Chromium-nickel stainless steel alloy article having oxide coating formed from the base metal suitable for brake apparatus
Disclosed is a chromium-nickel stainless steel alloy article having an adherent, wear resistant coating of metallic oxides and a method of forming an adherent, wear resistant coating of metallic oxides on a chromium-nickel stainless steel alloy article. The coating desirably has a thickness of from about 25.4 to about 102 microns (1 mil to about 4 mils) and is formed by exposure of the article to an oxidizing atmosphere, preferably air, preferably during heat treatment of the article. Such articles are useful, inter alia, as torque drive inserts for a friction disk for a multi-disk brake or clutch assembly. The drive inserts can be formed of an alloy such as 17-4PH stainless steel alloy having an adherent coating of lubricious oxides formed during frictional contact. It is believed that these lubricious oxides will form also if the heat treated base alloy is subject to temperatures greater than 815.6° C. (1500° F.) for a sufficient time in an oxidizing atmosphere.
1. A component for an aircraft brake assembly, the component comprising:
a) a substrate of 17-4PH OX HT alloy having a wear surface; and
b) an adherent coating of lubricious oxides comprising copper oxide, chromium oxides, and iron oxides, wherein the coating is formed from a base layer of iron oxide, chromium, nickel, and copper on the surface of the alloy, the base layer formed by heating a 17-4PH stainless steel alloy in flowing air for about two hours at about 1875° F. to 1925° F. with an air flow of about 10-30 cubic feet per hour, wherein the 17-4PH stainless steel alloy has the following composition
CHEMISTRY
Element
Min. wt. %
Max. wt. %
C
—
0.060
P
—
0.025
S
—
0.025
Si
0.50
1.00
Mn
—
0.70
Al
—
0.05
Cr
15.50
16.70
Ni
3.600
4.60
Nb
0.15
0.40
Cu
2.80
3.50
Ta
—
0.05
Sn
—
0.02
N
—
0.05
Fe
Balance
Balance
and further comprising a chromium-iron-nickel metallic phase.
2. The component of claim 1 wherein the coating is formed upon oxidation of the surface
3. The component of claim 2 in the form of a drive insert for a friction disk.
4. The component of claim 1 wherein the coating comprises oxides of Fe and a Cr 0.19 Fe 0.7 Ni 0.11 Phase.
5. The component of claim 4 in the form of a drive insert for a friction disk.
6. The component of claim 1 wherein the coating is self healing during sliding frictional engagement of the coated surface of the article with one of a hard chromium surface and a flame sprayed WC / Co composite alloy surface.
7. The component of claim 6 in the form of a drive insert for a friction disk.
8. The component of claim 1 in the form of a drive insert for a friction disk.
9. The component of 1 , wherein the coating comprises:
Phases
Chemical Formula
Structure
Magnetite
Fe 3 O 4
Cubic
Trevorite
NiFe 2 O 4
Cubic
Chromium-Iron-Nickel
Cr 0.19 Fe 0.7 Ni 0.11
Cubic
Iron
Fe
Cubic
Maghemite-Q
Fe 2 O 3
Tetragonal
Hematite
Fe 2 O 3
Rhombohedral
Eskolaite
Cr 2 O 3
Rhombohedral
Chromium Oxide
Cr 5 O 12
Orthorhombic
Tenorite
CuO
Monoclinic.
10. The component of claim 1 wherein the component comprises a drive insert that is part of a brake assembly having an increased dynamic stability against vibration during a braking event, as compared to an otherwise identical brake assembly having a drive insert made of an SAE AMS 5385 cobalt-base alloy.
11. The component of claim 1 wherein the coating is formed during frictional engagement with a second surface.
12. A component for an aircraft brake assembly, the component comprising a drive insert comprising:
a) a 17-4PH OX HT alloy having a wear surface and a base layer of iron oxide, chromium, nickel, and copper on the surface of the alloy, wherein the base layer is formed by heating a 7-4PH stainless steel alloy in flowing air for about two hours at about 1875° F. to 1925° F. with an air flow of about 10-30 cubic feet per hour, the 17-4PH stainless steel alloy having the following composition
CHEMISTRY
Element
Min. wt. %
Max. wt. %
C
—
0.060
P
—
0.025
S
—
0.025
Si
0.50
1.00
Mn
—
0.70
Al
—
0.05
Cr
15.50
16.70
Ni
3.600
4.60
Nb
0.15
0.40
Cu
2.80
3.50
Ta
—
0.05
Sn
—
0.02
N
—
0.05
Fe
Balance
Balance
, and wherein an adherent coating of lubricious oxides comprising copper oxide, chromium oxides, and iron oxides is formed upon frictional engagement of the base layer with a second surface, the coating further comprising a chromium-iron-nickel metallic phase.
13. The component of claim 12 wherein the lubricious oxides comprise ferrous oxides.
14. The component of claim 12 wherein the drive insert is part of a brake assembly having an increased dynamic stability against vibration during a braking event, as compared to an otherwise identical brake having a drive insert made of an SAE AMS 5385 cobalt-base alloy.
15. A component for an aircraft brake assembly, the component comprising:
a)a drive insert comprising a 17-4PH OX HT alloy having a wear surface, a chromium-iron-nickel metallic phase, and a base layer of iron oxide, chromium, nickel, and copper on the surface of the alloy, wherein the base layer is formed by heatinci a 17-4PH stainless steel alloy in flowing air for about two hours at about 1875° F. to 1925° F. with an air flow of about 10-30 cubic feet per hour, the 17-4PH stainless steel alloy having the following composition
CHEMISTRY
Element
Min. wt. %
Max. wt. %
C
—
0.060
P
—
0.025
S
—
0.025
Si
0.50
1.00
Mn
—
0.70
Al
—
0.05
Cr
15.50
16.70
Ni
3.600
4.60
Nb
0.15
0.40
Cu
2.80
3.50
Ta
—
0.05
Sn
—
0.02
N
—
0.05
Fe
Balance
Balance
, wherein the base layer forms an adherent coating of lubricious oxides comprising copper oxide, chromium oxides, and iron oxides, upon exposure of the insert to an oxidizing atmosphere at a temperature of greater than 815.6° C. (1500° F.).
16. The component of claim 15 wherein the drive insert is part of an aircraft brake assembly comprising a brake stack having a plurality of interleaved stator and rotor friction disks wherein at least one of the disks in the brake stack includes a plurality of torque drive notches spaced around its periphery.