レーザ積層造形における結晶集合組織形成機構解明のための改良CA法によるシミュレーション

抄録

Metal additive manufacturing (AM) technologies are attracting attentions not only as a forming process but also as microstructure controlling processes. In powder bed fusion (PBF) AM, crystal orientations can be controlled by scanning strategies of energy beam. To optimize microstructures, computer simulations for predicting microstructures play very important roles. In this work, we have developed simulation programs to explain the mechanism of the crystal orientation control. First, we simulated the shape of melt pool by analyzing the heat transfer using apparent heat conductivity when the penetration of laser beam through keyholes was taken into consideration because of the evaporation and accompanying convections. It was assumed that the primary crystal growth direction can be determined by the temperature gradient, and the crystals grow keeping the growth direction as generally recognized. The shapes of simulated melt pools agree well with experimental observations. The modified cellular automaton simulations successfully reproduced two typical textures with different preferential orientations along the building directions of 〈001〉 and 〈011〉 when the bidirectional scanning with and without a rotation of 90° was accomplished between the layers.

Fig. 8　Comparison of analysis results (lower side) with experimental results (upper side: after Ishimoto et al.^1）) of scan strategy X.