As additive manufacturing (AM) is moving into the production of more heavily loaded end-use components, particularly within the aerospace sector, improved understanding of the performance of AM parts under cyclic load is essential. Ti-6Al-4V is the most prevalent Ti alloy and widely used in aerospace. The presence of heterogeneous microstructures, i.e. the continuous changes in texture, grain shape, distributions of phase and composition, has been observed from the bottom to the top (along the z direction) of the AM-built. Here we propose to undertake an in-situ tensile-compressive loading of AM-built Ti-6Al-4V at 450°C combined with the neutron diffraction. The proposed experiment will provide a mechanistic understanding of deformation of AM-built Ti-6Al-4V under cyclic loads.