%0 journal article
%@ 0264-1275
%A Gussone, J.,Rackel, M.W.,Tumminello, S.,Barriobero-Vila, P.,Kreps, F.,Kelm, K.,Stark, A.,Schell, N.,Pyczak, F.,Haubrich, J.,Requena, G.

%D 2023
%J Materials & Design
%N 
%P 112154 
%R doi:10.1016/j.matdes.2023.112154
%T Microstructure formation during laser powder bed fusion of Ti-22Al-25Nb with low and high pre-heating temperatures
%U https://doi.org/10.1016/j.matdes.2023.112154
 
%X We compare microstructure formation during laser powder bed fusion (LPBF) of a Ti-22Al-25Nb alloy applying low and high pre-heating build plate temperatures. Fast cooling rates during low-temperature LPBF lead to metastable weakly ordered β phase, i.e., bcc–(Ti,Al,Nb) with pronounced 〈1 0 0〉 texture in build direction and nanosized segregations within grains elongated in the build direction. For high-temperature LPBF a Widmanstätten microstructure was observed with lenticular O phase precipitates within the β matrix. Microscopical and in situ high-energy synchrotron diffraction investigations demonstrate that the microstructure formation can be widely explained by the precipitation of O phase from supersaturated β rather than by a sequence of solid-state phase transformations, as it would be expected under thermodynamic equilibrium conditions. A detailed analysis of the microstructural gradient in the subsurface region, however, demonstrates that precipitation from metastable β cannot fully explain the observed microstructures, and that the process energy density, i.e., the intensity of the intrinsic heat treatment of LPBF, plays a relevant role. The investigation of the graded area near the surface of the LPBF materials produced with high pre-heating temperature is particularly interesting as it reveals preferred nucleation of the O phase at subgrain boundaries and dislocations.