后处理优化组织结构改善冷喷涂增材制造M2052合金阻尼性能

Microstructure Optimization of Cold Sprayed M2052 Alloy Using Post-Processing Heat Treatment for Tailoring Damping Capacity

摘要:

冷喷涂增材制造技术具有低的热输入，以及能够有效避免晶粒长大、相变和高热应力等缺陷形成的优势，越来越受到人们的关注。虽然冷喷涂方法能够有效地避免高阻尼锰铜合金在制备过程中的氧化和热裂纹的形成，但冷喷涂过程中粉末严重塑性变形产生的大量位错会导致冷喷涂锰铜合金阻尼性能明显降低。因此，对不同热处理工艺提升冷喷涂Mn-20Cu-5Ni-2Fe（M2052）合金阻尼性能的机理，以及相关的微观组织演变规律进行了研究。结果表明，在冷喷涂过程中，由于粉末颗粒变形不充分，因此形成了一些孔洞。在粉末颗粒边界处形成的孔洞经固溶处理后数量明显减少，这是因原子扩散促进了颗粒间的部分孔洞愈合。另外，在冷喷涂成形过程中粉末颗粒碰撞的界面处会产生巨大的热量，从而发生动态再结晶，形成尺寸约为200—400 nm的纳米晶粒。冷喷涂沉积M2052合金经850 ℃、1 h固溶处理和恒温420 ℃不同时间的时效处理后，晶粒发生再结晶和长大，形成了无畸变的等轴晶，这与时效处理导致冷喷涂M2052合金奥氏体调幅分解有关。随着时效时间的增加奥氏体调幅分解程度增加，导致富锰基体中锰含量的增加，从而促进了M2052合金马氏体相变温度的增加。冷喷态M2052合金经固溶（850 oC×1 h）+时效（420 oC×24 h）处理后，室温下呈现出了最佳的阻尼性能（Ψ_0.08%≈26%）。本研究为锰铜合金的阻尼性能的提高提供了理论依据。

Abstract:

Cold spray， as a solid-state additive manufacturing process， has been attracting an increasing interest due to low heat input， which avoids grain growth， phase transformation， and high thermal stress. This feature is beneficial for high damping Mn-Cu alloy through limiting oxidation and formation of hot cracks. However， high dislocation density formed because of extensive plastic deformation， pores， and cracks result in the low damping capacity in the as-deposited Mn-Cu alloy. Thus， new strategy was introduced for improving damping capacity in cold sprayed Mn-20Cu-5Ni-2Fe （M2052） alloy， and microstructure evolution was studied after different heat treatments. Insufficient plastic deformation of powders during cold spraying processing results in the formation of the pores at the boundaries of the powders. After solid solution at 850 ℃ for 1 h an obvious decrease in number of the pores is found， which is related to atomic diffusion at higher temperature. The dynamic recrystallization leads to the formation of a large number of nano-sized grains at the particle bonding interface. After solid solution at 850 ℃ for 1 h and ageing at 420 ℃ for different times recrystallization and grain coarsening take place. Ageing treatment at 420 ℃ for up to 72 h leads to spinodal decomposition of the fcc-austenite. With increasing ageing time martensitic transformation temperature of the cold sprayed M2052 alloy increases， which is attributed to the increase in the Mn content in the rich-Mn matrix due to the increase in the spinodal decomposition degree. The cold sprayed M2052 samples after solid solution at 850 ℃ for 1 h and ageing at 420 ℃ for 24 h show higher damping capacity Ψ_0.08%=2πQ^-1≈26%（at room temperature）.