Rapid elimination of porosity and brittleness in cold spray additive manufactured grade 2 titanium via in situ electro-plastic treatment

In this study, an in situ electro-plastic treatment (ISEPT) process was used to simultaneously eliminate porosity and brittleness in cold spray (CS) additive manufacturing (AM) of a grade 2 commercial purity titanium (CP Ti). The CS deposition conditions were optimized using a validated 3D CFD model to minimize oxidation while reducing porosity in the as-sprayed CP Ti. The ISEPT electric current and load were applied in the same direction (in situ) to improve the electro-plastic effect and to recrystallize CS CP Ti in an open-air environment. The rapid heating sourced from the applied current occurred at a temperature below 550 °C, the critical temperature for titanium oxidation, and at 24–30 mm/min deformation rate. The rapid nature of ISEPT treatment is associated with abolition of the necessary isothermal (oven) treatment for static recrystallization and corresponding time required for preheating in other rival thermomechanical treatments. The treated CP Ti structure exhibited transformation of CS splat structure to refined equiaxed grains. The porosity of the cold-sprayed structure was considerably reduced from 5 to as low as 0.1% after double ISEPT. The elongation was increased substantially from 0.5 for as-sprayed to 18% for the ISEPT-treated material. Similar improvements were observed in relation to CP Ti strength, hardness, and stiffness modulus. Results revealed that the ISEPT in the absence of controlled atmosphere contributed 0.06% to the Ti oxygen pick up, keeping the composition well within the acceptable range for CP Ti. The effect of ISEPT conditions on rapid elimination of porosity and progress of Ti recrystallization to cold-sprayed additively manufactured CP Ti has led to significant improvement in the material ductility in a short processing time at a relatively low temperature allowing elimination of costly controlled atmosphere.