S. Nagarjuna

On the variation of mechanical properties with solute content in Cu–Ti alloys

Abstract The variation of mechanical properties and electrical conductivity of Cu–Ti alloys of four compositions, viz. Cu–1.5 wt%Ti, Cu–2.7 wt%Ti, Cu–4.5 wt%Ti, and Cu–5.4 wt%Ti, have been studied in solution treated (ST), solution treated+peak aged (ST+PA), and solution treated+cold worked+peak aged (ST+CW+PA) conditions. In the ST condition, Ti is found to be a potential solid solution strengthener of copper showing greater effect than other elements like Zn, Ni, Al, Si, Be, and Sn. Solid solution strengthening in Cu–Ti alloys is attributed to the interaction of titanium atoms with screw dislocations and the effective interaction is more due to modulus mismatch than size misfit. Further, a marked change in the linear variation of tensile strength and elongation with Ti content is observed at about 4.0 wt%Ti beyond which, tensile strength increases sharply while elongation decreases further, which is attributed to fine scale precipitation formed during quenching of Cu–4.5 Ti and Cu–5.4 Ti alloys. On the other hand, hardness and tensile properties increase linearly up to 5.4 wt%Ti in the peak aged condition with or without prior cold work, due to uniform precipitation of Cu 4 Ti, β l phase in all the four alloys. The increase in yield and tensile strengths due to solid solution strengthening, cold work, and precipitation have been determined quantitatively in ST+CW+PA alloys. While electrical conductivity is less, the mechanical properties of Cu–Ti alloys are comparable with those of commercial Cu–Be alloys.

Effect of prior cold work on mechanical properties, electrical conductivity and microstructure of aged Cu-Ti alloys

The mechanical properties, electrical conductivity and microstructure of Cu-2.7wt%Ti and Cu-5.4wt%Ti alloys have been studied in different conditions employing hardness and resistivity measurements, tensile tests and optical, scanning and transmission electron microscopy. Ageing of undeformed as well as cold worked alloys raises their hardness, strength and electrical conductivity. The hardness increased from 120 VHN for solution treated Cu-2.7Ti to 455 VHN for ST + cold worked + peak aged Cu-5.4Ti alloy. While tensile stength increased from 430 to 1450 MPa, the ductility (elongation) decreased from 36 to 1.5%. A maximum conductivity of 25% International Annealed Copper Standard (IACS) for Cu-2.7Ti and 14.5% IACS for Cu-5.4Ti is obtained with the present treatments. Peak strength was obtained when the solution treated alloys are aged at 450°C for 16 hours due to precipitation of ordered, metastable and coherent β′, Cu4Ti phase having body centred tetragonal (bct) structure. While mechanical properties of Cu-Ti alloys are comparable, electrical conductivity is less than that of commercial Cu-Be-Co alloys.

Effect of Ti additions on the electrical resistivity of copper

Abstract Electrical resistivity of Cu Ti alloys containing 1.5, 2.7, 4.5 and 5.4 wt.% Ti, has been determined from the resistance values measured using Kelvins Bridge apparatus at room temperature. The resistivity in solution-treated alloys increases with Ti content linearly up to about 4.0 wt.% Ti, beyond which it decreases with further additions of Ti. However, in peak-aged condition, the resistivity continues to increase linearly up to 5.4 wt.% Ti without showing any decrease. Nordheims rule of resistivity is followed up to approximately 4.0 wt.% Ti in the solution-treated alloys. Further, Nordheims rule modified with the incorporation of the law of mixtures for two-phase systems ( ρ t = ρ m ν fm + ρ p ν fp ) is obeyed right up to 5.4 wt.% Ti in the peak-aged alloys. The difference in behaviour is attributed to the fine scale precipitation formed during quenching in solution-treated Cu—4.5Ti and Cu—5.4Ti alloys, as revealed by transmission electron microscopy (TEM). The contribution to the total resistivity by β ′-Cu 4 Ti precipitate and prior cold deformation is considerable in deformed and peak-aged Cu Ti alloys.

Age hardening studies in a Cu–4.5Ti–0.5Co alloy

Abstract Age hardening in a Cu–4.5Ti–0.5Co alloy has been studied at different aging temperatures and times. It has been observed that this alloy exhibits considerable age hardening with hardness increasing from 225 H V to a peak value of 320 H V on aging. Yield strength increases from 360 to 710 MPa and tensile strength from 610 to 890 MPa on aging the solution treated alloy for peak strength. The electrical conductivity of the alloy is found to be 4 and 8% International Annealed Copper Standard (IACS) in solution treated and peak aged conditions, respectively. Addition of cobalt to Cu–4.5Ti alloy reduces the aging temperature and time for attaining peak hardness. Ordered, metastable and coherent Cu 4 Ti (β l ) precipitate is found to be responsible for maximum strengthening of the alloy. Interestingly, absence of equilibrium precipitate Cu 3 Ti and presence of Cu 4 Ti phase have been noticed in the overaged condition. The absence of Cu 3 Ti is attributed to the addition of cobalt. In addition, intermetallic phases of Ti and Co like Ti 2 Co and TiCo have been observed in solution treated, peak aged and overaged conditions. Cold work prior to aging enhances the hardness, strength and electrical conductivity of the alloy. For example, 90% cold work followed by aging at 400°C for 1 h increases the hardness from 320 to 430 H V ; yield and tensile strengths, from 710 to 1185 and 890 to 1350 MPa, respectively, and electrical conductivity, marginally by 1% IACS. While mechanical properties are comparable, electrical conductivity of Cu–4.5Ti–0.5Co is less than that of the binary Cu–4.5Ti alloy in the solution treated as well as peak aged conditions.

Effect of cobalt additions on the age hardening of Cu-4.5Ti alloy

The effects of 0.9 and 1.8 wt% cobalt additions on the age hardening behaviour of Cu-4.5Ti alloy have been investigated. It has been observed that though Co addition results in the refinement of grain size and the Cu-Ti-Co alloys exhibit age hardening (giving rise to peak hardness on aging at 400°C for 16 hours), the peak hardness as well as the corresponding yield and tensile strengths were found to decrease with increasing cobalt content. The electrical conductivities of 0.9 and 1.8 wt% Co alloys were found to be 6% and 10% International Annealed Copper Standard (IACS) and 7% and 14% IACS in solution treated and peak aged conditions, respectively. Like in the binary Cu-Ti alloys, precipitation of ordered, metastable and coherent Cu4Ti(β1) precipitate was found to be responsible for maximum strengthening in these alloys. In addition, coarse intermetallic phases of Ti and Co, viz. Ti2Co and TiCo particles have been observed in all the conditions studied. The inferior mechanical properties of Cu-Ti-Co alloys compared with those of the binary Cu-Ti alloys are attributed to the depletion of Ti from matrix, which is consumed to form Ti2Co and TiCo phases.

On the variation of lattice parameter of Cu solid solution with solute content in Cu-Ti alloys

The properties and structure of age hardenable Cu-Ti alloys have been studied extensively to assess their suitability as a substitute for the toxic and expensive Cu-Be alloys. The earlier studies reported a sharp increase in hardness and strength and marked decrease in electrical resistivity in solution treated Cu-Ti alloys at Ti contents greater than 4.0 wt% and it was attributed to fine scale precipitation in the form of modulations in Cu-4.5Ti and Cu{sub 4}Ti, {beta}{sup 1} precipitate in Cu-5.4Ti alloys, formed during quenching itself. Further, such sharp changes were not observed in the peak aged condition due to uniform precipitation of Cu{sub 4}Ti, {beta}{sup 1} phase in all the four Cu-Ti alloys. However, the effect of solute content on the lattice parameter of {alpha}-Cu has not been investigated. The variation of lattice parameter of {alpha}-Cu with Ti content in solution treated (ST) and ST + peak aged conditions is presented in this paper.

Influence of prior cold work on age hardening of Cu–Ti–Zr alloys

Abstract The influence of prior cold work on age hardening behaviour of solution treated (ST) Cu–3Ti–0·1Zr and Cu–4Ti–0·1Zr alloys subjected to cold deformations of 50, 75 and 90% has been investigated by hardness and tensile tests and optical as well as transmission electron microscopy. Hardness of Cu–3Ti–0·1Zr and Cu–4Ti–0·1Zr alloys increased from 120 and 217 HV respectively in the ST condition to 365 and 433 HV respectively on 90% cold work and peak aging. Prior cold work reduced the peak aging time of the alloys while maintaining the same temperature, i.e. 450°C. Yield strength and tensile strength of Cu–3Ti–0·1Zr alloy reached maximum values of 940 and 1029 MPa respectively on 90% deformation and peak aging, while those of Cu–4Ti–0·1Zr alloy were 1258 and 1335 MPa respectively. The microstructure of the ST and deformed alloy exhibited elongated grains and deformation bands. The maximum strength on peak aging was obtained as a result of precipitation of ordered, metastable and coherent β′, Cu4Ti phase in addition to high dislocation density and deformation twins. These alloys were overaged as a result of the formation of incoherent and equilibrium β, Cu3Ti phase in the form of cellular structure. However, the morphology of the equilibrium β precipitate changed to globular form on high deformations.