{"id":{"repo_id":"anu","oai_identifier":"oai:openresearch-repository.anu.edu.au:1885/733750337"},"canonical_url":"https://search.dev.ndltd.org/etd/anu/oai:openresearch-repository.anu.edu.au:1885/733750337","repository":{"repo_id":"anu","name":"Australian National University","base_url":"https://openresearch-repository.anu.edu.au/server/oai/request"},"display":{"title":"Sputter deposition and plasma modification of tungsten alloys for nuclear fusion applications","abstract":"The ITER reactor aims to be first thermonuclear fusion device to demonstrate net fusion power. Critical plasma-facing components in the reactor will be made of tungsten, but helium plasma irradiation is known to embrittle tungsten metal. A future reactor will therefore need an alternative material to extend the lifetime of the components. This thesis investigated the use of tungsten alloy films as a plasma-facing material for a future reactor. Tantalum and chromium were chosen as the alloying elements, and 60 − 100 nm films were manufactured using magnetron sputter deposition at a variety of alloy concentrations. Tungsten alloy films are known to deposit in an undesirable A15 crystal phase. The films were heat treated at 650◦C for 1 hour, 2 hours and 4 hours to induce and investigate the phase transition from A15 to BCC structure. X-ray diffraction patterns confirmed the presence of an A15 structure prior to annealing. The A15 phase was very stable in comparison with past results, requiring over 2 hours at 650◦C to transition to BCC. This was speculated to be linked to oxygen trapped in the films during deposition. The phase transition was slower in alloyed films than a pure tungsten control, with the retarding effect of tantalum stronger than chromium, which suggested the alloying atoms further stabilised the deposited A15 structure. Resistivity of the films saw a reduction with annealing time characteristic of the phase transition. The annealed alloy films were then exposed to helium plasma in the Magnetised Plasma Interaction Experiment at 300◦C, 500◦C and 800◦C. Surface morphology changes were tracked with secondary electron imaging. At 800◦C, surface pits were seen, which were larger in a pure tungsten film than in low concentration alloy films. Advanced surface roughening was observed in the chromium films, while a high concentration tantalum film had no surface damage at all. X-ray diffraction patterns confirmed these trends, and showed an increase in microstrain with the surface roughening in the chromium alloys. These results suggest W-Ta alloy films may have superior irradiation resistance than W-Cr alloy films, but more work is needed to confirm the trends in alloy concentration.","abstract_html":"The ITER reactor aims to be first thermonuclear fusion device to demonstrate net fusion power. Critical plasma-facing components in the reactor will be made of tungsten, but helium plasma irradiation is known to embrittle tungsten metal. A future reactor will therefore need an alternative material to extend the lifetime of the components. This thesis investigated the use of tungsten alloy films as a plasma-facing material for a future reactor. Tantalum and chromium were chosen as the alloying elements, and 60 − 100 nm films were manufactured using magnetron sputter deposition at a variety of alloy concentrations. Tungsten alloy films are known to deposit in an undesirable A15 crystal phase. The films were heat treated at 650◦C for 1 hour, 2 hours and 4 hours to induce and investigate the phase transition from A15 to BCC structure. X-ray diffraction patterns confirmed the presence of an A15 structure prior to annealing. The A15 phase was very stable in comparison with past results, requiring over 2 hours at 650◦C to transition to BCC. This was speculated to be linked to oxygen trapped in the films during deposition. The phase transition was slower in alloyed films than a pure tungsten control, with the retarding effect of tantalum stronger than chromium, which suggested the alloying atoms further stabilised the deposited A15 structure. Resistivity of the films saw a reduction with annealing time characteristic of the phase transition. The annealed alloy films were then exposed to helium plasma in the Magnetised Plasma Interaction Experiment at 300◦C, 500◦C and 800◦C. Surface morphology changes were tracked with secondary electron imaging. At 800◦C, surface pits were seen, which were larger in a pure tungsten film than in low concentration alloy films. Advanced surface roughening was observed in the chromium films, while a high concentration tantalum film had no surface damage at all. X-ray diffraction patterns confirmed these trends, and showed an increase in microstrain with the surface roughening in the chromium alloys. These results suggest W-Ta alloy films may have superior irradiation resistance than W-Cr alloy films, but more work is needed to confirm the trends in alloy concentration.","abstract_has_math":false,"creators":["Mahoney, Nicholas"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025","date_published":"2025","updated_at":"2026-07-24T00:54:44Z","subjects":["Nuclear Fusion","ITER"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/1885/733750337","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Mahoney, Nicholas"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2025-05-13T05:55:19Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2025-05-13T05:55:19Z"]},{"key":"dc:date.issued","label":"Date","values":["2025"]},{"key":"dc:type","label":"Dc Type","values":["Thesis (Honours)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Nuclear Fusion","ITER"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/1885/733750337"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The ITER reactor aims to be first thermonuclear fusion device to demonstrate net fusion power. Critical plasma-facing components in the reactor will be made of tungsten, but helium plasma irradiation is known to embrittle tungsten metal. A future reactor will therefore need an alternative material to extend the lifetime of the components. This thesis investigated the use of tungsten alloy films as a plasma-facing material for a future reactor. Tantalum and chromium were chosen as the alloying elements, and 60 − 100 nm films were manufactured using magnetron sputter deposition at a variety of alloy concentrations. Tungsten alloy films are known to deposit in an undesirable A15 crystal phase. The films were heat treated at 650◦C for 1 hour, 2 hours and 4 hours to induce and investigate the phase transition from A15 to BCC structure. X-ray diffraction patterns confirmed the presence of an A15 structure prior to annealing. The A15 phase was very stable in comparison with past results, requiring over 2 hours at 650◦C to transition to BCC. This was speculated to be linked to oxygen trapped in the films during deposition. The phase transition was slower in alloyed films than a pure tungsten control, with the retarding effect of tantalum stronger than chromium, which suggested the alloying atoms further stabilised the deposited A15 structure. Resistivity of the films saw a reduction with annealing time characteristic of the phase transition. The annealed alloy films were then exposed to helium plasma in the Magnetised Plasma Interaction Experiment at 300◦C, 500◦C and 800◦C. Surface morphology changes were tracked with secondary electron imaging. At 800◦C, surface pits were seen, which were larger in a pure tungsten film than in low concentration alloy films. Advanced surface roughening was observed in the chromium films, while a high concentration tantalum film had no surface damage at all. X-ray diffraction patterns confirmed these trends, and showed an increase in microstrain with the surface roughening in the chromium alloys. These results suggest W-Ta alloy films may have superior irradiation resistance than W-Cr alloy films, but more work is needed to confirm the trends in alloy concentration."]},{"key":"dc:title","label":"Title","values":["Sputter deposition and plasma modification of tungsten alloys for nuclear fusion applications"]}]}],"canonical_facts":{"dc:creator":["Mahoney, Nicholas"],"dc:date.accessioned":["2025-05-13T05:55:19Z"],"dc:date.available":["2025-05-13T05:55:19Z"],"dc:date.issued":["2025"],"dc:description.abstract":["The ITER reactor aims to be first thermonuclear fusion device to demonstrate net fusion power. Critical plasma-facing components in the reactor will be made of tungsten, but helium plasma irradiation is known to embrittle tungsten metal. A future reactor will therefore need an alternative material to extend the lifetime of the components. This thesis investigated the use of tungsten alloy films as a plasma-facing material for a future reactor. Tantalum and chromium were chosen as the alloying elements, and 60 − 100 nm films were manufactured using magnetron sputter deposition at a variety of alloy concentrations. Tungsten alloy films are known to deposit in an undesirable A15 crystal phase. The films were heat treated at 650◦C for 1 hour, 2 hours and 4 hours to induce and investigate the phase transition from A15 to BCC structure. X-ray diffraction patterns confirmed the presence of an A15 structure prior to annealing. The A15 phase was very stable in comparison with past results, requiring over 2 hours at 650◦C to transition to BCC. This was speculated to be linked to oxygen trapped in the films during deposition. The phase transition was slower in alloyed films than a pure tungsten control, with the retarding effect of tantalum stronger than chromium, which suggested the alloying atoms further stabilised the deposited A15 structure. Resistivity of the films saw a reduction with annealing time characteristic of the phase transition. The annealed alloy films were then exposed to helium plasma in the Magnetised Plasma Interaction Experiment at 300◦C, 500◦C and 800◦C. Surface morphology changes were tracked with secondary electron imaging. At 800◦C, surface pits were seen, which were larger in a pure tungsten film than in low concentration alloy films. Advanced surface roughening was observed in the chromium films, while a high concentration tantalum film had no surface damage at all. X-ray diffraction patterns confirmed these trends, and showed an increase in microstrain with the surface roughening in the chromium alloys. These results suggest W-Ta alloy films may have superior irradiation resistance than W-Cr alloy films, but more work is needed to confirm the trends in alloy concentration."],"dc:identifier.uri":["https://hdl.handle.net/1885/733750337"],"dc:subject":["Nuclear Fusion","ITER"],"dc:title":["Sputter deposition and plasma modification of tungsten alloys for nuclear fusion applications"],"dc:type":["Thesis (Honours)"]},"updated_at":"2026-07-24T00:54:44Z"}