IMPRESSION TEST OF 63SN-37PB EUTECTIC ALLOY

Impression creep and stress relaxation experiments on the Sn-Pb eutectic alloy were carried out in the RSA II instrument modified to use a 0.5 mm diameter cylindrical punch under 1.5-47 MPa punching stress and within a temperature range of 25 degrees C to 110 degrees C. Based on a power law between the impression velocity and stress or between the stress rate and stress, the exponent increased with stress from 1 to 3.5 within the temperature range 80-110 degrees C and 2.5 to 6 within the range 25-65 degrees C. These exponents were generally comparable to those reported in the literature. Because of the change of stress exponent, several mechanisms have been proposed. However, the stress dependence was found to obey a hyperbolic sine function of stress for all the stresses and temperatures studied. Similarly before using the hyperbolic sine function, the activation energy was found to increase with stress, an abnormal behaviour. Fortunately, after using the hyperbolic sine function, a single activation energy, 55 kJ mol(-1) was obtained. Based on the present data, a single mechanism of interfacial viscous shearing between the two eutectic phases is proposed for both creep and stress relaxation. In addition to the effect of stress and temperature, the impression velocity based on this model should be directly proportional to the punch radius and inversely proportional to the nth (n = 1-3) power of the size of phase particles. These predictions are consistent with available information in the literature.