Heterogeneous α Phase Precipitation and Peculiar Aging Strengthening in Biomedical β-Type Ti-Nb-Ta-Zr Alloy Having Vortical Structure

Abstract

Microstructural evolution accompanying mechanical properties change by aging treatment at 723 K in cold swaged Ti 29Nb 13Ta 4.6Zr were investigated in order to obtain an optimized aging condition for getting excellent mechanical properties.The precipitate free zone exists in Ti 29Nb 13Ta 4.6Zr after aging treatment for various time periods. Such the precipitate free zone corresponds to Nb and Ta enriched region according to the result of element distribution analysis. With the increase in aging time, the area of the precipitate free zone decreases.Two types of a phase, acicular and ellipsoidal ones, are observed in Ti 29Nb 13Ta 4.6Zr after aging treatment for various time periods. The acicular a phase is precipitated in the Tiand Zr enriched region. While the size increases, the area fraction barely changes with aging time for acicular a phase, On the other hand, the ellipsoidal a phase precipitates at b grain boundary and its subgrain boundary. Both the size and area fraction increase with the increase in aging time for the ellipsoidal a phase.The lattice correspondence between acicular a phase and b matrix is Tensile strength of Ti 29Nb 13Ta 4.6Zr subjected to aging treatment after cold swaging is around 1200 GPa, regardless of aging time. On the other hand, elongation of those are decreased by the aging treatment up to 86.4 ks, increased at ones over 259.2 ks.

Theory-Guided Materials Design of Multi-Phase Ti-Nb Alloys with Bone-Matching Elastic Properties

“…Employing our theory-guided materials design strategy, it will become possible to pre-select most promising Nb compositions by quantum-mechanical calculations and avoid casting and testing of large numbers of samples from the whole compositional range. This can be essential in both on-going and future development of Ti-Nb binary alloys [ 56 , 57 , 58 , 59 ], ternary materials [ 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 ] (including Ti-Al-V [ 68 , 69 , 70 ] and Ti-Nb-V [ 71 , 72 ]), as well as higher-order alloys [ 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ] intended for bio-medical applications [ 83 , 84 , 85 , 86 , 87 , 88 ].…”

Effect of heterogeneous precipitation caused by segregation of substitutional and interstitial elements on mechanical properties of a β-type Ti alloy

“…In the case of the former, homogeneous precipitation can be seen at a grain-size scale, but precipitation near the GBs is not microscopically homogeneous. There is very little evidence of etching related to the precipitation of acicular α phases [13,14] within the grains of the TNTZ homogenized for 10.8 ks, whereas widely etched regions in grains and clearly nonetched regions at GBs are seen in the homogenized TNTZ aged for 43.2 ks. These widely etched regions are related to the dense precipitation of acicular α phase permeating throughout the grain with increasing aging time, while the non-etched GB regions are known as precipitate-free zones (PFZs) [15] that are related to segregation effects [16] and the migration of defects to the GBs during aging [17,18].…”

“…An orientation relationship of [0001] α //[001] IP //[110] β has been clarified using electron diffraction patterns along several beam directions; IP spots appearing at the misfit positions of β phase spots [24]. An interface phase has been reported in several β-type Ti alloys [14,25], with Sukedai et al [25] reporting that an unknown phase closely related to the ω phase is formed. Precipitates that grow from the GB into the grain can be seen in the bright-field image of the homogenized TNTZ aged for 259.2 ks given in Fig.…”

“…Note that this temperature is that required to precipitate the α phase in this alloy [13,14]. Both homogenized and non-homogenized TNTZ samples are used, with particular focus being given to the microstructure formed by heterogeneous precipitation of the α-phase during aging.…”

Relationship between Heterogeneous Microstructure and Fatigue Strength of Ti-Nb-Ta-Zr Alloy for Biomedical Materials Subjected to Aging Treatments

“…The wave-pattern is caused by the microsegregation of additional elements used for making the alloy. It is difficult to avoid microsegregation in the biomedical β-type titanium alloy because β−stabilizers with some immiscibility in the β-phase have high melting points [10,11]. On the other hand, a homogeneous structure is observed in the TNTZ subjected to the long-term homogenization process.…”