Elastic constants of Ti-15Mo single crystals and their evolution with thermal treatment

M Janovskaa,Jana Šmilauerová ,Pavla Stoklasová ,Petr Sedlák ,Tomáš Grabec ,Jitka Nejezchlebová ,Miloš Janeček ,Stanislav Krátký ,Hanuš Seiner

doi:10.1051/matecconf/202032112012

Abstract

Elastic constants of single crystals of metastable β-phase of the Ti-15Mo alloy were studied by ultrasonic methods with the aim to observe the dependence of these constants on formation of isothermal ω particles. Two ultrasonic methods were applied: resonant ultrasound spectroscopy for monitoring the temperature evolution of the elastic constants, and transient grating spectroscopy for identification of the local material symmetry at a fixed temperature. Samples with different heat treatments (isothermal ageing at 300 °C and ageing under the same temperature with uniaxial [111] loading) were studied. The results prove that the isothermal omega particles always exactly follow the original cubic symmetry of the β matrix, and that the evolutions of the elastic constants of the β-ω multi-phase crystals can be reliably approximated using Hill’s homogenizing procedure, assuming cubic elastic constants of the β-phase and isotropic elastic constants representing the ω particles.

Highlights

Metastable β-Ti alloys are used for many of industrial applications because of their variability of strength, toughness and fatigue resistance [1]
The results prove that the isothermal omega particles always exactly follow the original cubic symmetry of the β matrix, and that the evolutions of the elastic constants of the β-ω multi-phase crystals can be reliably approximated using Hill’s homogenizing procedure, assuming cubic elastic constants of the βphase and isotropic elastic constants representing the ω particles
Significant increase is observed for both shear elastic constants after the period of heat treatment, 16 % for C44 and 28 % for C

Summary

1.Introduction

Metastable β-Ti alloys are used for many of industrial applications because of their variability of strength, toughness and fatigue resistance [1]. Subsequent heating leads to formation of ω isothermal particles by coupled diffusional‐displacive transformation. Alloying elements are rejected from ω isothermal particles to the surrounding body-centered cubic matrix and a collapse of (1 1 1)β planes takes place simultaneously during this process [7]. The ω phase has a signi cant impact on the elasticity of the whole material, as was shown by Tane [8], so the exact measurement of elasticity can bring new information to explain this problem. Containing only 2 elements, this material is suitable for observing processes which take place during heat treatment of material, such as the ω particles formation. Ultrasonic methods are very sensitive tools for the measurement of minute changes of the elastic constants of a material and have already been used for the study of metastable β-Ti alloys [9], [10], [11]

Examined material

RUS measurement

TGS measurement

Experimental results and discussion

Conclusions