机械振动—激光熔覆Fe-Cr-Si合金界面结合特征及熔池温度

发布时间：2019-04-29 20:09

【摘要】：目前的工业运用中,经热处理后的45钢存在着表面硬度低、耐磨性差、易氧化等不足而限制了它的进一步广泛应用。通过采用高能激光束在被选定工件表面熔覆一层具有特殊性能的合金粉末,可以改善工件综合性能,这种表面改性技术称为激光熔覆技术。因此,通过激光熔覆在45钢表面制备出与基材成分接近、界面结合牢固、高硬耐磨且成本低廉的Fe-Cr-Si合金涂层便成为近年来材料科学和表面工程领域致力于研究的热点。本实验在45钢板材上进行不同机械振动参数辅助下,同步送粉法输送激光熔覆铁基自熔性粉末,获得Fe-Cr-Si合金熔覆层。对比不同振动参数下的实验试样宏观和微观结构,研究分析不同机械振动参数对熔覆层及结合界面性能差异。其中,通过OM分析涂层与基体材料的组织形貌,利用XRD、SEM等表征手段研究了熔覆层及熔覆层与基材间的结构和显微组织,同时借助EDS点扫描及线扫描手段,分析熔覆层与基材间相组成和元素分布,采用显微硬度计测试研究了合金涂层中的显微硬度分布,然后根据不同振动参数下的熔覆层相貌特征确定激光热源分布,进行熔覆过程数值模拟分析。最后,针对不同振动参数下结合界面处的元素分布规律,计算该元素的扩散系数与浓度和距离的关系。结果表明：1、在合理的振动参数范围内,涂层可获得良好的表面质量,且熔覆层与基体的结合性能好,为冶金结合。但在机械振动能量增加的情况下,涂层表面出现熔化瘤,且表面粗糙。2、机械振动能量相近下,分别对振幅占优和频率占优情况的激光熔覆过程进行有限元模拟。结果表明,振幅占优时激光熔池中心热量更为集中,熔池熔深增加,熔宽减小,温度梯度增加；频率占优时激光熔池产生均化现象,熔池熔深减小,熔宽增加。从不同振动参数的热循环曲线来看,振幅的作用是使温度梯度增加,频率的作用反之。根据冷却后残余应力场分布图和分布曲线可得：机械振动对激光熔覆残余应力的分布位置影响较小,但振幅占优和频率占优的激光熔覆试样中,沿扫略方向残余应力压应力值有一定的减小,说明机械振动对激光熔覆残余应力有缓释作用。3、Fe-Cr-Si合金粉末在激光熔覆过程中可形成以α-Fe或γ-Fe为基体的合金碳化物(Fe,Cr)7C3、(Fe, Cr)23C6和少量以Fe2B为代表的硼化物,这些碳化物和硼化物具有较高的强度和硬度。而根据机械振动能量计算,可知振幅对激振能的变化影响比较明显,频率作用较小。4、激光熔覆微观结构中发现,在熔覆层和基体间易形成2～3μm深色带状结构,为Cr、 Si等合金元素扩散速率不平衡导致的结果。本文测定界面处Fe-(Cr、Si)扩散中Cr、Si元素浓度分布曲线并计算扩散系数,结果可得,机械振动可使等浓度位置的扩散系数下降,界面处Cr、Si元素扩散系数与温度梯度和浓度有关,且振动参数中幅度对扩散系数的影响大于频率
[Abstract]:In the current industrial application, the low surface hardness, poor wear resistance and easy oxidation of 45 steel after heat treatment limit its further application. The comprehensive properties of the workpiece can be improved by cladding a layer of alloy powder with special properties on the surface of the selected workpiece by using a high energy laser beam. This surface modification technique is called laser cladding technology. Therefore, the preparation of Fe-Cr-Si alloy coating by laser cladding on the surface of 45 steel, which is close to the composition of substrate, strong interface bonding, high hardness and wear resistance, and low cost, has become the focus of research in material science and surface engineering field in recent years. In this experiment, the laser cladding iron-based self-fluxing powder was transferred by simultaneous powder feeding method under the aid of different mechanical vibration parameters on the 45 steel plate, and the Fe-Cr-Si alloy cladding layer was obtained. The macro-structure and microstructure of the experimental specimen under different vibration parameters were compared, and the difference of mechanical vibration parameters on the properties of cladding layer and bonding interface was studied and analyzed. The microstructure and morphology of the coating and the substrate were analyzed by OM, and the microstructure and microstructure of the cladding layer and substrate were studied by means of XRD,SEM. At the same time, by means of EDS point scanning and line scanning, the microstructure and microstructure of the cladding layer and the substrate were studied. The phase composition and element distribution between the cladding layer and the substrate are analyzed. The microhardness distribution in the alloy coating is studied by means of microhardness tester, and then the laser heat source distribution is determined according to the phase characteristics of the cladding layer under different vibration parameters. Numerical simulation analysis of cladding process was carried out. Finally, according to the distribution rule of elements at the interface under different vibration parameters, the relationship between the diffusion coefficient of the element and the concentration and distance of the element is calculated. The results show that: (1) in the range of reasonable vibration parameters, the coating can obtain good surface quality, and the bonding property between the cladding layer and the substrate is good, which is metallurgical bonding. However, with the increase of mechanical vibration energy, a melting tumor appears on the surface of the coating and the surface is rough. 2. When the mechanical vibration energy is similar, the laser cladding process with dominant amplitude and frequency is simulated by finite element method. The results show that the central heat of the laser pool is more concentrated when the amplitude is dominant, the penetration of the pool increases, the width of the pool decreases and the temperature gradient increases, and the homogenization of the laser pool occurs when the frequency is dominant, and the penetration of the pool decreases and the width of the molten pool increases. According to the thermal cycle curves of different vibration parameters, the effect of amplitude is to increase the temperature gradient, whereas the effect of frequency is vice versa. According to the distribution diagram and distribution curve of residual stress field after cooling, it can be concluded that mechanical vibration has little effect on the distribution position of residual stress in laser cladding, but in laser cladding sample with dominant amplitude and frequency, The residual stress and compressive stress along the sweep direction decrease to a certain extent, indicating that mechanical vibration can slow-release the residual stress of laser cladding. 3, During laser cladding, alloy carbides (Fe,Cr) 7C3and (Fe,Cr) 23C6 with 伪-Fe or 纬-Fe as matrix and a small amount of boride represented by Fe2B can be formed by laser cladding of Fe-Cr-Si alloy powder. These carbides and boride have high strength and hardness. According to the calculation of mechanical vibration energy, the influence of amplitude on excitation energy is obvious, and the effect of frequency is small. 4. In the microstructure of laser cladding, it is found that the dark band structure of 2 ~ 3 渭 m is easily formed between the cladding layer and the substrate, which is Cr,. The result of unbalanced diffusion rate of alloy elements such as Si. In this paper, the concentration distribution curve of Cr,Si element in Fe- (Cr,Si) diffusion at the interface is measured and the diffusion coefficient is calculated. The results show that mechanical vibration can decrease the diffusion coefficient at the equal concentration position and Cr, at the interface. The diffusion coefficient of Si element is related to temperature gradient and concentration, and the influence of amplitude on diffusion coefficient in vibration parameter is greater than that of frequency.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

【参考文献】