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The microstructure and mechanical properties of the printed specimens from the two sets ( new and recycled Ti-6Al-4 V powder ) were investigated before and after heat treatment .
 microstructure, mechanical properties, recycled, V, powder, heat treatment
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:
 microstructure, mechanical properties, recycled, V, powder, heat treatment