Influence of cooling rate on the precipitation kinetics of nanoscale isothermal ω-phase in metastable β-Ti alloy, Ti-5Al-5Mo-5V-3Cr

JOURNAL OF ALLOYS AND COMPOUNDS

卷:859

Article

Sharma, Deepak^1,2  Parfitt, David¹  Chen, Bo^1,3  Roebuck, Bryan⁴  Venero, Diego Alba⁵  Kada, Sitarama Raju²  Fabijanic, Daniel²  Fitzpatrick, Michael E.¹ 

[1] Coventry Univ, Inst Future Transport & Cities, Coventry CV1 5FB, W Midlands, England

[2] Deakin Univ, Inst Frontier Mat, Geelong, Vic 3216, Australia

[3] Univ Leicester, Dept Engn, Leicester LE1 7RH, Leics, England

[4] Natl Phys Lab, London TW11 0LW, England

[5] Rutherford Appleton Lab, ISIS Neutron & Muon Source, Didcot OX11 0QX, Oxon, England

关键词: Titanium alloys;    Kinetics;    Small-angle neutron scattering;    Electrical resistivity measurements;   

DOI  :  10.1016/j.jallcom.2020.157822

来源: Elsevier

【 摘 要 】

In metastable beta-Ti alloys, nanoscale isothermal (alpha-phase (omega(iso)) precipitates are regarded as the nucleation sites for the alpha strengthening phase. Here we investigate the precipitation kinetics of the omega(iso) precipitates as a function of cooling rate (air cooling and water quenching) after beta-solutionising. A combined in situ small-angle neutron scattering (SANS) and electrical resistivity measurement approach was used during ageing of Ti-5Al-5Mo-5V-3Cr wt% (Ti-5553) alloy at 300 degrees C and 325 degrees C up to 8 h. The SANS modelling was consistent with ellipsoid shaped particles for the omega(iso) precipitates, for both air-cooled and water-quenched samples. The precipitates attained a maximum size (equatorial diameter) of similar to 21 nm and similar to 17 nm after 2 h and 4 h of ageing the water-quenched and air-cooled samples respectively. Although the air-cooled samples showed delayed nucleation in comparison to water-quenched sample, the volume fraction became approximately the same (similar to 11%) after ageing for 8 h. The average value of the activation energy for omega(iso) nucleation from the beta-phase matrix was determined as 122 kJ mol(-1) from electrical resistivity data using a modified Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The hardness increased with ageing time, with water quenching leading to a higher final value of hardness than air cooling. (C) 2020 Elsevier B.V. All rights reserved.

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