Sintering behaviour of Co-28%Cr-6%Mo compacted blocks for dental prosthesis

In this work, the sintering behaviour of compacted CoCrMo blocks was investigated. The material was characterized in the as-received and sintered conditions through X-ray fluorescence, X-ray diffraction, density and scanning electron microscopy (SEM). The materials sinterability was evaluated by means of dilatometry and isothermal sintering at 800, 1000, 1200 and 1300 °C for different isothermal holding times. The particles of the as-received compacted blocks exhibited spherical shape with sizes ranging from 2 μm to 16 μm with a monomodal distribution. The as-received blocks presented a relative density of 57% and γCo(FCC) single-phase microstructure. After sintering, the specimens presented a γCo(FCC) + ɛCo(HCP) two-phase microstructure. Dilatometry data has indicated that the compacted blocks present discrete shrinkage anisotropy. Sintering starts close to 815 °C and a high shrinkage rate occurs near 1150 °C. The microstructure of the specimens sintered at 1200 °C has shown equiaxed grains and was highly dependent on the sintering time, with mean grain size ranging from 4.9 ± 1.3 μm (1200 °C – 60 min) to 28.4 ± 11.3 μm (1200 °C – 240 mm). The specimen sintered at 1200 °C – 240 min was in the final sintering stage and attained a densification near 90%. Sintering at 1300 °C – 60 min has led to exaggerated grain growth, with values of the order of 88.6 ± 16.7 μm and should be avoided because in addition it has not contributed to an increase in densification. The data from this work might be used to guide sintering cycles conditions for the manufacture of dental prostheses.