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Deformation bands, especially shear bands were intentionally formed in supersaturated Cu-4 at.% Ti alloy by groove-rolling with 75% area reduction. Cold deformation prior to the ageing process changed the precipitation behaviour of the alloy. The deformed structure with shear bands was maintained, without showing recovery and recrystallisation, even after prolonged ageing at 450°C for more than one day. The thermally stable shear bands act as nucleation initiation sites and prevent the expansion of discontinuous cellular precipitates. The hardness reached a value of 305 Hv and an electrical conductivity of 15% IACS (IACS = International Annealed Copper Standard. 100% IACS is defined as the conductivity corresponding to a volume resistivity at 20°C of 17.241 nΩ), compared to 283 Hv and 13% IACS for conventional solid-solutioned and peak-hardened alloy. In addition, the ageing time to reach the highest hardness was shortened from 720 to 180 min at 450°C. [ABSTRACT FROM AUTHOR]

The influence of precipitation morphology, including continuous precipitation (CP) and discontinuous precipitation (DP), on the mechanical behaviour of Cu–Ni–Si alloys was studied. The Cu–6Ni–1.5Si (in wt%) alloy was solution heat treated at 980 °C for 2 h and aged at 500 °C for 0.5 and 3 h to produce CP and DP structures. The DP specimen showed an abnormal increase in tensile ductility with increasing strain rate, unlike the CP counterpart. The impact toughness of the DP specimen was 1.6 times greater than that of CP specimen. The fracture mode in DP specimen was mostly dimpled rupture, while the mixed mode of cleavage fracture and dimpled rupture was noted on the CP specimen. [ABSTRACT FROM PUBLISHER]

A Cu alloy with discontinuous precipitation (DP) presents a mechanically lower strength, but a higher conductivity compared to an alloy with continuous precipitation (CP). We controlled the partial distribution of DP in the Cu matrix of Cu-4Ni-1Si alloy by changing aging time. Successive cold-working of the alloy showed that by controlling the CP and DP fractions, considerably wide ranges of strength and electrical conductivity, from 500 to 1170 MPa, and from 23 to 50% IACS, respectively, could be achieved. After cold-working, the DP region in the alloy was heavily deformed in comparison with the CP region, showing a drastic increase in strength, with only a small decrease in conductivity. • A very wide conductivity-strength combination can be obtained after cold working by controlling DP fraction in only one alloy. • DP fraction can be changed just according to the change of the aging time. • The DP region is more deformed, and the strength is more quickly increased than CP region in alloy. [ABSTRACT FROM AUTHOR]

The discontinuous precipitation (DP) was known to mechanically detrimental mechanism compared to normal precipitation (continuous precipitation, CP), while the DP has the higher conductivity because of low solute content in matrix. To get the optimum balance of strength and conductivity, the bimodal-structured Cu-4Ni-1Si alloy composed of two regions with CPs and DPs was fabricated. Bimodal-structured alloy occupied by 50% of each region shows remarkable high strength and conductivity combination (1088 MPa / 38%IACS) beyond the expected values which summated in alloys with fully CP or DP. The accelerated strengthening of bimodal-structured alloy is caused by uni-directional alignment and enhanced plastic deformation of DPs in alloy after cold-working. • Bimodal structured Cu-Ni-Si alloy was composed of two regions with continuous and discontinuous precipitates. • Bimodal structured alloy had best combination of strength and conductivity compared to the alloys with fully continuous or discontinuous precipitates • The unidirectional alignment of discontinuous precipitates during cold-working drastically increased the strength of Cu-Ni-Si alloy. [ABSTRACT FROM AUTHOR]