Abnormal Dynamic Grain Growth During Creep Deformation ofPowder-Metallurgy (PM) Grade Molybdenum Sheet

摘要

Commercial-purity, powder-metallurgy grade molybdenum sheet was subjected to tensile testing at slow strain rates, less than 1×10 -3 per second, and temperatures between 1300℃ and 1700℃. Above 1500℃, abnormal dynamic grain growth resulted after accumulation of a critical strain. Creep tests were performed under two conditions: constant-temperature strain-rate-change (SRC) tests over strain rates from 1×10 -6 to 5×10 -4 per second, and constant-temperature elongation-to-failure (EF) tests within this range. Data from these tests are used to characterize abnormal dynamic grain growth and its effect on creep deformation behavior of molybdenum. The molybdenum test coupons that underwent abnormal dynamic grain growth exhibited markedly different surface deformations and microstructures than the couponsrnthat did not. Mechanisms for the abnormal grain growth and for the causes of the differences in behavior as a function of temperature are discussed.