| The stainless steel powder prepared by gas atomization has deficiencies such as high oxygen content,relatively poor sphericity and a few satellite balls.Whereas,it is believed that rare earth elements can modify inclusions,purify the molten steel and play a role of microalloying in the production and optimizition of the performance of steel.In this paper,a series of OCr 13Ni8Mo2Al alloy powders with different additive rare earth yttrium were prepared by vacuum induction-melting gas atomization on the basis of the modification of oxygen in steel by rare earth elements.Consequently,3D printing of OCr 13Ni8Mo2A1 alloy powder containing rare earth element yttrium was conducted by selective laser melting technology.The effects of rare earth element yttrium on particle size distribution,particle size,surface morphology and microstructure,physical properties as well as microhardness of OCr 13Ni8Mo2A1 powders were systematically investigated by means of laser particle size distribution instrument,scanning electron microscopy,intelligent powder characteristic tester and micro hardness instrument.Further,the influence of rare earth element yttrium on the martensitic transformation temperature,the volume fraction of retained austenite and mechanical properties of Cr13Ni8Mo2Al 3D printed parts were explored.The results show that:1.The excellent comprehensive property of the metal powder can be achieved when the particle size is in the range of 15-53 μm.And the reduction of the atomizing pressure and nozzle diameter in a proper range favors the decrease of the average powder size,whilst increasing the apparent density and tap density of the powder.And,thus,the flowability of metal powder is improved.In the current work,the optimum atomization parameters are as follows:the tapping temperature is 1740℃,the nozzle diameter is 6 mm and the atomization pressure is 6.5 MPa.When the metal powder prepared under the optimum atomization parameters with the size distritution ranging from 15-53 μm,the apparent density of the powders is 3.915 g/cm3,the tap density is 4.78 g/cm3,the average particle size is 31.38 μm,the flowability is 23.45 s/50 g and the surface morphology is mainly spherical and subspherical,accompanied by a small number of satellite spherical particles.2.Rare earth yttrium can optimize the powder characteristics of OCr 13Ni8Mo2 A1 powder prepared by vacuum induction melting gas atomization.With the increase of the content of yttrium in the metal powder,the particle size distribution of the metal powder becomes narrower.And the average particle size of the powder decreases from 37.29 μm to 30.99 μm with the microhardness value increasing from HV320 to HV350.Meanwhile,the angle of repose decreased from 35.45° to 33.97 °,whilst the flowability decreased from 25.44 s/50 g to 25.11 s/50 g.On the other hand,the apparent density increased from 3.73 g/cm3 to 3.93 g/cm3 with the enhancement of sphericity of the powder.The satellite spherical particles decreased and the equiaxed crystal region in the inner structure of the powder is enlarged.3.Rare earth yttrium can improve the performance of selective laser melting forming 0Cr13Ni8Mo2Al printed components.The martensitic transformation starting temperature also decreased with a value of 60℃.Consequently,the content of retained austenite increased which contribute to an obvious improvement of toughness. |
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