高熵合金是一类新型金属材料，其相稳定性和相转变是重要科学问题。本文以高熵合金的相稳定性和相转变为主线开展研究，研究工作可丰富高熵合金相关理论，对新型高熵合金研发和应用具有科学意义和实用价值。针对高熵合金中固溶体的稳定性和金属间化合物析出，提出了微扰模型。不同于“高混合熵”理论中直接比较金属间化合物和固溶体的吉布斯自由能，该模型考虑高熵合金固溶体中析出金属间化合物时对体系总吉布斯自由能的影响，且计算结果与实验结果基本相符。通过对7085种高熵合金计算和分析，发现随元素数量的增加，可能生成的金属间化合物数量增加，生成金属间化合物相导致体系吉布斯自由能下降的可能性增加，使具有合金元素数量较多的高熵合金更倾向于形成多相组织。焓对高熵合金相稳定性起主导作用，并强于熵的作用。温度升高可以增加熵对体系吉布斯自由能的影响，从而提升高熵合金固溶体相的稳定性。调幅分解是固溶体相的另一种分解途径。通过卡恩-希利亚德方程获得了高熵合金发生调幅分解的有效判据，据此计算了高熵合金是否发生调幅分解和分解产物成分，且与实验结果基本相符。计算结果表明随着元素数量增加，可能发生调幅分解的成分方向数量增加，使得存在降低吉布斯自由能的方向的可能性增加，发生调幅分解的可能性上升。焓是发生调幅分解的驱动力，熵是阻碍调幅分解发生的阻力。温度越高，熵的作用越显著，合金越难发生调幅分解。揭示了高熵合金固溶体倾向于分解成两相的原因和熵在其中的作用。通过研究高熵非晶合金的相稳定性，发现在NbNiZrTiCo高熵非晶加热过程中出现了反常放热现象，发生从高能玻璃态向低能玻璃态转变的玻璃-玻璃转变，并伴随着剧烈的短程和中程原子重排和模量、硬度及热稳定性显著提高。并发现高熵在玻璃-玻璃转变过程中有诱导作用，并根此设计了两种具有类似玻璃-玻璃转变的高熵非晶合金，并为调节玻璃态结构及其性能开辟了一条新途径。基于高熵合金的相稳定性理论，利用混合焓作为高熵合金中碳化物稳定性的判据，设计并制备了具有较好相稳定性的碳化物增强高熵合金，该高熵合金具有优于工具钢的优异高温硬度。研究还发现可以利用含碳高熵合金固溶体的分解在合金表面生成高质量石墨烯，为制备高质量石墨烯提供了新的方法。

High-entropy alloys are a new type of metal material, and their phase stabilities and phase transitions are important scientific problems. This dissertation takes the phase stability of high-entropy alloys as the mainline, and the research can enrich the related theories of high-entropy alloys. This dissertation has scientific contributions and practical values to the development and application of new high-entropy alloys.Focusing on the phase stability of the solid solution of high-entropy alloys and the intermetallic precipitation of high-entropy alloys, we propose the perturbation model. This model considers the effect of the intermetallic precipitation from the solid solution on the overall Gibbs free energy, instead of comparing the Gibbs free energy of the intermetallic and solid solution directly as in the “high mixing entropy” theory, and the obtained results are basically consistent with the experimental results. By calculating and analyzing 7085 high-entropy alloys, it is found that the increase of the number of elements will increase the number of possible intermetallics and increase the possibility of the decrease of the overall Gibbs free energy with the formation of the intermetallic, and thus the high-entropy alloys with more elements will tend to form multiphase microstructure. The enthalpy is the dominant factor in the phase stability of high-entropy alloys, while the effect of entropy is rather weaker. The increase of temperature will increase the effect of entropy and thus increase the stability of solid solutions of high-entropy alloys.The spinodal decomposition is another decomposition process of the solid solution. The effective criterion of the occurrence of the spinodal decomposition in high-entropy alloys is obtained from the Cahn-Hilliard equation, and the spinodal decomposition and the composition of the produced phases of the high-entropy alloys are calculated, and the calculation results are basically consistent with the experimental results. The calculation results show that the increase of the number of elements will increase the number of possible compositional directions of the spinodal decomposition, and the solid solution is more likely to have a decomposition direction to decrease the Gibbs free energy and decompose. The enthalpy is the driving force of the spinodal decomposition, while the entropy can hinder the spinodal decomposition. A higher temperature can increase the effect of the entropy, and the solid solution is more difficult to decompose. The reason for the preferred pseudo-binary decomposition in high-entropy alloys and the effect of entropy are revealed.By studying the phase stability of high-entropy metallic glasses, the anomalous exotherm of the NbNiZrTiCo high-entropy metallic glass during heating is discovered, and a glass-to-glass transition from a high energy glass state to a low energy glass state occurs with significant short- and medium-range atomic rearrangement, increase of the modulus, hardness and thermal stability. The high-entropy is found to induce the glass-to-glass transition, and two high-entropy metallic glasses with similar glass-to-glass transitions are designed, and provides a new pathway for tuning the glass states and properties.Based on the proposed phase stability theory, the mixing enthalpy is applied as the criterion of the stability of carbides in high-entropy alloys. Carbide-strengthened high-entropy alloys with stable carbide are designed and prepared, and show excellent high-temperature hardness higher than tool steels. Besides, high-quality graphene is prepared on the surface of the alloy by harnessing the decomposition of a carbon-containing high-entropy alloy solid solution as a new method for high-quality graphene preparation.