2199
Thus , a very thin reaction layer ( < 500 nm ) forms between the WC particles and iron-based matrix .
 layer, WC, particles
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:
 layer, WC, particles