Page 25 - Demo

Issue 143 August 2024 PCMI Journal 25
PCM of Difficult-to-Etch Metals and Alloys: Nickel- and Cobalt-Based Superalloys
Emeritus Professor David Allen, Cranfield University
Table 8. Some cobalt-based superalloys, designations and modern applications
Superalloy UNS Werkstoff # General applications
Alloy 188
(Haynes International)
R30188 2.4683 Seal rings & packing for gas turbines
Alloy 25 (L-605)
(Haynes International)
R30605 2.4964 Jet engine parts, industrial furnaces,
balloon stents, heart valves
Elgiloy (Alloy 3J21)
(Elgiloy Specialty Metals)
R30003 2.4711 Springs, seals, orthodontics, implants,
watch parts, satellite communications
equipment and weapons systems
Phynox (Conichrome) R30003
R30008
2.4711
Havar
(Hamilton Precision Metals)
R30004 - Watch springs, diaphragms, implants
MP35N
(Carpenter Technology)
R30035 2.4999 Marine engineering, medical devices &
dental products
Duratherm 600
(Vacuumschmelze)
- 2.4781 Springs, corrosion-resistant membranes
for pressure gauges
Table 9. Chemical compositions of cobalt-based superalloys
Superalloy Co % Cr % Ni % Mo % Mn % C % Other % Fe %
Alloy 188 39 21 21 0 1.25 max 0.1 W 14% 3 max
Alloy 25
(L-605)
49 20 10 0 1.50 max 0.1 W 15% 3 max
Elgiloy /
Phynox
39-
41
19-21 14-16 6-8 1.5-2.5 0.15
max
Si 1.2%
max
Balance
Havar 41-
44
19-21 12-14 2-2.8 1.35-1.8 0.17-
0.23
W 2.7% Balance
MP35N 29-
39
19-21 33-37 9-10.5 0.15 max 0.025
max
Si 0.15%
max
1 max
Duratherm 600 42 12 26 4 0.5-1.5 W 4%
Ti 2%
Al 1%
Si 0.3-1.0%
8-10
The etchability of cobalt-based superalloys from experimental investigations of
spray etching in 38°Bé ferric chloride + 0.75% HCl solutions at 45°C is
summarised in Table 10.
The etchability of cobalt-based L-605 (Alloy 25) from experimental investigations
of surface microetching by immersion in methanol (80 ml), hydrochloric acid (20
ml) and ferric chloride (2 gm) solution is summarised in Table 11.
General Motors, USA [22] patented an etchant comprising “...an aqueous bath
consisting essentially of ≈35% to 55% of a 42° Baumé ferric chloride solution,
≈26% to 40% concentrated hydrochloric acid, ≈8% to 14% concentrated nitric