Peak Stir Zone Temperature During Friction Stir Processing
GENERAL ELECTRIC GLOBAL RESEARCH BANGALORE (INDIA)
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The stir zone SZ temperature cycle was measured during the friction stir processing FSP of NiAl bronze plates. The FSP was conducted using a tool design with a smooth concave shoulder and a 12.7-mm step-spiral pin. Temperature sensing was accomplished using sheathed thermocouples embedded in the tool path within the plates, while simultaneous optical pyrometry measurements of surface temperatures were also obtained. Peak SZ temperatures were 990 deg C to 1015 deg C 0.90 to 0.97 TMelt and were not affected by preheating to 400 deg C, although the dwell time above 900 deg C was increased by the preheating. Thermocouple data suggested little variation in peak temperature across the SZ, although thermocouples initially located on the advancing sides and at the centerlines of the tool traverses were displaced to the retreating sides, precluding direct assessment of the temperature variation across the SZ. Microstructure-based estimates of local peak SZ temperatures have been made on these and on other similarly processed materials. Altogether, the peak-temperature determinations from these different measurement techniques are in close agreement.
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