核壳网络结构钛氧、钛氮合金显微组织演变及力学行为研究

A nanocrystalline grain can be regarded to be composed of two parts: the core (grain interior) and the shell (grain boundary region) due to its high boundary volume percent. Because of significant strengthening of the shells and absence of space for dislocation motion in gain interiors, the nanocrytalline materials possess high strength and low ductility. It is suggested that the optimized combination of high strength and moderate plasticity can be obtained in case a core-shell structure is constructed in a microcrystalline grain. In this work, core-shell network structural bulk Ti alloys were successfully synthesized by means of a unique methodology combining nitriding of powders where the core-shell structure was engineered in the light of different solid solution level of nitrogen in particle boundary and particle inner and subsequent SPS treatment. Then their microstructure and mechanical properties can be tailored by heat treatment. We plan to elucidate the formation mechanism of the novel structure by studying the role of the diffusion behavior of O and N in Ti matrix and its interaction with phase transformation in microstructure evolution during sintering; study microstructure evolution in high temperature and its dependent relationship with mechanical behaviors to clarify the strengthening and deformation mechanisms; study the deformation process by means of finite elemete analysis, and establish the mechanical model. This work can not only open a new route for developing engineering structure materials with excellent properties, but also promote development of new preparation technologies.

由于高的界面体积百分数，纳米晶粒可视为由核（晶内）与壳（晶界）两部分构成，其中壳的强化作用显著，核却无法提供位错存储的足够空间，导致纳米晶材料强度极高而塑性极差。如果在粗晶内构造核壳结构，则有望综合纳米晶与粗晶材料的优势，在金属材料中实现强度与塑性的良好匹配。本项目通过渗氧、渗氮处理，利用氧、氮在微米尺度钛粉颗粒表里浓度不同构建核壳结构，然后烧结固化，得到核壳网络结构钛氧、钛氮合金，并通过热处理调整其结构和性能。研究氧、氮在钛基体中的扩散行为及与相变的相互作用机制对核壳网络结构形成过程的影响规律，揭示此结构的形成机理；研究核壳网络结构材料高温下的显微组织演变规律及与力学行为依赖关系，揭示其强化机理与塑性变形机制；完成变形过程的有限元模拟，并建立力学模型。此项工作不仅为发展高性能工程结构材料开辟了新途径，而且对材料制备技术的发展具有积极的促进作用。

本项目通过对钛粉进行渗氧、渗氮处理，利用氧、氮在微米尺度钛粉颗粒表里浓度不同构建核壳结构，然后进行等离子活化烧结，得到不同结构尺寸的核壳网络结构钛氧、钛氮合金，并通过热处理进一步调整其结构和性能。.利用光学显微镜（OM）、扫描电镜(SEM)、电子探针(EP)、X-射线衍射仪（XRD）、透射电子显微镜（TEM）、高分辨电子显微镜（HRTEM）以及维氏硬度计和力学试验机等方法研究了核壳网络结构钛氧、钛氮合金纯钽、纯铜宏观组织形貌、微观结构以及力学性能等。主要研究结论如下：.（1）通过等离子活化烧结法（SPS）得到了不同壳厚度的核壳网络结构(CS) Ti-N合金。氮含量在壳内浓度明显高于核内。随氮含量增加，壳厚度增加，强度增加而塑形下降。经过退火处理可调控强度和塑形，强度随壳体积百分比增加而升高，与有限元模拟结果相符合。.（2） 随温度升高，CS Ti-O合金强度持续下降。CS Ti-O合金机械性能明显优于普通纯钛及其退火态。CS Ti-O在500 oC和600 oC断裂延伸率分别达到12% 和77%，而其退火态在相同条件下则为完全脆性。其高强度和塑形主要来源于氧的固溶强化及特殊的核壳结构。.（3）CS Ti-O展现出优异的压缩力学性能，且其耐磨性也得到明显改善。抑制的亚表层塑形变形和磨损表面高氧含量导致其改善的耐磨性。.（4）通过将不同比例渗氧钛颗粒与原始颗粒混合，并进行后续SPS烧结，制备了不同连续度的核壳结构Ti-O合金。随强化相增加，强度增加而塑形降低。当强化相为70 wt.%时，材料强塑形匹配性能最好，耐磨性亦最高。.此项工作不仅为发展高性能工程结构材料开辟了新途径，而且对材料制备技术的发展具有积极的促进作用。