Keith Legg 847-680-9420

Overview of planned additional work

HCAT Program ReviewLong Beach

April 2001

Keith Legg 847-680-9420

What seems to work best? General coating conditions

Too hard (>1300HV) is bad excessive alloying into Co?

Overheating is bad alloy tempering particle overheating and

carbide dissolution Substrate heating improves

splat flow Full gage vs patch coatings

little or no difference (if anything recent data show more tendency for patch delamination)

Recently optimized coatings at Hill AFB doing very well

Survive 240 ksi at R=-0.5 Almen = 10 compressive

Strongest determinant of compressive stress is particle size

Ideal phase structure not yet known

Prop hub data show excellent results

High compressive residual stress (Almen = -20)

Keith Legg 847-680-9420

Issues to be resolved

Demonstration of coating integrity to 240 ksi, R=-1

Test on realistic sample size

Stress corrosion cracking If we need higher coating

compressive stress, does that worsen SCC?

WC-Co vs WC-CoCr In past WC-Co generally

showed less spalling than WC-CoCr. Recent work by Jerry Schell shows little difference.

Can we get equivalent optimized performance?

Optimization and testing Tests of full-scale pins

and cylinders Tests of high residual

stress and newly optimized coatings

Coating optimization for spalling resistance

Note - HVOF coatings can and should be optimized for desired property

Limited SCC and fatigue tests

to ensure spall-optimized coating does not cause problems elsewhere

Keith Legg 847-680-9420

Compressively stressed coatings

Keith Legg 847-680-9420

Effect of residual compressive stress

-400

-300

-200

-100

0

100

200

300

0 10 20 30 40

Stre

ss (

ksi)

Almen=0Almen=-10Almen=-20

Compressive residual stress decreases crack initiation and propagation

Reduces damaging tensile stress, increases compressive stress

might cause delamination if interface cracks build up

Compressive residual stress decreases crack initiation and propagation

Reduces damaging tensile stress, increases compressive stress

might cause delamination if interface cracks build up

240 max tensile

240 max compressive

180 max tensile

300 max compressive

Keith Legg 847-680-9420

Effect of compressive residual stress

40

-100

0 0.010 0.100

Str

ess (

ksi)

0

Depth (inch)

Substrate tensile

Coating compressive

Almen=-10Note - equal area

Almen=-20

Based on Wigren, Volvo Aerospace - actual numbers very rough

Based on Wigren, Volvo Aerospace - actual numbers very rough

Conclusion:• tensile<<compressive• substrate fatigue and SCC will be a little worse, but effects will be low for reasonably attainable compressive coating stresses

Shot peen:Large compressive stress near surfaceMuch smaller tensile stress deeper

Compressive coating:Large compressive stress in coatingMuch smaller tensile stress subsurface

Compressive coating + shot peen:Large compressive stress in coatingSome reduction of compressive near-surface stressSome increase in tensile stress subsurface

More compressive coating:Larger compressive stress in coatingLarger increase in tensile stress subsurface

More compressive coating + shot peen:Larger compressive stress in coatingMore reduction of compressive near-surface stressLarger increase in tensile stress subsurface

Note:Stresses and depths are rough

Keith Legg 847-680-9420

BIG samples

Keith Legg 847-680-9420

Small samples vs large

1/4” dia samples have non-optimal HVOF, but high current density gives better EHC

Most parts are >1” OD LG inner cylinders usually>2.5”

On small parts coating is larger percentage of total area

coating may carry significant load

especially thick coatings

Grazing incidenceGrazing incidence

Normal incidenceNormal incidence

1/4”

Always near normal incidence

Always near normal incidence

1 - 6”dia

Keith Legg 847-680-9420

Large sample testing

NAVAIR (Eui Lee) Evaluate spalling for full-

size samples Axial stress Stop-frame testing Evaluation of spalling

and delamination thresholds

Metcut (Phil Bretz) Same sample OD/ID,

design somewhat different

Stop-frame testing Evaluation of different

coating parameters based on results of small-sample tests

Evaluation of spalling thresholds

Time scale - ASAPTime scale - ASAP

Keith Legg 847-680-9420

Testing of landing gear cylinders

A-10 cylinder testing - Hill AFB

WC-Co Testing of actual

cylinders with newly-optimized coating done at OO-ALC

Flexure, rather than axial loads (simulates use)

Primary concern is performance of thick repair coatings

Simulated LG piston tests - BF Goodrich

WC-CoCr 5” and 10” dia simulated

LG pistons (not actual parts)

Flexural fatigue tests (not specifically spalling tests)

Time scale - in-progressTime scale - in-progress Time scale - 2 or 3 monthsTime scale - 2 or 3 months

Keith Legg 847-680-9420

Rig testing

Messier-Dowty F-18 E/F NLG Drag Brace

fatigue/endurance test spectrum loading including launch loads

F-18 E/F NLG full scale fatigue test

BF Goodrich Bombardier Dash8-400

MLG full scale fatigue qualification test

spectrum loading

Time scale - in-progressTime scale - in-progress

Time scale - begin shortlyTime scale - begin shortly

Keith Legg 847-680-9420

Process validation for high load regime

Testing of high residual stress coatings Small and large samples

Determination of optimum coating structure/phases Evaluation of “good” and “bad” coatings Definition of optimum coating properties and

deposition methods Process optimization for best coating performance at

high load Process window determination Evaluation of fatigue (a few points to define curve) and

stress corrosion crackingTime scale - begin shortlyTime scale - begin shortly

Keith Legg 847-680-9420

Final outcome expected

Determine whether HVOF can reach performance requirements of worst case - launch and landing for carrier-based aircraft

Based on full-scale testing and rig tests

If HVOF coatings cannot be used for worst case

define spalling limits, if less than fatigue life (designer need)

define where HVOF WC can and cannot be used (depot need)

Establish validity, or otherwise, of small-sample tests

Optimal material and process definition for high-load components

Must have adequate window and be doable by OEMs, vendors, depots

Determine whether we will need different process or material definitions for high and low-load parts

Not possible with EHC