深冷处理时间对激光粉末床熔化沉积TiC/TC4钛基复合材料组织演变及力学性能的影响

Insights into Deep Cryogenic Treatment Duration on Evolution Mechanism of TiC/TC4 Alloy Nanocomposites Fabricated by laser Powder Bed Fusion via Microstructure and Mechanical Properties

目的探明不同深冷处理时间对TiC/TC4钛基复合材料组织演变及其力学性能的影响规律,分析TiC/TC4钛基复合材料在深冷环境下的使用性能。方法利用低能球磨法得到石墨烯(GNPs)/TC4复合粉末,采用激光粉末床熔化沉积法制备TiC/TC4钛基复合材料,通过液氮浸泡法进行不同时间的深冷处理,然后恢复至室温进行拉伸试验。结果深冷处理过TiC/TC4钛基复合材料的拉伸强度均高于深冷处理过TC4合金的拉伸强度,断裂韧性却得到不同程度削弱。结论原位自生TiC的载荷传递作用可以增强TiC/TC4钛基复合材料在拉伸变形过程中的变形能力,使复合材料的拉伸强度得到提高;随深冷时间的持续延长,冷应力不仅会导致TC4合金原始细长针状马氏体断裂,还会驱使TiC/TC4钛基复合材料陶瓷增强相TiC发生不同程度的偏聚。此外,深冷处理后TiC/TC4钛基复合材料产生的晶格畸变现象会降低α-Ti基体一侧的应变值,使复合材料晶格畸变区域应变不均匀分布,弱化TiC/TC4钛基复合材料晶格畸变区域原子的变形协调能力,导致TiC/TC4钛基复合材料的断裂韧性值相对低。

The work aims to explore the influence of different deep cryogenic treatment duration(DCT)on the microstructure evolution and mechanical properties of TiC/TC4 alloy nanocomposites,and to analyze the performance of TiC/TC4 alloy nanocomposites under a cryogenic environment.The graphene nanoplatelets(GNPs)/TC4 composite powder preparation process was obtained by low-energy ball milling,and TiC/TC4 alloy nanocomposites were prepared by laser powder bed fusion(LPBF).Furthermore,the samples were cryogenically treated for different duration by liquid nitrogen immersion and then restored to room temperature for tensile tests.The results showed that the tensile strength of DCTed TiC/TC4 alloy nanocomposites was higher than that of DCTed TC4 alloys,and the fracture toughness was weakened to varying degrees.Therefore,it can be concluded that the load transfer effect of TiC can enhance the deformation capacity of the titanium matrix of TiC/TC4 titanium matrix composites during tensile deformation,thereby improving the tensile strength of the composites;As the deep cooling time continues to extend,the cold stress will not only cause the original needle-shaped martensite of the TC4 alloy to fracture,but also drive the ceramic reinforcement phase TiC of the TiC/TC4 alloy nanocomposites to undergo different degrees of segregation.Moreover,the lattice distortion phenomenon of TiC/TC4 alloy nanocomposites after cryogenic treatment will significantly reduce the strain value on one side of theα-Ti matrix,causing uneven strain distribution in the lattice distortion region of the composites and weakening the deformation coordination ability of atoms in the lattice distortion region.All these ultimately lead to the low fracture toughness of TiC/TC4 alloy nanocomposites.