YIELD STRESS BEHAVIOR OF METAL INJECTION-MOLDING SUSPENSIONS AT ELEVATED-TEMPERATURES

Yield behaviour of metal injection moulding (MIM) feedstocks was studi ed using a cone and plate controlled stress rheometer. Four feedstocks consisting of 58 vol % carbonyl iron (with 2 wt % nickel) in differen t ethylene vinyl acetate (EVA):beeswax ratio binder systems were studi ed at six temperatures ranging from 130 to 180 degrees C. The yield st ress was found by extrapolating to zero shear rate of the measured dat a obtained using a controlled stress rheometer over low shear rate reg ime. The yield stress, tau(y), was found to increase with decreasing t emperature. An Arrhenius equation was used to relate the dependence of yield stress on temperature and the corresponding activation energy f or yield, E(y), can be determined. For a given temperture, feedstocks with higher EVA content exhibited higher tau(y) and E(y) Moreover, the effect of temperature on yield stress was found to be greater for fee dstocks with higher EVA content.