Shape memory TiNi powders produced by plasma rotating electrode process for additive manufacturing

This study aimed to produce spherical TiNi powders suitable for additive manufacturing by plasma rotating electrode process(PREP).Scanning electron microscopy,X-ray diffractometry and differential scanning calorimetry were used to investigate the surface and inner micro-morphology,phase constituent and martensitic transformation temperature of the surface and inner of the atomized TiNi powders with different particle sizes.The results show that the powder surface becomes smoother and the grain becomes finer gradually with decreasing particle size.All the powders exhibit a main B2-TiNi phase,while large powders with the particle size≥178μm contain additional minor Ti2Ni and Ni3Ti secondary phases.These secondary phases are a result of the eutectoid decomposition during cooling.Particles with different particle sizes have experienced different cooling rates during atomization.Various cooling rates cause different martensitic transformation temperatures and routes of the TiNi powders;in particular,the transformation temperature decreases with decreasing particle size.

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

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 vc=3.14×10^(-7)·d^(-2)+1.18×10^(-2)·d^(3/2),and the relationship between secondary dendrite arm space and the particle size isλ=0.028d+0.11,as well as the relationship between SDAS and cooling rate isλ=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 ofα2 phase andγphase.With increase in particle size,the content ofγphase increases,and the hardness decreases accordingly.The 106–250μm particles are composed of multiple grains with the grain size of 70–80μm.The microstructure,phase composition and hardness of different TiAl powders with the same size are similar,but the elastic modulus is different.

Influence of Processing Parameters on Granularity Distribution of Superalloy Powders during PREP

In order to investigate the influence of processing parameters on the granularity distribution of superalloy powders during the atomization of plasma rotating electrode processing (PREP), in this paper FGH95 superalloy powders is prepared under different processing conditions by PREP and the influence of PREP processing parameters on the granularity distribution of FGH95 superalloy powders is discussed based on fractal geometry theory. The results show that with the increase of rotating velocity of the self-consuming electrode, the fractal dimension of the granularity distribution increases linearly, which results in the increase of the proportion of smaller powders. The change of interval between plasma gun and the self-consuming electrode has a little effect on the granularity distribution, also the fractal dimension of the granularity distribution changed a little correspondingly.

Numerical analysis on solidification process and heat transfer of FGH95 superalloy droplets during PREP

In order to understand the relation between microstructure of superalloypowders and its solidification progress, the processing parameters are optimized during plasmarotating electrode processing (PREP). It was predicted from the results that the droplet velocities,droplet temperature, and fractional solidification with flight time about FGH95 superalloy droplethave been carried out based on Newtonian heat transfer formulation coupled with the classicalheterogeneous nucleation and the specific solidification process. It has been found that the dropletdynamic and thermal behavior is strongly affected by the distribution of droplet diameters, theproportion of cooling atmosphere, but is relatively unaffected by the droplet superheat.

Surface characteristics of rapidly solidified nickel-based superalloy pow-ders prepared by PREP

The surface microstructure and the surface segregation of FGH 95 nickel-basedsuperalloy powders prepared through plasma rotating electrode processing (PREP) have beeninvestigated by using SEM and AES. The results indicate that the surface microstructure of powderschanges from dendrite into cellular stricture as the particle size of powders decrease, and thepredominant precipitates solidified on the particle surfaces were identified as MC' type carbidesenriched with Nb and Ti. It was also indicated that along with the depth of particle surfaces, thesegregation layer of S, C and O elements are thick, and that of Ti, Cr elements are thin for largesire powders while they are in reverse for median size particles.