气–液反应激光原位增材制造TiN增强钛基复合材料组织结构及力学性能研究

Microstructure and mechanical properties of in-situ laser additive manufacturing of TiN reinforced Ti6Al4V matrix composites based on gas–liquid reaction

摘要:

本文采用选区激光熔化(SLM)工艺制备了Ti6Al4V合金,并系统研究了激光能量密度(LED)对其致密度、显微硬度、压缩强度和塑性的影响。获得了SLM制备Ti6Al4V合金的最佳LED工艺窗口为84.8–163.6 J/mm_³。在最佳LED窗口内,在不同N₂浓度(3 vol.%、10 vol.%、30 vol.%)工作气氛中,以气–液反应方式SLM制备了TiN为增强相的Ti6Al4V基复合材料。该新工艺制备复合材料的原理为：钛合金高温熔池附近的N₂裂解为N原子/离子,N与熔融状态的Ti原位反应生成均匀分散的TiN增强相,并与熔化–凝固过程中的Ti合金基体复合,最终以SLM逐层成形的方式制备出TiN增强钛基复合材料。本文探究了N₂浓度对钛基复合材料组织结构和力学性能的影响规律。其中,3 vol.%的N₂工作气氛中SLM成形的复合材料的强度和塑性同时得到提升,阐述了其强韧化机理。

关键词:选区激光熔化;钛基复合材料;激光能量密度;TiN;气–液反应

Abstract:

In this study, the Ti6Al4V alloys were fabricated by selective laser melting (SLM) technology. The effect of laser energy density (LED) on the relative density, micorhardness, compression strength and plasticity of the Ti6Al4V alloys was systematically studied. The optimum LED processing window for SLM of Ti6Al4V alloys was in the range of 84.8–163.6 J/mm_³. In the optimum LED window, the TiN reinforced Ti6Al4V matrix composites were fabricated by SLM in different N₂ concentration (3 vol.%, 10 vol.% and 30 vol.%) atmospheres based on gas–liquid reaction. The principle of the novel technology for fabricating of the composites is as follows: decomposition of N₂ near the Ti6Al4V melt pool generates N atoms/ions, the gaseous N atoms/ions react with liquid Ti atoms to in-situ synthesize uniformly distributed TiN reinforcements which combine with the Ti6Al4V matrix during melting–solidification, finally, the TiN reinforced Ti6Al4V matrix composites are built by SLM layer-by-layer. Effect of N₂ concentration on the microstructure and mechanical properties of the Ti6Al4V matrix composites was researched. The composite fabricated by SLM in 3 vol.% N₂ atmosphere exhibited a good combination of high strength and high plasticity. The strengthening and toughening mechanisms were studied.

Key words:Selective laser melting; Titanium matrix composites; Laser energy density; TiN; Gas–liquid reaction