工艺参数对激光粉末床熔融K418B高温合金显微缺陷和组织的影响

Influence of process parameters on micro-defects and structure of K418B superalloy in laser powder bed fusion

摘要

采用激光粉末床熔融（laser powder bed fusion，LPBF）技术制备K418B高温合金，利用光学显微镜、扫描电镜和硬度仪分析工艺参数激光功率（140～220 W）和扫描速度（600～1400 mm/s）对显微缺陷、致密度、微观组织及硬度的影响。结果表明，激光功率和扫描速度均显著影响样品的相对密度与缺陷分布。低能量密度易产生不规则孔洞，高能量密度则易形成球形气孔与凝固裂纹；体积能量密度（volume energy density，VED）过低或过高都会降低致密度和性能。最佳工艺参数为激光功率180 W、扫描速度1400 mm/s，在该条件下样品致密度可达99.95%以上，表面缺陷少，仅有少量凝固裂纹，显微组织呈明显熔池边界和胞状结构，维氏硬度达366.8HV_0.2。微观组织观察显示，熔池边界处晶粒较粗大，内部可见细胞状柱状晶，局部连续跨越多个熔池，表现出快速凝固特征。硬度随VED先升后降，与孔隙含量及致密度变化一致。研究揭示热应力是裂纹产生的主要原因，为K418B合金LPBF成形的参数优化提供依据，对提升航空发动机关键部件制造质量具有工程应用价值。

Abstract

The K418B superalloy is fabricated utilizing laser powder bed fusion (LPBF) technology, and an analysis is conducted to examine the impact of process parameters on microdefect, density, microstructure, and hardness by OM, SEM and hardness tester. This is achieved by varying the laser power (ranging from 140 W to 220 W) and scanning speed (between 600 mm/s and 1400 mm/s). The findings reveal that both laser power and scanning speed significantly influence the relative density and defect distribution of the samples. Specifically, low energy density leads to the formation of irregular pores, whereas high energy density is associated with the emergence of spherical pores and solidification cracks. Excessive or insufficient volume energy density (VED) results in decreased density and impaired performance. The optimal processing conditions are identified as a laser power of 180 W and a scanning speed of 1400 mm/s, under which the sample density exceeds 99.95%, with minimal surface defects and only a small quantity of solidification cracks. Microstructure reveals distinct melt pool boundaries and cellular structure, accompanied by a Vickers hardness of 366.8 HV_0.2. Notably, the grains at the melt pool boundaries are coarse, with cellular columnar crystals spanning multiple melt pools, indicating rapid solidification. The hardness initially increases and then decreases with VED, aligning with changes in pore content and density. The study attributes cracks primarily to thermal stress and provides a foundational basis for optimizing LPBF processing parameters of K418B alloy, holding potential engineering applications for enhancing the manufacturing quality of critical aero engine components.

关键词

激光粉末床熔融 / K418B / 工艺参数 / 显微缺陷

Key words

laser powder bed fusion / K418B / process parameter / microscopic defect

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基金资助

国家自然科学基金资助项目(52474416)

航发产学研项目(HFZL2020CXY023)

清洁高效透平动力装备全国重点实验室课题资助(23Z510901917)