Microstructure characterization and thermal stability of tnm alloy fabricated by powder hot isostatic pressing

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.