Change in Crystal Structure and Material Properties with Deformation of Quenched Martensite in Ti-Nb Alloys

Abstract

The purpose of this study was to investigate and discuss the relationship between the crystal structure of martensites and the material properties, such as the Young's modulus and internal friction, in quenched Ti Nb alloys with plasto elastic deformation. In the alloys, minimal Young's modulus was indicated by the a′ martensite of Ti15Nb, and maximal internal friction was indicated by the a″martensite of Ti18Nb. After a weak plastic deformation of 5 rolling reduction, the Young's modulus of Ti (15,18, 20)Nb decreased, and the internal friction of Ti20Nb increased though that of Ti (15, 18)Nb hardly changed. From the XRD profiles, the extreme values of the material properties were predicted to be associated with the unit volume and phases (hexagonal close packed or orthorhombic) of the materials. It was also predicted to be associated with the change of phase from a′ to a″and from a″to a′ ＋a″or a″ ＋a″with different lattice parameters. Cyclic tensile test results after weak plastic deformation revealed characteristic changes in elastic incline, that is, an increase from ～40 GPa in Ti15Nb, and a decrease until ～40 GPa from the initial value followed by an increase in Ti18Nb and Ti20Nb. The consequent changing mechanism of material properties was suggested from the viewpoint of the changing behavior of the phase transformation and transition on martensites with plastic deformation or loaded elastic deformation.

Alloy Design, Thermodynamics, and Electron Microscopy of Ternary Ti-Ag-Nb Alloy with Liquid Phase Separation

“…Sharp peaks corresponding to FCC-Ag and broad peaks, whose position overlapped with that of Ag (111), were observed in the melt-spun ribbons of the Ti 53.4 Ag 33.3 Nb 13.3 alloy. The origin of the broad peaks in the melt-spun ribbons was not clarified in the present study, and can be considered to be related to the martensite phase formation in the Ti-Nb alloys [ 76 , 77 , 78 , 79 , 80 ]. Further identification of the broad peak in the XRD patterns with electron microscopy can be conducted in the future.…”

“…Sharp peaks corresponding to FCC-Ag were observed in the arc-melted ingots of the Ti 53.4 Ag 33.3 Nb 13.3 alloy, whereas no intermetallic compounds were observed. The broad peak overlapping with the sharp peak of the FCC-Ag (111) was observed only in the Ti 53.4 Ag 33.3 Nb 13.3 alloy, and the broad peak corresponding to the formation of the martensite phase in the Ti-Nb-rich phase [ 76 , 77 , 78 , 79 , 80 ].…”

Structural Changes due to Heating and Stress Loading of Metastable Quenched Martensite Structures in Ti–(10–20) mass% Nb Alloys

“…Figure 4 shows variations in the lattice constant, axial ratio, and unit volume after the orthorhombic conversion. Because it is difficult to distinguish between the two martensite phases, 13) only the change in the main phase was evaluated. The lattice constant was calculated to be shrinking due to the tensile loading because the tensile axis crossed the rotating axis of the specimen at right angles; therefore XRD only from the crystal plane that shrinks due to Poisson's ratio occurred.…”

“…Meanwhile, many studies have focused on TiNb alloys with compositions in the Ti(3542) mass% Nb (2227 at% Nb) range, which exhibit shape memory and superelastic functions; such functionalities are realized by utilizing the stress-induced ¡AA martensite structure of ¢-type titanium alloys. 58,14) Although several studies have examined the metallographic characteristics 1519) or material properties of (¡ + ¢)-type titanium alloys with the quenched martensite structure, 13,2022) the correlations between the material properties and stress and temperature applications remain unclear.…”

“…In our previous studies, 1113,27,28) we conducted experimental investigations of the Young's modulus, internal friction, tensile elasto-plastic deformation behavior, and phase transformation behavior associated with the plastic deformation of the quenched ¡A and ¡AA structures of TiNb alloys. Based on these results, we discuss the influence of the boundary crystal structure between the ¡A and ¡AA phases formed by quenching.…”