7115
The variation of microhardness within the molten pool was ascribed to the number of grain boundaries and the stress characteristics of different kinds of microstructures under mechanical load .
 concept or principle: variation; concept or principle: microhardness; concept or principle: molten pool; concept or principle: grain boundaries; machanical property: stress; material: microstructures; application: mechanical
Given options, please tell me the categories of all the listed entity words.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} 
 Entities: variation, microhardness, molten pool, grain boundaries, stress, microstructures, mechanical 
Answer:
 concept or principle: variation; concept or principle: microhardness; concept or principle: molten pool; concept or principle: grain boundaries; machanical property: stress; material: microstructures; application: mechanical