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Some of the primary barriers to widespread adoption of metal additive manufacturing ( AM ) are persistent defect formation in built components , high material costs , and lack of consistency in powder feedstock .
 metal additive manufacturing, AM, defect, components, material, consistency, powder feedstock
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 metal additive manufacturing, AM, defect, components, material, consistency, powder feedstock