Microstructure Characterization and Thermal Stability of TNM Alloy Fabricated by Powder Hot Isostatic Pressing

Yichao Wang,Xiangyi Xue,Jinshan Li,Zhongwei Yin,Yonghao Yu,Fengming Qiang,Hongchao Kou

doi:10.3390/met11111720

Abstract

A TNM alloy ingot was fabricated with powder hot isostatic pressing (P-HIP) and short-time exposure treatment conducted at 750–1050 °C for 2–5 h. The tensile mechanical properties were investigated at room temperature and 800 °C. The results revealed that a fully lamellar microstructure of P-HIPed TNM alloy with only 0.3 vol.% β0 phase could be obtained by hot isostatic pressing at 1260 °C, under the pressure of 170 MPa, held for 4 h. When the exposure temperature was below 850 °C, the α2 lamellae were transformed into nano-scaled (α2 + γ) lamellae (i.e., the α2→α2 + γ transformation). With increases in the exposure temperature, the β0 phase began to precipitate within the α2 lamellae (α2→β0 transformation) at 950 °C. The α2→γ and the α2→β0 transformation both happened at 950–1050 °C, and the higher exposure temperature accelerated the diffusion of Mo and facilitated the α2→β0 transformation. The yield strength and elongation at RT and 800 °C were both improved after short-time high-temperature exposure treatment. The uniform distribution and nano-scaled interfacial β0 phase provided precipitation strengthening and were not harmful to the elongation.

Highlights

The TNM alloys, nominal chemical composition Ti-(42–45)Al-(3–5)Nb-(0.1–2)Mo(0.1–0.2)B, are considered to be attractive options for producing light high-temperature structural materials due to their low density, high modulus of elasticity, high creep resistance and oxidation resistance at elevated temperatures [1,2]
A high-magnification micrograph is shown in Figure 1b, from which can be observed that only a very small amount of β0 particles were located at the colony boundaries
◦ C, under a pressure of 170 MPa for 4 h, in which the powder hot isostatic pressing at powder hot isostatic pressing at 1260 °C, under a pressure of 170 MPa for 4 h, in which resulting volume fraction of the waswas onlyonly

Summary

Introduction

The TNM alloys, nominal chemical composition Ti-(42–45)Al-(3–5)Nb-(0.1–2)Mo(0.1–0.2)B (in at.% percent), are considered to be attractive options for producing light high-temperature structural materials due to their low density, high modulus of elasticity, high creep resistance and oxidation resistance at elevated temperatures [1,2]. The fully lamellar microstructure with a balance of mechanical properties is more suitable for high-temperature structures [4,5]. Tailoring a fully lamellar microstructure and good thermal stability of the microstructure at elevated temperatures are significant concerns to extend the service temperature of TNM alloys for aero-engine applications. The disordered β phase with ductile properties in the TNM alloy is attributed to thermal formability [8]. It is difficult to obtain a fully lamellar microstructure and results in a deterioration of the tensile mechanical properties [9,10]. Many approaches have been applied to eliminate the ordered β0 phase to achieve a fully lamellar structure through different processes

Methods

Results

Conclusion