Lamellar Precipitation in an Cu-4.5 at. % In Alloy

Microchimica Acta, 2004

The morphology and kinetics of the discontinuous precipitation reaction in a Cu-4.5 at.% In alloy were studied by means of analytical electron microscopy. Upon discontinuous precipitation an =(Cu 7 In 3) lamellar two-phase microstructure was observed, where is the In-depleted solid solution and the precipitate phase. Indium concentration profiles were determined parallel to the moving reaction front for individual lamellae. A local analysis was applied to characterize the kinetics of the discontinuous precipitation reaction and allowed the determination of the local grain-boundary diffusivity.

Materials Sciences and Applications, 2011

The study of the discontinuous precipitation reaction and the lamellar precipitate dissolution in the alloy Cu-In system provoked a considerable benefit and has been the subject of many theoretical and experimental investigations. The aim of this work is to make the evidence on the one hand the effect of the plastic deformation on the mechanism of the discontinuous precipitation reaction such as nucleation, growth and lamellar coarsening and in other hand the effect of temperature on the characteristics and front behavior movement of the opposite reaction (discontinuous dissolution). Different techniques of analysis have been used in this respect such as the optical microscopy, the differential thermal analysis and the microhardness Vickers. The obtained results confirm various works achieved in this field.

Materials Chemistry and Physics, 1998

The relation between the continuous and discontinuous precipitations, and the discontinuous precipitation kinetics and mechanisms in Cu-I3 wt.% Sn and AI-20 wt.% Ag alloys, have been investigated by metallographic observations, differential scanning calorimetry, X-ray diffraction and microhardness measurements. During ageing of the supersaturated solid solution of A1-Ag, after the preprecipitation of the Guinier Preston zones and the continuous precipitation of the plates of the n'ansition phase Y', the cellular precipitation of the equilibrium phase "/occurs and grows from the grain boundaries but lamelIae are not perpendicular to the reaction fi'ont. At high temperature intergranular precipitation occurs without the reaction front or cell. Both types of precipitation occur in the Cu-13 wt.% Sn alloy but very slowly. However, continuous precipitation predominates after a high deformation amount and reduces the amount of chemical driving energy available for both the initiation and propagation of discontinuous precipitation.

1971

Materials Chemistry and Physics, 2001

The cellular precipitation in Cu-9 wt.% Sb alloy is studied with optical and scanning electron microscopy and X-ray diffraction. The first goal of the present paper is to give an overview of the different sites of discontinuous precipitation as grain boundaries, different interface boundaries and dislocations. Moreover, a coarser lamellar spacing is first observed in the cellular product of discontinuous precipitation before the formation of a finer cell at the reaction front of the coarser one. The second goal concerns the mechanism of dissolution which is discontinuous at relatively lower temperature and continuous at higher one.

1998

1993

The distribution, morphology, chemistry, and crystallography of the precipitates formed during aging of an Al-Cu-Zn-Mg-Ag alloy have been studied using analytical transmission electron microscopy. The first precipitates to appear during aging at 150°C were thin hexagonalshaped plate-like precipitates which formed on the {lll}Al planes. These precipitates had a facecentred orthorhombic crystal structure and their composition was essentially CuA1, although they contained a trace of silver. At peak hardness the microstructure consisted of the plate-like precipitates on {lll}Al planes and 0' precipitates on {lOO}A1 planes. Overaging resulted in the precipitation of equilibrium 8, CuAl,, which exhibited a lath morphology and a n orientation-relationship with the matrix (210)Al 1 I (llOIy; (OO1)A1 misoriented from (OOl), by-6". Prolonged overaging at 250°C resulted in the formation of cuboid-shaped Al,(Cu,Zn),Mg, precipitates which had a cubic crystal structure and a cube:cube orientation-relationship with the matrix.

Materials Science and Engineering, 1976

Discontinuous precipitation in a Cu-4% Ti binary alloy is studied through transmission electron microscopy. Different types of contrast conditions are used and moire fringes and interfacial dislocations are revealed. The grain refinement that occurs during discontinuous precipitate growth is due to translational and rotational subgrain boundaries formed on account of the different habit planes of precipitates from the different nucleation sites. It is also shown that discontinuous precipitation is absent in a Cu-2.1% Ti-2.4%Al and a Cu-2.1% Ti-5% A1 alloys over a wide range of aging temperatures. However, a pronounced tendency for localised precipitation is observed in these alloys. It is found that the ternary Cu-Ti-A1 alloys have lower coherent solvus temperatures. Solute supersaturation is therefore relieved through precipitation of the equilibrium phase by heterogenous nucleation at grain boundaries, twin boundaries, dislocations and other structural imperfections where a lower activation energy barrier is present.

ABSTRACT Purpose: This research was aimed to investigate the mechanism of Ni 3 Al phase precipitation during longterm process of ageing Cu-Ni-Al. type alloys with particular account of the precipitates morphology changes, including the changes in their size with varying temperature and ageing time, so as to determine an effect of the elastic strain energy on these changes. Design/methodology/approach: Samples of cold-rolled strips from the CuNi16Al5 alloy were solution -treated at 900°C for 1h in argon atmosphere, water quenched and next aged at the temperatures of 450 and 550°C for up to 380 and 760 hours, respectively. Their microstructure was investigated by transmission electron microscopy. Findings: It was found that decomposition of supersaturated solid solution proceeds by nucleation and growth of the coherent precipitates of the L1 2 -Ni 3 Al phase. Their morphology changes as a result of competitive influence of an elastic strain energy, surface energy on the matrix-precipitate inter-phase boundary, and the energy of elastic interaction between precipitates. The L1 2 -Ni 3 Al precipitates nucleate as the spherical ones and grow, forming intermediate sub-structures, until they reach a cubic form with the planes parallel to the{100} planes of a matrix and take privileged positions along the <110> directions. Clear deviations from the LSW coagulation theory and its modifications, demonstrated by the slow-down of the process, have been observed. In the extreme case, growth of the precipitates can be completely stopped in some time ranges of the ageing process. Research limitations/implications: Further research should be concentrated on the precipitation kinetics within a wider range of volumetric fraction of the Ni 3 Al phase in a copper matrix. Practical implications: This effect can be used in practice to stabilise mechanical properties at elevated temperature. Originality/value: The paper contributes to better understanding of the precipitation mechanism in the alloys examined.

In Al-2.0 at%Cu-1.0 at%Mg alloy, fine-scale precipitates that occur during aging have been investigated by using differential scanning calorimetry (DSC) to search for the phase transition temperatures (formation and dissolution of precipitates). The microhardness measurements (HV) are used to correlate between the developed reaction peaks in DSC and the observed peaks in the microhardness (HV). The scanning electron microscopy (SEM) is utilized to examine the surface microstructure of the precipitated phases and to confirm the obtained results. During the aging treatment the supersaturation is gradually reduced. The strength increases when fine coherent and/or semicoherent precipitates nucleate. The precipitation kinetics can be characterized by analyzing the DSC curves. The kinetics of the early stage precipitates were found to be controlled by the migration of Cu and Mg atoms in the matrix. Whereas, the later precipitates as S00, S0 and S are controlled by diffusion of Mg and Cu in the alloy.