EDDY CURRENT NONDESTRUCTIVE EVALUATION OF LASER GLAZED METALLIC SURFACES

LASER TREATMENT OF METALLIC SURFACES ENCOMPASSES HARDENING, ALLOYING, CLADDING, PENETRATION WELDING AND LASER GLAZING DEPENDING UPON THE PROPERTIES OF THE LASER AND THE DURATION OF APPLICATION. OF INTEREST IN THIS PROPOSAL IS LASER GLAZING WHICH UTILIZES THE HIGH POWER DENSITIES OF FOCUSED LASER BEAMS IN CONJUNCTION WITH SHORT INTERACTION TIMES TO CONFINE THE THERMAL EFFECTS TO A SHALLOW SURFACE LAYER. THIS LAYER BECOMES AMORPHOUS IN NATURE AND EXHIBITS FAVORABLE CHARACTERISTICS INCLUDING HARDNESS, CORROSION RESISTANCE AND HIGH FRACTURE STRENGTH. THERE IS A NEED TO CONTROL THE THICKNESS OF THE SURFACE LAYER AND TO CHARACTERIZE ANY DEFECTS IN THE SURFACE LAYER AND THE ADJACENT SUBSTRATE. THIS PROPOSAL SUGGESTS THE APPLICATION OF EDDY CURRENT NONDESTRUCTIVE EVALUATION (NDE) TECHNIQUES TO ACHIEVE CONTROL OF SURFACE LAYERS AND TO IDENTIFY DEFECTS. EDDY CURRENT METHODS RELY ON THE INTERACTION OF A TIME-VARYING ELECTROMAGNETIC FIELD WITH THE MATERIAL UNDER TEST WITH THE RESULTS OBTAINED BY PROBES MOUNTED EXTERNAL TO THE MATERIAL SURFACE. THE TARGET OF OPPORTUNITY IS THE COMBINATION OF EDDY CURRENT NDE METHODS WITH LASER GLAZING TECHNIQUES TO ACHIEVE THE OBJECTIVES OF ESTABLISHING A SUITABLE LASER GLAZING MODEL, DETERMING THE APPLICABILITY OF EDDY CURRENT NDE TECHNIQUES, MEASURING PROPERTIES OF LASER GLAZED LAYERS IN KNOWN ALLOYS AND IN CAST IRON AND HIGH SPEED STEELS OF INTEREST IN ENERGY-RELATED INDUSTRIES, AND OPTIMIZING THE SYSTEM PARAMETERS. THE ANTICIPATED RESULT WOULD BE A RESEARCH TOOL FOR MONITORING AND CONTROLLING THE DEPTH OF MELT AND FOR CHARACTERIZING DEFECTS IN SURFACE LAYERS AND ADJACENT SUBSTRATE MATERIALS. THIS WOULD FACILITATE THE CONTROLLED FABRICATION OF QUALITY AMORPHOUS FILMS THAT EXHIBIT SUPERIOR PROPERTIES WITH RESPECT TO CORROSION AND STRENGTH.