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The swirl structure is more pronounced in Ti 6-4 than in Zr 702 substrate which may contribute to its high cracking susceptibility .
 concept or principle: structure; material: Ti; material: Zr; material: substrate; concept or principle: cracking
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: structure; material: Ti; material: Zr; material: substrate; concept or principle: cracking