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Influence of laser-directed energy deposition process parameters and thermal post-treatments on Nb-rich secondary phases in single-track Alloy 718 specimens
Journal of Laser Applications ( IF 1.7 ) Pub Date : 2021-05-18 , DOI: 10.2351/7.0000259
Suhas Sreekanth 1 , Kjell Hurtig 1 , Shrikant Joshi 1 , Joel Andersson 1
Affiliation  

In this article, process parameters such as laser power, deposition speed, and powder feed rate are varied at three levels, and their effect on geometrical characteristics and microstructural features of laser-direct energy deposited single-track Alloy 718 specimens is analyzed. Furthermore, the influence of standard heat treatments recommended for wrought form of Alloy 718 is investigated on as-built deposits. The main aim of the research is to curtail the amount of secondary Nb-rich precipitates such as Laves and NbCs either during the process or by subsequent heat treatments. The volume fraction analysis of Nb-rich phases shows that processing at high laser power conditions is ideal for minimizing segregation. Upon subjecting as-built deposits to (i) solution treatment, (ii) solution treatment and aging, and (iii) direct aging, a difference in volume fraction of Nb-rich phases is noticed compared to the as-built condition. Characterization of size, morphology, phase constitution through volume fraction estimation, and elemental concentrations employing electron dispersive spectroscopy analysis indicates dissolution of Nb-rich phases when subjected to heat treatments. The delta phase precipitation preferentially occurs in the top and bottom regions and sparsely in the middle region of the specimens subjected to solution heat treatment. In case of specimens subjected to direct aging (718 °C/8 h and 621 °C/8 h), delta phase is not discernable, indicating that a higher temperature (>900 °C) treatment may be necessary for delta precipitation and growth.

中文翻译:

激光定向能量沉积工艺参数和热后处理对单道合金 718 试样中富铌二次相的影响

在本文中,激光功率、沉积速度和送粉速度等工艺参数在三个层次上变化,分析了它们对激光直接能量沉积单道合金 718 试样几何特征和显微组织特征的影响。此外,还研究了推荐用于合金 718 锻造形式的标准热处理对竣工沉积物的影响。研究的主要目的是在工艺过程中或通过后续热处理减少二次富铌沉淀物(如 Laves 和 NbC​​s)的数量。富铌相的体积分数分析表明,在高激光功率条件下进行加工是最大限度地减少偏析的理想选择。在对竣工沉积物进行 (i) 固溶处理、(ii) 固溶处理和老化以及 (iii) 直接老化后,与竣工条件相比,富铌相的体积分数存在差异。使用电子色散光谱分析通过体积分数估计表征的尺寸、形态、相构成和元素浓度表明,当进行热处理时,富 Nb 相会溶解。δ相析出优先发生在固溶热处理试样的顶部和底部区域,而在中部区域则稀疏。如果样品经受直接老化(718 °C/8 h 和 621 °C/8 h),则无法辨别出 delta 相,这表明可能需要更高的温度(>900 °C)处理才能使 delta 沉淀和生长. 通过体积分数估算获得的Nb相组成以及采用电子弥散光谱分析的元素浓度表明,经过热处理后,富含Nb的相会溶解。δ相析出优先发生在固溶热处理试样的顶部和底部区域,而在中部区域则稀疏。如果样品经受直接老化(718 °C/8 h 和 621 °C/8 h),则无法辨别出 delta 相,这表明可能需要更高的温度(>900 °C)处理才能使 delta 沉淀和生长. 通过体积分数估计的相构成和采用电子色散光谱分析的元素浓度表明,当进行热处理时,富 Nb 相会溶解。δ相析出优先发生在固溶热处理试样的顶部和底部区域,而在中部区域则稀疏。如果样品经受直接老化(718 °C/8 h 和 621 °C/8 h),则无法辨别出 delta 相,这表明可能需要更高的温度(>900 °C)处理才能使 delta 沉淀和生长. δ相析出优先发生在固溶热处理试样的顶部和底部区域,而在中部区域则稀疏。如果样品经受直接老化(718 °C/8 h 和 621 °C/8 h),则无法辨别出 delta 相,这表明可能需要更高的温度(>900 °C)处理才能使 delta 沉淀和生长。δ相析出优先发生在固溶热处理试样的顶部和底部区域,而在中部区域则稀疏。如果样品直接老化(718°C / 8 h和621°C / 8 h),则无法识别δ相,表明δ沉淀和生长可能需要更高的温度(> 900°C)处理。 .
更新日期:2021-05-28
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