5599
In the mechanically ground sample , hardness increased nearly two-fold up to 75 μm beneath the sample ’ s surface , and X-ray diffraction indicated an in-plane compressive stress , grain refinement , and micro-strain on the mechanically ground sample .
 sample, hardness, sample, s, X-ray diffraction, compressive stress, grain refinement, sample
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:
 sample, hardness, sample, s, X-ray diffraction, compressive stress, grain refinement, sample