Undercooling versus stress induced martensitic phase transformation: The case of MgO – partially stabilized zirconia

•Distinctive differences between cooling and stress induced t→m transformations.•Presence of an energy barrier in Gibbs enthalpy plays key role in variant selection.•Stress induced t→m transformations leads to a sequential growth of m-phase lamellae.•Cooling induced t→m transformations is characterized by an homogeneous nucleation.•Presence of residual stresses introduces energy barrier and stability to the t-phase.