1. Keith Legg 847-680-9420 Overview of planned additional work HCAT Program Review Long Beach April 2001

2. 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)

3. 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

4. Keith Legg 847-680-9420 Compressively stressed coatings

5. Keith Legg 847-680-9420 Effect of residual compressive stress 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 tensile240 max compressive180 max tensile 300 max compressive

6. Keith Legg 847-680-9420 Effect of compressive residual stress 40 -100 0 0.0100.100 Stress (ksi) 0 Depth (inch) Substrate tensile Coating compressive Almen=-10 Note - equal area Almen=-20 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 surface Much smaller tensile stress deeper Compressive coating: Large compressive stress in coating Much smaller tensile stress subsurface Compressive coating + shot peen: Large compressive stress in coating Some reduction of compressive near-surface stress Some increase in tensile stress subsurface More compressive coating: Larger compressive stress in coating Larger increase in tensile stress subsurface More compressive coating + shot peen: Larger compressive stress in coating More reduction of compressive near-surface stress Larger increase in tensile stress subsurface Note: Stresses and depths are rough

7. Keith Legg 847-680-9420 BIG samples

8. 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 incidence Grazing incidence Normal incidence Normal incidence 1/4” Always near normal incidence Always near normal incidence 1 - 6” dia

9. 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 - ASAP

10. 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-progress Time scale - 2 or 3 months

11. 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-progress Time scale - begin shortly

12. 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 cracking Time scale - begin shortly

13. 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