循环载荷处理对非晶合金结构与性能的影响

In present work, the main goal is to reveal the effects of applied cycling load on the structure and properties of bulk metallic glasses (BMGs, or called bulk amorphous alloys (BAAs)), and explore new ways for enhancing the plasticity of BMGs. In this research, Ti-, Zr- and Fe-based BMGs, which possess difference plasticity, are selected as the model materials for study. Cycling load will be applied to act on the BMG samples using a fatigue testing machine. The influence of cycling load and cycling amount on the structure relaxation, density, elastic modulus, thermal stability and mechanical properties of the studied BMGs will be investigated and made clear. The positron annihilation lifetime (PAL) within the BMG samples before and after applying cycling load will be measured. The variation of PAL spectrum and resolved PAL spectra which corresponding to the defects with different size scale versus the cycling load processing parameters will be revealed. Then, we will try to correlate the defects with different size scale with the property of the BMGs, trying to understand the affecting mechanism of cycling load treatment on structure relaxation, defects and property of BMGs as well as the deforming mechanism of BMGs. Through isothermal annealing of the BMG samples treated by cycling load at the near Tg temperature, the effects of annealing on the effects resulted by cycling load treatment on BMGs will be revealed. Based on the experimental study, new ideals or new method for enhancing the plasticity of BMGs will be proposed. The present study will offer experimental and scientific supports for understanding the deforming mechanism of BMGs and for exploring new ways to enhance the plasticity of glassy alloys. The obtained results in present work would be important and valuable.

本项目的目标是认识施加低于屈服强度的循环载荷对非晶合金结构与性能的影响，探索提高非晶合金塑性的新思路。拟采用Ti基、Zr基、Fe基块体非晶合金为研究材料，实验研究循环载荷大小、循环载荷处理周次数对循环载荷处理后非晶合金的结构弛豫、模量、热稳定性和力学性能的影响规律；采用正电子湮灭技术测试分析循环载荷处理前后非晶合金的正电子寿命变化，揭示循环载荷处理对非晶合金正电子寿命谱和对应于不同尺度缺陷的正电子寿命分量的影响规律；建立不同尺度缺陷与非晶合金宏观性能间的关联；认识循环载荷作用对非晶合金结构弛豫、缺陷、宏观性能的影响机制，探讨非晶合金的形变机制；并通过非晶转变温度Tg附近等温退火，揭示退火热处理效应对非晶合金循环载荷处理效应的影响。在实验研究的基础上，提出改善非晶合金塑性的思路和方法。为认识非晶合金形变机制和提高非晶合金塑性提供科学依据和实验基础。研究工作具有重要理论意义和潜在实用价值。

本研究已完成了项目的研究任务，实现了项目的预期目标。取得了一些重要研究成果。本项目取得的主要研究进展以下：.通过工艺优化制备出了气孔等缺陷少、质量高的铸态非晶合金样品，并研发出系列非晶形成能力强的Ti基块体非晶合金，一些Ti基块体非晶合金的临界尺寸达20-30 mm以上。 制备出的高质量块体非晶合金样品为研究循环载荷处理对非晶合金微结构与性能的本征影响提供了实验研究基础。采用在弹性变形范围内施加低于屈服强度的循环载荷处理非晶合金材料的研究方法，发现循环载荷处理对非晶合金力学性能存在显著影响，循环载荷处理可提高非晶合金的塑性变形能力，塑性变形量的提升幅度与施加的循环应力大小和循环处理周次数有关。在给定循环载荷作用下，存在塑性增加最大的最佳循环处理周次数。循环应力越大时，最佳循环周次数越小。研究发现，循环载荷处理可使Vitl锆基非晶合金（Zr41.2Ti13.8Cu12.5Ni10.0Be22.5非晶合金）的塑性变形量从0.7%提高至22.5%，提升幅度达32倍以上。冷热(-196℃—150℃)循环处理不降低非晶合金的塑性变形能力，但在Tg以下进行结构弛豫等温退火会使循环载荷处理带来的塑性增加效益消失。研究发现循环载荷处理可使非晶合金内不同尺度缺陷的尺寸和浓度发生显著变化，原子尺度至纳米尺度缺陷的尺寸和浓度对非晶合金塑性变形能力有显著影响。增加该尺度缺陷的浓度有利于剪切带开动，循环载荷处理显著增加非晶合金内该尺度缺陷的浓度，因而大幅提升非晶合金的塑性变形能力。研究成果为探索改善非晶合金塑性的新方法和新途径提供了科学依据。本项目还研发出非晶形成能力强的块体高熵非晶合金和成形质量好的非晶合金模压成形技术，为非晶合金应用提供了新的技术基础。