激光表面重熔蠕墨铸铁气门座微观特性分析和裂纹抑制研究  

Microscopic Characteristic Analysis and Crack Suppression of Laser-Surface Remelting of Vermicular-Graphite Cast-Iron Valve Seats

作　　者：庞铭 谭雯丹 Pang Ming;Tan Wendan(Airport College,Civil Aviation University of China,Tianjin 300300,China)

机构地区：[1]中国民航大学机场学院

出　　处：《激光与光电子学进展》2019年第21期108-114,共7页Laser & Optoelectronics Progress

基　　金：国家自然科学基金(U1633111,51206179);中央高校基本科研业务费项目中国民航大学专项(3122018D020);内蒙古自然科学基金(2017MS0540);中国民航大学蓝天青年科研资金

摘　　要：利用额定功率为3kW的Nd∶YAG固体激光器开展激光重熔蠕墨铸铁气门座实验,通过扫描电镜、显微硬度仪,采用荧光粉探伤方法分析激光表面重熔蠕墨铸铁气门座的宏观形貌、显微组织、硬度分布以及重熔层是否存在裂纹。结果表明:经激光表面重熔后,重熔层中部区域组织为枝晶组织,在枝晶组织间弥散分布着针状物和颗粒状物;石墨的扩散降低了材料熔点,由于激光的快速加热和冷却等,重熔层与基体交界处形貌为锯齿形,且在热影响区观察到马氏体壳和莱氏体壳的双壳组织;不同区域的加热和冷却速度的差异导致重熔区表面到基体硬度逐渐降低;调控激光参数可以有效抑制气门座激光重熔层的裂纹。在激光功率为500W,离焦量为-1mm,激光扫描速度小于等于5mm/s的重熔工艺参数下,可以获得无裂纹的重熔层。Experiments on the laser-surface remelting of vermicular-graphite cast-iron valve seats are performed in this study using a Nd…YAG solid-state laser with a rated power of 3 kW.The macroscopic morphology,microstructure,hardness distribution,and cracks of the remelting layer of the laser-surface remelting of the vermicular-graphite cast-iron valve seats are analyzed using a scanning electron microscope,microhardness tester,and phosphor flaw detection method.The results show that after the surface of the vermicular-graphite cast-iron valve seats is remelted using a laser,the dendritic structures appear in the central region of the remelting layer and the needles and granules are dispersed among the dendritic structures.The morphology of the interface between the remelting layer and substrate is serrated,and the bivalve structure of the martensite and ledeburite shells is observed in the heat-affected zone because of factors such as the diffusion of graphite reducing the melting point of the material in the vicinity of the graphite and rapid heating and cooling of the laser.The hardness from the remelting-zone surface to the substrate gradually decreases because of the differences in the heating and cooling rates in the different regions of laser remelting of the valve seats.The cracks in the laser remelting layer of the valve seats can be restrained by adjusting the laser parameters.A remelting layer without cracks on the surface of the vermiculargraphite cast-iron valve seats of laser remelting can be obtained under the laser remelting process with parameters of laser power P=500 W,defocusing amountΔf=-1 mm,and laser scanning velocity V≤5 mm/s.

关 键 词：激光器 激光表面重熔 蠕墨铸铁 气门座 显微组织 硬度 裂纹 

分 类 号：TG164.4[金属学及工艺—热处理] TG157[金属学及工艺—金属学]