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In fusion zone , due to acicular α′ formation , the microhardness is higher than base metal and heat affected zone .
 concept or principle: fusion zone; concept or principle: microhardness; material: base metal; concept or principle: heat affected zone
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: fusion zone; concept or principle: microhardness; material: base metal; concept or principle: heat affected zone