As a novel light-weight and high-temperature structural material,the TiAl intermetallics have the characteristics of low density,high specific strength and specific modulus,excellent high-temperature mechanical properties,and so on. The TiAl intermetallics show broad application potential in aerospace,automotive industry,and other fields,which are expected to partially replace nickel-based superalloys,titanium alloys and heat-resistant steels. However,TiAl intermetallics have high brittleness and poor ductility,so it is difficult to form by traditional forming processes,such as forging,rolling. TiAl intermetallics are mostlyfabricated by near-net shape forming technologies,such as precision casting,powder metallurgy,additive manufacturing. Additive manufacturing has the advantages of low cost,short cycle and good flexibility,so it is especially suitable for the forming of TiAl intermetallics,which has gradually attracted extensive attention of scientific researchers in recent years. Additive manufacturing requires powders with high sphericity,good fluidity,low impurity element content,and suitable particle size. However,the preparation of special powders for additive manufacturing is difficult,because the cost is high,and the content of spherical powders is low,and the batch stability of powders is poor. Therefore,the preparation of special powders for additive manufacturing has become one of the key topics in the development and application of additive manufacturing. The TiAl intermetallic powders prepared by traditional gas atomization(GA)have high impurity element content,owing to the high reactivity between TiAl intermetallics and crucible(Al2O3). Therefore,TiAl intermetallic powders by crucible-less gas atomization technology are gradually favored by researchers at home and abroad. At present,crucible-less gas atomization technology mainly includes plasma rotating electrode processing(PREP)and electrode induction melting gas atomization(EIGA). The powders prepared by PREP have high sphericity,good surface morphology and low impurity element content. But the PREP equipment is complex and its cost is high. Moreover,the coarse powders of 100~250 μm account for about 70%,so the proportion of fine powders is low. In contrast,the average particle size of the powders prepared by EIGA is less than 100 μm,so the proportion of fine powders is higher. In addition,the powders have the advantages of good sphericity,low impurity element content,high production efficiency,low cost,and so on. Consequently,EIGA is more suitable for preparing TiAl intermetallic powders for additive manufacturing. However,so far,there are few reports on the preparation of TiAl intermetallic powders for additive manufacturing by EIGA. The work was intended to prepare high-quality TiAl intermetallic powders for additive manufacturing,and revealed the relationship between powders’properties and particle size. Ti-48Al-2Cr-2Nb intermetallic powders were prepared by EIGA50-500 electrode induction melting gas atomization equipment from ALD Company in Germany. The melting chamber and atomization chamber were vac-uumized to 10-3 Pa,then high-purity argon gas was injected,and the tip of tapered Ti-48Al-2Cr-2Nb alloy electrode rod was slowly sent into the induction coil in the melting chamber. The bar material was melted into continuous droplets under the heating of the induction coil. The droplets were broken into fine droplets by high speed argon gas when passing through the atomizing nozzle. And then the fine droplets were cooled and solidified to form spherical powder in the atomization chamber. Thelaser particle size analyzer,scanning electron microscope(SEM),optical microscopy(OM),X-ray diffraction(XRD),inductively coupled plasma atomic emission spectrometer,oxygen nitrogen hydrogen analyzer and nanoindentation tester were employed to characterize the particle size distribution, impurity element content,micromorphology,hollow powder ratio,phase structure,nanohardness and elastic modulus of the Ti-48Al2Cr-2Nb intermetallics. The results showed that the particle size mostly ranged from 15 to 105 μm,and the particle size distribution followed Gaussian distribution. In addition,D10,D50 and D90(D10,D50 and D90 were the corresponding particle size values when the powder cumulative distribution reaches 10%,50% and 90%,respectively)were 16.50,45.51 and 108.95 μm. The powders were mainly spherical and spherical-like,but there were also a few abnormal powders,such as satellite powders,ellipsoidal powders,wrapped powders and twin powders. With the increase of particle size,the surface microstructure changed from smooth surface to condensed shrinkage trace,and the cross-section microstructure evolved from microcrystalline to cellular dendrite and dendrite,and the porosity of the powders increased gradually. When particle size(d)≤75 μm,the powders were comprised of a primary α2 phase and a small amount of γ phase. With the increase of the particle size,the content of γ phase decreased and α2 phase increased. When d≥75 μm, the main phase of the powders changed to γ phase. The average content of oxygen,nitrogen and hydrogen were 0.092%,0.0058% and 0.002%,respectively. The content of oxygen decreased with the increase of the particle size,while the content of nitrogen and hydrogen changed little with the particle size. Furthermore,with the increase of the particle size,the nanohardness as well as elastic modulus decreased steadily. In summary,Ti-48Al-2Cr-2Nb intermetallics powders prepared by EIGA could meet the technical requirements of additive manufacturing for particle size distribution,sphericity and impurity element content. The surface microstructure,cross-section structure,phase composition,hollow powder percentage and impurity element content of the powders were closely linked to the particle size of powders. © 2024 Editorial Office of Chinese Journal of Rare Metals. All rights reserved.
