【作者】 张晨；

【导师】 蒋丽；

【作者基本信息】 大连理工大学 ， 材料科学与工程， 2025， 硕士

【摘要】 中/高熵合金突破了传统合金设计的成分限制,为材料性能的精准调控开辟了新维度。其中,具有单相体心立方结构的难熔中/高熵合金因其优异的强度而备受关注,但是难熔中/高熵合金的本征特性导致材料在获得高强度的同时,往往伴随着塑性不足。TiZrNb中熵合金是最新发展起来的一类具有较好室温塑性的难熔中熵合金,其在室温下的拉伸屈服强度为830 MPa,延伸率达到了13%,良好的室温塑性使其性能的可调范围大大增加,具有较好的应用潜力。本课题以TiZrNb为基础合金,通过掺杂与主元原子尺寸差异较大的小尺寸非金属元素O和N,增加基体的晶格畸变,以期望调控TiZrNb合金的综合力学性能,获得强度-塑性良好结合的合金。本工作探究了非金属元素O和N对TiZrNb合金的微观组织以及室温、高温力学性能的影响,并对其强化机制进行了研究,具体内容如下:（1）对TiZrNb合金进行O、N掺杂分别建立了合金体系（TiZrNb）_100-xO_x（x=0.5,1,2,4,6 at.%）和（TiZrNb）_100-xN_x（x=1,2,3,3.5,4 at.%）,探究不同含量的O和N掺杂对微观组织的形貌及晶粒尺寸、元素分布、相结构演变的影响。结果表明,不同含量的O掺杂和N掺杂均未使TiZrNb合金的相组成发生变化,两个合金体系均保持单相体心立方结构。少量掺杂时,两个合金系的微观组织均呈现出树枝晶形貌。随着掺杂量的增加,微观组织均从树枝晶向等轴晶转变。根据EPMA-WDS点扫描和面扫描结果,Zr元素和Nb元素存在轻微的排斥,分别倾向于在枝晶上和枝晶间偏聚,Ti元素呈现均匀分布,O元素和N元素都均匀分布在基体上。（2）对两个合金体系分别进行室温压缩试验以及800℃和1000℃的高温压缩试验,探究不同含量的O和N掺杂对室温和高温力学性能的调控作用。结果表明,两个合金体系的屈服强度均随掺杂量的增加而提高,且在过量掺杂时均快速发生断裂。其中,O掺杂系列中的O₄合金综合力学性能最好,室温屈服强度为1300 MPa,800℃和1000℃高温屈服强度分别为545 MPa和143 MPa,压缩应变量均保持在60%以上。N掺杂系列中的N₃合金综合力学性能最佳,室温屈服强度为1400 MPa,800℃和1000℃高温屈服强度分别为510 MPa和151 MPa,压缩应变量均在60%左右。（3）采用Toda-Caraballo和Labusch模型对O掺杂和N掺杂两个体系中的强化机制进行简单分析,结果表明两个合金系都以固溶强化为主,细晶强化为辅。其中,固溶强化均占据两个合金系强度的90%以上。对同等含量O掺杂和N掺杂产生的强化效果进行对比,发现当少量掺杂（<1 at.%）时,两者的强韧化效果几乎相似,而当掺杂量逐渐增加至2 at.%以上时,O掺杂对合金塑性的保持能力明显更优异,O₄合金在强度提高的同时,仍然保持着80%的应变,而N₄合金塑性急剧下降,应变不足20%。从强度-塑性结合上来看,O掺杂对合金室温及高温力学性能的优化效果要优于N掺杂。更多还原

【Abstract】 Medium/high-entropy alloys have broken through the compositional limitations of traditional alloy design,opening new dimensions for the precise regulation of material properties.Among them,refractory medium/high-entropy alloys with a single-phase body-centered cubic（BCC）structure have attracted significant attention due to their exceptional strength.However,the intrinsic characteristics of these alloys often result in insufficient ductility alongside high strength.The TiZrNb medium-entropy alloy is a recently developed refractory medium-entropy alloy with relatively good room-temperature ductility,exhibiting a tensile yield strength of 830 MPa and an elongation of 13%.Its favorable room-temperature ductility greatly expands the adjustable range of its properties,demonstrating considerable application potential.This study focuses on the TiZrNb base alloy and introduces small-sized nonmetallic elements O and N,which have significant atomic size differences from the principal elements,to increase lattice distortion in the matrix.The aim is to regulate the comprehensive mechanical properties of the TiZrNb alloy and achieve a good balance between strength and ductility.This work investigates the effects of nonmetallic elements O and N on the microstructure,as well as the room-temperature and high-temperature mechanical properties of the TiZrNb alloy,and studies the underlying strengthening mechanisms.The specific research contents are as follows:（1）Alloy systems of（TiZrNb）_100-xO_x（x=0.5,1,2,4,6 at.%）and（TiZrNb）_100-xN_x（x=1,2,3,3.5,4 at.%）were established by doping TiZrNb with O and N,respectively,to explore the effects of different O and N doping concentrations on the morphology and grain size of the microstructure,elemental distribution,and phase structure evolution.The results show that neither O nor N doping alters the phase composition of the TiZrNb alloy,with both systems maintaining a single-phase BCC structure.At low doping levels,both alloy systems exhibit a dendritic microstructure.As the doping concentration increases,the microstructure transitions from dendritic to equiaxed grains.According to EPMA-WDS point and area scanning results,Zr and Nb show slight repulsion,tending to segregate in dendritic and interdendritic regions,respectively,while Ti remains uniformly distributed.Both O and N are homogeneously distributed in the matrix.（2）Room-temperature compression tests,as well as high-temperature compression tests at800℃ and 1000℃,were conducted on both alloy systems to investigate the regulatory effects of O and N doping on mechanical properties at different temperatures.The results indicate that the yield strength of both alloy systems increases with higher doping concentrations,but excessive doping leads to rapid fracture.In the O-doped series,the O₄ alloy exhibits the best overall mechanical performance,with a room-temperature yield strength of 1300 MPa,high-temperature yield strengths of 545 MPa at 800℃ and 143 MPa at 1000℃,and compressive strains exceeding 60%.In the N-doped series,the N₃ alloy demonstrates the optimal comprehensive mechanical properties,with a room-temperature yield strength of 1400 MPa,high-temperature yield strengths of 510 MPa at 800℃ and 151 MPa at 1000℃,and compressive strains around 60%.（3）The strengthening mechanisms of the O-doped and N-doped systems were analyzed using the Toda-Caraballo and Labusch models.The results indicate that both alloy systems are primarily strengthened by solid solution strengthening,with grain boundary strengthening playing a secondary role.Solid solution strengthening accounts for over 90%of the strength in both systems.A comparison of the strengthening effects of O and N at equivalent doping levels reveals that at low concentrations（<1 at.%）,their strengthening and toughening effects are nearly identical.However,as the doping concentration increases to 2 at.%or higher,O doping demonstrates significantly better ductility retention.The O₄ alloy maintains 80%strain while achieving higher strength,whereas the N₄ alloy experiences a sharp decline in ductility,with strain below 20%.From the perspective of strength-ductility balance,O doping proves more effective than N doping in optimizing the room-temperature and high-temperature mechanical properties of the alloy.更多还原