title: Investigation on fabrication, interface formation, and properties of hot-processed titanium-doped copper/diamond composites

authors: Ma, Jingnan

abstract: Efficient thermal management is crucial for next-generation high-power electronic devices, driving the need for high-performance heat sink materials. Copper/diamond composites have emerged as promising candidates due to their exceptional thermal conductivity (TC) and tailorable coefficient of thermal expansion (CTE). However, their performance is limited by weak interfacial bonding, caused by the poor chemical affinity between copper and diamond and severe phonon scattering due to mismatched lattice vibrations. To address these challenges, interface engineering strategies such as pre-coating diamond particles or pre-alloying the copper matrix with carbide-forming elements (e.g., Ti, W, Zr, Cr, B) have been extensively explored. Among these, titanium has shown promise through the formation of a stable titanium carbide (TiC) layer, which significantly enhances interfacial bonding and composite performance. This thesis investigates the thermophysical and mechanical performance of titanium-doped copper/diamond composites fabricated via hot-processing techniques, hot-forging and hot-pressing, with focuses on optimizing fabrication parameters, elucidating interface formation mechanisms, and establishing the relationship between the interfacial microstructure and composites performance. 
Ti-coated diamond/Cu composites were successfully fabricated via hot-forging, and the effects of forging temperature, diamond volume fraction, and deformation degree were systematically evaluated. The study highlights the crucial role of hot-forging temperature in optimizing TiC interface formation and enhancing interfacial bonding. 800°C is the optimal hot forging temperature to facilitate the dynamic formation of TiC interface layer and ensure a high interface coverage rate on the diamond particles. Additionally, the volume fraction of diamond affects the interface microstructure and TC of the hot-forged composites by affecting the heating behaviour of the composites during induction heating. The relatively large deformation degree can effectively contribute to the densification and interfacial bonding of the composites. 800 °C hot-forged composite with 45 vol% diamond and 80% deformation degree exhibited excellent TC of 529 W/mK, along with a high tensile strength of 241 MPa, attributed to the synergy of uniform distribution of diamond in the matrix, a rough interface, and strong interfacial bonding between the copper and the diamond.
The fabrication of copper/diamond composites via hot-pressing, was further investigated employing two interfacial engineering strategies: titanium carbide formation through diamond surface metallization and copper matrix alloying with titanium additives. The results show that diamond metallization shows a better effectiveness in enhancing both mechanical and thermophysical performance than matrix alloying. Notably, Cu/50 vol% Ti-coated diamond composite fabricated at 540 MPa achieved an exceptional TC of 565 W/mK and a tensile strength of about 147 MPa. For the copper-Ti/diamond composite containing 0.5 wt% Ti processed at 1050 °C, it exhibited a comparable TC (554 W/mK), but a relatively low tensile strength (93 MPa). The optimal processing pressures for maximizing TC and mechanical strength in hot-pressed Cu/Ti-coated diamond composites differ due to interface microstructure: continuous interface enhances mechanical strength through strong interfacial bonding, whereas jagged interface arranged in parallel on the diamond surface minimizes interfacial thermal resistance. A comparative study between the two processing routes revealed that hot-forging outperforms hot-pressing at high diamond content (55 vol%) due to greater matrix deformation and more uniform diamond distribution, whereas hot-pressing becomes advantageous at lower diamond fractions (45-50 vol%), where applied pressure provides effective densification and interfacial microstructure becomes the dominant factor governing composite performance. 
A detailed investigation into interface formation mechanisms was conducted on 540 MPa hot-pressed composites with 50 vol% Ti-coated diamond. The results revealed that the distinct atomic configuration of individual diamond facets govern the nucleation and growth behaviour of TiC at the interface, giving rise to different interfacial microstructures: a continuous Cu/TiC/diamond structure on diamond-{100} facets, and a multilayered Cu/Cu (Ti)/TiC/diamond structure on diamond-{111} facets. Beyond the formation of TiC interlayer on both facets, the semi-coherent orientation relationships (ORs) were identified between TiC and both diamond-{111} facet and copper: (11 ̅1 ̅) TiC // (11 ̅1 ̅) Diamond and [1 ̅1 ̅0] TiC // [1 ̅1 ̅0] Diamond, (111) TiC// (1 ̅11) Cu, [01 ̅1] TiC// [211] Cu. These ensure a high degree of atomic ordering at the interface, enhancing phonon transmission across the interface. Concurrently, Cu segregation at TiC grain boundaries refines grains and strengthens interfacial bonding, further reducing thermal resistance. Furthermore, sub-stoichiometric TiCx present on both facets introduces a mixed metallic-covalent bonding character, facilitating electron-mediated heat transport and promoting nanotwin formation, which migrates phonon scattering by enhancing dislocation mobility. 
Overall, this work demonstrates that the thermophysical and mechanical performance of copper/diamond composite is governed by the synergistic interplay between processing parameters and interfacial microstructure. The facet-dependent atomic configuration of diamond surface dictate distinct interfacial microstructures, while processing parameters such as temperature and pressure provide effective levers for controlling TiC stoichiometry, interlayer continuity, and interfacial bonding strength. Together, these factors determine the balance between thermal transport efficiency and mechanical strength, establishing a rational framework for interface engineering in high-performance Cu/diamond composites.

text: Investigation on fabrication, interface formation, and properties of hot-processed titanium-doped copper/diamond composites Efficient thermal management is crucial for next-generation high-power electronic devices, driving the need for high-performance heat sink materials. Copper/diamond composites have emerged as promising candidates due to their exceptional thermal conductivity (TC) and tailorable coefficient of thermal expansion (CTE). However, their performance is limited by weak interfacial bonding, caused by the poor chemical affinity between copper and diamond and severe phonon scattering due to mismatched lattice vibrations. To address these challenges, interface engineering strategies such as pre-coating diamond particles or pre-alloying the copper matrix with carbide-forming elements (e.g., Ti, W, Zr, Cr, B) have been extensively explored. Among these, titanium has shown promise through the formation of a stable titanium carbide (TiC) layer, which significantly enhances interfacial bonding and composite performance. This thesis investigates the thermophysical and mechanical performance of titanium-doped copper/diamond composites fabricated via hot-processing techniques, hot-forging and hot-pressing, with focuses on optimizing fabrication parameters, elucidating interface formation mechanisms, and establishing the relationship between the interfacial microstructure and composites performance. 
Ti-coated diamond/Cu composites were successfully fabricated via hot-forging, and the effects of forging temperature, diamond volume fraction, and deformation degree were systematically evaluated. The study highlights the crucial role of hot-forging temperature in optimizing TiC interface formation and enhancing interfacial bonding. 800°C is the optimal hot forging temperature to facilitate the dynamic formation of TiC interface layer and ensure a high interface coverage rate on the diamond particles. Additionally, the volume fraction of diamond affects the interface microstructure and TC of the hot-forged composites by affecting the heating behaviour of the composites during induction heating. The relatively large deformation degree can effectively contribute to the densification and interfacial bonding of the composites. 800 °C hot-forged composite with 45 vol% diamond and 80% deformation degree exhibited excellent TC of 529 W/mK, along with a high tensile strength of 241 MPa, attributed to the synergy of uniform distribution of diamond in the matrix, a rough interface, and strong interfacial bonding between the copper and the diamond.
The fabrication of copper/diamond composites via hot-pressing, was further investigated employing two interfacial engineering strategies: titanium carbide formation through diamond surface metallization and copper matrix alloying with titanium additives. The results show that diamond metallization shows a better effectiveness in enhancing both mechanical and thermophysical performance than matrix alloying. Notably, Cu/50 vol% Ti-coated diamond composite fabricated at 540 MPa achieved an exceptional TC of 565 W/mK and a tensile strength of about 147 MPa. For the copper-Ti/diamond composite containing 0.5 wt% Ti processed at 1050 °C, it exhibited a comparable TC (554 W/mK), but a relatively low tensile strength (93 MPa). The optimal processing pressures for maximizing TC and mechanical strength in hot-pressed Cu/Ti-coated diamond composites differ due to interface microstructure: continuous interface enhances mechanical strength through strong interfacial bonding, whereas jagged interface arranged in parallel on the diamond surface minimizes interfacial thermal resistance. A comparative study between the two processing routes revealed that hot-forging outperforms hot-pressing at high diamond content (55 vol%) due to greater matrix deformation and more uniform diamond distribution, whereas hot-pressing becomes advantageous at lower diamond fractions (45-50 vol%), where applied pressure provides effective densification and interfacial microstructure becomes the dominant factor governing composite performance. 
A detailed investigation into interface formation mechanisms was conducted on 540 MPa hot-pressed composites with 50 vol% Ti-coated diamond. The results revealed that the distinct atomic configuration of individual diamond facets govern the nucleation and growth behaviour of TiC at the interface, giving rise to different interfacial microstructures: a continuous Cu/TiC/diamond structure on diamond-{100} facets, and a multilayered Cu/Cu (Ti)/TiC/diamond structure on diamond-{111} facets. Beyond the formation of TiC interlayer on both facets, the semi-coherent orientation relationships (ORs) were identified between TiC and both diamond-{111} facet and copper: (11 ̅1 ̅) TiC // (11 ̅1 ̅) Diamond and [1 ̅1 ̅0] TiC // [1 ̅1 ̅0] Diamond, (111) TiC// (1 ̅11) Cu, [01 ̅1] TiC// [211] Cu. These ensure a high degree of atomic ordering at the interface, enhancing phonon transmission across the interface. Concurrently, Cu segregation at TiC grain boundaries refines grains and strengthens interfacial bonding, further reducing thermal resistance. Furthermore, sub-stoichiometric TiCx present on both facets introduces a mixed metallic-covalent bonding character, facilitating electron-mediated heat transport and promoting nanotwin formation, which migrates phonon scattering by enhancing dislocation mobility. 
Overall, this work demonstrates that the thermophysical and mechanical performance of copper/diamond composite is governed by the synergistic interplay between processing parameters and interfacial microstructure. The facet-dependent atomic configuration of diamond surface dictate distinct interfacial microstructures, while processing parameters such as temperature and pressure provide effective levers for controlling TiC stoichiometry, interlayer continuity, and interfacial bonding strength. Together, these factors determine the balance between thermal transport efficiency and mechanical strength, establishing a rational framework for interface engineering in high-performance Cu/diamond composites.

year: 2025

title: Putting the burden of proof in its place: When are differential allocations legitimate?

authors: Dare, Tim

subjects: allocations legitimate

abstract: It is widely assumed that legitimate differential allocations of the burden of proof are ubiquitous: that in all cases in which opposing views are being debated, one side has the responsibility of proving their claim and if they fail, the opposing view wins by default. We argue that the cases in which one party has the burden of proof are exceptions. In general, participants in reasoned discourse are all required to provide reasons for the claims they make. We distinguish between truth-directed and non-truth-directed discourse, argue that the paradigm contexts in which there are legitimate differential allocations of the burden of proof (law and formal debate) are non-truth-directed, and suggest that in truth-directed contexts, except in certain special cases, differential allocation of the burden of proof is not warranted.

text: Putting the burden of proof in its place: When are differential allocations legitimate? It is widely assumed that legitimate differential allocations of the burden of proof are ubiquitous: that in all cases in which opposing views are being debated, one side has the responsibility of proving their claim and if they fail, the opposing view wins by default. We argue that the cases in which one party has the burden of proof are exceptions. In general, participants in reasoned discourse are all required to provide reasons for the claims they make. We distinguish between truth-directed and non-truth-directed discourse, argue that the paradigm contexts in which there are legitimate differential allocations of the burden of proof (law and formal debate) are non-truth-directed, and suggest that in truth-directed contexts, except in certain special cases, differential allocation of the burden of proof is not warranted.

year: 2008

title: Exploring patient experiences and power dynamics in an acute general surgical ward: A mixed methods study exploring patient and staff
perceptions of the inpatient experience at Waikato Hospital

authors: Drake, Emma Rose

subjects: Nursing

abstract: Background: Alongside health outcomes, patient experiences are considered crucial in identifying the quality of a health care setting. General surgery comprise the largest range of pathologies and accounts for the highest number of patient discharges of any surgical specialty. As a way to address the power imbalance between healthcare staff and patients, patient-centred models of care are increasingly being adopted and implemented within hospitals including surgery. This study aims to investigate the current experiences of acutely admitted patients in a general surgical ward at Waikato Hospital, including opportunities for and challenges to improvement initiatives. Furthermore, the study examines relevant staff members perspectives of the inpatient experience and seeks to determine the efficacy of a proposed intervention focusing on empowering patients and their families.
Methods: The study was a mixed method design involving two phases. Phase I obtained qualitative data from semi-structured interviews with six patients and twelve staff members. Themes which emerged from the qualitative data in phase I were used to inform the development of phase II, as well as to inform a proposed patient self- assessment intervention. Phase II obtained quantitative data through Likert scale response surveys provided to acute patients on, or near to, their day of discharge from the surgical ward over a two month period.
Results: A total of six patients and 12 healthcare staff (senior registered nurses, n=3; surgical registered nurse managers, n=2; surgical fellows, n=2; surgical registrar, n=1; dietitian, n=1; social worker, n=1; occupational therapist, n=1; and physiotherapist n=1) were involved in phase I. A total of 53 surveys were returned from patients in Phase II (63.1% response rate). Qualitative data from phase I was analysed using a general inductive approach. This revealed three themes including power and control concerns for patients, the hierarchy of the health care team and the surrounding stressors of the organisation and environment. Analysis of the quantitative data collected descriptive statistics and calculated chi-squares. Of note were the statistically significant differences particularly between patients of Māori ethnicity comparatively to non-Māori, and according to gender and reason in hospital. There were no statistically significant differences for patients according to age group.
Conclusion: This study identified both the experiences of patients and staff in an acute general surgical context. The study found that the proposed patient self- assessment intervention was not immediately recommended. This was due to the current recommendations from patients who identified their strong preference was for face-to-face communication with staff. It was also due to staff members identification of a perceived inability to consistently provide person-centred care which corresponded with the patient self-assessment data. Acute general surgical care needs of patients were perceived by staff as taking precedent and current workplace stressors, including staffing and skill mix deficits and perceived lack of staff wellbeing supports, were strong inhibitors for staff to provide their preferred capacity of patient-centred care.

text: Exploring patient experiences and power dynamics in an acute general surgical ward: A mixed methods study exploring patient and staff
perceptions of the inpatient experience at Waikato Hospital Background: Alongside health outcomes, patient experiences are considered crucial in identifying the quality of a health care setting. General surgery comprise the largest range of pathologies and accounts for the highest number of patient discharges of any surgical specialty. As a way to address the power imbalance between healthcare staff and patients, patient-centred models of care are increasingly being adopted and implemented within hospitals including surgery. This study aims to investigate the current experiences of acutely admitted patients in a general surgical ward at Waikato Hospital, including opportunities for and challenges to improvement initiatives. Furthermore, the study examines relevant staff members perspectives of the inpatient experience and seeks to determine the efficacy of a proposed intervention focusing on empowering patients and their families.
Methods: The study was a mixed method design involving two phases. Phase I obtained qualitative data from semi-structured interviews with six patients and twelve staff members. Themes which emerged from the qualitative data in phase I were used to inform the development of phase II, as well as to inform a proposed patient self- assessment intervention. Phase II obtained quantitative data through Likert scale response surveys provided to acute patients on, or near to, their day of discharge from the surgical ward over a two month period.
Results: A total of six patients and 12 healthcare staff (senior registered nurses, n=3; surgical registered nurse managers, n=2; surgical fellows, n=2; surgical registrar, n=1; dietitian, n=1; social worker, n=1; occupational therapist, n=1; and physiotherapist n=1) were involved in phase I. A total of 53 surveys were returned from patients in Phase II (63.1% response rate). Qualitative data from phase I was analysed using a general inductive approach. This revealed three themes including power and control concerns for patients, the hierarchy of the health care team and the surrounding stressors of the organisation and environment. Analysis of the quantitative data collected descriptive statistics and calculated chi-squares. Of note were the statistically significant differences particularly between patients of Māori ethnicity comparatively to non-Māori, and according to gender and reason in hospital. There were no statistically significant differences for patients according to age group.
Conclusion: This study identified both the experiences of patients and staff in an acute general surgical context. The study found that the proposed patient self- assessment intervention was not immediately recommended. This was due to the current recommendations from patients who identified their strong preference was for face-to-face communication with staff. It was also due to staff members identification of a perceived inability to consistently provide person-centred care which corresponded with the patient self-assessment data. Acute general surgical care needs of patients were perceived by staff as taking precedent and current workplace stressors, including staffing and skill mix deficits and perceived lack of staff wellbeing supports, were strong inhibitors for staff to provide their preferred capacity of patient-centred care.

year: 2022