title: Effect of thermomechanical processing on the mechanical properties of cost-effective powder metallurgy titanium-based materials

authors: Romero Villarreal, Carlos

subjects: Titanium alloys

abstract: Despite their excellent balance of properties, titanium alloys are still a niche material whose range of applications is limited by the high cost of their manufacturing. With recent developments, powder metallurgy (PM) approaches, in particular the blended elemental (BE) route, are able to reduce considerably the cost of manufacturing while keeping a reasonable performance, mostly in terms of tensile strength and ductility. The cost reduction of the BE approach derives from the simplification of the process by removing a large amount of re-melting and ingot breakdown operations, regardless of the use of the approach as a net-shape technology. However, in terms of fatigue behaviour, the performance of these alloys is generally worse than conventional processes unless additional steps are applied. This thesis aims to study the mechanical behaviour, with emphasis on the fatigue behaviour, of two cost-effective titanium alloys in order to find the key processing, microstructural and texture parameters that control their performance, with the goal of achieving similar properties to conventional wrought alloys with a reduction of the cost. These alloys, a conventional Ti-6Al-4V composition and a non-conventional low-cost Ti-5Fe composition, were processed following the blended elemental approach and thermomechanical processing, via hot extrusion, was subsequently applied. A variety of microstructures and textures were achieved under different extrusion conditions, which were further modified by applying additional heat treatments.
The tensile behaviour of both Ti-6Al-4V and Ti-5Fe alloys is strongly dependent on the processing conditions. Fully lamellar microstructures (from processing in the β phase) showed similar strength levels but considerably lower ductility compared to alloys with bimodal microstructures and stronger texture (from processing in the α+β phase). In the case of Ti-5Fe, moreover, there was a Fe partitioning effect that, when the processing temperature is low enough, leads to a sharp increase in both the strength and the ability to deform past necking took place. Heat treatments in Ti-6Al-4V alloys were useful in order to increase the strength as well as to keep the ductility similar or even increase it to higher values. The tensile behaviour of Ti-5Fe alloys was more tuneable, achieving higher differences in strength and ductility with the as-extruded conditions, even though this happened by trading-off. Overall, Ti-6Al-4V alloys outperformed Ti-5Fe alloys as their strength was typically higher (associated to their higher amount of alloying elements) as well as their ductility, due to their higher ability to deform past necking, which was very limited for Ti-5Fe alloys in most cases.
The fatigue behaviour of the alloys was found to as dependent on the chemistry as on the microstructure and the texture. While the Ti-6Al-4V alloy is not affected by the residual porosity left after thermomechanical processing, the Ti-5Fe alloy shows pores in the region where fatigue damage begins. In the Ti-6Al-4V alloy, it was found that texturing had a much stronger effect on the fatigue strength of the alloy than microstructural refinement. Therefore, the PM Ti-6Al-4V alloy processed in the α+β phase had a higher fatigue strength than alloys processed in the β phase, regardless if the latter has fully lamellar or acicular microstructure. In the case of the Ti-5Fe alloy, two conditions processed in the α+β phase were studied, and it was found that the Fe concentration in transformed β (which is higher when there is a larger amount of primary α) had a critical effect on the fatigue behaviour, overriding the effect of texture or microstructural refinement. This leads to the Ti-5Fe alloy processed at a lower temperature in the α+β phase showing a much lower fatigue strength compared with the alloy processed just below the β transus, despite the fact that its texture and microstructure were, in theory, optimal for fatigue behaviour.
It is concluded that, in order to process cost-effective Ti alloys with fatigue performance comparable to wrought alloys with conventional compositions (with fatigue strength in the range of 650 MPa), thermomechanical processing in the α+β phase must be applied to make use of the strong texturing of the alloy. However, in the case of alloys containing β-eutectoid elements like Fe, the range of temperatures is limited as the partitioning of the alloying element results in severe reduction of the fatigue strength.

text: Effect of thermomechanical processing on the mechanical properties of cost-effective powder metallurgy titanium-based materials Despite their excellent balance of properties, titanium alloys are still a niche material whose range of applications is limited by the high cost of their manufacturing. With recent developments, powder metallurgy (PM) approaches, in particular the blended elemental (BE) route, are able to reduce considerably the cost of manufacturing while keeping a reasonable performance, mostly in terms of tensile strength and ductility. The cost reduction of the BE approach derives from the simplification of the process by removing a large amount of re-melting and ingot breakdown operations, regardless of the use of the approach as a net-shape technology. However, in terms of fatigue behaviour, the performance of these alloys is generally worse than conventional processes unless additional steps are applied. This thesis aims to study the mechanical behaviour, with emphasis on the fatigue behaviour, of two cost-effective titanium alloys in order to find the key processing, microstructural and texture parameters that control their performance, with the goal of achieving similar properties to conventional wrought alloys with a reduction of the cost. These alloys, a conventional Ti-6Al-4V composition and a non-conventional low-cost Ti-5Fe composition, were processed following the blended elemental approach and thermomechanical processing, via hot extrusion, was subsequently applied. A variety of microstructures and textures were achieved under different extrusion conditions, which were further modified by applying additional heat treatments.
The tensile behaviour of both Ti-6Al-4V and Ti-5Fe alloys is strongly dependent on the processing conditions. Fully lamellar microstructures (from processing in the β phase) showed similar strength levels but considerably lower ductility compared to alloys with bimodal microstructures and stronger texture (from processing in the α+β phase). In the case of Ti-5Fe, moreover, there was a Fe partitioning effect that, when the processing temperature is low enough, leads to a sharp increase in both the strength and the ability to deform past necking took place. Heat treatments in Ti-6Al-4V alloys were useful in order to increase the strength as well as to keep the ductility similar or even increase it to higher values. The tensile behaviour of Ti-5Fe alloys was more tuneable, achieving higher differences in strength and ductility with the as-extruded conditions, even though this happened by trading-off. Overall, Ti-6Al-4V alloys outperformed Ti-5Fe alloys as their strength was typically higher (associated to their higher amount of alloying elements) as well as their ductility, due to their higher ability to deform past necking, which was very limited for Ti-5Fe alloys in most cases.
The fatigue behaviour of the alloys was found to as dependent on the chemistry as on the microstructure and the texture. While the Ti-6Al-4V alloy is not affected by the residual porosity left after thermomechanical processing, the Ti-5Fe alloy shows pores in the region where fatigue damage begins. In the Ti-6Al-4V alloy, it was found that texturing had a much stronger effect on the fatigue strength of the alloy than microstructural refinement. Therefore, the PM Ti-6Al-4V alloy processed in the α+β phase had a higher fatigue strength than alloys processed in the β phase, regardless if the latter has fully lamellar or acicular microstructure. In the case of the Ti-5Fe alloy, two conditions processed in the α+β phase were studied, and it was found that the Fe concentration in transformed β (which is higher when there is a larger amount of primary α) had a critical effect on the fatigue behaviour, overriding the effect of texture or microstructural refinement. This leads to the Ti-5Fe alloy processed at a lower temperature in the α+β phase showing a much lower fatigue strength compared with the alloy processed just below the β transus, despite the fact that its texture and microstructure were, in theory, optimal for fatigue behaviour.
It is concluded that, in order to process cost-effective Ti alloys with fatigue performance comparable to wrought alloys with conventional compositions (with fatigue strength in the range of 650 MPa), thermomechanical processing in the α+β phase must be applied to make use of the strong texturing of the alloy. However, in the case of alloys containing β-eutectoid elements like Fe, the range of temperatures is limited as the partitioning of the alloying element results in severe reduction of the fatigue strength.

year: 2020

title: Total site utility systems optimisation for milk powder production

authors: Walmsley, Timothy Gordon

abstract: This study applies the Total Site Heat Integration method, in conjunction with a detailed process and utility model, to investigate three methods to increase the energy efficiency of the utility supply system for milk powder production. Sequentially explored opportunities are: (1) increasing boiler efficiency through condensing economisers, (2) waste heat recovery from the chiller unit, and (3) Combined Heat and Power (CHP) for electricity production. The basis for the analysis is the anticipated future milk powder process design, which incorporates results from recent studies that have focused on improving the process design and integration of the heat treatment and evaporator systems and recovering heat from the spray dryer exhaust, which show a combined specific fuel consumption reduction of 29.6 % and a relatively small increase in electricity use of 4.5 %. To maximise boiler efficiency, the study concludes that a condensing economiser for the flue gas can be indirectly matched with heating fluidised bed air flows through the boiler condensate system, which results in specific fuel use reduction of 227 MJ/tp. Chiller waste heat can be upgraded and integrated as a heat source to replace the equivalent specific fuel use of 101 MJ/tp through integration with the site low temperature hot water loop. By designing the steam system to maximise electricity generation in a new turbine, results show that 51 % of the site’s electricity demand may be satisfied by CHP. The combined effect of implementing these three utility systems opportunities is a specific fuel use of 3,868 MJ/tₚ, of which 530 MJ/tₚ result from electricity production, and a specific grid electricity demand of 113.4 kWh/tₚ.

text: Total site utility systems optimisation for milk powder production This study applies the Total Site Heat Integration method, in conjunction with a detailed process and utility model, to investigate three methods to increase the energy efficiency of the utility supply system for milk powder production. Sequentially explored opportunities are: (1) increasing boiler efficiency through condensing economisers, (2) waste heat recovery from the chiller unit, and (3) Combined Heat and Power (CHP) for electricity production. The basis for the analysis is the anticipated future milk powder process design, which incorporates results from recent studies that have focused on improving the process design and integration of the heat treatment and evaporator systems and recovering heat from the spray dryer exhaust, which show a combined specific fuel consumption reduction of 29.6 % and a relatively small increase in electricity use of 4.5 %. To maximise boiler efficiency, the study concludes that a condensing economiser for the flue gas can be indirectly matched with heating fluidised bed air flows through the boiler condensate system, which results in specific fuel use reduction of 227 MJ/tp. Chiller waste heat can be upgraded and integrated as a heat source to replace the equivalent specific fuel use of 101 MJ/tp through integration with the site low temperature hot water loop. By designing the steam system to maximise electricity generation in a new turbine, results show that 51 % of the site’s electricity demand may be satisfied by CHP. The combined effect of implementing these three utility systems opportunities is a specific fuel use of 3,868 MJ/tₚ, of which 530 MJ/tₚ result from electricity production, and a specific grid electricity demand of 113.4 kWh/tₚ.

year: 2016

title: Ko au tēnei

authors: Temara, Pou

subjects: Tuhinga auaha

abstract: He puha tēnei, he momo rotarota. E kōrero ana tēnei puha mō te pepeha o Tūhoe, arā, ko Maungapōhatu te maunga, ko Waikare te awa ko Tamakaimoana te hapu, ko Taiturakina rāua ko Pōhokorua ngā tāngata, ko Tūhoe te iwi.

Kua roa tēnei pepeha e mau ana i ngā kākahu Māori o nehe, ā, nō ngā rautau ki muri te tawhito o te pepeha nei. Kua mate noa atu te hunga nā rātau i waihanga. Ko rātau e mōhio ana ki te horopaki i titoa ai ā rātau pepeha. Taka iho ki nāianei kāore anō kia rerekē ngā kupu o te pepeha.

Engari kua rerekē te ao me tōna tai, he whakatipuranga hou kua hua ake hai noho i te whenua. He rerekē ōnā whakaaro, he rerekē te ahurea. Kua roa e noho tahi ana ēnei whakatipuranga me ngā iwi huhua o te ao, he rauiwi te ahurea. Kua whakatōria hoki te whakaaro o aua ahurea maha ki te hinengaro o te Māori. Kua riro ngā whakaaro i te ao whānui koia nei kai te tohutohu i te whakaaro o te Māori o ēnei rā.

Me pēhea te whakauru atu i te whakaaro o mohoā nei ki te whakaaro o ukiuki, kia whai tikanga ai ki te ngākau o nāianei ki te pepeha o mua? Kua tawhito o rātau kākahu. E hia ngā kaupapa, ngā pakanga, ngā kaikiritanga, ngā mamae i roto i taua wā. Kua tae ki te wā hai whakamautanga mā ō nāianei Māori i ngā kākahu o ēnei rā ki ngā pepeha o mua, kia whai wāhi ai ki te ahurea me te whakaaro o ēnei rā.

Ehara i te mea me whakaae te iwi katoa ki ngā whakaaro kua tāpiritia ki te pepeha nei. Engari hai aha mā wai? Ko te rotarota he kupu nā te kaitito, he kupu motuhenga nō tōna ngākau, hai tohu i tāna titiro ki te ao, ā, kia uru atu ai ia ki te ao me ngā whakaaro o mua.

text: Ko au tēnei He puha tēnei, he momo rotarota. E kōrero ana tēnei puha mō te pepeha o Tūhoe, arā, ko Maungapōhatu te maunga, ko Waikare te awa ko Tamakaimoana te hapu, ko Taiturakina rāua ko Pōhokorua ngā tāngata, ko Tūhoe te iwi.

Kua roa tēnei pepeha e mau ana i ngā kākahu Māori o nehe, ā, nō ngā rautau ki muri te tawhito o te pepeha nei. Kua mate noa atu te hunga nā rātau i waihanga. Ko rātau e mōhio ana ki te horopaki i titoa ai ā rātau pepeha. Taka iho ki nāianei kāore anō kia rerekē ngā kupu o te pepeha.

Engari kua rerekē te ao me tōna tai, he whakatipuranga hou kua hua ake hai noho i te whenua. He rerekē ōnā whakaaro, he rerekē te ahurea. Kua roa e noho tahi ana ēnei whakatipuranga me ngā iwi huhua o te ao, he rauiwi te ahurea. Kua whakatōria hoki te whakaaro o aua ahurea maha ki te hinengaro o te Māori. Kua riro ngā whakaaro i te ao whānui koia nei kai te tohutohu i te whakaaro o te Māori o ēnei rā.

Me pēhea te whakauru atu i te whakaaro o mohoā nei ki te whakaaro o ukiuki, kia whai tikanga ai ki te ngākau o nāianei ki te pepeha o mua? Kua tawhito o rātau kākahu. E hia ngā kaupapa, ngā pakanga, ngā kaikiritanga, ngā mamae i roto i taua wā. Kua tae ki te wā hai whakamautanga mā ō nāianei Māori i ngā kākahu o ēnei rā ki ngā pepeha o mua, kia whai wāhi ai ki te ahurea me te whakaaro o ēnei rā.

Ehara i te mea me whakaae te iwi katoa ki ngā whakaaro kua tāpiritia ki te pepeha nei. Engari hai aha mā wai? Ko te rotarota he kupu nā te kaitito, he kupu motuhenga nō tōna ngākau, hai tohu i tāna titiro ki te ao, ā, kia uru atu ai ia ki te ao me ngā whakaaro o mua.

year: 2017