Effect of Cu-induced eutectoid transformation on microstructure and mechanical properties of Ti–6Al–4V alloy by laser wire deposition

Microstructure transformation and mechanical properties of Ti–6Al–4V based on laser wire deposition were studied with the addition of different contents Cu. With the addition of 5.4 wt% Cu, deposited alloy firstly transformed into martensite under rapid cooling conditions. In subsequent cyclic heating of additive manufacturing, martensite decomposed into α phase and nodular Ti₂Cu phase. With the addition of 6.8 wt% Cu, active eutectoid reaction was stimulated in the deposited alloy that directly transformed into nanoscale lamellar α+Ti₂Cu microstructure under fast cooling conditions. However, under the subsequent cyclic heating, nanoscale Ti₂Cu served as nucleation site, developed into micron-size pro-eutectoid Ti₂Cu. Couple the effect of refine grain strengthening, solid solution strengthening and dispersion strengthening, tensile strength of deposite was increased approximately 58%, and tensile strain was only reduced approximately 6% after 5.4 wt% Cu was added. When the addition was 6.8 wt% Cu, the tensile strength declined by about 6%, and tensile strain dropped by probably 66%, since stress concentration was easily caused by micron-size pro-eutectoid Ti₂Cu in deposit.