[论文解读] Effect of varying preheating temperatures in electron beam powder bed fusion: Part I Assessment of the effective powder cake thermal conductivity

Gitanjali Shanbhag, Mihaela Vlasea|arXiv (Cornell University)|Jul 30, 2021

Additive Manufacturing Materials and Processes参考文献 52被引用 4

一句话总结

本研究探讨了预热温度（650–730 °C）对电子束粉末床熔融（EB-PBF）中Ti-6Al-4V粉末坯体有效热导率的影响。通过X射线计算机断层扫描与经验建模，研究发现热导率随温度升高呈线性增加，从1.75 W/m·K升至2.11 W/m·K，这是由于堆积密度、接触面积比和配位数提高所致。

ABSTRACT

One of the major barriers in adapting the existing EB-PBF process parameters to a new powder material system is controlling the preheating conditions such that every layer of powder results in enough partial sintering to create a coherent powder cake. To be able to understand the powder sintering process and adapt it to other materials, we must look at the degree of sintering and the effective thermal conductivity of the powder bed. An in-depth understanding of these characteristics will help tailor the preheating conditions and furthermore, make it easier to remove/de-powder intricate parts after build completion without compromising the advantages of the preheating phenomenon. This study evaluates the impact of preheating temperature on the in-situ powder cake properties. Three different preheat temperatures, 650 °C, 690 °C and 730 °C, are employed to a Ti-6Al-4V powder cake and in each standalone build, unique powder-capture artefacts are fabricated to be able to analyze the in-situ powder cake properties using X-ray computed tomography. An empirically-derived model for thermal conductivity of the powder cake as a result of changing the preheating temperatures, was obtained. The results demonstrated that the effective thermal conductivity of the powder cake at a given preheating temperature strongly depends on the packing density, contact size ratio and coordination number. An increase in preheating temperature, lead to a linear increase in the packing density (from 58.42% to 61.87%), contact size ratio (from 0.45 to 0.48), coordination number (from 3.36 to 3.58) and the effective thermal conductivity (from 1.75 W/m/K to 2.11 W/m/K) of the powder cake.

研究动机与目标

• 理解不同预热温度如何影响EB-PBF中粉末坯体的原位热学与结构特性。
• 量化不同预热条件下Ti-6Al-4V粉末坯体的有效热导率。
• 将微观结构参数（堆积密度、接触面积比和配位数）与热导率变化相关联。
• 建立基于经验数据的有效热导率模型，作为预热温度的函数。
• 通过改善对粉末坯体结合力与热响应的控制，支持工艺优化与后处理除粉。

提出的方法

• 在三个预热温度（650 °C、690 °C和730 °C）下进行独立的EB-PBF成形实验。
• 制备独特的粉末捕获试样，以保留原位粉末坯体的形貌，供后处理分析。
• 采用X射线计算机断层扫描（XCT）测量包括堆积密度、接触面积比和配位数在内的微观结构参数。
• 基于测量的微观结构数据，建立预热温度与有效热导率之间关系的经验模型。
• 利用测量的微观结构演化数据计算有效热导率，并通过实验趋势验证模型。
• 分析热导率与结构参数之间的相互依赖关系，以分离预热的影响。

实验结果

研究问题

• RQ1 预热温度如何影响EB-PBF中Ti-6Al-4V粉末坯体的有效热导率？
• RQ2 随着预热温度升高，堆积密度、接触面积比和配位数等微观结构参数发生何种变化？
• RQ3 微观结构参数与有效热导率变化之间的相关性程度如何？
• RQ4 能否基于预热温度与微观结构，通过经验模型准确预测有效热导率？
• RQ5 预热温度的变化如何影响粉末坯体的结合力与烧结行为？

主要发现

• Ti-6Al-4V粉末坯体的有效热导率随温度从650 °C升至730 °C呈线性增加，从1.75 W/m·K升至2.11 W/m·K。
• 随着预热温度升高，堆积密度从58.42%增至61.87%，表明粉末层更致密。
• 接触面积比从0.45增至0.48，反映出热致烧结导致颗粒间接触面积增加。
• 配位数从3.36增至3.58，表明高温下颗粒网络更稳定且相互连接。
• 观察到的热导率增加直接归因于热预热驱动的微观结构演化。
• 基于经验推导的模型成功捕捉了预热温度与有效热导率之间的线性关系。