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Nevertheless , there is still a need for a systematic review of the properties of various WAAM-processed materials , the defects associated with different alloys , and a summary of current and future research directions that are aimed at quality improvements for the alloy classes of interest .
 concept or principle: properties; concept or principle: materials; concept or principle: defects; material: alloys; concept or principle: research; concept or principle: quality; material: alloy
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: 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:
 concept or principle: properties; concept or principle: materials; concept or principle: defects; material: alloys; concept or principle: research; concept or principle: quality; material: alloy