Neutron diffraction study on martensitic transformation under compressive stress in an ordered Fe3Pt

We have studied the structure change of an ordered Fe3Pt (degree of order ∼0.75) under a compressive stress applied in the [001] direction by neutron diffraction. In the absence of the stress, the alloy exhibits a weak first order martensitic transformation at 90 K from the L12-type cubic structure to the L60-type tetragonal structure. Under the compressive stress of 100 MPa, the first order nature of the thermally-induced martensitic transformation was undetectable in the temperature range of between 70 K and 270 K. The first order nature of the stress-induced martensitic transformation was also undetectable in the stress range of between 6 MPa and 300 MPa when tested at 120 K and higher temperatures. Under these conditions, the lattice parameters change continuously both in the cooling process and in the stress-applying process. Despite the disappearance of the first order nature of martensitic transformation, a significant stress-induced softening of lattice, which is regarded as a precursor phenomenon of martensitic transformation, was observed between 120 K and 265 K but not at 93 K and 295 K.We have studied the structure change of an ordered Fe3Pt (degree of order ∼0.75) under a compressive stress applied in the [001] direction by neutron diffraction. In the absence of the stress, the alloy exhibits a weak first order martensitic transformation at 90 K from the L12-type cubic structure to the L60-type tetragonal structure. Under the compressive stress of 100 MPa, the first order nature of the thermally-induced martensitic transformation was undetectable in the temperature range of between 70 K and 270 K. The first order nature of the stress-induced martensitic transformation was also undetectable in the stress range of between 6 MPa and 300 MPa when tested at 120 K and higher temperatures. Under these conditions, the lattice parameters change continuously both in the cooling process and in the stress-applying process. Despite the disappearance of the first order nature of martensitic transformation, a significant stress-induced softening of lattice, which is regarded as a precursor phenomenon...