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During wear testing , a grain refinement was observed directly beneath the wear scar in these materials in a focused ion beam channel observed under scanning electron microscopy .
 wear, testing, grain refinement, wear, materials, ion, beam, scanning electron microscopy
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:
 wear, testing, grain refinement, wear, materials, ion, beam, scanning electron microscopy