Surface hardening of Ti-6Al-4V alloy using combined electroless Ni-B plating and diffusion treatments

The electroless plating process allows the production of a nickel-boron coating on the surface of a Ti-6Al-4V alloy, by immersion in a nickel chloride aqueous solution using dimethylamine borane (DMAB) as a reducing agent. A series of diffusion treatments was carried out tit temperatures ranging from 400 to 900 degreesC in order to achieve deep case hardening. The characterisation of both the electroless coating and the diffusion treated alloy was performed using XRD, SEM, EDS, and glow discharge optical spectrometry (GDOS). Microhardness and compositional profiles were carried out in order to reveal the hardening effect and the nickel and boron penetration. The results showed that a significant improvement in the hardness can be achieved by choosing the correct treatment parameters. Surface hardnesses up to 850 HV and a depth of hardening larger than 500 mum were achieved at 900 degreesC in an inert atmosphere.