EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The recent development of additive manufacturing techniques permits to architecture materials with controlled pores network including both macro and micro pores. The possibility is particularly attractive for designing new orthopaedic implants. Indeed, the pores network allows not only to cleverly reduce the stiffness mismatch between the implant and the surrounding bone tissue but also to improve vascularization and bone ingrowth. As the well-known titanium alloy Ti-6Al-4V (Ti64) is a routinely used in orthopaedic implants, the additive manufacturing of Ti64 has been studied.
Among the additive manufacturing techniques, robocasting process is the one which has been preferred to typical powder bed fusion processes in order to control more precisely both macro and micro pores network. This 3D printing process consists of extruding a paste filled with Ti64 particles, debinding the organic components of the paste and pressureless sintering the final structures.

The control of the heat treatment (time, temperature, heating rate, atmosphere, …) during sintering step as well as the characteristics of Ti64 particles (size, surface contamination, …) will condition the size and distribution of the pores. In order to evaluate the evolution of these Ti64 structures during the heat treatment, an in-situ synchrotron coupled XRD/micro-tomography (μCT) study have been carried out. One the one hand, continuous acquisition of energy dispersive XRD spectra allows to follow the alpha-beta phase transformation of TA6V during the heat treatment. On the other hand, fast acquisition of μCT 3D images permit to efficiently determine the evolution of the microstructure of TA6V structure and of the pores within it.
We will show how the porous network can be designed by varying the sintering temperature, holding time, particles size distribution and also the upstream debinding step. Among other things, the shrinkage of the initial interconnected pore and formation of closed micro pores has successfully been reported.