title: Additive manufacturing of Ti64 alloy in-situ modified with additions of boron or oxygen

authors: Jackson, Benjamin Ivan

subjects: Additive manufacturing

abstract: Selective laser melting (SLM) is a metal additive manufacturing process that enables the production of complex, near net shape, parts with fully functional mechanical properties. The use of titanium alloys in SLM is a good fit due to a high material utilisation and net shape production with this expensive material. While titanium alloys have attractive properties of high specific strength and excellent corrosion resistance, these and other attributes may be modified through various methods for further improvements of the material. Strengthening mechanisms of interstitial hardening and particulate reinforcement are viable approaches for enhancing titanium alloys, however these often increase processing difficulty. Near net shape processes, like SLM, have the potential to produce functional parts with these modified properties.
This study explored the use of SLM for the fabrication of titanium parts, modified in-situ during processing with small amounts of boron or oxygen to develop enhanced properties. The in-situ incorporation of these different elements was performed during SLM using blended powders. Simple mixing of feedstock Ti64 alloy powder with small amounts of either amorphous boron or TiO₂, and subsequent SLM consolidation, has the potential to develop interstitial (oxygen) and particulate (boron) strengthened materials. 
This work analytically compares the properties of samples created using different process parameters, related through energy density. By examining variation in porosity and hardness with respect to these process parameters, it was possible to establish optimum processing conditions for manufacturing the in-situ modified material. Novel samples were developed for SLM that simplify the multi-level, multi-factor investigation of these process parameters into a single specimen for easy preparation and testing. Further investigation of how processing may influence the distribution and homogeneity of the modified material was studied through the influence of stress relief and sub-beta transus annealing heat treatments. Characterisation of these materials and treatment conditions were performed to determine the effect the additives have on the mechanical and wear properties. 
Most significantly this work demonstrated that small amounts (approx. 0.2 wt%) of boron or oxygen could be effectively combined with Ti64 via SLM processing. Optimised parameters (resulting in energy density of 54.4 J/mm³) were able to produce high density parts with uniform incorporation. Typical microstructures were developed for SLM produced Ti64, consisting of columnar colonies of fine lamellar martensite that extend in the build direction. Additional oxygen changed this very little, however boron had a significant effect, refining the grain structure and preventing the formation of columnar colonies. Enhancements in compressive strength and hardness resulted from boron or oxygen addition with compressive yield strength increased by up to 10% and 16% respectively. Improvements in these properties were retained in the different heat treatment conditions when compared to unmodified Ti64. While strengthening of Ti64 was achieved by inclusion of the additives, little improvement in wear performance was found.
This work identifies a viable method of modifying properties of titanium through in-situ processes during SLM. The findings of this study will have implications for the production of Ti64 alloys during the SLM processes and may guide future work on developing materials specific for additive manufacturing.

text: Additive manufacturing of Ti64 alloy in-situ modified with additions of boron or oxygen Selective laser melting (SLM) is a metal additive manufacturing process that enables the production of complex, near net shape, parts with fully functional mechanical properties. The use of titanium alloys in SLM is a good fit due to a high material utilisation and net shape production with this expensive material. While titanium alloys have attractive properties of high specific strength and excellent corrosion resistance, these and other attributes may be modified through various methods for further improvements of the material. Strengthening mechanisms of interstitial hardening and particulate reinforcement are viable approaches for enhancing titanium alloys, however these often increase processing difficulty. Near net shape processes, like SLM, have the potential to produce functional parts with these modified properties.
This study explored the use of SLM for the fabrication of titanium parts, modified in-situ during processing with small amounts of boron or oxygen to develop enhanced properties. The in-situ incorporation of these different elements was performed during SLM using blended powders. Simple mixing of feedstock Ti64 alloy powder with small amounts of either amorphous boron or TiO₂, and subsequent SLM consolidation, has the potential to develop interstitial (oxygen) and particulate (boron) strengthened materials. 
This work analytically compares the properties of samples created using different process parameters, related through energy density. By examining variation in porosity and hardness with respect to these process parameters, it was possible to establish optimum processing conditions for manufacturing the in-situ modified material. Novel samples were developed for SLM that simplify the multi-level, multi-factor investigation of these process parameters into a single specimen for easy preparation and testing. Further investigation of how processing may influence the distribution and homogeneity of the modified material was studied through the influence of stress relief and sub-beta transus annealing heat treatments. Characterisation of these materials and treatment conditions were performed to determine the effect the additives have on the mechanical and wear properties. 
Most significantly this work demonstrated that small amounts (approx. 0.2 wt%) of boron or oxygen could be effectively combined with Ti64 via SLM processing. Optimised parameters (resulting in energy density of 54.4 J/mm³) were able to produce high density parts with uniform incorporation. Typical microstructures were developed for SLM produced Ti64, consisting of columnar colonies of fine lamellar martensite that extend in the build direction. Additional oxygen changed this very little, however boron had a significant effect, refining the grain structure and preventing the formation of columnar colonies. Enhancements in compressive strength and hardness resulted from boron or oxygen addition with compressive yield strength increased by up to 10% and 16% respectively. Improvements in these properties were retained in the different heat treatment conditions when compared to unmodified Ti64. While strengthening of Ti64 was achieved by inclusion of the additives, little improvement in wear performance was found.
This work identifies a viable method of modifying properties of titanium through in-situ processes during SLM. The findings of this study will have implications for the production of Ti64 alloys during the SLM processes and may guide future work on developing materials specific for additive manufacturing.

year: 2022

title: Investigation of extractable materials from biochar

authors: Yang, Wenjuan

subjects: Biochar

abstract: Biochar has been used to improve soil productivity and has been a subject of discussion since 1804. However, research and development of biochar for environmental purposes on a global scale are a recent development. Due to the increase of its uses and interest in biochar as soil amendment, there is a need to understand the intrinsic chemistry of biochar to understand how this might affect its action in the soil. 

In this work two principal topics were addressed: 
1)	Investigation of volatile organic compounds in biochar that has been derived from various biomasses and the effect of different temperatures of pyrolysis
2)	Identification of some chemical structures of biochar. 

GC-MS analysis identified 60 extractable organic compounds. With respect to pyrolysis temperature, GC-MS results of Green Waste chars and Sucrose chars shows that extractable organic compounds changed their proportions with differing pyrolysis temperatures.  MALDI-TOF and high resolution mass spectrometry results suggested that the characteristic ions for biochar  that appear in MALDI-TOF spectra with m/z values of 301,317, 413,429 and 453 are plasticizers whereas 685/ 701 are ions, [M+Na] ⁺/ [M+K] ⁺ respectively that are intrinsic to biochar.

text: Investigation of extractable materials from biochar Biochar has been used to improve soil productivity and has been a subject of discussion since 1804. However, research and development of biochar for environmental purposes on a global scale are a recent development. Due to the increase of its uses and interest in biochar as soil amendment, there is a need to understand the intrinsic chemistry of biochar to understand how this might affect its action in the soil. 

In this work two principal topics were addressed: 
1)	Investigation of volatile organic compounds in biochar that has been derived from various biomasses and the effect of different temperatures of pyrolysis
2)	Identification of some chemical structures of biochar. 

GC-MS analysis identified 60 extractable organic compounds. With respect to pyrolysis temperature, GC-MS results of Green Waste chars and Sucrose chars shows that extractable organic compounds changed their proportions with differing pyrolysis temperatures.  MALDI-TOF and high resolution mass spectrometry results suggested that the characteristic ions for biochar  that appear in MALDI-TOF spectra with m/z values of 301,317, 413,429 and 453 are plasticizers whereas 685/ 701 are ions, [M+Na] ⁺/ [M+K] ⁺ respectively that are intrinsic to biochar.

year: 2012

title: Aroha

authors: Maxwell, Te Kahautu

abstract: Waita Tira. Lyrics composed by Te Kahautu Maxwell, muscial score composed by Raharuha Mitai, Thomas Mitai, Renee Mitai. Performed by Ōpōtiki Mai Tawhiti (Kapa Haka group) (3mins)

Waiata ā Tira: Aroha
Whakaeke: Pinepine Te Kura
Mōteatea: Tērā te haeata
Waiata ā Ringa: Tiaho Mai
Poi: E ia, e ia
Haka: Ranginui
Whakawātea: Te Tiriti o Waitangi

text: Aroha Waita Tira. Lyrics composed by Te Kahautu Maxwell, muscial score composed by Raharuha Mitai, Thomas Mitai, Renee Mitai. Performed by Ōpōtiki Mai Tawhiti (Kapa Haka group) (3mins)

Waiata ā Tira: Aroha
Whakaeke: Pinepine Te Kura
Mōteatea: Tērā te haeata
Waiata ā Ringa: Tiaho Mai
Poi: E ia, e ia
Haka: Ranginui
Whakawātea: Te Tiriti o Waitangi

year: 2020-02-06