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An evaluation of the life test for 80Ni-20Cr alloys specified in ASTM B 76 has been made. It is shown that the emissivity of the wire is not constant after the pretreatment but requires about an additional four hours at the test temperature. The convection coefficient increases continuously during the life test causing more power to be dissipated by convection as the test progresses.
The small resistance change during the test is a balance between relatively large changes in both the resistivity and the dimension of the sample. A unique expression is developed that enables the change in resistivity to be determined from electrical data. Calculated decreases in chromium and in the diameter of the wire are compared to experimental values. Failure occurs after the alloy has lost about 6 percent chromium and about 10 percent of its cross-sectional area.
Vice presidentMember of ASTM, Engineering and Research, Wilbur B. Driver Co., Newark, N. J.
Stock #: JTE10102J