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The results show that Zr 702 is a suitable substrate for Zr-based metallic glass structure since crack-free weld joints can be obtained owing to the formation of ductile α-Zr , while Ti 6-4 is not an appropriate substrate since it has high cracking susceptibility due to the formation of a large amount of hard and brittle intermetallics near the foil-substrate interface .
 material: Zr; material: substrate; material: metallic glass; concept or principle: crack-free weld; material: be; machanical property: ductile; material: Ti; material: substrate; concept or principle: cracking; machanical property: brittle; concept or principle: interface
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:
 material: Zr; material: substrate; material: metallic glass; concept or principle: crack-free weld; material: be; machanical property: ductile; material: Ti; material: substrate; concept or principle: cracking; machanical property: brittle; concept or principle: interface