基于同步辐射X射线的B4C/Al复合材料原位拉伸变形和损伤研究

Investigations on the in situ tensile deformation and damage of B4C/Al composites based on synchrotron X-rays

对B4C质量分数分别为15wt.%和30wt.%的B4C/Al复合材料进行了准静态拉伸实验研究,采用基于同步辐射X射线的同时相衬成像和衍射测量技术对B4C/Al的变形损伤过程进行了原位实时表征,再结合X射线数字图像相关技术(XDIC),首次获得了B4C/Al复合材料拉伸过程中的多尺度力学响应:宏观应力-应变曲线、细观变形场和微观晶格衍射谱。应力-应变曲线表明30wt.% B4C/Al较15wt.% B4C/Al具有更高的屈服强度和更强的应变硬化效应,但延展性较差;细观应变场揭示出30wt.% B4C/Al的应变集中区密度更高、更容易扩展联合形成宏观裂纹,导致材料脆断;衍射谱则显示两种复合材料基体的衍射峰峰移和展宽都很小,说明弹塑性变形可能主要集中在颗粒-基体界面。颗粒间距对颗粒增强金属基复合材料应变集中区的密度和其延展性有显著影响,调整颗粒间距有助于平衡其强度和延展性。本文也讨论了XDIC的系统误差,表明位移误差和应变误差控制可分别控制在0.01pixel和0.1%以下。

Quasi-static tensile tests are conducted on 15wt.% and 30wt.% B4C/Al composites, along with in situ synchrotron X-ray imaging and diffraction measurements. With X-ray digital image correlation (XDIC), we have obtained the multi-scale mechanical response of B4C/Al composites during the tensile loading: macro stress-strain curves, mesoscopic strain fields and micro crystal diffraction patterns. The stress-strain curves indicate that 30wt.% B4C/Al has a higher yield strength and stronger strain hardening effect but lower ductility than 15wt.% B4C/Al. The mesoscopic strain fields indicate that the strain localizations in 30wt.% B4C/Al has appear denser, and is more likely to grow and coalesce to form macroscopic cracks, leading to brittle fracture. The diffraction patterns show that the diffraction peak shift and broadening for the two composites are both very small. The reason may be that plastic deformation mainly concentrates in the particle-matrix interface regions. Theoretical analysis shows that inter-particle distance can significantly affect the density of strain localizations and thus ductility of the particle reinforced metal matrix composites. Controlling the inter-particle distance can help balance their strength and ductility when we design such composites. We also analyze the systematic error of XDIC, find that the displacement error and strain error can be controlled below 0.01pixel and 0.1%, respectively.