摘要
利用团簇结构模型设计了五种不同Nb含量的Ti-Zr-Nb合金,并在纯钛基板上进行了激光定向能量沉积试验。系统分析了Nb含量对沉积态合金凝固组织和性能的影响规律。结果表明,不同成分沉积态合金均由单相的β-Ti近等轴晶组成。但随着Nb含量的增加,其在β-Ti中的固溶量增加,合金成分过冷度增大,因此β-Ti晶格畸变增大,晶粒细化。受组织演化的影响,沉积态合金的力学、摩擦磨损和耐蚀性能随Nb含量的增加呈现出递增的变化趋势,而成形性呈现出递减的变化趋势。因此,应将Nb含量(原子数分数)限制为3.75%~5.00%,以使合金的力学、摩擦学、化学与成形性能之间实现良好的平衡。
Objective In recent years, the laser-directed energy deposition(L-DED) of titanium alloys has attracted extensive attention. However, most relevant research is focused on traditional titanium alloys. These alloys are developed by traditional casting or forging technologies without taking into account the metallurgical properties of L-DED. The intrinsic high cooling rate and high thermal gradient of the L-DED process often lead to a tendency toward almost exclusively columnar or dendritic grains, making anisotropic mechanical properties, and being, therefore, undesirable. Attempts to optimize the L-DED processing parameters reveals that it is difficult to change the conditions to promote equiaxed growth of titanium grains, limiting L-DED potential advantage in the fabrication of high-performance titanium alloys.L-DED titanium alloys have good compatibility between melt and solid structure to effectively control the structure, as it directly dominates the microstructure formation and property control throughout the forming process. The Ti-Zr congruent alloy is a good candidate in this regard because it has a single melting temperature, which gives it high structural stability. But a considerable disadvantage of this alloy is its insufficient strength(747 MPa). Alloying is a promising potential in resolving the problem associated with the congruent alloy. The basic structure in this study is Ti-Zr congruent alloy, the alloying component is Nb with effective strengthening, and the cluster formula of Ti-Zr-Nb alloys is constructed using the cluster model. The as-fabricated alloys’ microstructure and properties are thoroughly investigated.Methods The alloys are designed using a cluster model and then fabricated by the laser additive manufacturing on a pure titanium plate. An X-ray diffractometer is used to identify constituent phases. The microstructure and composition are studied using the scanning electron microscopy in conjunction with an energy dispersive spectrometer microprobe system. A digital microhardness tester is used to assess the microhardness. A room-temperature compressive test is performed on a universal tester. The dry sliding friction and wear properties are evaluated by a wear tester. An electrochemical workstation is used to measure the electrochemical properties in the HCl solution with concentration of 1 mol/L. Finally, using a laser confocal microscope, the surface roughness is determined.Results and Discussions All as-deposited alloys are made up of a single β-Ti solid solution with near-equiaxed crystal morphology. The difference is that the lattice constant of β-Ti increases and its grain refines as Nb content increases(Fig. 3), which results from increased Nb in β-Ti and an expanded growth-limiting factor, respectively. Owing to the combined effects of solid solution strengthening and grain refinement, the hardness(Fig. 6), strength, and plasticity(Table 4) of the as-deposited alloys monotonously increase with the increase in Nb content. Increasing Nb content improves the antifriction and wear resistance of as-deposited alloys(Fig. 9) because increased hardness improves the antiabrasion ability of as-deposited alloys. Because Nb2O5 improves passive film passivation by reducing anion vacancy concentrations, and because Nb ions can replace Ti cations to increase passive film stability, the corrosion resistance of the as-deposited alloys gradually improves with increasing Nb content(Fig. 11). As the Nb content increases, the surface roughness of the as-deposited alloys decreases due to the fluidity and spreadability of the melt(Fig. 13).Conclusions The microstructure of all as-deposited alloys consists of single β-Ti near-equiaxed crystals. As the Nb content increases, the phase lattice constant increases, and its grains refine, resulting in a monotonous increase in hardness, strength, wear, and corrosion resistance that are superior to those of as-deposited Ti-Zr congruent alloy. However, the formability changes in the opposite direction. To balance the relationships between formability and other properties, the Nb content(atomic fraction) should be limited to 3.75%--5.00%.
作者
刘宁夏
王存山
梁彦鹏
张静涛
Liu Ningxia;Wang Cunshan;Liang Yanpeng;Zhang Jingtao(Key Laboratory for Materials Modification by Laser,Ion,and Electron Beams,Ministry of Education,Dalian University of Technology,Dalian 116024,Liaoning,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2022年第22期179-190,共12页
Chinese Journal of Lasers
基金
国家重点研发计划(2016YFB1100103)
国家自然科学基金(51371041)。
作者简介
通信作者:王存山,Laser@dlut.edu.cn。
