Probing the temperature field and residual stress transformation in multi-track, multi-layered system

A three-dimensional sequential coupled thermo-mechanical modelling is performed for multi-track, multi-layer deposition of Nickel-based superalloy, namely IN625; through laser powder bed fusion (LPBF) technique for real-time monitoring of the thermal response, cooling characteristics and in-process transformation in residual stress in successively built height. The maximum temperature of 1100 K is estimated at the top section, whereas 810 K is at the middle section during solidification. This spatial transition in temperature distribution over the same built structure is caused by differences in local cooling rates. The steel substrate/backing plate that was utilised demonstrated a heat sink effect and contributed to altering the cooling properties and residual stress behaviour in the lower portion of the fabricated built structure. The conduction mode of heat transfer is found to be effective at the bottom section, while the propensity of convective mode is enhanced upon increasing the built height. Cooling rate is highly influenced by the temperature gradient, hence similar pattern is achieved for both solidification parameters during the deposition process. Tensile longitudinal (S11 303 MPa) and transverse (S22 455 MPa) residual stress is obtained at the location of 4.5 mm from the bottom side, compensated by compressive stress of 180 MPa, on the top and bottom side to maintain structural equilibrium. Reversal of stress field from tensile to compressive and vice-versa couldn’t happen at built (IN625)/substrate (Steel) interface probably due to insignificant difference in coefficient of thermal expansion, i.e., 10 – 12 10-6 /K for both alloys.