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The formation of different kinds of microstructures in the molten pool was controlled by the temperature gradient ( which determined the direction of grain growth ) and the cooling rate ( which determined the size of grain growth ) .
 microstructures, molten pool, temperature gradient, grain growth, cooling rate, grain growth
Please list all entity words in the text that fit the category. Output format is "word1, 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:
 microstructures, molten pool, temperature gradient, grain growth, cooling rate, grain growth