为了制定新型β凝固γ-TiAl合金合理的热加工和热处理工艺，研究其相变行为和组织变化规律具有极其重要的指导意义。本工作设计出一种新型的Ti-Al-Mn-Nb合金，该合金的名义成分(原子分数，%)为Ti-43Al-1.5Mn-3Nb-0.2Si-0.2C-0.1B，采用Pandat热力学软件计算、EPMA、TEM、EBSD和XRD等方法，系统研究了该新型合金在1440 ℃至1000 ℃温度范围内的组织演变行为。结果表明，铸态合金组织由片层组织(α₂/γ)和片层组织周围少量β_o/γ混合相组成。合金的凝固和固态相变路径为：liquid→liquid + β→β→β + α→α→α + γ→(α₂ + γ)→(α₂ + γ) + β_o→(α₂ + γ) + β_o + γ_g，其β转变温度(T_β )约为1420 ℃，γ相溶解温度(T_{γ, solv})约为1280 ℃，共析转变温度(T_eut)约为1160 ℃。当温度略低于T_{γ, solv}时，由α相析出的γ呈片层状，α相和γ相始终存在Blackburn位向关系：(111) _γ //(0001){}_{{\alpha }_{\mathrm{2}}}、<\mathrm{1}\overline{\mathrm{1}}\mathrm{0})> _γ //<\mathrm{11}\overline{\mathrm{2}}\mathrm{0}>{}_{{\alpha }_{\mathrm{2}}}；由α相析出的β_o呈块状，遵循Burgers位向关系：(110){}_{{\beta }_{\mathrm{O}}}//(0001){}_{{\alpha }_{\mathrm{2}}}、<111>{}_{{\beta }_{\mathrm{O}}}//<\mathrm{11}\overline{\mathrm{2}}\mathrm{0}>{}_{{\alpha }_{\mathrm{2}}}。新型合金淬火组织的Vickers硬度位于385~512 HV范围内，随着淬火温度的升高淬火组织显微硬度提高，在β单相区淬火后生成的马氏体组织使得硬度达到512 HV。该新型合金同时具有β和α单相区，对发展可调控出全片层结构的易变形、高承温新型β凝固γ-TiAl合金具有重要指导意义。

γ-TiAl based alloys are advanced structural materials use in the automotive and aerospace industries. Their notable characteristics, including low density, high specific yield strength, and exceptional resistance to creep and oxidation, make them highly viable for being used as structural components in high-temperature applications of internal combustion engines. The novel β-solidifying γ-TiAl alloy designed in this study demonstrated excellent oxidation resistance at temperatures of 750, 800, and 850 ^oC. However, research regarding the solid-state phase transformations and microstructure control of this alloy is lacking. The study of the phase transformation behavior and microstructural evolution of alloys is crucial for developing appropriate thermal processing and heat treatment techniques for β-solidifying γ-TiAl alloys. This work introduces a novel Ti-Al-Mn-Nb alloy, with a nominal composition of Ti-43Al-1.5Mn-3Nb-0.2Si-0.2C-0.1B (atomic fraction, %). Using Pandat software for thermodynamic calculations, along with techniques such as EPMA, TEM, EBSD, and XRD, an extensive and meticulous investigation of the microstructural transformations within the range from 1440 ^oC to 1000 ^oC for this innovative alloy was undertaken. The results indicate that the as-cast microstructure of the alloy comprises a lamellar colony (α₂/γ), grain γ phase, and a small amount of β_o. The solidification pathway of the alloy can be determined as follows: liquid→liquid + β→β→β + α→α→α + γ→(α₂ + γ)→(α₂ + γ) + β_o→(α₂ + γ) + β_o + γ_g. The temperature at which the alloy exists as a single β phase (T_β ) is approximately 1420 ^oC, while the decomposition temperature of γ phase (T_γ,solv) is approximately 1280 ^oC; additionally, the eutectoid transformation temperature (T_eut) is approximately 1160 ^oC. Slightly below T_{γ, solv}, the γ precipitated from the α phase exhibits a lamellar structure. The α and γ phases consistently demonstrate a Blackburn orientation relationship: (111) _γ //(0001){}_{{\alpha }_{\mathrm{2}}} and <\mathrm{1}\overline{\mathrm{1}}\mathrm{0}> _γ //<\mathrm{11}\overline{\mathrm{2}}\mathrm{0}>{}_{{\alpha }_{\mathrm{2}}}, respectively. The secondary β_o phase precipitated from the α phase appears as a block shape and follows the Burgers orientation relationship: (110){}_{{\beta }_{\mathrm{O}}}//(0001){}_{{\alpha }_{\mathrm{2}}} and <111>{}_{{\beta }_{\mathrm{O}}}//<\mathrm{11}\overline{\mathrm{2}}\mathrm{0}>{}_{{\alpha }_{\mathrm{2}}}. The Vickers hardness of the quenched microstructure of the novel alloy ranges between 385 and 512 HV. With an increase in the quenching temperature, there is an observable enhancement in the microhardness of the quenched microstructure. The martensite microstructure formed after quenching in the β single-phase area contributes to the hardness of 512 HV. This novel alloy encompasses the β and α single-phase areas; thereby holding significant implications for the development of novel, highly deformable, and high-temperature-resistant β-solidifying γ-TiAl alloys characterized with fully lamellar structures.