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The improved mechanical response during tensile testing was due to the inter-locking microstructure forming a strong bond at the interface and solid solutions strengthening from the intermixing of the Fe and Ni increased the interface strength , beyond the sum of parts .
 concept or principle: mechanical response; process characterization: tensile testing; concept or principle: microstructure; manufacturing process: forming; concept or principle: interface; material: solid solutions; material: Fe; material: Ni; 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:
 concept or principle: mechanical response; process characterization: tensile testing; concept or principle: microstructure; manufacturing process: forming; concept or principle: interface; material: solid solutions; material: Fe; material: Ni; concept or principle: interface