选区激光熔化成形镍基合金结构的工艺研究

发布时间：2018-09-09 09:00

【摘要】：选区激光熔化(Selective Laser Melting,SLM)技术是增材制造领域的重要发展方向,该技术以高能量激光束为能量源,通过对二维选择性熔化,累加成形三维实体,与传统机加工相比,在加工复杂形状金属零件时,利用“降维”的方式,将复杂三维实体通过二维扫描分层成形,不受加工位置的限制,成形工艺简单、适用性广。当前,SLM技术已广泛用于航空航天、汽车、生物医疗等领域,但研究多集中于不锈钢与钛合金粉末,对镍基高温合金直接成形研究较少,其熔化成形特性、工艺控制与优化、结构成形工艺等有待深入探讨。本文采用Ni60粉末为成形材料,对选区激光熔化技术进行了系统的基础技术研究。首先,利用有限元软件对成形过程温度场进行模拟,确定了激光能量与单层粉末熔深的映射关系。其次,通过单道单层成形实验对激光频率、脉冲宽度、扫描速度、离焦量进行单因素分析,得到了各参数对熔道成形尺寸的工艺规律;研究了轨迹搭接率与倾斜角度对成形质量的影响规律;确定了不同工艺参数下线能量输入与粉末成形规律之间的关系,并通过正交实验分析获得了各参数对成形稳定性的影响程度;最后,通过优选的工艺参数,对典型样件进行加工实验,得到了成形精度良好的特征结构,并对沉积材料的硬度、微观组织、致密性等指标进行了分析测试。研究结果表明:当搭接率为50%时,相邻熔道间搭接紧密,成形质量最佳;当成形倾斜结构与水平夹角大于33°时,所成形的倾斜结构不易出现变形、下陷等缺陷;正交分析表明,对成形质量的影响顺序依次为扫描速度脉冲宽度激光频率;硬度测试结果显示,成形硬度在两个方向出现相异性,平行剖面的硬度值在580-620HV之间,而垂直剖面的硬度值在610-640HV之间,且层间硬度高于层内硬度;选择优化的激光工艺参数与扫描轨迹,获得了致密的金属零件。由于分层单层层厚较小,有效减少了成形中的缺陷,微观组织无明显缺陷,致密度达到97.49%。
[Abstract]:Selective laser melting (Selective Laser Melting,SLM) technology is an important development direction in the field of material augmentation manufacturing. The technology takes high energy laser beam as the energy source, and by selectively melting two-dimensional, accumulates and forms three-dimensional solid, compared with traditional machining. In the process of machining metal parts with complex shape, the complex three-dimensional solid is formed by two-dimensional scanning and stratification by "dimensionality reduction", which is not limited by machining position, and the forming process is simple and applicable. At present, SLM technology has been widely used in aerospace, automobile, biomedical and other fields, but the research is mostly focused on stainless steel and titanium alloy powder, and the research on direct forming of nickel-based superalloy is less, its melting forming characteristics, process control and optimization. The structure forming technology needs to be discussed deeply. In this paper, Ni60 powder is used as the forming material, and the selective laser melting technology is studied systematically. Firstly, the temperature field of the forming process is simulated by the finite element software, and the mapping relationship between laser energy and the penetration depth of the single layer powder is determined. Secondly, single factor analysis of laser frequency, pulse width, scanning speed and defocus is carried out through single-pass single-layer forming experiment. The influence of trajectory lap ratio and tilt angle on forming quality was studied, and the relationship between linear energy input and powder forming law under different process parameters was determined. The influence of each parameter on the forming stability is obtained by orthogonal experiment. Finally, through the processing experiment of the typical sample, the characteristic structure with good forming accuracy is obtained, and the hardness of the deposited material is obtained. The microstructures and densification were analyzed and tested. The results show that when the lap ratio is 50, the overlap between adjacent fuses is close and the forming quality is the best. When the angle between the formed inclined structure and the horizontal angle is greater than 33 掳, the formed inclined structure is not easy to be deformed, and the defects such as subsidence are not easy to occur, and the orthogonal analysis shows that, The order of influence on forming quality is laser frequency of scanning velocity pulse width, hardness test results show that the hardness is different in two directions, the hardness value of parallel profile is between 580-620HV, and the hardness value of vertical section is between 610-640HV. The interlayer hardness is higher than that of the inner layer, and the dense metal parts are obtained by selecting the optimized laser process parameters and scanning track. Because of the small thickness of the laminated single layer, the defects in the forming process are effectively reduced, and the microstructure has no obvious defect, and the density reaches 97.49%.
【学位授予单位】：青岛理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG665

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