中空环形激光离焦量对熔道凹凸缺陷自愈合效应的影响

Impact of Hollow Ring Laser Defocused Amount on Melting Channel Bump Defect Self Healing Effect

"形貌自愈合效应"是激光金属直接成形过程中可能出现的一个重要现象,在堆积过程中依靠自身工艺参数的调整,可以控制多层堆积的熔道从堆积表面可能出现的凹凸不平状态重新恢复到平整状态。在"中空激光、光内送粉"新工艺的方法下,通过调整环形激光离焦量能产生明显的熔道凹凸缺陷的自愈合效应。对激光离焦量与单层堆积厚度影响规律进行了理论分析,获得激光离焦量与单层熔覆高度的关系曲线,并在具有"栅栏凸起"的304不锈钢基板上堆积多组薄壁墙试样进行试验验证,同时利用游标卡尺、扫描电镜及显微硬度计对愈合完好的薄壁墙的宽度、微观组织及显微硬度进行了分析。结果表明,不同的激光离焦量对其形貌自愈合能力影响显著,当离焦量为0^-3 mm时,薄壁墙形貌原有的起伏不平"自愈合现象"并不会出现;当离焦量为-3 mm^-5 mm时,薄壁墙形貌的起伏不平随层数增加被逐渐修复,若干层后表面光滑平整,"自愈合现象"得到验证;通过自愈合修复的薄壁墙,宽度变化很小,与基体冶金结合良好,组织致密均匀,从墙顶至基体硬度值呈缓慢下降趋势。

＂Morphology self healing effect＂ is an important phenomenon that may happen in the direct laser melt forming process, which can adjust the process parameters of itself and control the multi-level melting channel accumulation surface from a bump unstable state to a stable state in the process of accumulation. By adopting the new process of ＂hollow laser, internal laser powder feeding＂, adjusting the ring laser defocused amount can effectively result in self healing effect of melting channel bump defect. The impact of laser defocused amount on monolayer thickness accumulation is theoretically analyzed and resulted in a curved diagram between laser defocused amount and monolayer thickness accumulation and it has been tested as accumulate multiple thin wall samples in 304 stainless steel substrate with ＂fence bulge＂. At the same time, the thin wall width, microstructure and thickness have been analyzed by venire caliper, scanning electron microscope and micro hardness instrument. The study has shown that there is a significant impact of different laser defocused amounts on the self healing capabilities. When the defocused amount is 0--3 mm, the surface topography of the thin wall is undulating, and ＂the self healing phenomenon＂ has not been shown. While the defocused amount is -3 mm--5 mm, the thin wall undulating surface will become smooth gradually in several levels, and the ＂self healing phenomenon＂ has been verified. The thin wall by self healing repair combines well with the substrate metallurgy and the width slightly changing. The structure is dense and uniform, and the hardness value from the wall top to the substrate increases slowly.