title: Turning waste into useful materials: fabrication of titanium alloy matrix composite from the Ti-6Al-4V swarf

authors: Zhai, Yutao

subjects: Ti-6Al-4V

abstract: The rapid development of various high-precision technologies in the aerospace, military and civil fields has put forward higher and higher requirements for the performance of materials. Traditional titanium alloys have become inadequate in the face of the comprehensive requirements of the application environment, so composite materials have increasingly become the focus of material researchers. titanium boride (TiB) is the most attractive reinforcement because of the balance and stability of its thermal, physical, and mechanical properties. Boron is essentially insoluble in Ti and its alloys, so it does not cause lattice embrittlement. In this thesis, a Ti-6Al-4V matrix composite reinforced by in-situ synthesized TiB whiskers were successfully fabricated by hot pressing of a mixture of Ti-6Al-4V alloy swarf and boron powder.

Hot pressing temperature significantly affects the densification and properties of the fabricated titanium alloy matrix composites. With the increase of hot processing temperature from 1050ºC to 1250ºC, the porosity of the fabricated composites was decreased from 12.8% to 2.7%. When the hot-pressing temperature was reached to 1250ºC, the Ti-6Al-4V-3TiB composite could be successfully consolidated with a well-bonded prior swarf boundaries (no obvious voids were appeared at the prior swarf boundary) and less TiBx phases (most are TiB), leading to a reasonable ultimate tensile strength (1121MPa) and yield stress (1028MPa) were achieved.

The amount of boron addition (1vol%, 3vol%, 5vol%, 7vol%) influences the phase constitutions, microstructure, and mechanical properties of the fabricated swarf Ti-6Al-4V matrix composites hot-pressed at 1250°C. The UTS and YS of the fabricated composite was first increased when the boron addition was increased from 1vol% to 3vol%, and then decreased with the boron addition was further increased to 7vol%. However, the ductility of the fabricated composites was continually decreased with increasing the boron addition amount, and this is attributed to the increase amount of agglomerated TiB reinforcement phases. The Ti-6Al-4V-3TiB (adding 3vol% of boron) had the optimal mechanical properties among all of the fabricated composites, having a UTS of 1108MPa-1127MPa, YS of 1025MPa-1034MPa, and a strain to fracture of 3.45% - 3.98%.

Comparing to the hot-pressed Ti-6Al-4V-3TiB composite, The post-processed (extrusion at 950°C) composite had finer grain size and smaller lamellar spacing, which contributed to slightly increase the composite’s ductility to 4.18% - 5.19%, but the strengthen effect of TiB reinforcement effect was reduced due to the formation of voids between the reinforcing phase and the matrix phase introduced by severe plastic deformation.

Various heat treatments were carried out for the hot-pressed and hot extruded Ti-6Al-4V-3TiB composites to tailor the composite’s microstructure for achieving desired strength-ductility balance. After STA-955 (955℃ 1 hr water quenching + 550℃ 6hrs air cooling) and STA-855 (855℃ 1 hr water quenching + 550℃ 6hrs air cooling), the strength of hot-pressed and hot extruded composites were improved, due to the acicular secondary α phase and nano-size secondary α phase, respectively. The hot extruded composite had the best mechanical properties after STA-955, with a UTS of 1259MPa - 1263MPa, YS of 1165MPa - 1170MPa, and a strain to fracture of 3.15% - 3.28%.

text: Turning waste into useful materials: fabrication of titanium alloy matrix composite from the Ti-6Al-4V swarf The rapid development of various high-precision technologies in the aerospace, military and civil fields has put forward higher and higher requirements for the performance of materials. Traditional titanium alloys have become inadequate in the face of the comprehensive requirements of the application environment, so composite materials have increasingly become the focus of material researchers. titanium boride (TiB) is the most attractive reinforcement because of the balance and stability of its thermal, physical, and mechanical properties. Boron is essentially insoluble in Ti and its alloys, so it does not cause lattice embrittlement. In this thesis, a Ti-6Al-4V matrix composite reinforced by in-situ synthesized TiB whiskers were successfully fabricated by hot pressing of a mixture of Ti-6Al-4V alloy swarf and boron powder.

Hot pressing temperature significantly affects the densification and properties of the fabricated titanium alloy matrix composites. With the increase of hot processing temperature from 1050ºC to 1250ºC, the porosity of the fabricated composites was decreased from 12.8% to 2.7%. When the hot-pressing temperature was reached to 1250ºC, the Ti-6Al-4V-3TiB composite could be successfully consolidated with a well-bonded prior swarf boundaries (no obvious voids were appeared at the prior swarf boundary) and less TiBx phases (most are TiB), leading to a reasonable ultimate tensile strength (1121MPa) and yield stress (1028MPa) were achieved.

The amount of boron addition (1vol%, 3vol%, 5vol%, 7vol%) influences the phase constitutions, microstructure, and mechanical properties of the fabricated swarf Ti-6Al-4V matrix composites hot-pressed at 1250°C. The UTS and YS of the fabricated composite was first increased when the boron addition was increased from 1vol% to 3vol%, and then decreased with the boron addition was further increased to 7vol%. However, the ductility of the fabricated composites was continually decreased with increasing the boron addition amount, and this is attributed to the increase amount of agglomerated TiB reinforcement phases. The Ti-6Al-4V-3TiB (adding 3vol% of boron) had the optimal mechanical properties among all of the fabricated composites, having a UTS of 1108MPa-1127MPa, YS of 1025MPa-1034MPa, and a strain to fracture of 3.45% - 3.98%.

Comparing to the hot-pressed Ti-6Al-4V-3TiB composite, The post-processed (extrusion at 950°C) composite had finer grain size and smaller lamellar spacing, which contributed to slightly increase the composite’s ductility to 4.18% - 5.19%, but the strengthen effect of TiB reinforcement effect was reduced due to the formation of voids between the reinforcing phase and the matrix phase introduced by severe plastic deformation.

Various heat treatments were carried out for the hot-pressed and hot extruded Ti-6Al-4V-3TiB composites to tailor the composite’s microstructure for achieving desired strength-ductility balance. After STA-955 (955℃ 1 hr water quenching + 550℃ 6hrs air cooling) and STA-855 (855℃ 1 hr water quenching + 550℃ 6hrs air cooling), the strength of hot-pressed and hot extruded composites were improved, due to the acicular secondary α phase and nano-size secondary α phase, respectively. The hot extruded composite had the best mechanical properties after STA-955, with a UTS of 1259MPa - 1263MPa, YS of 1165MPa - 1170MPa, and a strain to fracture of 3.15% - 3.28%.

year: 2020

title: Once despised now desired: innovative land use and management of multilayered Pumice Soils in the Taupo and Galatea areas, central North Island, New Zealand

authors: Lowe, David J.

abstract: The tour brings together innovative land use change and management associated with dairy farming, and land-based effluent disposal, on weakly weathered and multi-layered, glass-rich, Pumice Soils (Vitrands) in the Taupo and Galatea areas. These changes and their effects, together with environmental and sustainability issues, form a central theme of the trip. Four main stops are planned, two before lunch and two after: (1) plantation pine-to-dairy farm conversion and impacts, the Taupo eruption deposits (AD 232 ± 10) and the Taupo soil, at Tahorakuri; (2) overview of the application of secondary-treated wastewater and nitrogen leaching and uptake, Rotokawa; (3) a sequence of five Holocene tephras and buried soils, including Kaharoa eruption deposits (AD 1314 ± 12) and the Galatea soil, Smeith Farm, Murupara; and (4) enhancing pasture production on ‘new’ soils formed by excavating and mixing (‘flipping’) buried soil horizons (paleosols) on Smeith’s farm. During the trip − which helps mark Waikato University’s 50th anniversary − we will see a spectacular range of volcanic and fluvial landscapes and deposits, together with impacts of tectonism, as we traverse the famous Taupo Volcanic Zone ((TVZ) in the central volcanic region. Landforms and soils dominated by tephras (volcanic ash) become generally younger towards the loci of volcanic activity. Extensive areas of soils have been formed repeatedly from the fragmental eruptive products of the two most frequently active and productive rhyolite (silica-rich) volcanic centres known, namely Taupo and Okataina. Thus soil stratigraphy and upbuilding pedogenesis form a second theme on the trip. The first part of the guidebook thus contains sections including (i) volcanism and its products, (ii) Quaternary volcanism in TVZ including deposits erupted recently from Taupo and Tarawera volcanoes from which Pumice Soils have been formed, (iii) tephra-derived soils including Pumice Soils, their classification, special problems, and (low) fertility, (iv) allophane and its formation, and (v) the interplay between geological and pedological processes relating to tephras (upbuilding pedogenesis). The second part then comprises notes and illustrations pertaining to each stop (note that figure and table numbers are self-contained at each stop, or not used). Broad overviews of the region’s geology are covered by Leonard et al. (2010), and the soils are outlined by Rijkse and Guinto (2010) and S-map. Further compilations of data are available in tour guides by Lowe (2008) and Lowe et al. (2010).

text: Once despised now desired: innovative land use and management of multilayered Pumice Soils in the Taupo and Galatea areas, central North Island, New Zealand The tour brings together innovative land use change and management associated with dairy farming, and land-based effluent disposal, on weakly weathered and multi-layered, glass-rich, Pumice Soils (Vitrands) in the Taupo and Galatea areas. These changes and their effects, together with environmental and sustainability issues, form a central theme of the trip. Four main stops are planned, two before lunch and two after: (1) plantation pine-to-dairy farm conversion and impacts, the Taupo eruption deposits (AD 232 ± 10) and the Taupo soil, at Tahorakuri; (2) overview of the application of secondary-treated wastewater and nitrogen leaching and uptake, Rotokawa; (3) a sequence of five Holocene tephras and buried soils, including Kaharoa eruption deposits (AD 1314 ± 12) and the Galatea soil, Smeith Farm, Murupara; and (4) enhancing pasture production on ‘new’ soils formed by excavating and mixing (‘flipping’) buried soil horizons (paleosols) on Smeith’s farm. During the trip − which helps mark Waikato University’s 50th anniversary − we will see a spectacular range of volcanic and fluvial landscapes and deposits, together with impacts of tectonism, as we traverse the famous Taupo Volcanic Zone ((TVZ) in the central volcanic region. Landforms and soils dominated by tephras (volcanic ash) become generally younger towards the loci of volcanic activity. Extensive areas of soils have been formed repeatedly from the fragmental eruptive products of the two most frequently active and productive rhyolite (silica-rich) volcanic centres known, namely Taupo and Okataina. Thus soil stratigraphy and upbuilding pedogenesis form a second theme on the trip. The first part of the guidebook thus contains sections including (i) volcanism and its products, (ii) Quaternary volcanism in TVZ including deposits erupted recently from Taupo and Tarawera volcanoes from which Pumice Soils have been formed, (iii) tephra-derived soils including Pumice Soils, their classification, special problems, and (low) fertility, (iv) allophane and its formation, and (v) the interplay between geological and pedological processes relating to tephras (upbuilding pedogenesis). The second part then comprises notes and illustrations pertaining to each stop (note that figure and table numbers are self-contained at each stop, or not used). Broad overviews of the region’s geology are covered by Leonard et al. (2010), and the soils are outlined by Rijkse and Guinto (2010) and S-map. Further compilations of data are available in tour guides by Lowe (2008) and Lowe et al. (2010).

year: 2014-12-02

title: Te Nahi o Te Taniwha: Teeth of the Taniwha

authors: Rout, Matthew

abstract: This report outlines the scope of the project He oranga whānau: mahi ngātahi Whānau livelihoods within the context of work and Māori economies of wellbeing, which has been funded by Ngā Pae o te Māramatanga—the New Zealand Māori Centre of Research Excellence. Its purpose is to set the direction and design for the research project. To say the creation of such economies will be a complex task is an understatement. Three factors make this task a ‘wicked problem’.

text: Te Nahi o Te Taniwha: Teeth of the Taniwha This report outlines the scope of the project He oranga whānau: mahi ngātahi Whānau livelihoods within the context of work and Māori economies of wellbeing, which has been funded by Ngā Pae o te Māramatanga—the New Zealand Māori Centre of Research Excellence. Its purpose is to set the direction and design for the research project. To say the creation of such economies will be a complex task is an understatement. Three factors make this task a ‘wicked problem’.

year: 2022