title: The Synthesis of High Strength Titanium Alloy and Titanium Alloy Matrix Composite by Powder Compact Extrusion from Blended Elemental Powders

authors: Lu, Huiyang

subjects: Titanium

abstract: Powder compact extrusion (PCE) from blended elemental powders is an effective way to produce titanium alloys and titanium matrix composites with high performance. Its main advantage is cost effectiveness, where high cost pre-alloyed powders are replaced by lower cost elemental powders and a need for lengthy sintering times to achieve sufficiently high enough density is removed. However a blended elemental approach has some disadvantages, for example the ductility and strength of PCE materials are normally lower than those obtained in cast alloys. This thesis is a study of the feasibility of producing a high strength titanium alloy and titanium matrix composite using PCE from blended elemental powders. It investigates and seeks to address the effects of inhomogeneous elemental distribution on structure and properties. In this study two very different ways of producing a high strength titanium alloy using PCE through a blended elemental approach are investigated. The first approach is through the synthesis of the high strength alloy Ti-4%Al-4%Mo-4%Sn-0.5%Si and the second approach investigates the feasibility of achieving high strength by producing a titanium alloy composite and for this TiB/Ti6Al4V was chosen for this study.
For synthesising the alloy Ti-4%Al-4%Mo-4%Sn-0.5%Si, the effect of extrusion temperature, different starting powders and heat treatment on the microstructure and mechanical properties were studied. The extrusion temperature has a significant effect on the degree of elemental dissolution. An increase in the extrusion temperature significantly improves the dissolution of Si and Mo. However, an extrusion temperature of 1350oC is still not enough to achieve complete dissolution of the elemental particles, especially Si and Mo particles. The results showed that by using an extrusion temperature 1350oC with a holding time of 5 min prior to extrusion, elemental dissolution was much improved and a relatively homogenous microstructure was achieved. As-extruded bars with undissolved elemental particles showed low tensile strength without any ductility, while those samples without any inhomogeneities in the microstructure caused by undissolved particles and defects showed an ultimate tensile strength and elongation to fracture of 1423MPa and 5.1%, respectively.
After achieving dissolution of the elemental particles, some localized areas with an inhomogeneous elemental distribution still existed. The diffusion interactions between different elements during high temperature processing were also discussed in this thesis. The study also showed that some dendrites such as Ti5Si3 and β Ti grew during cooling due to the local elemental inhomogeneities. These dendrites are detrimental to the mechanical properties of the alloy, being the main reason for premature failure during tensile testing, leading to a large variation in tensile properties. The precipitation of dendrites was monitored.
When the starting powders were dominated by gas atomized (GA) titanium powders, a good combination of tensile strength and ductility was achieved which showed a UTS of 1220-1250 MPa with an elongation to fracture of 7-11%. GA titanium powders have a beneficial effect on elemental diffusion and the achievement of more uniformity in mechanical properties.
A beta transus temperature of 1075oC has been confirmed. The solutioning temperature and the concentration of beta stabilizer, especially Mo, in the beta matrix has a significant effect on martensite phase transformation. After heat treatment the microstructural homogeneity and tensile properties were significantly improved. The cooling rate after solutioning plays a key role in determining the morphology of the α lamellar structure and the α colony and beta grainsize. A faster cooling rate causes a decrease in the width of the α lamellae, the size of the α colonies and the beta grain size. After heat treatment an ultimate tensile strength of 1584MPa, a yield strength of 1505MPa and an elongation to fracture of 2.5% were obtained.
The method of synthesis of this alloy by powder compact extrusion from a pre-consolidated compact was also introduced. The effect of extrusion temperature on microstructure and mechanical properties was investigated. When the extrusion temperature is increased to 1200oC a fine lamellae microstructure with good tensile properties giving a yield strength, UTS and elongation to fracture of 1278MPa, 1421MPa and 7.2%, respectively, were achieved. Good tensile properties were obtained at elevated temperature, and for testing between 300oC and 500oC the tensile strength decreased from 907MPa to 720MPa, but the elongation to fracture increased from 10% to 13%.
For synthesis of TiB/Ti6Al4V composite, a Ti-6wt%Al-4wt%V alloy (Ti6Al4V) matrix composite, reinforced by in-situ synthesized TiB whiskers (TiBw) was successfully fabricated by powder compact extrusion, using a blended powder mixture. The microstructural characterization of the various extruded samples showed that the different starting powders, pre-alloyed powder plus boron powder or titanium plus Al-40V master alloy powder plus boron powder, had a significant effect on the morphology of the in-situ synthesized TiB whiskers. It is also evident that the TiB whiskers affected the microstructural evolution of the Ti6Al4V matrix. The tensile test results indicated that a composite with a dispersion of fine TiB whiskers with high aspect ratios exhibited a high ultimate tensile stress (UTS) and yield stress (YS) of 1436MPa and 1361MPa, respectively, a reasonably good tensile ductility reflected by an elongation to fracture of 5.6% was also achieved. This is a significant improvement compared with as-extruded monolithic Ti6Al4V alloy produced in this study.

text: The Synthesis of High Strength Titanium Alloy and Titanium Alloy Matrix Composite by Powder Compact Extrusion from Blended Elemental Powders Powder compact extrusion (PCE) from blended elemental powders is an effective way to produce titanium alloys and titanium matrix composites with high performance. Its main advantage is cost effectiveness, where high cost pre-alloyed powders are replaced by lower cost elemental powders and a need for lengthy sintering times to achieve sufficiently high enough density is removed. However a blended elemental approach has some disadvantages, for example the ductility and strength of PCE materials are normally lower than those obtained in cast alloys. This thesis is a study of the feasibility of producing a high strength titanium alloy and titanium matrix composite using PCE from blended elemental powders. It investigates and seeks to address the effects of inhomogeneous elemental distribution on structure and properties. In this study two very different ways of producing a high strength titanium alloy using PCE through a blended elemental approach are investigated. The first approach is through the synthesis of the high strength alloy Ti-4%Al-4%Mo-4%Sn-0.5%Si and the second approach investigates the feasibility of achieving high strength by producing a titanium alloy composite and for this TiB/Ti6Al4V was chosen for this study.
For synthesising the alloy Ti-4%Al-4%Mo-4%Sn-0.5%Si, the effect of extrusion temperature, different starting powders and heat treatment on the microstructure and mechanical properties were studied. The extrusion temperature has a significant effect on the degree of elemental dissolution. An increase in the extrusion temperature significantly improves the dissolution of Si and Mo. However, an extrusion temperature of 1350oC is still not enough to achieve complete dissolution of the elemental particles, especially Si and Mo particles. The results showed that by using an extrusion temperature 1350oC with a holding time of 5 min prior to extrusion, elemental dissolution was much improved and a relatively homogenous microstructure was achieved. As-extruded bars with undissolved elemental particles showed low tensile strength without any ductility, while those samples without any inhomogeneities in the microstructure caused by undissolved particles and defects showed an ultimate tensile strength and elongation to fracture of 1423MPa and 5.1%, respectively.
After achieving dissolution of the elemental particles, some localized areas with an inhomogeneous elemental distribution still existed. The diffusion interactions between different elements during high temperature processing were also discussed in this thesis. The study also showed that some dendrites such as Ti5Si3 and β Ti grew during cooling due to the local elemental inhomogeneities. These dendrites are detrimental to the mechanical properties of the alloy, being the main reason for premature failure during tensile testing, leading to a large variation in tensile properties. The precipitation of dendrites was monitored.
When the starting powders were dominated by gas atomized (GA) titanium powders, a good combination of tensile strength and ductility was achieved which showed a UTS of 1220-1250 MPa with an elongation to fracture of 7-11%. GA titanium powders have a beneficial effect on elemental diffusion and the achievement of more uniformity in mechanical properties.
A beta transus temperature of 1075oC has been confirmed. The solutioning temperature and the concentration of beta stabilizer, especially Mo, in the beta matrix has a significant effect on martensite phase transformation. After heat treatment the microstructural homogeneity and tensile properties were significantly improved. The cooling rate after solutioning plays a key role in determining the morphology of the α lamellar structure and the α colony and beta grainsize. A faster cooling rate causes a decrease in the width of the α lamellae, the size of the α colonies and the beta grain size. After heat treatment an ultimate tensile strength of 1584MPa, a yield strength of 1505MPa and an elongation to fracture of 2.5% were obtained.
The method of synthesis of this alloy by powder compact extrusion from a pre-consolidated compact was also introduced. The effect of extrusion temperature on microstructure and mechanical properties was investigated. When the extrusion temperature is increased to 1200oC a fine lamellae microstructure with good tensile properties giving a yield strength, UTS and elongation to fracture of 1278MPa, 1421MPa and 7.2%, respectively, were achieved. Good tensile properties were obtained at elevated temperature, and for testing between 300oC and 500oC the tensile strength decreased from 907MPa to 720MPa, but the elongation to fracture increased from 10% to 13%.
For synthesis of TiB/Ti6Al4V composite, a Ti-6wt%Al-4wt%V alloy (Ti6Al4V) matrix composite, reinforced by in-situ synthesized TiB whiskers (TiBw) was successfully fabricated by powder compact extrusion, using a blended powder mixture. The microstructural characterization of the various extruded samples showed that the different starting powders, pre-alloyed powder plus boron powder or titanium plus Al-40V master alloy powder plus boron powder, had a significant effect on the morphology of the in-situ synthesized TiB whiskers. It is also evident that the TiB whiskers affected the microstructural evolution of the Ti6Al4V matrix. The tensile test results indicated that a composite with a dispersion of fine TiB whiskers with high aspect ratios exhibited a high ultimate tensile stress (UTS) and yield stress (YS) of 1436MPa and 1361MPa, respectively, a reasonably good tensile ductility reflected by an elongation to fracture of 5.6% was also achieved. This is a significant improvement compared with as-extruded monolithic Ti6Al4V alloy produced in this study.

year: 2016

title: Health Literacy: A Hermeneutic Study of New Zealand Baby Boomers

authors: Davey, Janet

subjects: Health literacy

abstract: Health literacy has traditionally been conceptualised as individual skills in a health context. Although there is growing consensus that health literacy is a multidimensional construct, interacting with socio-cultural contextual influences, such aspects are under-researched. In particular, there is limited research regarding the interrelationships between individuals’ and primary healthcare professionals’ (PHCPs) health literacy beliefs and experiences. Despite the predicted impact of the ageing population on healthcare costs and services, little empirical research has been conducted in New Zealand (NZ) on the health-related behaviour of the influential baby boomer cohort. The purpose of this thesis is to explore the phenomenon of health literacy among NZ baby boomers and PHCPs.  

Using hermeneutics as both the theoretical lens and the research method, this research draws on in-depth interviews to understand the participants’ constructions of health literacy and how their constructions influence healthcare goals and service encounters. The research takes a broad perspective of health literacy to answer the overarching research question, How are the roles and practices of health literacy perceived/constructed and performed in primary healthcare?

This thesis makes an original contribution to knowledge as the first empirical investigation of health literacy of NZ baby boomers (46 participants) and NZ primary healthcare professionals (11 participants). Specifically, this research contributes to health literacy knowledge in a geographic area (NZ) and among individuals within a generational cohort not defined by health condition or health risk. 

NZ baby boomers construct health literacy as a highly contextualised social practice linked to [a]symmetries in health-related information, power, autonomy, and patient-practitioner roles. These participants stress the importance of an individual’s personal health context, capabilities, relational processes, and networks in health literacy. Interpreting these baby boomers’ health literacy behaviours leads to five categories of description - seeker, decider, networker, sensemaker, and manager, which are appropriately framed within two horizons of self and interactivity, providing conceptual space within which individuals move and adapt their health literacy roles, responsibilities, and behaviours. 

In the PHCPs’ experiences regarding baby boomers’ health literacy there are underlying power and information imbalances, conflicting authority concerns, and [de-]professionalisation issues. Using categories of description, the PHCPs’ health literacy behaviours are described as – knowledge broker, ethical agent, and enabler. Iteratively drawing on pre-understandings, these meanings are theorised in a collective notion of managed empowerment that implies a negotiated balance between PHCP expert control and professional expertise, and patient-consumer autonomy and expertise. 

This study extends the understanding of health literacy by presenting an empirically-based conceptual framework, depicting health literacy operating across multiple levels, relationships, and networks, variably influenced by contextual factors of the postmodern health context; the communication and information revolution; and neo-liberalism and consumerism. The thesis contributes to health literacy knowledge by illustrating the fundamental role of relational processes in co-producing individuals’ health literacy and in subsequently reaching individuals’ health goals. Primary healthcare service providers, policy makers, and health promotion advocates can benefit from this study as it reveals particular health literacy roles and behaviours likely to be influential in encouraging individuals’ authentic involvement in their healthcare.

text: Health Literacy: A Hermeneutic Study of New Zealand Baby Boomers Health literacy has traditionally been conceptualised as individual skills in a health context. Although there is growing consensus that health literacy is a multidimensional construct, interacting with socio-cultural contextual influences, such aspects are under-researched. In particular, there is limited research regarding the interrelationships between individuals’ and primary healthcare professionals’ (PHCPs) health literacy beliefs and experiences. Despite the predicted impact of the ageing population on healthcare costs and services, little empirical research has been conducted in New Zealand (NZ) on the health-related behaviour of the influential baby boomer cohort. The purpose of this thesis is to explore the phenomenon of health literacy among NZ baby boomers and PHCPs.  

Using hermeneutics as both the theoretical lens and the research method, this research draws on in-depth interviews to understand the participants’ constructions of health literacy and how their constructions influence healthcare goals and service encounters. The research takes a broad perspective of health literacy to answer the overarching research question, How are the roles and practices of health literacy perceived/constructed and performed in primary healthcare?

This thesis makes an original contribution to knowledge as the first empirical investigation of health literacy of NZ baby boomers (46 participants) and NZ primary healthcare professionals (11 participants). Specifically, this research contributes to health literacy knowledge in a geographic area (NZ) and among individuals within a generational cohort not defined by health condition or health risk. 

NZ baby boomers construct health literacy as a highly contextualised social practice linked to [a]symmetries in health-related information, power, autonomy, and patient-practitioner roles. These participants stress the importance of an individual’s personal health context, capabilities, relational processes, and networks in health literacy. Interpreting these baby boomers’ health literacy behaviours leads to five categories of description - seeker, decider, networker, sensemaker, and manager, which are appropriately framed within two horizons of self and interactivity, providing conceptual space within which individuals move and adapt their health literacy roles, responsibilities, and behaviours. 

In the PHCPs’ experiences regarding baby boomers’ health literacy there are underlying power and information imbalances, conflicting authority concerns, and [de-]professionalisation issues. Using categories of description, the PHCPs’ health literacy behaviours are described as – knowledge broker, ethical agent, and enabler. Iteratively drawing on pre-understandings, these meanings are theorised in a collective notion of managed empowerment that implies a negotiated balance between PHCP expert control and professional expertise, and patient-consumer autonomy and expertise. 

This study extends the understanding of health literacy by presenting an empirically-based conceptual framework, depicting health literacy operating across multiple levels, relationships, and networks, variably influenced by contextual factors of the postmodern health context; the communication and information revolution; and neo-liberalism and consumerism. The thesis contributes to health literacy knowledge by illustrating the fundamental role of relational processes in co-producing individuals’ health literacy and in subsequently reaching individuals’ health goals. Primary healthcare service providers, policy makers, and health promotion advocates can benefit from this study as it reveals particular health literacy roles and behaviours likely to be influential in encouraging individuals’ authentic involvement in their healthcare.

year: 2015

title: Traditional plant harvesting in contemporary fragmented and urban landscapes

authors: Wehi, Priscilla M.

subjects: ethnobiology

abstract: Ecosystem fragmentation and destruction can lead to restrictive administration policies on traditional harvesting by indigenous peoples from remaining ecosystem tracts. In New Zealand, concerns about endangered species and governmental policies that focus on species and ecosystem preservation have resulted in severely curtailed traditional harvesting rights. Although provision has been made for limited gathering of traditional plants from government-administered conservation lands, it is unclear how much harvesting is undertaken on these lands and elsewhere and what this harvest might consist of. We interviewed seven expert Maori elders from the Waikato, New Zealand, to identify plant species they currently harvested and from where. We compared these data with the data we collected on permits issued for plant collecting on conservation lands in the same region. We sought to gain information on indigenous plant harvesting to determine the extent of permitted harvesting from conservation lands in the Waikato and to identify issues that might affect plant harvesting and management. Elders identified 58 species they harvest regularly or consider culturally important; over 50% of these species are harvested for medicinal use. Permit data from 1996 to 2006 indicated no apparent relationship between species of reported cultural significance and the number of permits issued for each of these species. Currently, few plant species are harvested from conservation lands, although some unofficial harvesting occurs. Elders instead reported that medicinal plants are frequently collected from urban and other public areas. They reported that plant species used for dyeing, carving, and weaving are difficult to access. Elders also discussed concerns such as spraying of roadsides, which resulted in the death of medicinal species, and use of commercial hybrids in urban planning. Local government may have an increasingly important role in supporting native traditions through urban planning, which takes account of cultural harvesting needs while potentially reducing future harvesting pressure on conservation lands. We suggest that active participation by the Māori community in the development and management of urban harvesting resources will result in positive outcomes.

text: Traditional plant harvesting in contemporary fragmented and urban landscapes Ecosystem fragmentation and destruction can lead to restrictive administration policies on traditional harvesting by indigenous peoples from remaining ecosystem tracts. In New Zealand, concerns about endangered species and governmental policies that focus on species and ecosystem preservation have resulted in severely curtailed traditional harvesting rights. Although provision has been made for limited gathering of traditional plants from government-administered conservation lands, it is unclear how much harvesting is undertaken on these lands and elsewhere and what this harvest might consist of. We interviewed seven expert Maori elders from the Waikato, New Zealand, to identify plant species they currently harvested and from where. We compared these data with the data we collected on permits issued for plant collecting on conservation lands in the same region. We sought to gain information on indigenous plant harvesting to determine the extent of permitted harvesting from conservation lands in the Waikato and to identify issues that might affect plant harvesting and management. Elders identified 58 species they harvest regularly or consider culturally important; over 50% of these species are harvested for medicinal use. Permit data from 1996 to 2006 indicated no apparent relationship between species of reported cultural significance and the number of permits issued for each of these species. Currently, few plant species are harvested from conservation lands, although some unofficial harvesting occurs. Elders instead reported that medicinal plants are frequently collected from urban and other public areas. They reported that plant species used for dyeing, carving, and weaving are difficult to access. Elders also discussed concerns such as spraying of roadsides, which resulted in the death of medicinal species, and use of commercial hybrids in urban planning. Local government may have an increasingly important role in supporting native traditions through urban planning, which takes account of cultural harvesting needs while potentially reducing future harvesting pressure on conservation lands. We suggest that active participation by the Māori community in the development and management of urban harvesting resources will result in positive outcomes.

year: 2010