铸铁激光熔覆结合区微裂影响因素及工艺优化研究

发布时间：2018-06-28 22:23

本文选题：激光熔覆 + 灰铸铁　；参考：《中国石油大学(华东)》2015年硕士论文

【摘要】：铸铁以其良好的性能广泛应用于重型装备,铸铁表面激光熔覆加工可以有效提高铸铁装备使用性能。由于工况恶劣,熔覆结合区易产生微裂纹不断演化为宏观裂纹,石墨相是铸铁的重要组成部分并未得到深入的研究,石墨相形态与聚集方式对熔覆结合强度与微裂纹萌生产生很大影响。本课题以分析铸铁激光熔覆过程中石墨相应力特征,明确最优激光工艺参数为目标,探寻石墨相应力影响因素与裂纹萌生机制,确定最优激光工艺参数。主要开展了以下内容的研究工作:为探究与熔覆材料相容特性,选用铁基熔覆合金粉末进行铸铁表面激光熔覆实验,分析熔覆试样结合区组织特性、石墨相形态特征及石墨相尖端微裂现象。通过采用剪切实验装置对熔覆试样进行测试,计算单位面积基体与熔覆层平均结合强度,明确石墨相周围区域组织及微裂纹对熔覆质量的影响机制。根据熔覆实验实际工况,对激光热源进行改进,采用生死单元技术实现粉末动态添加,建立激光熔覆热力耦合模型,分析激光熔覆热响应规律。采用正交试验对铸铁激光熔覆过程仿真模拟,提取激光熔覆结合区最大残余应力影响因素,指导激光熔覆工艺方案制定,为石墨相微观模型的建立提供数据支持。为明确石墨相尖端微裂纹萌生机理,根据铸铁激光熔覆实验与热力耦合模型,建立石墨-环境相微观模型,研究石墨长度、尖端角度等形态参数和对接、平行、垂直等聚集方式对石墨相尖端应力影响规律,定量分析石墨相应力变化特征。以激光熔覆热力耦合模型和石墨-环境相微观模型为基础,结合正交试验设计方法,分析激光熔覆裂纹萌生影响因素,考虑铸铁激光熔覆过程石墨相作用,分别从结合区残余应力角度与石墨相尖端应力角度确定最优激光工艺参数,降低应力,进一步减少裂纹萌生,提高熔覆质量。
[Abstract]:Cast iron is widely used in heavy equipment due to its good properties. Laser cladding on cast iron surface can effectively improve the performance of cast iron equipment. Because of the bad working conditions, microcracks in the cladding bonding zone tend to evolve into macroscopic cracks, and the graphite phase is an important part of cast iron has not been deeply studied. The morphology and aggregation mode of graphite have great influence on the cladding bonding strength and micro-crack initiation. The aim of this paper is to analyze the corresponding force characteristics of graphite in laser cladding process of cast iron, to determine the optimum laser process parameters, to explore the influencing factors of graphite corresponding force and the mechanism of crack initiation, and to determine the optimal laser technological parameters. The main research work is as follows: in order to study the compatibility with cladding materials, iron-base cladding alloy powder is selected for laser cladding experiment on cast iron surface, and the microstructure of the bonding zone of cladding sample is analyzed. The morphologic characteristics of graphite phase and the phenomenon of microcrack at the tip of graphite phase. The average bonding strength between the matrix and the cladding layer was calculated by means of the shear test device, and the influence mechanism of the microstructure around the graphite phase and the micro-crack on the cladding quality was determined by calculating the average bonding strength between the matrix and the cladding layer per unit area. According to the actual condition of cladding experiment, the laser heat source is improved, the powder dynamic addition is realized by the birth and death element technique, the coupled thermal model of laser cladding is established, and the thermal response law of laser cladding is analyzed. The process of laser cladding of cast iron was simulated by orthogonal test. The factors affecting the maximum residual stress in laser cladding bonding zone were extracted to guide the formulation of laser cladding process and to provide data support for the establishment of micro model of graphite phase. In order to clarify the mechanism of micro-crack initiation at the tip of graphite phase, a graphite-environmental micromodel was established according to the coupled model of laser cladding and thermodynamics of cast iron. The morphological parameters such as graphite length and tip angle were studied and parallel to each other. The effect of vertical equiaggregation mode on the stress at the tip of graphite phase is studied and the variation characteristics of graphite corresponding forces are quantitatively analyzed. Based on the thermal coupling model of laser cladding and the graphite-environment microcosmic model, combined with the orthogonal test design method, the factors affecting laser cladding crack initiation were analyzed, and the graphite phase action in laser cladding process of cast iron was considered. The optimum laser processing parameters are determined from the angle of residual stress in bonding zone and the angle of stress at the tip of graphite phase, which can reduce the stress, further reduce the crack initiation and improve the quality of cladding.
【学位授予单位】：中国石油大学(华东)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

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