Boron and graphene nanoparticles as solid lubricant in micro milling of nickel titanium shape memory alloys

Nickel titanium shape memory alloys (NiTi SMAs) are employed in a number of applications, however they are difficult to machine due to their high ductility, temperature sensitivity, and severe work hardening. Rapid tool wear and poor workpiece quality are inherent with their machining. Thus, new innovations are crucial to enhance their machinability. The usage of graphene and hexagonal boron nitride solid lubricant nanoparticles to enhance minimum quantity lubricant in micro-milling was investigated in this study. Evaluated parameters were ratio of undeformed chip thickness to cutting edge radius, composition of nanoparticles and cutting environment. Analysis of variance was employed to investigate the influence of process parameters and their interactions on flank wear, burr formation, surface roughness and cutting force. Graphene was found to be more effective than boron nitride in terms of reducing flank wear, burr size and cutting forces. Hexagonal boron nitride yielded better surface finish owing to smaller amount and size of nanoparticles. The work clearly shows the important of type and size of nanoparticles in improving machining performance. Additionally, the impact of simultaneously using chilled air and graphene nanoparticles in further improving process performance is reported.