SLM球形Ni粉的制备与打印工艺性能

Preparation and Performance of Spherical Ni Powder for SLM Processing

针对选区激光熔化(SLM)的技术特点,采用低温喷雾干燥与热处理相结合的新方法,制备得到了物相纯净、球形度高、流动性好且粒径分布窄的球形Ni粉。比较分析了喷雾干燥法制备的Ni粉和气雾化法生产的商业化Ni粉的显微组织和激光吸收率及其对3D打印件组织和性能的影响。结果发现,喷雾干燥法制备Ni粉的激光吸收率是气雾化法生产Ni粉的2倍以上;打印过程中形成更宽的熔道,且颗粒熔化后表面张力和颗粒间液桥力均较小,大大减少了金属粉末打印中极易出现的表面球化现象。喷雾干燥法制备Ni粉打印件的相对密度达到99.2%,其显微组织由细小的柱状晶和胞状晶构成,且柱状晶穿过层间边界生长,使打印件具有致密的层间结合。

3D printing has attracted increasing interests in the field of metallic materials as it can effectively shorten the production cycle and create parts with complex shapes,which can hardly be produced by traditional methods.However,the gas atomization,as the mainstream method of preparing metal and alloy powders to meet the requirements of the processing of selective laser melting (SLM)at present,still has some limitations,such as hollow and/or satellite balls in the powder.This influences directly the density and performance of the printing parts.Moreover,the laser absorption in the smooth surface of powder particle is generally less than 10% in the laser processing,which hinders rapid heating of the powder.It has been found that the material can obtain multiple absorption of laser energy by increasing the surface roughness of powder particles,which can effectively improve the laser absorption rate and is beneficial to get the dense printing parts.Based on this,a novel method combining low temperature spray-drying with heat treatment was developed to prepare Ni powder with high purity,good sphericity, high flowability and narrow particle size distribution.The microstructure and laser absorptivity of the pre- pared Ni powder were compared with those of the commercial Ni powder prepared by gas atomization, and their influences on the microstructure and properties of the 3D printed bulk materials were investigat- ed.it is found that the laser absorptivity of the Ni powder prepared by spray-drying is more than 2times as high as that of the commercial Ni powder.This leads to a wider melting channel,smaller surface tension and liquid-bridging force between particles in the printing process.As a result,the spheroidization phenomenon occurred on the surface of the printed bulk material can be avoided by the use of the spraydried powder,and the relative density is achieved as 99.2%at the as-printed state.In the microstructure of the printed bulk material,in addition to the cellular crystals,there are a number of fine columnar crystals,grown across the interlaminar boundaries,which is favorable for a high bonding strength between the interlayers.