Significance of the Martensitic State of Ti Grade 4 in the Evolution of Microstructure and Mechanical Properties Induced by ECAP-Conform
摘要
Severe plastic deformation by continuous equal-channel angular pressing (ECAP-Conform) is employed to enhance the mechanical performance of Ti Grade 4. ECAP-Conform has been applied to the material in an initially martensitic state. Special attention is given to the mechanisms of structural transformations in Ti Grade 4 with increasing strain. It is demonstrated that the strain-induced transformation of an initially refined state, composed of ultrafine martensite bands (with dimensions < 1 μm), results in a tensile strength increase up to 895 MPa after just a single ECAP-Conform pass. This increase in strength is notably higher than the value achieved by ECAP of the hot-rolled state (840 MPa). With further straining (up to e ≈ 2.4), the strength of the material in the initially martensitic state increases to 1085 MPa, compared to 1040 MPa for the initially hot-rolled state. Post-processing of the initially martensitic state by drawing to d = 6 mm leads to a further increase in strength to 1265 MPa. The effects of imposed strain and annealing on materials with initially different phase compositions are discussed.