Microstructures, tensile properties, and fracture mechanisms of Inconel 718 formed by HDR-LMD with PREP and GA powders
Microstructures, tensile properties, and fracture mechanisms of Inconel 718 formed by HDR-LMD with PREP and GA powders
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DOI：
10.1007/s00170-018-1662-1
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发表时间：
2018-02
期刊：
影响因子：
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通讯作者：
Chongliang Zhong;J. Chen;A. Gasser;S. Sui;J. Schleifenbaum
中科院分区：
文献类型：
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作者：
Chongliang Zhong;J. Chen;A. Gasser;S. Sui;J. Schleifenbaum
为了提高激光金属沉积（LMD）的生产率，目前研究的重点是提高LMD的沉积速率，以发展高沉积速率LMD（HDR-LMD）。等离子旋转电极法（PREP）和气体雾化法（GA）是制备LMD粉末最常用的方法。在所提出的工作中，显微组织，拉伸性能和断裂机制的Inconel 718的HDR-LMD形成PREP和GA粉末已被检查。最初，在相同的实验条件下用不同的粉末构建块。然后，对构建的样品进行热处理，然后制造成拉伸测试样品，之后对其进行测试以确定其拉伸性能。最后，进行了微观组织和断口分析。根据晶粒形貌的光学显微镜观察、晶粒取向的EBSD分析以及孪晶界和晶界取向的分析结果，GA样品比PREP样品具有更高的再结晶程度。PREP样品中的晶间δ相为针状，GA样品中的δ相为球状。拉伸试验表明，GA试样的准静态性能略高于PREP试样。基于断裂分析，已经观察到不同的断裂机制：在PREP样品中，已经识别出沿晶断裂;在GA样品中，已经观察到混合断裂-沿晶断裂和穿晶断裂。此外，在GA样品中发现的孔对于拉伸性能可能不是绝对有害的。这一假设得到以下事实的支持：GA样品具有显著较高的孔隙率，但同时具有较高的拉伸性能;孔周围的断裂表面上的韧窝发育良好且细小;孔内形成的裂纹没有延伸到孔外。
For the purpose of improving the productivity of laser metal deposition (LMD), the focus of current research is set on increasing the deposition rate for it, in order to develop high-deposition-rate LMD (HDR-LMD). Plasma rotating electrode process (PREP) and gas atomization (GA) are the most commonly used processes for producing LMD powders. In the presented work, the microstructures, the tensile properties, and the fracture mechanisms of Inconel 718 formed by HDR-LMD with PREP and GA powders have been examined. Initially, blocks were built up with different powders under identical experimental conditions. Afterwards, the samples built were heat treated, and then manufactured to tensile test specimens, after which they were tested in order to determine their tensile properties. Finally, microstructure and fracture analysis has been conducted. According to the results of the optical microscope observations for grain morphology, the EBSD analysis for grain orientations, and the analysis of twin boundary and grain boundary orientation, the GA sample has a higher recrystallization degree than the PREP sample. In addition, the intergranular δ phases are needle-like in the PREP sample, and some spherical δ phases have been observed in the GA sample. The tensile test shows that the quasistatic properties of the GA sample are slightly higher than those of the PREP sample. Based on the fracture analysis, different fracture mechanisms have been observed: in PREP sample, intergranular fracture has been identified; in GA sample, mixed fracture - both intergranular fracture and trans-granular fracture - has been observed. Furthermore, the pores found in the GA sample may be not definitely detrimental for the tensile properties. This hypothesis is supported by the following facts: the GA samples have significantly higher porosity, but meanwhile higher tensile properties; the dimples on the fracture surface that are around the pores develop well and fine; cracks formed in the pores did not extend to the outside of the pores.