Abstract Invar 36 alloy, which presented extremely low coefficient of thermal expansion (CTE), was fabricated by selective laser melting with island scanning strategy. The microstructures and CTE were systematically characterized. The as-SLMed Invar 36 is mainly composed of fcc γ phase and sparse bcc α precipitates, which are consistent with the phases of the wrought one. The grains grow along the maximum temperature gradient directions, as the microstructure on the side surface is dominated by large columnar grains. The cross-section shows a large number of small columnar grains in the melt pool. The low laser energy density results in the lack-of fusion pores and corresponding high level porosity up to 15%. When the laser energy density is 99.2 J/mm3 and 198.4 J/mm3, excellent quality is obtained, as the porosity is only within 0.2–0.4%. Due to the porosity and nickel element evaporation, the CTE is 1.72–1.96 × 10–6 °C−1 that is lower than that of wrought one. Besides, lower than 99.2 J/mm3, the decreasing laser energy density leads to the reduction of CTE, since the pores provide extra space for internal thermal expansion. Higher than 99.2 J/mm3, the metal vaporization rate and vapor pressure are enhanced with the increasing laser energy density, and then the loss of nickel element leads to the reduction of CTE.

中文翻译：

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选择性激光熔化制造 Invar 36 合金的显微组织和独特的低热膨胀

摘要 采用岛扫描策略选择性激光熔化制备了具有极低热膨胀系数（CTE）的因瓦36合金。系统地表征了微观结构和CTE。SLMed Invar 36 主要由 fcc γ 相和稀疏的 bcc α 相组成，这与锻造相一致。晶粒沿最大温度梯度方向生长，因为侧面的显微组织以大柱状晶粒为主。横截面显示熔池中有大量小的柱状晶粒。低激光能量密度导致缺乏融合孔和相应的高达 15% 的高孔隙率。当激光能量密度为 99.2 J/mm3 和 198.4 J/mm3 时，可获得优异的质量，孔隙率仅在 0.2-0.4% 以内。由于孔隙率和镍元素蒸发，CTE 为 1.72-1.96 × 10-6 °C-1，低于锻造的 CTE。此外，低于 99.2 J/mm3，降低的激光能量密度导致 CTE 降低，因为孔隙为内部热膨胀提供了额外的空间。高于 99.2 J/mm3，金属汽化速率和蒸气压随着激光能量密度的增加而增加，然后镍元素的损失导致 CTE 降低。