Study of second phase precipitates in nanostructured commercially pure titanium

The results of studies on the process of precipitation of dispersed second phases in commercially pure titanium Grade 4 and the effect of secondary precipitates on its structure and mechanical properties in two states, coarse-grained and nanostructured ones, are presented. The nanostructured state was obtained by high-pressure torsion (HPT) under a pressure of 6 GPa up to N =10 revolutions at room temperature. A particular consideration is given to the study of changes in the phase composition and microstructure of titanium subjected to deformation processing after annealing at an elevated temperature of 700 degrees C for 30 minutes. In this work, by means of studies in a transmission electron microscope, it was shown that at a temperature of 700 degrees C and higher, in the structure of the samples, nanoparticles of the second phases which differ in size and morphology are precipitated in both states. The nature of the observed particles was studied in SEM, by indexing the electron diffraction patterns taken from the particles, and by carrying out X-ray phase analysis by the transmission method. Particles of the second phases are modifications of the high-temperature beta-phase of titanium. The HPT treatment of the alloy, according to the XRD data, leads to an increase in the volume fraction of precipitated particles after annealing and, as a result, to an increase in the microhardness of the states under study. The results of microhardness measurements at varying regimes of deformation and annealing are presented. Combination of HPT up to N = 5 revolutions and annealing at 700 degrees C for 30 minutes followed by additional torsion straining also up to N = 5 revolutions provides the highest microhardness values in commercially pure titanium, which reaches 423 HV.

Automated summary

This study investigates the precipitation of dispersed second phases in commercially pure titanium Grade 4, focusing on the impact of secondary precipitates on structure and mechanical properties in coarse-grained and nanostructured states. The results show that high-temperature beta-phase modifications precipitate in both states at temperatures of 700 degrees C and higher, leading to an increase in microhardness after annealing.