Characterization of additive manufacturing metal powders using the FT4 powder rheometer

粉末床融合是一种基于粉末薄层反复扩散和熔化的增材制造技术。随着技术从研究到生产的发展，成品零件的质量控制的重要性增加。粉末原料、扩散动力学和缺陷形成之间的关系仍然没有完全理解，但目前的理解是，扩散后形成的粉末空隙可以在成品零件中产生缺陷。因此，高质量的粉末必须具有能够铺展致密、均匀层、无空隙和偏析的特性。这些特性必须在粉末的整个寿命期内得到保持，包括回收、处理和延长储存期。尽管粉末的铺展性很重要，但对于铺展性的定量描述或标准却不存在。目前，AM粉末的特征在于通过测试捕捉一些，但不是全部，铺展相关的属性，而新的AM特定标准正在提出。该提案涉及麦吉尔大学和先进粉末和涂料（AP&C）之间的联合调查，以了解使用弗里曼技术FT4粉末流变仪表征粉末铺展性的优点和缺点。与传统的基于重力的测量（如霍尔流量计）相比，FT 4产生的数据应该更能代表与铺展相关的性能，因为它能够对粉末体施加精确的压缩力、拉伸力和剪切力。FT 4测试参数是否能与特定的粉末铺展技术相匹配将在本项目的过程中确定。如果FT4能够准确解析与铺展相关的特性，该仪器将用于评估新的粉末生产技术，并为AP &C及其客户的质量管理体系提供支持。

Powder Bed Fusion is a Additive Manufacturing technique based on the repeated spreading and melting of thinlayers of powder. As the technology evolves from the research to production, the importance of quality controlof finished parts increases. The relationships between powder feedstock, spreading dynamics and defectformation are still not fully understood, but the current understanding is that that powder voids formed afterspreading can seed defects in the finished part. Thus, high quality powders must have properties which enablethe spreading of dense, homogenous layers, free of voids and segregation. These properties must be maintainedthroughout the powder lifetime, which can include recycling, handling and extended storage periods. Despitethe importance of powder spreadability, no universal description or standard for quantitative spreadabilityexists. Currently, AM powder is characterized by tests which capture some, but not all, of the spreading-relatedproperties, while new AM-specific standards are being proposed.This proposal concerns a joint investigation between McGill University and Advanced Powders andCoatings(AP&C) to understand the strengths and weaknesses of characterizing powder spreadability using theFreeman Technology FT4 powder rheometer. Compared to conventional, gravity-based measurements like theHall flow meter, the data generated from the FT4 should should be more representative of spreading-relatedproperties because of the ability to apply precise compressive, tensile and shear forces to the powder bulk.Whether FT4 test parameters can be matched to specific powder spreading techniques will be determined overthe course of this project. If the FT4 can accurately resolve properties related to spreading, the instrument willbe used to evaluate new powder production techniques as well as support the quality management systems ofAP&C and their customers.