Use of additives for porosity control in the manufacturing of MAX phase components by powder bed fusion processes

Porosity is a major concern in the manufacturing of MAX phase components through powder bed fusion process. Three factors, powder characteristics, processing parameters, and internal reactions have been identified as key factors governing densifications of these printed parts. While investigations on the first two factors are quite common, the last one seems less explored. In this study, micro-alloying (substitution) on the M-site was selected as a possible way of tuning the internal reaction. A lower diffusion material niobium was adopted as a substitutional component through the relation (2-x)Ti:(1+x)Al:C:yNb$(2 - x){\rm{Ti}}:(1 + x){\rm{Al}}:{\rm{C}}:y{\rm{Nb}}$,that combine three pre-existing concepts on powder mixture, including stoichiometric, near-stoichiometric, and the solid solution on M-site. Two powder mixtures in prescribed ratio related to two different combinations of x and y values arbitrarily chosen denoted by Nb1 and Nb3 were considered for investigation. A comparison of density and area fraction quantifying the distribution of pores and compact areas on the upper surface of the sample was made. A skeletal density of 94.85% and a compact area fraction of 68.24% were outstanding characteristics displayed in the Nb1 and Nb3 series, respectively, with a significant dependence on the processing parameters. The advantages and disadvantages of these two powder mixtures are discussed.