Wear-resistant coatings for cobalt-base alloys

Journal Article · Sat Apr 01 04:00:00 EST 2000 · Advanced Materials and Processes

OSTI ID:20023251

Cockeram, B V

High interfacial stresses and coating failure are expected when a hard coating protects a more-compliant substrate in applications involving high-stress wear contact. Assuming that small differences in stiffness (or modulus) between the coating and substrate are required for a wear-resistant coating in such applications, four approaches have been taken to develop such coatings for cobalt-base alloys. Hardness, scratch adhesion, and nano-indentation testing identified the most promising candidates for cobalt-base alloys: A thin coating with hard Cr{sub 2}N and less-stiff Cr-N(ss) layers; a thick, four-layered coating with a 4{mu}m inner layer of Cr-N(ss)/ 1 {mu}m layer of Cr{sub 2}N/4 {micro}m layer of Cr-N(ss)/1 {micro} outer layer of Cr{sub 2}N; a duplex approach of ion nitriding to harden the subsurface,followed by application of a dual-layered Cr{sub 2}N/Cr-N(ss) coating; and ion nitriding alone. The low scratch adhesion values and high modulus/hardness values indicate that ZrN, TiN, and plasma carburized coatings represent less beneficial approaches. Two different cobalt-base alloys were studied in this work: Haynes 25 and Stellite 3 (Stoody Deloro Stellite). Based on weight change, profilometry measurements, and metallographic and SEM examinations after four-ball wear testing, the thin Cr{sub 2}N/CrN(ss) coated coupons exhibited a significantly lower wear rate than the uncoated Haynes 25 coupons. Of greater importance, the thin Cr{sub 2}N/Cr-N(ss) coatings were adherent on the Stellite 3 intermediate balls and Haynes 25 cups, and prevented the wear of the cobalt-base substrate. based on these results, the thin Cr{sub 2}N/Cr-N(ss) coating was the best coating candidate, and this coating could result in a reduced wear rate and less cobalt wear debris. The ion nitrided coupons exhibited slightly higher wear than the thin Cr{sub 2}N/Cr-N(ss) coated coupons, while the wear of the thin duplex coated coupons was the highest. However, the nitride layer was adherent and protected the Haynes 25 substrate. Therefore, modification of the ion nitriding conditions or surface lapping after nitriding are approaches that may improve the wear resistance of the ion nitriding and duplex coatings.

• Research Organization: Bettis Atomic Power Lab., West Mifflin, PA (US)
• OSTI ID: 20023251
• Journal Information: Advanced Materials and Processes, Journal Name: Advanced Materials and Processes Journal Issue: 4 Vol. 157; ISSN 0882-7958; ISSN AMAPEX
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
36 MATERIALS SCIENCE
CHROMIUM NITRIDES
COBALT BASE ALLOYS
HARDNESS
MECHANICAL TESTS
MICROSTRUCTURE
PROTECTIVE COATINGS
REACTOR MATERIALS
ROUGHNESS
TITANIUM NITRIDES
WEAR RESISTANCE
ZIRCONIUM NITRIDES