Surface hardening of Ti – 6Al – 4V alloy by diffusion treatment of electroless Ni – B coatings

Electroless nickel – boron coatings on Ti – 6Al – 4V alloy were obtained by immersion in nickel chloride aqueous solutions with both dimethylamine amine borane and sodium borohydride as reducing agents. On some samples, a graphite layer was deposited by physical vapour deposition before the electroless deposition. Heat treatments at 800°C for 40 h were performed to obtain surface hardening of the titanium alloy. The effect of different deposition agents on the depth of hardening was studied by XRD, SEM, EDS and glow discharge optical spectrometry. Surface hardness >1000 HV and depth of hardening >500 mm were achieved by diffusion of layers obtained with sodium borohydride as reducing agent.