Solidification Behavior and Microstructures Characteristics of Ti-48Al-3Nb-1.5Ta Powder Produced by Supreme-Speed Plasma Rotating Electrode Process

doi:10.1007/s40195-023-01539-2

Abstract

Abstract:

In this study, the characteristics and solidification behavior of Ti-48Al-3Nb-1.5Ta powder produced by supreme-speed plasma rotating electrode process (SS-PREP®) were investigated. The microstructure, phase and characteristics were analyzed by scanning electron microscopy, X-ray diffraction and other methods. The atomization mechanism is direct drop formation. The relationship between the particle size and cooling rate is $v_{{\text{c}}} = 3.14 \times 10^{ - 7} \cdot d^{ - 2} + 1.18 \times 10^{ - 2} \cdot d^{{ - \frac{3}{2}}}$, and the relationship between secondary dendrite arm space and the particle size is $\lambda = 0.028d + 0.11$, as well as the relationship between SDAS and cooling rate is $\lambda = 4.84 \times 10^{5} \cdot T^{ - 1.43}$. With increase in particle size, the surface structure gradually changes from the featureless smooth structure to dendritic and cellular dendritic morphology, and the flow ability becomes better. The carbides mainly exist within 5 nm of the surface and the oxidation layer is about 20 nm thick. Ti-48Al-3Nb-1.5Ta powder was mainly composed of α₂ phase and γ phase. With increase in particle size, the content of γ phase increases, and the hardness decreases accordingly. The 106–250 μm particles are composed of multiple grains with the grain size of 70–80 μm. The microstructure, phase composition and hardness of different TiAl powders with the same size are similar, but the elastic modulus is different.

Key words: Supreme-speed plasma rotating electrode process (SS-PREP®), TiAl alloy, Atomization, Powder, Microstructure

Zhenbo Zuo, Rui Hu, Xian Luo, Qingxiang Wang, Chenxi Li, Zhen Zhu, Jian Lan, Shujin Liang, Hongkui Tang, Kang Zhang. Solidification Behavior and Microstructures Characteristics of Ti-48Al-3Nb-1.5Ta Powder Produced by Supreme-Speed Plasma Rotating Electrode Process[J]. Acta Metallurgica Sinica (English Letters), 2023, 36(8): 1221-1234.

Figures/Tables 26

Table 1 Main SS-PREP® processing parameters

Atmosphere	Rotating speed (r/min)	Current (A)	PV (mm)
Ar & He (high-purity)	28,000	1200	30

Fig. 1 Schematic diagram of SS-PREP®

Fig. 2 Typical morphology of Ti-48Al-3Nb-1.5Ta powder

Fig. 3 Laser particle size distribution of Ti-48Al-3Nb-1.5Ta powder

Table 2 Basic characteristics of Ti-48Al-3Nb-1.5Ta powders

Flow ability	Apparent density	Tap density	Oxygen content
23.9 s/50 g	2.54 g/cm³	2.79 g/cm³	1000 ppm

Fig. 4 Hollow powder analyze by Micro-CT

Fig. 5 Simultaneous thermal analysis of Ti-48Al-3Nb-1.5Ta powder

Table 3 He physical property parameters [29]

Thermal conductivity, k_g (W/m °C)	Density, ρ_g (kg/m³)	Dynamic viscosity, μ_g (Pa$\cdot$s)
0.14	0.18	1.99 × 10^-5

Table 4 TiAl parameters involved in calculation of droplet cooling rate

Density, ρ (kg/m³)	Equivalent specific heat capacity, C_p (J/(k_g$\cdot$K)⁻¹)	Temperature of droplets, T_d (K)	Temperature of environment, T_f (K)
4200	1315.97 [30]	1697	298

Fig. 6 Function curve between particle diameter and cooling rate

Fig. 7 Surface and cross-sectional morphologies of Ti-48Al-3Nb-1.5Ta: a, b 15-45 μm; c, d 45-106 μm; e, f 106-250 μm

Fig. 8 Elemental map distribution of alloying elements in Ti-48Al-3Nb-1.5Ta powder: a Al, b Ta, c Nb, d Ti and e morphology

Fig.9 Relationship between particle diameters with secondary dendrite arm spaces

Fig. 10 Relationship between cooling rate and secondary dendrite arm space

Fig. 11 AES surface profile of Ti-48Al-3Nb-1.5Ta powder: a O; b C; c Ti; d Al; e Nb; f Ta

Fig. 12 AES depth profile of Ti-48Al-3Nb-1.5Ta powder

Fig. 13 Ti-48Al-3Nb-1.5Ta powder EBSD: a

Fig. 14 XRD patterns of Ti-48Al-3Nb-1.5Ta powders with different sizes

Fig. 15 Hardness and modulus variation with the increase in Ti-48Al-3Nb-1.5Ta particle sizes

Fig. 16 Composition comparison of nonspherical and spherical powder

Table 5 Ti-48Al-3Nb-1.5Ta powder characteristics with different sizes

Size (μm)	Flow ability (s/50 g)	Apparent density (g/cm³)	Tap density (g/cm³)	Hausner ratio	D10 (μm)	D50 (μm)	D90 (μm)	Hollow powder ratio (%)
15-45	27.4	2.47	2.60	1.05	28.43	43.29	61.44	0
45-106	23	2.47	2.68	1.09	52.26	80.85	125.6	0
106-250	24.2	2.53	2.71	1.07	76.45	122.9	182.3	0.06

Fig. 17 Powder characters with different sizes

Fig. 18 Powder sphericity of different sizes

Fig. 19 Surface morphology of 15-45 μm powders: a, b Ti4522XD; c, d Ti4822; e, f Ti-48Al-3Nb-1.5Ta

Fig. 20 XRD patterns of different TiAl alloys

Table 6 Nanoindentation results of different TiAl alloy powders (unit: GPa)

Alloy	Ti-48Al-3Nb-1.5Ta	Ti4822	Ti4522XD
Hardness	${8.22}_{-0.77}^{+0.76}$	${7.68}_{-0.79}^{+1.16}$	${7.61}_{-0.56}^{+0.95}$
Modulus	${132.61}_{-10.46}^{+11.57}$	${120.64}_{-26.92}^{+11.57}$	${110.14}_{-17.64}^{+13.77}$

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