Continuous and discontinuous precipitation of Cu-4Ti-1Al alloy

Cu-Ti alloys can be widely used in the electronic and elastic components and therefore have become the ideal substitute materials for Cu-Be alloys because of its high strength, high elasticity and good stress relaxation resistance. In this work, the phase transformation of Cu-4Ti-1Al alloy during aging at different temperatures was investigated by scanning transmission electron microscopy (STEM) and its aging properties were studied. The results show that obvious clustering occurs in supersaturated solid solution of Cu-4Ti-1Al alloy after aging at 400 ℃ for 1 h. With increasing aging time, clustering begins to transform into ordering. Meanwhile, the modulated structure of Cu-4Ti-1Al alloy coarsens gradually and the coherent and metastable β'-Cu4Ti precipitates continuously within the grains. The orientation relationship between β'-Cu4Ti and matrix is [001]p//[001]Cu and [100]p//[310]Cu. After Cu-4Ti-1Al alloy aged at 600℃ for 1 h, cellular colonies containing α, a slightly supersaturated matrix and β-Cu4Ti phase appear at grain boundaries, while the β'-Cu4Ti precipitates within the grains. The orientation relationship between the cellular lamellae of α and β-Cu4Ti is (111)α||(010)β and [101]α||[501]β. After Cu-4Ti-1Al alloy aged at 650℃ for 1 h, the size and content of cellular structures precipitated by discontinuous decomposition increase and rod-shaped incoherent precipitates form inside grains. Al addition plays three roles as follows: (i) Al can harden the matrix by solution strengthening; (ii) It postpones ordering of Cu-4Ti-1Al alloy; (iii) It lowers the coherent solvus temperature of metastable β'-Cu4Ti phase. © 2022, China Science Publishing & Media Ltd. All right reserved.