**4. Conclusions**


in increasing the hardness of CrFeCoNiNbx alloys. The hardness increased from HV144 of CrFeCoNi alloy to HV652 of CrFeCoNiNb alloy.


**Author Contributions:** C.-H.T. conceived and designed the experiments; C.-Y.Y. and M.-C.T. performed the experiments; all of the authors analyzed the data; C.-Y.Y. and M.-C.T. contributed reagents/materials/analysis tools; C.-H.T. wrote the paper. All of the authors have read and approved the final manuscript.

**Funding:** We are grateful to the Ministry of Science and Technology of Republic of China for its financial support under the project MOST 106-2221-E-034-008.

**Conflicts of Interest:** The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
