Qualification challenges for additive manufacturing in high temperature nuclear applications

Abstract

There is an increasing interest in using additive manufacturing for structural materials, including pressureretaining components. This requires that the manufacturing methods be included in Codes and Standards, such as the Boiler Pressure Vessel Code. This work is already moving forward with the development of a Section III Division 1 Code Case to include 316 stainless steel that is manufactured using powder bed fusion, an additive manufacturing technique. However, Code Cases will become significantly more challenging when time-dependent properties must be considered, such as in Section III, Division 5. Section III, Division 5 requires design models based on creep as well as creep-fatigue interaction. Testing for this is time intensive and costly. Additive manufacturing properties are a result of feedstock material as well as processing methods/parameters. The individual machines take what used to be centralized material fabrication (into large plates of castings) and spread the process out to many separate facilities. This decentralized fabrication, paired with the rapidly changing landscape of additive techniques and equipment manufacturers, has created difficulty in quality control and producing code cases. For lowtemperature code cases, this has been circumvented by requiring witness specimens that meet specified property requirements. Additional witness specimens to cover timedependent properties would significantly increase the cost and delay processes, so similar methods may not be effective for high temperature applications. This paper covers fabrication and modeling/simulation challenges associated with qualification of additive manufacturing processes for hightemperature structural materials.