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

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, and the relationship between secondary dendrite arm space and the particle size is = 0.028d + 0.11 , as well as the relationship between SDAS and cooling rate is = 4.84 × 10 5 ⋅ 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 α 2 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.

Evolution Behavior of Rapidly Solidified Microstructure of a Ti-48Al-3Nb-1.5Ta Alloy Powder during Hot Isostatic Pressing

“…During the HIP process in the α 2 +γ two-phase region, as the "atomic volume" of γ-phase is smaller than that of α 2 phase, the excess production of γ-phase is promoted under isostatic pressure, resulting in the abnormal increase in the volume fraction of γ-phase [23], which is exactly the opposite of the transformation during manufacturing powders. With the increase in HIP temperatures, the α 2 phase content decreased gradually, while the γ phase content increased gradually as the number of γ peaks and the intensity of the main γ peaks both increased in XRD patterns, which is consistent with the DSC analysis result of the powders in the previous study [15]. Namely, there is a long endothermic trend below 1261 • C for Ti-48Al-3Nb-1.5Ta powders, which is the process by which the non-equilibrium α 2 phase transforms into equilibrium γ phase.…”

“…the increase in HIP temperatures, the α2 phase content decreased gradually, while th phase content increased gradually as the number of γ peaks and the intensity of the m γ peaks both increased in XRD patterns, which is consistent with the DSC analysis res of the powders in the previous study [15]. Namely, there is a long endothermic trend low 1261 °C for Ti−48Al−3Nb−1.5Ta powders, which is the process by which the non-eq librium α2 phase transforms into equilibrium γ phase.…”

“…The particle distribution was determined by a laser particle analyzer (Bettersize BT-9300, Better, Dandong, China) according to ASTM B822-17, as shown in Figure 1b. Other details about Ti-48Al-3Nb-1.5Ta powders can be found in the previous study [15]. The prealloyed powders with the size of 45-250 µm were poured into 45# steel capsules and degassed at 673 K for 4 h to remove air, and then the stem on the top of the capsule was welded when the vacuum of the capsule reached 1 × 10 −4 Pa.…”

Powder Synthesis and Characterization of Al0.5CoCrFeNi High-Entropy Alloy for Additive Manufacturing Prepared by the Plasma Rotating Electrode Process

“…The function between the cooling rate ( v c ) and the powder diameter ( d ) is given as v c = normald T p normald t = 6 h ρ C p d ( T normald − T normalf ) where T p is the liquidus temperature for the Al 0.5 CoCrFeNi HEA; h indicates the interfacial heat transfer coefficient; C p indicates the equivalent specific heat capacity; ρ indicates the density of the molten liquid droplet; T d indicates the temperature of droplet; and T f is the temperature of gas. The value of h can be obtained from the following equation from a previous study . The values of C p , ρ, T d , and T f refer to a previous report …”

“…The value of h can be obtained from the following equation from a previous study. 25 The values of C p , ρ, T d , and T f refer to a previous report. 26 where k g represents the thermal conductivity; d represents the droplet diameter; ρ g represents the density of cooling gas; μ g represents the dynamic viscosity of cooling gas; and U represents the relative velocity of droplets.…”