典型选区激光熔化粉末的特性及其成型件组织结构的研究

发布时间：2018-05-17 20:36

本文选题：选区激光熔化 + 合金粉末　；参考：《兰州理工大学》2017年硕士论文

【摘要】：选区激光熔化技术(Selective Laser Melting,SLM)是近年来出现的一种新型的快速制造技术。通过此种技术所制造的零件广泛应用于国防工业、航空航天、模具机械和个性化定制等领域。由于国内起步相对较晚,在选区激光熔化技术方面我国与发达国家还有一定的差距,目前,高质量选区激光熔化金属粉末主要依赖进口,国外厂商常将原材料与设备捆绑高价销量,极大地制约了我国的金属选区激光熔化技术的发展;而且国内外学者对于选区熔化的研究大多集中在激光工艺参数及某种金属粉末成型的机械性能等方面,对于粉末粒度分布等特性的研究较少。因此,本文以SLM专用GH4169,GH3625,316L合金粉末为例,进行选区激光熔化粉末的特性及成型件组织结构的研究,通过大量试验得出最佳工艺,以期为金属粉末制备及成型工艺的优化提供有益指导。在粉末为同一批次的情况下,详细研究了GH4169的粉末粒径分布,通过大量的成型试验,结果表明:粒度过小、粉末易团聚,铺粉过程中易出现波浪纹,不能形成平整均匀的选区熔化平面,不适合成型件的制备;粒度过大,会增加粉末颗粒与颗粒之间的孔隙,在快速熔化与冷却的过程中液体不能充分的填充孔隙易造成孔洞;粒度在15-53μm之间,平均粒径约为32μm左右的粉末,进行选区熔化之后可以得到高质量的成型件,经过金相腐蚀观察可知其内部组织呈现胞状结晶形态,“微熔池”内的“亚微米长柱状晶”(亚晶)由于温度场复杂多变的影响,也显示出了多种不同的结晶形貌,通过对拉伸件的测试得出其延伸率为36.3%、屈服强度929Mpa、抗拉强度1058Mpa左右,显示出了良好的拉伸性能,断裂方式为韧性断裂与解理断裂的混合断裂;通过GH4169得出的试验结果,将粉末的粒度分配比例运用到GH3625与316L粉末的生产与筛分上,通过成型试验可以得到性能良好的成型件,对适于选区激光熔化粉末的生产提供了一定的指导作用,经过金相分析可知,GH3625、316L与GH4169的结晶形貌一致,组织均为胞状晶,由于材料成分以及工艺的影响“微熔池”内部“亚微米长柱状晶”的直径、位向分布均有所不同,GH3625与316L的断裂方式为韧性断裂。通过本文的试验结果,与一些企业联合进行粉末的试制,在经过粉末的筛分与级配之后,经过选区激光熔化,得到了外观漂亮,成型效果良好的产品。
[Abstract]:Selective Laser melting (SLM) is a new rapid manufacturing technology. The parts manufactured by this technology are widely used in the fields of defense industry, aerospace, mould machinery and personalized customization. Due to the relatively late start in China and the gap between China and the developed countries in the area of selective laser melting technology, at present, the high quality selective laser melting metal powder mainly depends on imports. Foreign manufacturers often bundle the raw materials and equipment to sell at a high price, which greatly restricts the development of laser melting technology in our country. Moreover, the researches on selective melting mostly focus on laser processing parameters and mechanical properties of a certain metal powder, but few on the properties of particle size distribution. Therefore, taking GH4169 / GH3625316L alloy powder for SLM as an example, the characteristics of selected laser melting powder and the microstructure of molded parts are studied. The optimum process is obtained through a large number of experiments. In order to provide useful guidance for metal powder preparation and optimization of molding process. In the case of the same batch of powder, the particle size distribution of GH4169 powder is studied in detail. The results show that the particle size is too small, the powder is easy to agglomerate, and the wavy grain is easy to appear in the process of powder laying. If the particle size is too large, the porosity between powder particles and particles will be increased, and in the process of rapid melting and cooling, the porosity will be easily caused by the insufficient filling of the pores in the process of rapid melting and cooling. When the particle size is 15-53 渭 m and the average particle size is about 32 渭 m, high quality molded parts can be obtained after selective melting. The "submicron columnar crystal" (sub-crystal) in the "micromelting pool" also shows many different crystal morphologies due to the complex and changeable temperature field. The elongation ratio is 36.3%, yield strength is 929 MPA, tensile strength is about 1058Mpa, which shows good tensile properties, the fracture mode is the mixed fracture of ductile fracture and cleavage fracture, and the test results obtained by GH4169 show that the tensile strength is about 929MPA, and the tensile strength is about 1058Mpa. The granularity distribution ratio of the powder is applied to the production and screening of GH3625 and 316L powder, and the forming parts with good properties can be obtained by forming test, which provides some guidance for the production of selected laser melted powder. Metallographic analysis shows that the crystal morphology of GH3625316L is the same as that of GH4169, and the microstructures are all cellular crystals. The diameter of "sub-micron columnar crystals" in the "micro-melting pool" is affected by the composition of the material and the process. The fracture mode of GH3625 and 316L is ductile fracture. According to the experimental results of this paper, the powder was produced in combination with some enterprises. After the powder was sifted and graded, the products with beautiful appearance and good forming effect were obtained by selective laser melting.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TF124.3;TG665

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