激光立体成形退火态Zr_(55)Cu_(30)Al_(10)Ni_5粉末的晶化行为

Crystallization Behavior of Laser Solid Forming of Annealed Zr_(55)Cu_(30)Al_(10)Ni_5 Powder

将等离子旋转电极法所制Zr_(55)Cu_(30)Al_(10)Ni_5(Zr55)粉末在1000 K退火处理后作为沉积材料,应用激光立体成形技术沉积Zr55块体非晶合金,考察工艺参数及退火态粉末尺寸对熔覆层晶化行为的影响。结果表明,不同尺寸退火态粉末组织均由Al_5Ni_3Zr_2、CuZr_2和Al_2Zr_3相组成。以不同激光线能量熔覆后,试样的熔池区主要为非晶,晶化区由熔池底部到热影响区依次分布NiZr2纳米晶、CuZr_2+ZrCu枝状共晶和CuZr_2+ZrCu球粒状共晶,共晶尺寸随着距熔池区距离的增加而减小。当激光线能量较低时,熔覆层均保持较高含量的非晶相。随着激光线能量的增大,尺寸为75~106μm的退火态粉末所制试样的晶化程度无明显加强,而尺寸为106~150μm的退火态粉末所制试样的晶化程度显著加剧。Zr55合金熔覆沉积层的晶化差异受粉末本身相结构影响较小,主要由熔覆不同尺寸粉末时熔池及热影响区的热历史决定。

Laser solid forming （LSF） provides an innovative way in building the bulk metallic glasses （BMGs） due to its inherently rapid heating and cooling process and point by point additive manufacturing process, which can eliminate the limitation of critical casting size of BMGs. The annealed powder has been demonstrated to be applicable to the preparation of BMGs with high content of amorphous phase using LSF. In this work, the plasma rotating electrode processed （PREPed） Zr55Cu30Al10Ni5 （Zr55） powders annealed at 1000 K are used for LSF of Zr55 BMGs. The influences of powder size and laser processing parameter on the crystallization characteristic of the deposit are investigated, and the crystallization be- havior of the remelted zone （RZ） and heat affected zone （HAZ） is analyzed. It is found that the microstructures of the pre-annealed Zr55 powders are composed of the Al5Ni3Zr2, CuZr2 and Al2Zr3 phases. As the heat input increases from 7.0 J/mm to 15.7 J/mm, the every deposited layer presents a periodic repeating gradient microstructure （amorphous, NiZr2 nanocrystal. CuZr2 ＋ZrCu dendrite-like eutectic, CuZr2 ＋ZrCu spherulite-like eutectic） from the molten pool to the HAZ. The size of the eutectic phase in the HAZ decreases as the increase of distance from the featureless amorphous zone. On condition that the laser heat input is less than 7.0 J/mm, the deposits contain a high content of amorphous phase. As the in- crease of laser heat input, the crystallization degree of HAZ does not increase obviously for the deposit prepared by the powder with size range of 75-106 μm. However, the crystallization degree of HAZ increases significantly for the deposit prepared by the powder with size range of 106-150 μm. That is because the lower overheating temperature and shorter existing time of the molten pool enhances the heredity of Al5Ni3Zr2 clusters and other intermetallic clusters in remelted alloy melt during LSF of coarser powder, which decreases the thermal stability of the already-deposited layer and induces the severe crys- tallization. It is deduced that the raw state of annealed powders has a minimal impact on the crystallization behavior of the Zr55 deposited layers when the content of AIsNi3Zr2 phase is same in different sizes of annealed powders. The thermal history of RZ and HAZ during deposition is the primary factor to affect the crystallization behavior in the Zr55 deposits fabricated by different powder sizes.