Correlation between Solution Treatment Temperature, MicroStructure, and Yield Strength of Forged Ti-17 Alloys

Yoko Yamabe-Mitarai,Yoshio Itsumi,Norie Motohashi,Syuji Kuroda,Akira Ishida,Takanobu Hiroto,Hideyuki Murakami

doi:10.3390/cryst11060625

Yoko Yamabe-Mitarai, Yoshio Itsumi + Show 5 more

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https://doi.org/10.3390/cryst11060625

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Abstract

The Ti compressor disks of aviation jet engines are produced by forging. Their microstructure, which depends on the forging conditions, strongly affects their mechanical properties. In this study, changes in the microstructure of Ti-17 alloy as a result of different solution-treatment (ST) temperatures and the related tensile yield strengths were investigated to elucidate the correlation between the ST temperature, microstructure, and yield strength. Ti-17 alloys ingots were isothermally forged at 800 °C and solution-treated at 750, 800, and 850 °C. The microstructure and yield strength were investigated for samples subjected to different ST temperatures. The primary α phase formed during the ST, and the secondary α phase formed during the aging treatment at 620 °C. The yield strength increased with increasing volume fraction of the primary α phase and increased further upon formation of the secondary α phase during the tensile test at room temperature. The correlation of the primary and secondary α phases with yield strength was clarified for tensile properties at room temperature, 450, and 600 °C. An equation to predict the yield strength was constructed using the volume fraction of the primary and secondary α phases.

Highlights

The compressor disks of aviation jet engines are manufactured by forging using Ti alloys such as α + β Ti-6Al-4V, near-β Ti-6246 (Ti-6Al-2Sn-4Zr-6Mo), and Ti-17 (Ti-5Al-2Sn-2Zr-4Cr-4Mo) alloys
The total volume fraction of the α phase was measured by X-ray diffraction (XRD, Rigaku SmartLab, Tokyo, Japan), as described in the paragraph, because the secondary α phase was too small for measurement of its volume fraction from the microstructure images
In the solution-treated samples, the primary α phase precipitated in the Crystals 2β021p, 1h1,axsFeO.RIPnEEoRuRrEVpIErWevious study, the primary α phase precipitated with a plate- or nee5dolfe1-2 like morphology with a Burgers orientation relationship during cooling after forging [25]

Summary

Introduction

The compressor disks of aviation jet engines are manufactured by forging using Ti alloys such as α + β Ti-6Al-4V (wt %), near-β Ti-6246 (Ti-6Al-2Sn-4Zr-6Mo), and Ti-17 (Ti-5Al-2Sn-2Zr-4Cr-4Mo) alloys. The hot deformation behavior of Ti-6246 samples 10 mm in diameter and 12 mm in height was investigated under dynamic material modeling theory and a processing map showing the optimum processing conditions was constructed [3]. An investigation of the hot deformation behavior of industrial-sized discshaped Ti-6246 revealed the optimum processing conditions to attain a microstructure that led to the desired mechanical properties [4]. The influence of a solution treatment followed by an aging treatment on the microstructure and mechanical properties of industrial-sized Ti-6246 was investigated, revealing that a solution treatment at a temperature near the β-transus temperature gave the highest strength and ductility [5]. Globularization of the α phase and recrystallization of Ti-6246 forged in the α + β region were systematically investigated, and a prediction model developed using the Avrami approach and the machine learning approach was suggested for modeling dynamic globularization [6]

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