激光熔覆碳纳米管增强Ni基复合涂层研究

发布时间：2019-04-27 12:33

【摘要】：高速重载列车在运行制动过程中产生的巨大摩擦力和热量将导致制动盘产生大量的损耗和裂纹从而缩短使用寿命,这将大大增加运营成本,因此对制动盘的表面改性尤为重要。本文运用激光熔覆技术,使用同步送粉的方式在45钢表面制备了CNTs/Si C/Ni复合涂层,主要对碳纳米管的纯化、复合粉末的球磨、激光工艺参数以及碳化硅和碳纳米管的含量进行研究,通过对涂层的显微组织、摩擦系数、磨损量和硬度的分析,探索了碳纳米管的增强机理,得出以下结论:(1)随着硝酸回流的时间增加,碳纳米管的纯化和分散明显改善。当回流时间为9h时,CNTs分散最均匀,失重比为18.4%。损失的质量主要为杂质粒子和碳纳米管壁缺陷处的碳原子,碳纳米管管壁出现大量的羟基和羧基官能团,有利于加强碳纳米管的活性。随着回流时间的延长,碳纳米管分散增加,但硝酸对碳纳米管过度氧化,导致CNTs大量的断裂,碳纳米管管壁变薄严重。(2)随着球磨转速的提高,粉末分散呈先变好后变差的趋势。当球磨转速为300r/min时,粉末分散最均匀,碳纳米管损伤最小,且碳纳米管未出现分层团聚。但转速过低,粉末团聚严重;转速过高,碳纳米管被大量的切断,导致碳纳米管结构完整性被严重破坏。(3)当碳化硅含量为15%时,熔覆层组织形貌达到最优值,且硬度和耐磨性也最好,硬度为394.6HV_(0.2),为基板的1.6倍;磨损量最小仅为0.0368g。当碳纳米管为16%vol时达到最佳,熔覆层晶粒大小最为均匀,碳纳米管分布在晶界处。涂层机械性能最好,硬度为446.5HV_(0.2),为基板的2.2倍,摩擦系数稳定为0.149。碳纳米管含量继续增加则出现团聚,涂层的表面出现烧损、显微组织粗大、出现气孔和孔洞、且性能也变差。(4)随着激光功率、扫描速度、送粉速率和气流量的增加,涂层的组织和性能都呈现先变好后变差的趋势。当激光功率为1400W,扫描速度为250mm/min,送粉速率为30g/min,气流量为4L/min时,熔覆层的表面光滑、连续完整、组织均匀致密,与基板的结合良好,性能最佳。
[Abstract]:The huge friction and heat generated by the high-speed and heavy-duty train during the braking process will lead to a large number of losses and cracks in the brake disc, which will shorten the service life, which will greatly increase the operating cost. Therefore, the surface modification of the brake disc is particularly important. In this paper, laser cladding technology was used to prepare CNTs/Si C/Ni composite coating on 45 steel surface by simultaneous powder feeding. The purification of carbon nanotubes and ball milling of composite powder were carried out. The laser processing parameters and the content of silicon carbide and carbon nanotubes were studied. By analyzing the microstructure, friction coefficient, wear and hardness of the coatings, the strengthening mechanism of carbon nanotubes was explored. The conclusions are as follows: (1) the purification and dispersion of CNTs were improved with the increase of nitric acid reflux time. When the reflux time was 9 h, the dispersion of CNTs was the most uniform, and the weight loss ratio was 18.4%. The loss of mass is mainly due to the impurity particles and carbon atoms in the wall defects of carbon nanotubes. A large number of hydroxyl and carboxyl functional groups appear in the wall of carbon nanotubes, which is beneficial to the enhancement of the activity of carbon nanotubes. With the prolongation of reflux time, the dispersion of CNTs increased, but the excessive oxidation of nitric acid on CNTs resulted in a large number of fracture of CNTs, and the wall of CNTs became thinner. (2) with the increase of milling speed, the carbon nanotubes (CNTs) became thinner. The powder dispersion showed the trend of first improving and then getting worse. When the milling speed is 300r/min, the powder dispersion is the most uniform, the damage of carbon nanotubes is the least, and there is no stratification agglomeration of carbon nanotubes. But the rotate speed is too low, the powder reunite seriously; When the rotation speed is too high, the carbon nanotubes are cut off by a large amount, resulting in serious damage to the structural integrity of carbon nanotubes. (3) when the silicon carbide content is 15%, the microstructure morphology of the cladding layer reaches the optimal value, and the hardness and wear resistance of the cladding layer are also the best. The hardness is 394.6 HV0.2, which is 1.6 times of that of substrate. The minimum amount of wear is 0.0368 g. When the carbon nanotubes are 16%vol, the grain size of the cladding layer is the most uniform, and the carbon nanotubes are distributed at the grain boundary. The mechanical properties of the coating are the best, the hardness is 446.5 HV0.2, which is 2.2 times that of the substrate, and the friction coefficient is 0.149. If the content of carbon nanotubes continues to increase, agglomeration will occur, the surface of the coating will be burned out, the microstructure is coarse, the pores and voids appear, and the properties of the coatings will become worse. (4) with the increase of laser power, scanning speed, powder feeding rate and gas flow rate, the coating surface will be agglomerated. The microstructure and properties of the coatings show the trend of first improving and then worse. When the laser power is 1400W, the scanning speed is 250mm / min, the rate of powder feeding is 30g / min and the gas flow rate is 4L/min, the surface of the cladding layer is smooth, continuous and intact, the microstructure is uniform and dense, the bonding with the substrate is good, and the performance is the best.
【学位授予单位】：华东交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U270.35;TG174.4

【相似文献】