摘要
目的研究C元素在激光熔覆Ti NiCuZrNbTa难熔高熵合金沉积态各相结构中的扩散行为及其对组织微观硬度的影响,为合金性能调控提供新途径。方法以聚乙烯醇为碳源,采用激光熔覆的方式在铜基底制备Ti NiCuZrNbTa难熔高熵合金,研究C元素对高熵合金底部、中部、顶部区域组织、物相与硬度的影响。结果Ti NiCuZrNbTa合金试样横截面顶部组织主要由细小等轴晶、富Zr网状枝晶以及弥散于基体的Ta/Nb颗粒相共同构成;随着凝固速率的逐渐降低,中部区域形成以粗大枝晶为主要特征的结构,点状/细小条状的Ta/Nb相主要分布在枝晶臂间的交汇处;而底部区域由于靠近基底,凝固时较大的温度梯度导致局部形成了垂直于界面方向的柱状晶,且产生向中部组织晶粒过渡的趋势。在合金不同相中,C元素主要分布于相界,Ti、Zr、Ta等强碳化物元素也会与C结合形成弥散分布的碳化物颗粒,起到强化作用。其中,O元素产生“介导扩散”方式,对C在不同相中的扩散起到一定促进作用。沿沉积方向靠近铜基底的熔覆层硬度约为465HV,随着C含量的增加,熔覆层硬度增加至约527HV。结论在该难熔高熵合金体系中,各相中的C元素含量随着熔覆层厚度的增加而增加,适当含量的C元素在不同相中扩散形成的固溶强化和弥散强化能够有效阻碍位错运动,提升表面硬度。
To advance the regulation of TiNiCuZrNbTa refractory high-entropy alloy(RHEA)properties,the work aims to investigate C diffusion in various phase structures and its impact on the microstructural hardness.A TiNiCuZrNbTa RHEA cladding layer was fabricated on a copper substrate via laser cladding with polyvinyl alcohol(PVA)as carbon source.The effects of C on the microstructure,phase composition,and hardness across the bottom,middle,and top regions of the alloy were systematically studied.The top region at the cross section of the alloy primarily exhibited fine equiaxed grains,with Zr-rich phases forming dendritic networks and fine Ta/Nb particle phases dispersed within the matrix.Conversely,with the gradual decrease in solidification rate,the middle region featured coarse dendritic structures,where Ta/Nb phases manifested as dots or fine strips concentrated at dendrite arm intersections.The bottom region,adjacent to the substrate,experienced a higher thermal gradient during solidification,resulting in the formation of columnar crystals perpendicular to the interface,exhibiting a structural transition towards the coarser dendritic morphology of the middle region.In the different phases of the alloy,strong carbide-forming elements(Ti,Zr,Ta)combined with C to generate dispersed carbide particles,enhancing the strength.Notably,oxygen(O)promoted C diffusion across phases via a“mediated diffusion”mechanism.Along the build direction of the cladding layer,the hardness near the copper substrate measured approximately 465HV.With the increasing C content,the hardness rose correspondingly,reaching approximately 527HV in the cladding layer.Within this RHEA system,the C concentration in each phase escalates along the cladding layer.Optimal C diffusion in different phases facilitates solid solution and dispersion strengthening,effectively impeding dislocation movement and enhancing surface hardness.
作者
王嘉伟
邵泽西
吴斌涛
夏明许
WANG Jiawei;SHAO Zexi;WU Bintao;XIA Mingxu(School of Materials and New Energy,Ningxia University,Yinchuan 750400,China;School of Chemical Engineering and Technology and State Key Laboratory for Chemical Engineering,Tianjin University,Tianjin 300350,China)
出处
《精密成形工程》
北大核心
2025年第12期35-44,共10页
Journal of Netshape Forming Engineering
基金
国家自然科学基金联合基金项目(U24A2006)
宁夏自然科学基金杰出青年项目(2024AAC04002)。
