SURFACE STRENGTHENING OF ADVANCED STRUCTURAL CERAMICS WITH HIGH ENERGY ELECTRON BEAMS

THE USE OF HIGH ENERGY (E~ 1-5 MeV) ELECTRON BEAMS (HEEB) AT HIGH AVERAGE POWER (P~200 kW - 1MW) ALLOWS THE INTRODUCTION OF DEEP-LAYER COMPRESSIVE STRESSES (Q~100,000 PSI) INTO THE SURFACE OF ADVANCED STRUCTURAL CERAMICS. SURFACE STRESS LEVELS OF THIS MAGNITUDE WILL RESULT IN A SIGNIFICANT ENHANCEMENT OF BEND STRENGTH, REDUCING FRACTURES RELATED TO THE AS-FABRICATED SURFACE DEFECT POPULATION. CERAMICS WITH HEEB-INDUCED, DEEP-LAYER (2-10 MM) COMPRESSIVE STRESSES WILL ALSO TOLERATE DEEPER SURFACE ABRASION DURING USE. THE STRENGTHENING PROCESS UTILIZES THE DEEP PENETRATION VOLUMETRIC HEATING ABILITY OF HIGH ENERGY ELECTRON BEAMS TO ESTABLISH A TEMPERATURE GRADIENT AT THE CERAMIC SURFACE. FOR HIGH TEMPERATURE STRUCTURAL CERAMICS WITH LOW CREEP RATES, THE GRADIENT MUST BE MAINTAINED FOR SEVERAL MINUTES AT HIGH (1500-2200oC) TEMPERATURES. SCIENCES RESEARCH LABORATORY (SRL) HAS DEVELOPED A NEW GENERATION OF PULSED INDUCTION LINEAR ACCELERATORS WHICH ALLOW RELIABLE, COST EFFCIEINT PRODUCTION OF HIGH AVERAGE POWER ELECTRON BEAMS WITH THE NECESSARY PARAMETERS FOR CERAMIC SURFACE STRENGTHENING. A UNIQUE FEATURE OF THESE ACCELERATORS IS THE HIGH REPETITION RATE (>5000 PPS) ALL-SOLID-STATE PULSED POWER DRIVERS WHICH MAKE THESE ACCELERATORS SCALABLE TO MW POWER LEVELS AT AN ELECTRON BEAM COST OF LESS THAN $2/WATT. THE INDUCTION ACCELERATOR TECHNOLOGY DEVELOPED BY SRL IS CONSISTENT WITH THE POWER DENSITIES (100-1000 W/CM2) AND BEAM ENERGIES (2-5 MEV) REQUIRED FOR CERAMIC STRENGTHENING. A HEEB CERAMIC STRENGTHENING SYSTEM BASED ON THIS TECHNOLOGY IS DESCRIBED. EXPERIMENTS TO BE CONDUCTED IN PHASE II, BASED ON PHASE I SIMULATIONS AND DESIGNS WILL DEMONSTRATE THE INTRODUCTION OF SURFACE COMPRESSIVE STRESSES INTO THE HIGH TEMPERATURE STRUCTURAL CERAMICS RELEVANT TO DOD APPLICATIONS. ANTICIPATED BENEFITS: ADVANCED, HIGH PURITY CERAMICS ARE CANDIDATE STRUCTURAL MATERIALS FOR USE IN ENGINES AT HIGH TEMPERATURES. ENHANCED SURFACE PROPERTIES ARE NEEDED TO IMPROVE THE FRACTURE RESISTANCE OF THESE MATERIALS. THE PROPOSED PROCESS WILL INTRODUCE LARGER SURFAVE COMPRESSIVE STRESSES AND PRODUCE THIS STRENGTHENING LAYER TO GREATER DEPTH THAN IS POSSIBLE WITH CONVENTIONAL METHODS.