title: Influence of ageing heating rates on the microstructure and mechanical properties of Ti-5553 alloy

authors: Jia, Mengqi

subjects: fatigue

abstract: The Ti-5553 alloy, a high-strength β-titanium alloy, is increasingly recognised for its exceptional mechanical properties, making it a preferred material for critical aerospace applications. This thesis examines the effects of varying ageing heating rates on the microstructure and mechanical properties of the forged Ti-5553 alloy, focusing on hardness, tensile properties, and fatigue performance. Following solution treatment at 810°C, the alloy was aged at 610°C with heating rates of 1°C/min, 5°C/min, 10°C/min, and 15°C/min. Detailed microstructural analysis was conducted using Scanning Electron Microscopy (SEM) and Energy Dispersive X ray Spectroscopy (EDX). The microstructural examination revealed that different ageing heating rates caused only minor variations in the alloy's bimodal microstructure. Slower ageing heating rates produced a relatively fine, homogeneously distributed primary α phase within the β grains, while faster rates resulted in a slightly coarser bimodal microstructure. Chemical homogeneity analysis confirmed a consistent distribution of critical elements, with α stabilisers concentrated in the primary α phase and β stabilisers in the β phase, ensuring stable phase compositions across all samples. The observed slight microstructural changes were reflected in the alloy's mechanical properties. Hardness across different ageing heating rates varied between 357.4 HV and 372.6 HV. The ultimate tensile strength (UTS) declined from 1307.2 MPa at 1°C/min to 1264.5 MPa at 15°C/min, while ductility improved from 15.6% to 17.1% over the same range. The alloy demonstrated good fatigue resistance at lower stress amplitudes and ageing heating rates, enduring over 10 million cycles at 337.5 MPa under the 1°C/min condition. However, fatigue life decreased with higher stress amplitudes and ageing heating rates, highlighting the alloy's sensitivity to more extreme conditions. In summary, while the varying ageing heating rates resulted in only minor changes to the microstructure, these alterations had some impact on the mechanical properties of the Ti-5553 alloy. These findings highlight the importance of precise microstructural control in optimising the alloy's performance, especially in applications where achieving a balance between strength, ductility, and fatigue resistance is crucial.

text: Influence of ageing heating rates on the microstructure and mechanical properties of Ti-5553 alloy The Ti-5553 alloy, a high-strength β-titanium alloy, is increasingly recognised for its exceptional mechanical properties, making it a preferred material for critical aerospace applications. This thesis examines the effects of varying ageing heating rates on the microstructure and mechanical properties of the forged Ti-5553 alloy, focusing on hardness, tensile properties, and fatigue performance. Following solution treatment at 810°C, the alloy was aged at 610°C with heating rates of 1°C/min, 5°C/min, 10°C/min, and 15°C/min. Detailed microstructural analysis was conducted using Scanning Electron Microscopy (SEM) and Energy Dispersive X ray Spectroscopy (EDX). The microstructural examination revealed that different ageing heating rates caused only minor variations in the alloy's bimodal microstructure. Slower ageing heating rates produced a relatively fine, homogeneously distributed primary α phase within the β grains, while faster rates resulted in a slightly coarser bimodal microstructure. Chemical homogeneity analysis confirmed a consistent distribution of critical elements, with α stabilisers concentrated in the primary α phase and β stabilisers in the β phase, ensuring stable phase compositions across all samples. The observed slight microstructural changes were reflected in the alloy's mechanical properties. Hardness across different ageing heating rates varied between 357.4 HV and 372.6 HV. The ultimate tensile strength (UTS) declined from 1307.2 MPa at 1°C/min to 1264.5 MPa at 15°C/min, while ductility improved from 15.6% to 17.1% over the same range. The alloy demonstrated good fatigue resistance at lower stress amplitudes and ageing heating rates, enduring over 10 million cycles at 337.5 MPa under the 1°C/min condition. However, fatigue life decreased with higher stress amplitudes and ageing heating rates, highlighting the alloy's sensitivity to more extreme conditions. In summary, while the varying ageing heating rates resulted in only minor changes to the microstructure, these alterations had some impact on the mechanical properties of the Ti-5553 alloy. These findings highlight the importance of precise microstructural control in optimising the alloy's performance, especially in applications where achieving a balance between strength, ductility, and fatigue resistance is crucial.

year: 2024-09-15

title: Effect of milling parameters on microstructure of Ti/Al composite powder produced by discus milling

authors: Raynova, Stiliana (Stella) Rousseva

subjects: TiAl

abstract: The motivation of this research is to develop a process for producing Ti/Al composite powders that enable synthesis of a single-phase TiAl intermetallic bulk material, which is then used as a target for physical vapour deposition (PVD) coating. This study reports the effects of milling time, amount of process control agent (PCA) added as well as the powder-to-medium ratio on the microstructure of the Ti/Al composite powder. Optical microscopy and scanning electron microscopy (SEM) were used to evaluate the level of mixing and the resulting powder particle size. X-ray diffraction analysis and differential thermal analysis were used for determining the phase constituents and the solid state reaction temperature of the as-milled powders.

text: Effect of milling parameters on microstructure of Ti/Al composite powder produced by discus milling The motivation of this research is to develop a process for producing Ti/Al composite powders that enable synthesis of a single-phase TiAl intermetallic bulk material, which is then used as a target for physical vapour deposition (PVD) coating. This study reports the effects of milling time, amount of process control agent (PCA) added as well as the powder-to-medium ratio on the microstructure of the Ti/Al composite powder. Optical microscopy and scanning electron microscopy (SEM) were used to evaluate the level of mixing and the resulting powder particle size. X-ray diffraction analysis and differential thermal analysis were used for determining the phase constituents and the solid state reaction temperature of the as-milled powders.

year: 2006

title: The embodied and lived experiences of welfare and care for highly impaired, high performance para-sport athletes in Aotearoa New Zealand

authors: Lowry, Amanda

abstract: Aligning with calls in critical disability studies to bring the body and impairment into disability sport, this thesis examines the welfare and care experiences of highly impaired athletes in high-performance sport. While a focus on athlete welfare has gained some international prominence, and a duty of care is increasingly invoked as an organisational and coaching responsibility, these developments remain largely disconnected from disability.  
The research is centred around two main objectives. First, to amplify the lived and embodied experiences of highly impaired, high performance disabled athletes as they prepare for, train, and compete in sport, and those who support them. Second, to understand how sporting institutions and regulations (within the broader context of government funding and national health care provision) influence welfare and care practices for high performance disabled athletes. 
Crip methodologies and Indigenous Māori storytelling methodologies such as pūrākau centres lived experience as a site of resistance and knowledge production. Using a reflexive, qualitative approach, including semi-structured interviews, autoethnographic vignettes, and visual ethnography, I expose how impairment effects are managed in ableist sporting environments that valorise normative athlete ideals. I interviewed 11 high-performance paraathletes, seven organisational representatives and two support workers. 
The research highlights the material, emotional, and temporal labour of care in highperformance sport. Findings are organised around three core themes: the embodied labour of care, impairment effects and interdependence; the tension between crip time, care time, and performance time; the intersecting structural, institutional, and ableist barriers that shape and constrain highly impaired athletes’ participation in disability sport.  
The first theme shows how high-performance sport privileges autonomous, efficient, and normative bodies, while marginalising those whose messy, gritty embodied impairment effects demand more time, support, and interdependence. The findings bring to the fore biosocial, psycho-emotional costs of navigating care and its impact on athlete welfare. The second theme uncovers how the rhythms of highly impaired bodies disrupt the linear, clockbound time of high-performance sport, revealing the incompatibility between care time and high performance cultures. It highlights the vital yet invisible labour of support workers, ii unacknowledged in contemporary sporting discourse. The third theme addresses the barriers that highly impaired athletes face when navigating ableist institutional and organisational structures. It exposes the complexity of the ableist disability sporting landscape and the gap between duty of care rhetoric and practice. 
Ultimately, this thesis calls for a radical reimagining of disability sport, one that centres interdependence, affirms bodily difference, and addresses the structural failures that marginalise highly impaired athletes.

text: The embodied and lived experiences of welfare and care for highly impaired, high performance para-sport athletes in Aotearoa New Zealand Aligning with calls in critical disability studies to bring the body and impairment into disability sport, this thesis examines the welfare and care experiences of highly impaired athletes in high-performance sport. While a focus on athlete welfare has gained some international prominence, and a duty of care is increasingly invoked as an organisational and coaching responsibility, these developments remain largely disconnected from disability.  
The research is centred around two main objectives. First, to amplify the lived and embodied experiences of highly impaired, high performance disabled athletes as they prepare for, train, and compete in sport, and those who support them. Second, to understand how sporting institutions and regulations (within the broader context of government funding and national health care provision) influence welfare and care practices for high performance disabled athletes. 
Crip methodologies and Indigenous Māori storytelling methodologies such as pūrākau centres lived experience as a site of resistance and knowledge production. Using a reflexive, qualitative approach, including semi-structured interviews, autoethnographic vignettes, and visual ethnography, I expose how impairment effects are managed in ableist sporting environments that valorise normative athlete ideals. I interviewed 11 high-performance paraathletes, seven organisational representatives and two support workers. 
The research highlights the material, emotional, and temporal labour of care in highperformance sport. Findings are organised around three core themes: the embodied labour of care, impairment effects and interdependence; the tension between crip time, care time, and performance time; the intersecting structural, institutional, and ableist barriers that shape and constrain highly impaired athletes’ participation in disability sport.  
The first theme shows how high-performance sport privileges autonomous, efficient, and normative bodies, while marginalising those whose messy, gritty embodied impairment effects demand more time, support, and interdependence. The findings bring to the fore biosocial, psycho-emotional costs of navigating care and its impact on athlete welfare. The second theme uncovers how the rhythms of highly impaired bodies disrupt the linear, clockbound time of high-performance sport, revealing the incompatibility between care time and high performance cultures. It highlights the vital yet invisible labour of support workers, ii unacknowledged in contemporary sporting discourse. The third theme addresses the barriers that highly impaired athletes face when navigating ableist institutional and organisational structures. It exposes the complexity of the ableist disability sporting landscape and the gap between duty of care rhetoric and practice. 
Ultimately, this thesis calls for a radical reimagining of disability sport, one that centres interdependence, affirms bodily difference, and addresses the structural failures that marginalise highly impaired athletes.

year: 2025-10