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This paper reviews the microstructure and mechanical properties of various metals , including titanium and its alloys , aluminum and its alloys , Ni-based alloy , steel and other intermetallic materials fabricated by the various WAAM processes .
 concept or principle: microstructure; concept or principle: mechanical properties; material: metals; material: titanium; material: alloys; material: aluminum; material: alloys; material: Ni-based alloy; material: steel; material: intermetallic; concept or principle: fabricated; manufacturing process: WAAM; concept or principle: processes
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: microstructure; concept or principle: mechanical properties; material: metals; material: titanium; material: alloys; material: aluminum; material: alloys; material: Ni-based alloy; material: steel; material: intermetallic; concept or principle: fabricated; manufacturing process: WAAM; concept or principle: processes