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But due to high cooling rates , high thermal gradients and a layer-wise processing , parts produced by selective laser melting are subject to different kinds of defects .
 cooling rates, thermal gradients, selective laser melting, defects
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:
 cooling rates, thermal gradients, selective laser melting, defects