Thermo-Mechanical Treatments of Cu-Ti Alloys

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مريم محمد مرغم



Copper and copper – base alloys are widely used for numerous applications demanding good mechanical properties , resistance to corrosion , good electrical onductivity (EC) , pleasing colour and ease of fabrication [1,2] . Among the alloys having a good combination of high strength and high thermal as well as electrical conductivity, age hardenable Cu-Be alloys are most widly used but they have the limitation of toxicity and high cost of production. Cu- Ti binary alloys are precipitation strengthened by spinodal decomposition mechanism [3-5] involving composition modulations and long range ordering in the initial stages of aging. The tensile strength value of 930N/mm2 was obtained for Cu-5.4wt%Ti alloy by the precipitation of a coherent and metastable fine precipitate of Cu4Ti (β`) and electrical conductivity of 24.5%IACS was obtained for Cu-1.5wt%Ti alloy on peak aging [6]. Experiments on cold compression followed by aging of Cu-Ti alloys have indicated that the most effective hardening of the matertial results from continuous precipitation of very fine particles within the matrix. These particles were reported to be β` -type, Cu4Ti phase. The β`-β transformation and particles coarsening within the matrix as well as a long grain boundaries were responsible for the overaging of Cu-1.5wt%Ti and Cu-3.5wt%Ti alloys It is well know that plate like particles are β – type, Cu3Ti phase. Discontinuous precipitation was found to start at the grain boundaries and expand into grain interior. At the higher aging temperature a classic widmanstätten morphology forms giving rise to a coarse microstructure comprised of α and the equilibrium phase β. Those results were confirmed by X-ray analysis, which found that a few percent of Cu3Ti, β precipitates are formed during aging at high temperature for long time for both Cu- Ti alloys (i.e. Cu-1.5wt%Ti and Cu-3.5wt%Ti).