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°C, 1600°C and 1650°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°C. Fracture stress data were analyzed according to W eibull statistics and the method of maximum likelihood. Upon increase of sintering temperature from 1550°C to 1650°C, the spring constant and the W eibull characteristic strength of the alumina springs increases by 15% and 32%, respectively. On the other hand, sintering temperature has a negligible influence on W eibull'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.