Weldable, crack-resistant co-based alloy, overlay method, and components

1. A wear-and corrosion-resistant alloy for forming a weld overlay over a metallic component, the alloy consisting of, by approximate weight %:

C

0.2-0.4

Cr

22-27

Mo

11-14

Ni

3-4

Co

Balance

Si

up to about 1

Mn

up to about 1

Fe

up to about 1

W

up to about 1

B + Cu

up to about 3

wherein the alloy further contains Nb as a carbide-former in a concentration to provide a weight ratio of Nb to C between 2.3:1 and 7:1 to stoichiometrically offset between about 30% and about 90% of the C in the alloy, such that Nb is consumed in the formation of carbides and is not available for formation of brittle intermetallic phases and such that carbon is thereby consumed by Nb in the formation of Nb carbides, which carbon is therefore unavailable to consume Mo and Cr by formation of Mo and Cr carbides; and

wherein the alloy has an electron vacancy number between 2.3 and 2.80 as calculated using SAE specification AS5491 (Revision B), with no contribution from the carbide-former element.

2. A method for forming a wear-and corrosion-resistant overlay on a metal substrate comprising:

applying to the metal substrate the alloy of claim 1 ; and

solidifying the molten material on the substrate to form said overlay comprising said Co—Cr—Mo alloy.

3. The method of claim 2 wherein the overlay has a surface area which is greater than 1 m 2 and has a thickness between about 50 microns and 10 mm.

4. The method of claim 2 wherein the substrate is is Fe-based.

5. The wear-and corrosion-resistant alloy of claim 1 wherein said electron vacancy number is between 2.32 and 2.75.

6. The wear- and corrosion-resistant alloy of claim 1 wherein said electron vacancy number is between 2.4 and 2.6.