Mo is a lubricant element, during wear testing, it reduces the friction coéffision which reducing the amonut of material lost

but what about the changes in mechanical behavior if  we added Mo in the alloy..?

Talking in general, Ni should improve the alloy tenacity, yield strength and will lead your alloy to have a more stable behaviour when temperatures rises. Molibdenum will enhance the quenching process, so it will allow you to have a more quenched and hardened alloy.

However, as always, actual behaviour depends on the concentration of each element and the interaction with Co-Cr. In particular, I believe that too much Nichel may lead to the segregation of Cromium at grain boundaries, as a consequence your alloy may become brittle.

Check on Campbell's book "ELements of MEtallurgy and Engineering Alloys" ASM

Regards,

Alberto

Thanks Billel, Volker and Alberto.........

But i have one more query related to CoCrMo alloy. Firstly, what is the impact strength of the cast CoCrMo alloy and what changes in the impact strength of the alloy if we add more wt. %Ni and Mo separately.

Molybednum enhance abrasion resistance and Nickel enhance toughness and impact strength

Co-Cr alloys find application as dental implants. I think Cr and Mo may be improving the corrosion resistance, while Ni effect is to increase the ductility which is the problem in these alloys. I have no experience working on these alloys. But you may see whether these may help your work:-

1) "Nickel, Cobalt, and Their Alloys" edited by Joseph R. Davis, ASM international 2000.

2) "Metals for Biomedical Devices", edited by M Niinomi, Woodhead Publsihing limited and CRC Press, 2010.

3) "Effects of Ni and Mo on the microstructure and some other properties of Co–Cr dental alloys", Tanja Matkovi´c, Prosper Matkovi´c, Jadranka Malina, Journal of Alloys and Compounds 366 (2004) 293–297.

4) "Significant Improvement in Mechanical Properties of Biomedical Co-Cr-Mo Alloys with Combination of N Addition and Cr-Enrichment", Sang-Hak Lee, Naoyuki Nomura and Akihiko Chiba, Materials Transactions, Vol. 49, No. 2 (2008) pp. 260 to 264 (The Japan Institute of Metals).

5) http://en.wikipedia.org/wiki/Cobalt-chrome