AMP_06_September_2021

FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 1 4 6 Ar atmosphere. Cooling was controlled by conduction through the copper grips (no forced air or quench cooling). Strain was monitored and controlled through measure- ment of the diameter at the midpoint of the samples close to the thermocouple attachment using a Keyence optical micrometer. The specimens were heated to below β-transus tem- perature (1775°F, 969°C), at 18°F/s (10°C/s) heating rate by direct resistance heating. Specimens were soaked at 1775°F (969° C) for up to 6.2 sec, and two cooling rates were employed for these tests: 1000° F/min (actual: 875 to 885°F/min due to cooling limitation) and 250°F/min. Tests were conducted under three strain conditions as summarized in Table 1: unconstrained cooling, con- stant strain rate to 3% total strain, and constant strain rate to 6% total strain. In the coefficient of thermal expansion (CTE)-only tests for samples 8D-1 and 9A-2, the sample was heated to the target temperature at a rate of 10°C/s without constraint on the sample. Maximum temperature was held for 2 sec, then samples were cooled at the rates indicated in Table 1 with no load on the specimen. Strain was mon- itored for these “free end” tests. In the remaining tests, the specimens were tested with strain rates that matched the cooling rates. Over the cooling temperature range, the sample was constantly strained; therefore, the fast- er cooling rates necessarily also included higher strain rates. The strain in the reported results represents the strain present due to thermal contraction only. In this short summary, only the 1000°F/min tests are shown (highlighted in Table 1). The full-study report will be pre- sented at Heat Treat 2021 and will be available in the proceedings. 7 TABLE 1 — GLEEBLE TEST CONDITIONS Sample Start temp, °F (°C) Cooling rate, °F/min Cooling rate, °C/min Final temp, °F (°C) Delay for cooling, sec Strain rate, s -1 Total applied strain 8D-1 1775 (969) 1000 538 1102 (594) 0 N/A CTE only 9A-2 1775 (969) 250 134 998 (537) 0 N/A CTE only 9A-1 1775 (969) 1000 538 1187 (642) 11 6.14 x 10 -4 3% 11A-1 1775 (969) 250 134 1025 (552) 11 1.56 x 10 -4 3% 8B-1 1775 (969) 1000 538 1189 (643) 11 1.22 x 10 -3 6% 7B-1 1775 (969) 250 134 1025 (552) 11 3.15 x 10 -4 6% Fig. 3 — Tests for 1000°F/min cooling rate for 3% and 6% strain. Stress for both tests are shown in blue shades, strain shown in red/orange, and temperature shown in black. 8