Metallic scaffolds with lightweight,low elastic modulus,and high energy-absorbing capacity are widely utilized in industrial applications but usually require post-heat treatment to enhance their comprehen-sive mechani...Metallic scaffolds with lightweight,low elastic modulus,and high energy-absorbing capacity are widely utilized in industrial applications but usually require post-heat treatment to enhance their comprehen-sive mechanical properties.However,it is unclear how to utilize the impact ofβ-Nb on the surrounding matrix for NiTiNb ternary alloys to achieve strength-ductility-superelasticity enhancement.Here,we pre-pared rhomboidal dodecahedral NiTiNb porous scaffolds with a porosity of 85.9%by additive manufac-turing.Subsequently,annealing treatment was employed to drastically reduce the phase transformation temperatures and expand the thermal hysteresis.Interestingly,the 850℃ annealed scaffold exhibited exceeding double compressive strength of the as-built sample,with a remarkable improvement in ductil-ity and superelasticity.From the microstructure perspective,high-temperature annealing caused a further eutectic reaction of the unmelted Nb particles with the NiTi matrix and the transformation of mesh-likeβ-Nb into dispersedly distributed sphericalβ-Nb particles.The microstructure evolution after defor-mation indicated that stress-induced martensitic transformation occurred in the matrix away from the NiTi-Nb eutectic region whereas almost no martensite formed nearbyβ-Nb particles.Atom probe tomog-raphy characterization revealed an element diffusion zone in several nanometers surrounding theβ-Nb particle,where the substitution of Nb with Ti led to a higher Ni:Ti atomic ratio,lowering transforma-tion temperatures.Molecular dynamics simulations illustrated thatβ-Nb particles can not only entangle dislocations internally,acting as reinforcements but also hinder the twin growth,contributing to strain hardening.This work elucidates the influence ofβ-Nb particles on the deformation mechanism of the NiTi-Nb eutectic region through in-depth atomic-scale investigation,which can provide inspiration for the improvement of comprehensive mechanical properties of NiTiNb alloys.展开更多
采用Nd:YAG脉冲激光器实现了200μm厚热轧态Ni Ti Nb形状记忆合金的激光焊接,研究激光平均功率、激光脉宽和激光频率等主要工艺参数对焊接接头形貌的影响,分析了焊缝热影响区显微组织、力学性能的变化规律。结果表明:激光平均功率、激...采用Nd:YAG脉冲激光器实现了200μm厚热轧态Ni Ti Nb形状记忆合金的激光焊接,研究激光平均功率、激光脉宽和激光频率等主要工艺参数对焊接接头形貌的影响,分析了焊缝热影响区显微组织、力学性能的变化规律。结果表明:激光平均功率、激光脉宽和激光频率需要良好匹配才能获得较好性能的焊接接头。当激光平均功率为16.8 W、激光脉宽为4.5 ms、激光频率为4.5 Hz时,焊缝的抗拉强度最高,达到母材的95%。随着激光平均功率、激光脉宽的增加,焊缝热影响区的宽度先增加后减小。激光频率增加后,热影响区晶粒变粗。当频率为27Hz时,在靠近热影响区的焊缝出现了一个粗大树枝晶区域。母材断口的韧窝大而深,为典型的韧性断裂。焊缝断口的韧窝小而浅,呈鱼卵形。热影响区的显微硬度高于母材的,低于焊缝中心区域的。展开更多
基金financial supports of National Natural Science Foundation of China under Grant Nos.52274387 and 52311530772.
文摘Metallic scaffolds with lightweight,low elastic modulus,and high energy-absorbing capacity are widely utilized in industrial applications but usually require post-heat treatment to enhance their comprehen-sive mechanical properties.However,it is unclear how to utilize the impact ofβ-Nb on the surrounding matrix for NiTiNb ternary alloys to achieve strength-ductility-superelasticity enhancement.Here,we pre-pared rhomboidal dodecahedral NiTiNb porous scaffolds with a porosity of 85.9%by additive manufac-turing.Subsequently,annealing treatment was employed to drastically reduce the phase transformation temperatures and expand the thermal hysteresis.Interestingly,the 850℃ annealed scaffold exhibited exceeding double compressive strength of the as-built sample,with a remarkable improvement in ductil-ity and superelasticity.From the microstructure perspective,high-temperature annealing caused a further eutectic reaction of the unmelted Nb particles with the NiTi matrix and the transformation of mesh-likeβ-Nb into dispersedly distributed sphericalβ-Nb particles.The microstructure evolution after defor-mation indicated that stress-induced martensitic transformation occurred in the matrix away from the NiTi-Nb eutectic region whereas almost no martensite formed nearbyβ-Nb particles.Atom probe tomog-raphy characterization revealed an element diffusion zone in several nanometers surrounding theβ-Nb particle,where the substitution of Nb with Ti led to a higher Ni:Ti atomic ratio,lowering transforma-tion temperatures.Molecular dynamics simulations illustrated thatβ-Nb particles can not only entangle dislocations internally,acting as reinforcements but also hinder the twin growth,contributing to strain hardening.This work elucidates the influence ofβ-Nb particles on the deformation mechanism of the NiTi-Nb eutectic region through in-depth atomic-scale investigation,which can provide inspiration for the improvement of comprehensive mechanical properties of NiTiNb alloys.
