Theα_(2)decomposition inγ-TiAl-based alloys during long-term service at elevated temperatures affects the mechanical properties and reliability of components.However,the formation mechanism of the precipitates,β_(0...Theα_(2)decomposition inγ-TiAl-based alloys during long-term service at elevated temperatures affects the mechanical properties and reliability of components.However,the formation mechanism of the precipitates,β_(0)phase in Mo-modifiedγ-TiAl alloys in particular,has not been clarified.In the present work,the formation of a novelα_(2)+β_(0)modulated micro structure in Ti-43.5 Al-4Nb-1Mo-0.5B(at%)alloy at 700℃has been investigated by using scanning and transmission electron microscopy.Six equivalentβ_(0)phase variants nucleate at theα_(2)/γlamellar interfaces and grow into a plate shape withinα_(2)lamellae.Theβ_(0)phase mainly exists as clusters of three or multiple plates.This distinctive growth pattern exhibits notable differences from conventional phase transformation modes,offering a fresh perspective for comprehending phase transformation behaviors.The formation of theβ_(0)phase inα_(2)lamellae is controlled by the diffusion of Nb/Mo atoms(mainly Mo).The lattice distortion between theβ_(0)andα_(2)phases promotes the nucleation of newβ_(0)plates,revealing the significant impact of interphase interactions on the micro structural evolution.The lattice of the centralα_(2)phase enclosed byβ_(0)variants is rotated around the[0001]α_(2)axis of theα_(2)matrix by 10.53°to minimize the elastic strain energy.The results offer insights into the mechanism ofα_(2)decomposition as a function of alloy composition,providing a basis for controlling the micro structure and improving the mechanical properties ofβ-stabilizedγ-TiAl alloys,and thus opening new window of opportunity in the design and development of hightemperature structural materials.展开更多
Borides play a direct role in determining the mechanical properties of boron-containing TiAl alloy castings.Studying the growth habits of borides is crucial for controlling their morphology and size.In this study,SEM ...Borides play a direct role in determining the mechanical properties of boron-containing TiAl alloy castings.Studying the growth habits of borides is crucial for controlling their morphology and size.In this study,SEM and HRTEM techniques were employed to characterize TiB_(2)particles in Ti-45Al-2Mn-2Nb-1.25B alloy.TiB_(2)particles in the alloys mainly exhibit blocky,needlelike,ribbon-like and sixfold symmetrical morphologies.Atomic-scale characterization revealed that blocky and ribbon-like TiB_(2)particles exhibit different major axes,[0001]and[1120],respectively.A novel sixfold symmetrical TiB_(2)particle was observed,formed by the combination of these two particle types.The change in B atom supersaturation during the solidificatioin process was found to be the primary factor influencing the major axes of TiB_(2)particles.During the early stages of soidification,the high supersaturatiorn of B atoms in the melt led to equilibrium conditions.TiB_(2)particles grew predominantly in a blocky shape with[0001]as the major axis.As the supersaturation of B atoms decreased,the scarcity of B atoms caused crystal growth to deviate from equilibrium,the(1120)plane exhibited the fastest growth rate due to its requirement for the shortest range of atomic rearrangement and highest attachment energy,TiB_(2)particles assumed aribbon-like shape.Consequently,the growth of TiB_(2)particles underwent a transition between these two growth mechanisms,forming a sixfold symmetrical morphology.This finding helps understand the growth behavior of precipitates in TiAl alloy solidification,enabling control of boride morphology and improving alloy performance,thus providing theoretical insights into strengthening phase formation in metals.展开更多
基金financially supported by the National Natural Science Foundation of China(No.52471054)the CAS Project for Young Scientists in Basic Research(No.YSBR025)+1 种基金the Major Special Science and Technology Project of Yunnan Province(No.202302AB080009)the National Key Research and Development Program of China(No.2021YFB3702605)
文摘Theα_(2)decomposition inγ-TiAl-based alloys during long-term service at elevated temperatures affects the mechanical properties and reliability of components.However,the formation mechanism of the precipitates,β_(0)phase in Mo-modifiedγ-TiAl alloys in particular,has not been clarified.In the present work,the formation of a novelα_(2)+β_(0)modulated micro structure in Ti-43.5 Al-4Nb-1Mo-0.5B(at%)alloy at 700℃has been investigated by using scanning and transmission electron microscopy.Six equivalentβ_(0)phase variants nucleate at theα_(2)/γlamellar interfaces and grow into a plate shape withinα_(2)lamellae.Theβ_(0)phase mainly exists as clusters of three or multiple plates.This distinctive growth pattern exhibits notable differences from conventional phase transformation modes,offering a fresh perspective for comprehending phase transformation behaviors.The formation of theβ_(0)phase inα_(2)lamellae is controlled by the diffusion of Nb/Mo atoms(mainly Mo).The lattice distortion between theβ_(0)andα_(2)phases promotes the nucleation of newβ_(0)plates,revealing the significant impact of interphase interactions on the micro structural evolution.The lattice of the centralα_(2)phase enclosed byβ_(0)variants is rotated around the[0001]α_(2)axis of theα_(2)matrix by 10.53°to minimize the elastic strain energy.The results offer insights into the mechanism ofα_(2)decomposition as a function of alloy composition,providing a basis for controlling the micro structure and improving the mechanical properties ofβ-stabilizedγ-TiAl alloys,and thus opening new window of opportunity in the design and development of hightemperature structural materials.
基金financially supported by the National Natural Science Foundation of China(No.52471054)CAS Project for Young Scientists in Basic Research(No.YSBR-025)the Major Special Science and Technology Project of Yunnan Province(No.202302AB080009)
文摘Borides play a direct role in determining the mechanical properties of boron-containing TiAl alloy castings.Studying the growth habits of borides is crucial for controlling their morphology and size.In this study,SEM and HRTEM techniques were employed to characterize TiB_(2)particles in Ti-45Al-2Mn-2Nb-1.25B alloy.TiB_(2)particles in the alloys mainly exhibit blocky,needlelike,ribbon-like and sixfold symmetrical morphologies.Atomic-scale characterization revealed that blocky and ribbon-like TiB_(2)particles exhibit different major axes,[0001]and[1120],respectively.A novel sixfold symmetrical TiB_(2)particle was observed,formed by the combination of these two particle types.The change in B atom supersaturation during the solidificatioin process was found to be the primary factor influencing the major axes of TiB_(2)particles.During the early stages of soidification,the high supersaturatiorn of B atoms in the melt led to equilibrium conditions.TiB_(2)particles grew predominantly in a blocky shape with[0001]as the major axis.As the supersaturation of B atoms decreased,the scarcity of B atoms caused crystal growth to deviate from equilibrium,the(1120)plane exhibited the fastest growth rate due to its requirement for the shortest range of atomic rearrangement and highest attachment energy,TiB_(2)particles assumed aribbon-like shape.Consequently,the growth of TiB_(2)particles underwent a transition between these two growth mechanisms,forming a sixfold symmetrical morphology.This finding helps understand the growth behavior of precipitates in TiAl alloy solidification,enabling control of boride morphology and improving alloy performance,thus providing theoretical insights into strengthening phase formation in metals.
