Fatigue and corrosion performance of model Mg-Zn-Zr alloys subjected to the High Pressure Torsion Extrusion

镁合金作为植入材料的应用受到限制，因为其强度低，通常低于人体骨强度。此外，它们在强化沉淀物的存在下表现出低的耐腐蚀性。为了避免这些缺点，将在项目中使用高压扭转挤压（HPTE），以增加固溶退火合金的强度，因为（亚）晶界强化而不会形成在腐蚀环境中可能至关重要的沉淀物。因此，该项目的主要目的是研究商业生物相容性镁合金在不同HPTE路线和随后的热处理过程中的微观结构和织构演变，以及所开发的微观结构和织构对单调和循环机械性能的影响，即使在腐蚀性环境中。具体而言，将开展以下工作： 建立最佳HPTE加工条件（挤出和旋转速率、温度），用于从商业生物相容性镁合金中生产散装无缺陷样本。- HPTE产生的梯度结构中沉淀过程动力学的研究。 在空气和模拟血液的液体中评价最有前途的样品的耐腐蚀性和疲劳性能，揭示HPTE用于植入物材料微观结构改性的潜力。 HPTE试样的宏观疲劳性能与其微观组织状态的相关性。预计HPTE处理将有利于提高镁合金在循环载荷下的性能，这不仅归功于微观组织的细化。更重要的是，由于在HPTE下的应变梯度，在挤出棒的外围形成具有更细晶粒尺寸的梯度显微组织。典型的HPTE纹理，这将修改参与变形的滑移系统的激活的影响，也将阐明。金属间化合物的性质，存在和分布，影响在HPTE加工过程中的再结晶事件，可能是有害的耐腐蚀性方面，什么将被仔细evaluated.These项目的目标应达到通过使用创新的方法：我们将使用一种新的方法，通过高压扭转挤压严重塑性变形，以获得大规模的散装超细晶粒试样。除了经典的衍射和金相分析，我们将使用EBSD和ACOM-STEM对UFG镁合金的晶粒结构进行分析，以量化晶粒尺寸，孪晶密度和GB特性。最后，我们将研究UFG试样在不同介质中的疲劳性能，并系统地探索以下微观结构参数的变化：晶粒尺寸和形状，梯度结构的存在，体积分数，尺寸和空间分布的金属间化合物颗粒，位错和孪晶密度。

Application of Mg alloys as implant materials is limited due to their low strength, which is often lower than the human bone strength. Furthermore, they demonstrate low corrosion resistance in the presence of strengthening precipitates. To avoid those disadvantages, High Pressure Torsion Extrusion (HPTE) will be used within the project to increase the strength of a solution annealed alloy due to (sub)grain boundary strengthening without forming precipitates which might be critical in corrosive environments. Therefore, the main aim of the project is to study the microstructure and texture evolution in a commercial biocompatible Mg alloy during different HPTE routes and subsequent thermal treatment, and the effect of the developed microstructure and texture on the monotonic and cyclic mechanical properties, even in corrosive environments. In particular, the following efforts will be undertaken: - Establishing the optimal HPTE processing conditions (extrusion and rotation rates, temperature) for manufacturing of bulk flawless specimen out of commercial biocompatible Mg alloy. - Study of the precipitation process kinetics in the gradient structure resulting from HPTE.- Evaluation of the corrosion resistance and fatigue properties of most promising specimens in air and in liquids mimicking the blood revealing the potential of HPTE for microstructure modification of implant material.- Correlation of the macroscopic fatigue performance of HPTE specimens with their microstructural state.It is expected that the HPTE processing will be beneficial for the enhancement of the Mg alloy performance under cyclic loading not only thanks to the microstructure refinement. More important is the formation of gradient microstructure with a finer grain size at the periphery of the extruded rod due to the strain gradient at HPTE. The influence of the typical HPTE texture, which will modify the activation of slip systems involved in the deformation, will be also elucidated. The nature, presence, and distribution of intermetallic precipitates, affecting the recrystallization events during the HPTE processing, might be detrimental in terms of corrosion resistance, what will be carefully evaluated.These project goals shall be reached by the use of innovative approaches: we are going to use a novel method of severe plastic deformation by high pressure torsion extrusion to obtain large scale bulk ultrafine grained specimens. In addition to classical diffraction and metallographic analysis, we will use EBSD and ACOM-STEM for the grain structure analysis of UFG Mg alloy to quantify grain size, twin density, and GB character. Finally, we will study the fatigue properties of UFG specimens in different media and systematically explore variations of the following microstructural parameters: grain size and shape, presence of gradient structure, volume fraction, size, and spatial distribution of intermetallic particles, dislocation and twin density.