Investigation On Microstructural Characteristic And Grain Boundary Engineering Of Commercial Purity W-1%La₂O₃Alloy

As fusion energy with magnetic confinement hasnumerousdistinctive superiorities, which include infinite fuel,environmental friendly, excellent security et al., it is one of the strategicenergy for future long-term sustainable development. The selection ofplasma facing materials is severe challenge of fusion energy’sdevelopment. Tungsten has a high energy threshold for physicalsputtering and does not form hydrides or co-deposits with tritium.Tungsten can also offer distinctive physical properties, which includes thehighest melting point of all metal, the lowest vapor pressure, goodthermal conductivity, and high temperature strength. Consequently, theyare considered as the most promising plasma-facing material for futurefusion reactors. However, tungsten has fatal drawbacks, namely, itsinherent brittleness at low temperatures and a relatively highductile-brittle transition temperature （DBTT）. Investigation on themicrostructure and ductility of tungsten and its alloy is essential to itssuccessful using in fusion reactor. In this paper, firstly, we investigated themicrostructure ofW-1%La₂O₃alloy using X-ray diffractometer, optical microscopy,scanning electron microscopy and transmission electron microscopy. Theobservation results show that theW-1%La₂O₃alloy gets a superiorcompactness with no porosities and cracks, and has plenty of particlesdispersed in the matrix compared with pure tungsten. Further, not onlymicron-sized La₂O₃particles, several kinds of other submicron-sizedphases including WO3, WO2, W₃O₈and La2（WO4）3were also confirmedto exist in the W-La₂O₃alloy through analyses of chemical compositionand electron diffraction patterns, which suggests that an inadequatehydrogen reduction occurredseriouslyduring the alloy preparationprocedure. This inadequate reduction and the huge dispersion particlestend to be the most unfavorable factors in the mechanical performance ofthe alloys. Possible forming processes of these particles are alsodiscussed. Secondly, we exploratory researched the treatment process toimprove the brittleness at low temperatures and a relatively high DBTTof W-1%La₂O₃alloy via the grain boundary engineering thread. Thenumerical control material thermal processing simulation testing machinewas used in this investigation. Results show that, the treatment processwhich consists of small plastic deformation then recoverythermal-treatment approach the recrystallization temperature can improvethe brittleness at low temperatures and DBTT effectively. Notably,5% deformation then1200oC annealing is the best treatment process, and itsyield strength also has a decent boost.