Influence of Sintering Temperature on the Mechanical Properties of Alumina Springs

Low-pressure injection molding (LPIM) was used to produce helical alumina springs. Three sets of springs were sintered at 1550 degrees C, 1600 degrees C and 1650 degrees C to observe the effects on spring constant and fracture stress. Sintered alumina springs were obtained with densities ranging from 94.0% to 97.5% of the theoretical limit. Spring constants were measured from room temperature up to 1100 degrees C. Fracture stress data were analyzed according to Weibull statistics and the method of maximum likelihood. Upon increase of sintering temperature from 1550 degrees C to 1650 degrees C, the spring constant and the Weibull characteristic strength of the alumina springs increases by 15% and 32%, respectively. On the other hand, sintering temperature has a negligible influence on Weibull's modulus. This is because internal bubbles and surface defects introduced in the production stage of the ceramic springs more than the reduction in porosity with increasing sintering temperature are critical in determining the reliability of the ceramic springs.