钛合金激光表面氮化层成形特征及分析

Forming Characteristics and Analysis of Nitrided Layers during the Laser Nitriding titanium Alloy

摘要:

利用半导体激光器在氮气气氛中对钛合金表面进行氮化,为了研究线能量,激光功率和扫描速度对Ti-6Al-4V合金氮化层表面成形,熔池几何形貌,熔宽,熔深及成形系数的影响,采用光镜,扫描电镜拍摄氮化层表面成形及其横截面形貌,用显微硬度计测量氮化层硬度值。结果表明氮化层表面形貌由表面光滑和表面粗糙型两种区域组成。熔池表面温度较低时,增加激光束与基材的相互作用时间,对表面成形影响不大。相同线能量下随激光功率增大,氮化层熔深熔宽均呈增大趋势,成形系数减小；当激光功率相同时,随扫描速度减小,熔深熔宽均呈增大趋势,成形系数减小；成形系数很小时氮化层会产生沿纵向分布的裂纹。对流形式及强弱导致形成不同的界面形态,如：半球形界面,指状界面和W形界面等,而且熔合界面会发生多次弯曲。

Abstract:

Ti-6Al-4V alloy was nitrided in nitrogen atmosphere using diode laser, in order to study the influence of line energy, laser power and scanning speed on the surface morphology, molten pool geometry, width, the penetration depth and the forming coefficient of the nitrided layers, the surface and cross-section pictures of the nitrided layers were taken by optical and scanning electron microscopy, and the hardness was measured by microhardness tester. The results show that the surface morphology are composed of the smooth and rough surface, When the surface temperature of the molten pool is low, increasing the interaction time has little effect on the surface morphology. With the increase of laser power under the same line energy, the melting depth and width of the nitrided layer increases, and the forming coefficient decreases. As the scanning speed decreases under the same laser power, the penetration depth and width increases, and the forming coefficient reduces; When the forming coefficient is very small, the nitrided layers will produce longitudinally distributed crack. The convection form and the strength result in the formation of a hemispherical interface, a finger interface and a W-shaped interface and so on, besides, multiple inflections happen in the slope of the boundaries of molten pool.