The rapid solidification of undercooled liquid Ti_(50)Al_(48)Mo_(2)alloy was achieved by the electromagnetic lev-itation(EML)technique.At small and medium undercoolings,primary(βTi)dendrite reacted with sur-rounding ...The rapid solidification of undercooled liquid Ti_(50)Al_(48)Mo_(2)alloy was achieved by the electromagnetic lev-itation(EML)technique.At small and medium undercoolings,primary(βTi)dendrite reacted with sur-rounding liquid to drive a peritectic transformation into the(αTi)phase.The solutal Mo and Al segrega-tions were located within the dendrite center and the grain boundary during peritectic transformation,consequently B2 phase in the dendrite center andγphase at the grain boundary formed.Once under-cooling exceeded 253 K,the peritectic transformation was completely inhibited,and the formation of the B2 phase andγphase was completely suppressed.The ultrafine eutectoid structure was formed and a complete solute trapping effect was realized.Homogeneous solute distribution facilitated the forma-tion of thicker passivation film with lower defect density and higher film resistance on the alloy surface.Moreover,this weakened micro-galvanic effect reduced the susceptibility to pitting corrosion,and conse-quently the corrosion resistance of the alloy was improved.展开更多
Rapid solidification of undercooled liquid Ti50Al44Mo6alloy was realized by electromagnetic levitation.Primary(βTi)dendrite grew rapidly from melt with decreasing temperature.As undercooling increased,nucleation rate...Rapid solidification of undercooled liquid Ti50Al44Mo6alloy was realized by electromagnetic levitation.Primary(βTi)dendrite grew rapidly from melt with decreasing temperature.As undercooling increased,nucleation rate and growth driving force of primary(βTi)dendrites increased.Growth velocity of primary(βTi)dendrite increased significantly,reaching 13.5 m·s^(-1)at the maximum undercooling(233 K).After solidification,primary(βTi)dendrite decomposed simultaneously throughβ→α→α_(2)transformation and martensite transformationβ→γ.Homogeneity of solute distribution in primary(βTi)phase affects the solid-state phase transformation mode.Solid-state phase transition was mainly dominated by diffusion-controlledβ→α→α_(2)transformation at small undercooling.Solid-state phase transition gradually was dominated by displacive martensite transformation at deep undercoolings,and corresponding microstructure was mainly characterized by more refined martensite needles.The refined microstructure and martensite transformation domination contributed to the formation of passivation films with improved corrosion resistance.Moreover,this weakens micro-galvanic effect,significantly reduces size of pits,maintains corrosion scales over pits to effectively alleviate the corrosion process,and consequently enhances corrosion resistance.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52225406,52073232,and 52088101)the National Key Research and Development Program of China(Nos.2021YFA0716301 and 2021YFB3700801)the Science Fund for Scientific and Technological Innovation Team of Shaanxi Province(No.2021TD-14).
文摘The rapid solidification of undercooled liquid Ti_(50)Al_(48)Mo_(2)alloy was achieved by the electromagnetic lev-itation(EML)technique.At small and medium undercoolings,primary(βTi)dendrite reacted with sur-rounding liquid to drive a peritectic transformation into the(αTi)phase.The solutal Mo and Al segrega-tions were located within the dendrite center and the grain boundary during peritectic transformation,consequently B2 phase in the dendrite center andγphase at the grain boundary formed.Once under-cooling exceeded 253 K,the peritectic transformation was completely inhibited,and the formation of the B2 phase andγphase was completely suppressed.The ultrafine eutectoid structure was formed and a complete solute trapping effect was realized.Homogeneous solute distribution facilitated the forma-tion of thicker passivation film with lower defect density and higher film resistance on the alloy surface.Moreover,this weakened micro-galvanic effect reduced the susceptibility to pitting corrosion,and conse-quently the corrosion resistance of the alloy was improved.
基金financially supported by the National Natural Science Foundation of China(52225406,52073232 and 52088101)the Science Fund for Scientific and Technological Innovation Team of Shaanxi Province(2021TD-14)
文摘Rapid solidification of undercooled liquid Ti50Al44Mo6alloy was realized by electromagnetic levitation.Primary(βTi)dendrite grew rapidly from melt with decreasing temperature.As undercooling increased,nucleation rate and growth driving force of primary(βTi)dendrites increased.Growth velocity of primary(βTi)dendrite increased significantly,reaching 13.5 m·s^(-1)at the maximum undercooling(233 K).After solidification,primary(βTi)dendrite decomposed simultaneously throughβ→α→α_(2)transformation and martensite transformationβ→γ.Homogeneity of solute distribution in primary(βTi)phase affects the solid-state phase transformation mode.Solid-state phase transition was mainly dominated by diffusion-controlledβ→α→α_(2)transformation at small undercooling.Solid-state phase transition gradually was dominated by displacive martensite transformation at deep undercoolings,and corresponding microstructure was mainly characterized by more refined martensite needles.The refined microstructure and martensite transformation domination contributed to the formation of passivation films with improved corrosion resistance.Moreover,this weakens micro-galvanic effect,significantly reduces size of pits,maintains corrosion scales over pits to effectively alleviate the corrosion process,and consequently enhances corrosion resistance.
