Metallurgical Evaluation of Grit Blasted Versus Non-Grit Blasted Iridium Alloy Clad Vent Set Cup Surfaces

摘要

Metallurgical evaluations were conducted to determine what, if any, grain size differences exist between grit blasted and non-grit blasted DOP-26 iridium alloy cup surfaces and if grit blasting imparts sufficient compressive cold work to induce abnormal grain growth during subsequent temperature exposures. Metallographic measurements indicated that grit blasting cold worked the outside cup surface to a depth of approximately 19 (micro)m. Subsequent processing through the air burn-off (635 C/4h) and vacuum outgassing (1250 C/1h) operations was found to uniformly recrystallize the cold worked surface to produce grains with an average diameter of approximately 8.5 (micro)m (American Society for Testing and Materials (ASTM) grain size number 11). Follow-on heat treatments at 1375 C, 1500 C, and 1900 C for durations ranging from 1 min to 70 h yielded uniform grain sizes and no abnormal grain growth from grit blasting. Abnormal grain growth was noted at the 1500 C and 1900 C heat treatments in areas of cold work from excessive clamping during sample preparation.