Effect of Direct Aging on Heat-Affected Zone and Tensile Properties of Electrospark-Deposited Alloy 718
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The degradation of high-temperature components in the aerospace industry becomes a greater concern with the use of higher operating temperatures and increased operating cycles. Although the repair of defects can extend component lifespans, welding often results in a heat-affected zone (HAZ) or fusion zone with reduced mechanical properties. Due to the low energy input of electrospark deposition (ESD), repaired components should be less susceptible to mechanical property deterioration. ESD of alloy 718 on solution-annealed and aged alloy 718 base metal is evaluated in the as-deposited and direct-aged condition. HAZ formation is measured at 80 µm on an annealed substrate and 40 µm on an aged substrate. Direct aging of depositions eliminates the heat-affected zone and introduces strengthening phases in the deposition that results in a hardness equivalent to that of the aged base metal. The yield strength of as-deposited and direct-aged alloy 718 depositions is equivalent to the annealed and aged base metal, respectively, whereas the ultimate strength is, respectively, 16 and 8 pct lower. Decreased ultimate strength is attributed to lower fracture toughness of brittle secondary phases and splat boundaries from the ESD process that remain after the direct aging heat treatment.
This work was performed with funding support from the Natural Sciences and Engineering Research Council of Canada (NSERC), Huys Industries, and the CWB Welding Foundation, in collaboration with the Centre for Advanced Materials Joining and the Multi-Scale Additive Manufacturing Lab at the University of Waterloo.
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