On the continuous and discontinuous precipitation of the L12 phase in Cu-Ni-Al alloys

Abstract

L12 precipitate hardened Cu-Ni-Al alloys offer high strength, corrosion resistance and anti-biofouling properties, making them useful in marine engineering applications. Optimisation of their mechanical properties requires a full understanding of their complex precipitate nucleation and coarsening mechanisms. In this work, the microstructural characteristics and hardness of three Cu-Ni-Al alloys with compositions of Cu(95-x)NixAl5 (x = 5, 15, 25 at%) were investigated in the homogenised state and following heat treatments at 700˚C for 1, 10, 100 and 1000 hours. L12 precipitates were observed in the alloys containing ≥ 15 at% Ni. In these alloys, the L12 phase was found to precipitate via both continuous and discontinuous routes following all exposures at 700˚C. The coarsening behaviours of the continuous and discontinuous L12 distributions were characterised and correlated to measurements of hardness and lattice misfit. The alloys containing 15 and 25 at% Ni exhibited peak hardness after 1 h at 700˚C, which corresponded to average particle diameters of 30 nm, respectively. These results were rationalised through calculations of the change in the critical resolved shear stress associated with the transition from weakly to strongly coupled superpartial dislocations. The discontinuous reaction was observed to be led by L12 phase formation, which extended into the neighbouring grain, ahead of the reorientation front of the matrix.

Microstructure and mechanical behaviors of Gasar porous Cu/G4335V steel joint brazed by Ag-28Cu-0.75Ni alloy

“…), as was previously reported [28]. The phase diagram of the Cu-Ni binary alloy shows that the Cu-Ni system is an unlimited solubility system [29]. Moreover, Cu and Ni possess the same facecentered cubic lattice type, which makes for a good affinity between them [30].…”

Invited viewpoint: in situ nanostructured lamellar composites

“…To date, there is no theory of the DP transformation that allows for the prediction of the occurrence and extent of the transformation in an alloy. While theoretical and experimental work on the DP transformation has been published, these are not capable of providing the predictive guidance needed for alloy development [4][5][6][7]. A comprehensive theory of the DP transformation taking account of the kinetic competition with CP and other factors such as the transformation velocity/lamellar spacing/phase mismatch strain/element partitioning/driving force correlation is still to be developed.…”

Effect of Al Content on Microstructure and Properties of Cu-14Ni-xAl Alloys

“…At the beginning of aging, Ni3Al phase nucleates and grows in the form of continuous precipitation. With the extension of aging time and the increase of aging temperature, large discontinuously precipitated colonies would nucleate from grain boundaries and grow into the grain [8,9]. Based on previous studies, the hardness and strength of the Cu-Ni-Al alloys can be greatly improved through the aging induced Ni3Al precipitates.…”