alloys. First, the effect of addition of grain refiner, in the form of powder addition, on micro structural and mechanical properties of LM6 (A423) and LM25 (A356) alloys was investigated. Afterwards, a suitable method to produce the novel grain refiner in the form of master alloy was developed and the effect of addition of master alloy on grain refinement of the previously mentioned Al-Si alloys was studied.

The development of low-cost Titanium alloys can be tackled by reducing the cost of the raw materi... more The development of low-cost Titanium alloys can be tackled by reducing the cost of the raw materials a nd/or reducing processing costs. Material savings can be performed replacing V by additions of other beta-phase stabi lizers as Fe and Cr, while reducing processing costs are possible du e to the use of near-net-shape techniques as Powder Metallurgy. Both aspects have

Powder Metallurgy, 2011

ABSTRACT This work studies a set of low cost beta alloys with the composition Ti?7Fe, processed b... more ABSTRACT This work studies a set of low cost beta alloys with the composition Ti?7Fe, processed by conventional powder metallurgy (PM). The materials were prepared by conventional blending of elemental Ti hydride?dehydride powder with three different Fe powder additions: water atomised Fe, Fe carbonyl and master alloy Fe?25Ti. The optimal sintering behaviour and the best mechanical properties were attained with the use of Fe carbonyl powder, which reached a sintered density of up to 93% of the theoretical density, with UTS values of 800 MPa in the ?as sintered? condition. Coarse water atomised powder particles promoted reactive sintering, and coarse porosity was found due to the coalescence of Kirkendall porosity and by the pores generated during the exothermic reaction between Ti and Fe. The addition of Fe?25Ti produced brittle materials, as its low purity (91?5%) was found to be unsuitable for formulating Ti alloys.

Powder Metallurgy, 2011

ABSTRACT The use and development of titanium and titanium alloys have been strongly correlated to... more ABSTRACT The use and development of titanium and titanium alloys have been strongly correlated to high technology industries where costs are not the most important aspect. Titanium could see its market grow by the application of lower cost and more efficient processing methods such as powder metallurgy. This work deals with the characterisation of two types of powders: commercial prealloyed powder and powder produced from master alloy combining mechanical milling and conventional blending to adjust the particle size. The characteristics of the powders, sintering behaviour and final properties of the parts indicate that the master alloy approach leads to better compressibility than the prealloyed powders and, therefore, to lower dimensional change during sintering. The most important result is that it is possible to obtain Ti alloys with properties similar to or better than alloys from prealloyed powders and to obtain homogeneous microstructures, which allows the composition to be adjusted to requirements.