金属空心微球泡沫材料由于具有轻质，高比强度，高吸能性能等特点被广泛应用于轻质结构和吸能材料领域。因此，研发更高强度和吸能性能的金属空心微球泡沫材料并对其变形失效和吸能机理进行研究具有重要意义。本论文采用高熵合金作为基体，Al₂O₃空心陶瓷微球作为填充颗粒，利用渗流铸造法研发了两种新型金属空心微球泡沫材料，并对它们的静动态力学性能及变形破坏宏微观机理展开了系统的研究工作，取得的主要创新成果如下：

（1）探索并优化了利用渗流铸造法制备高熵合金空心微球泡沫的工艺，确定了优选的预热温度及渗流压力。成功制备出CoCrFeMnNi高熵合金泡沫材料和AlCoCrFeNi_2.1共晶高熵合金泡沫材料。

（2）研究了CoCrFeMnNi空心微球泡沫室温下的准静态压缩力学性能，发现其在具有高强度的同时显示出极高的能量吸收能力，超过几乎所有已报道的同类金属泡沫。宏观变形方面，CoCrFeMnNi 基体良好的断裂韧性使得其泡沫复合材料以一种均匀、分散的韧性方式破坏，变形机制主要为孔棱的塑性弯曲，避免了由裂纹失稳扩展导致的应力跌落和灾变失效。微观组织演化方面，在变形早期阶段，变形机制为位错平面滑移，而在变形后期，试样中出现大量变形孪晶，这些孪晶界阻碍了剪切带的扩展，有效延缓了断裂的发生。通过这些位错滑移和孪 晶，基体得以进行大量的塑性变形，同时具有持续的应变硬化能力。因此，泡沫 具有平稳且宽广的应力平台，进而拥有良好的吸能特性。

（3）研究了CoCrFeMnNi空心微球泡沫在液氮温度下的静动态压缩和吸能性能，并对变形机制和微观组织演化进行了研究。相比于室温，液氮温度下泡沫材料的强度和吸能性能进一步提升，并且没有发生显著的脆化，这和CoCrFeMnNi优异的低温韧性有关。在低温下基体的层错能降低，进一步增加了变形孪晶的活性，同时也促进了剪切带扩展，这些交叉的孪晶和剪切带将基体分割成编织状结构，使得更多原子层在变形中发生错动进而耗散大量能量。同时一些二次孪晶在剪切带内部形成，提供应变硬化。而在动态加载下，则出现了HCP相变，与FCC变形孪晶一起形成纳米层片双相（NLDP）结构，进一步提高了强度和应变硬化能力。

（4）研究了AlCoCrFeNi_2.1共晶高熵合金空心微球泡沫在室温下的静动态压缩和吸能性能，发现其同时具有高强度、高吸能总量和高吸能效率，是一种理想的吸能材料。这种良好的强度和吸能性能的结合来自于基体独特的FCC/B2双相共晶结构。较硬的B2相通过载荷分配和产生背应力强化加强了柔软的FCC相；同时，由于两相强度和刚度的不同，在两相间产生应变梯度，随着变形的增加会诱发剪切带的形成，进而造成断裂，提供了多种能量耗散机制。而柔韧的FCC相通过位错滑移、层错、孪晶等塑性变形机制容纳了大量塑性变形并提供应变硬化能力，阻碍了裂纹的形核和扩展，避免了灾难性破坏。这种两相之间的协同作用使应变硬化和剪切带、裂纹带来的软化达到平衡，使得共晶高熵泡沫在高强度的同时具有良好的吸能性能。在动态下，变形更加严重和突然，使得泡沫发生提前致密化，提高了应力水平。此外，在FCC相中发现了大量的交叉层错和L-C锁，提供了额外的应变硬化源。

Metal matrix syntactic foams are widely used as lightweight structural and energy-absorbing materials because of their lightweight, high specific strength, and high energy absorption. Therefore, it is essential to develop metal matrix syntactic foams with higher strength and energy absorption properties and to investigate their deformation and energy absorption mechanisms. In this thesis, two new metal matrix syntactic foams were developed using high-entropy alloy as the matrix and Al₂O₃cenospheres as the filler particles. Furthermore, their quasi-static and dynamic mechanical properties and deformation failure macroscopic mechanisms were systematically investigated.

(1) We explored and optimized the process of fabricating high-entropy alloy syntactic foams using the infiltration casting method and determined the preferred preheating temperature and gas pressure for infiltration. As a result, the CoCrFeMnNi high-entropy alloy syntactic foam and AlCoCrFeNi_2.1 eutectic high-entropy alloy syntactic foam were successfully prepared.

(2) The quasi-static compressive properties of CoCrFeMnNi syntactic foam at room temperature were investigated and found to exhibit ultra-high energy absorption while having high strength, exceeding almost all reported metal matrix syntactic foams. In terms of macroscopic deformation, the excellent fracture toughness of the CoCrFeMnNi matrix allows the foam to deform in a homogeneous and diffusive ductile manner, and the deformation mechanism is mainly plastic bending of the cell struts, which avoids stress drop and catastrophic failure caused by unstable crack expansion. In terms of microstructure evolution, the deformation mechanism is planar dislocation slip in the early stage of deformation, while in the later stage of deformation, numerous deformation twins appear in the matrix, and these twin boundaries impede the expansion of shear bands, effectively retarding the onset of fracture. Through these dislocation slips and deformation twins, the matrix can undergo a large amount of plastic deformation while having a continuous strain hardening capability. As a result, the foam has a smooth and broad stress plateau and thus exhibits good energy absorption properties.

(3) The quasi-static and dynamic compression and energy absorption properties of CoCrFeMnNi syntactic foam at 77K were studied, and the deformation mechanisms and microstructure evolution were investigated. Compared with room temperature, the strength and energy absorption properties at 77K were further enhanced, and no significant embrittlement occurred, which can be attributed to the excellent cryogenic fracture toughness of CoCrFeMnNi. The decreased stacking fault energy of the matrix at 77K further increases the activity of deformation twins and promotes shear band propagation. These crossed twins and shear bands divide the matrix into a weave-like structure, allowing more atomic layers to participate in the deformation and thus dissipating a large amount of energy. At the same time, some secondary twins formed inside the shear band and provided strain hardening. Under dynamic loading, an HCP phase transformation occurs, together with the FCC deformation twins forming a nano-laminated dual-phase (NLDP) structure, further improving the strength and strain hardening capability.

(4) The quasi-static and dynamic compression and energy absorption properties of AlCoCrFeNi_2.1 eutectic high-entropy alloy syntactic foam at room temperature were investigated, and it was found to be an ideal energy-absorbing material with high strength, high energy absorption capacity and efficiency at the same time. This good combination of strength and energy-absorbing properties comes from the unique FCC/B2 dual-phase eutectic structure of the matrix. The hard B2 phase strengthens the softer FCC phase through load partitioning and back stress strengthening; at the same time, the differences in strength and stiffness of the two phases generate a strain gradient between them, which induce the formation of shear bands with increasing deformation, thereby causing fracture and providing a variety of energy dissipation mechanisms. The ductile FCC phase, on the other hand, accommodates a large amount of plastic deformation and provides strain hardening through dislocation slip, stacking faults, and twinning, which hinders crack nucleation and expansion and avoids catastrophic failure. This synergistic effect between the two phases balances strain hardening and softening from shear bands and cracks, resulting in good energy absorption properties and high strength. Under dynamic compression, the deformation is more severe and abrupt, allowing the foam to undergo premature densification, which raises the stress level. In addition, massive crossed stacking faults and L-C locks are found in the FCC phase, providing an additional source of strain hardening.