The influence of interfacial structure on the mechanical properties of liquid-phase-sintered aluminum-ceramic composites

The effect of interfacial structure on the mechanical properties of aluminum-ceramic composite materials fabricated by liquid phase sintering was studied. The composites were based on two matrix alloys (powder metallurgy alloys 201 and 601) reinforced with either Al2O3 or SiC particulate. Characterization of the interfacial regions demonstrated that the SiC-matrix interfaces were faceted whereas the Al2O3-matrix interfaces had an incomplete layer of a silicon-rich amorphous phase. Preferential attack of the particles during sintering is believed to cause the crystallographic facets to form on SiC. Locally high silicon concentrations near Al2O3 particles led to the formation of a glassy phase from the reduction of Al2O3. The difference in interfacial structure resulted in a higher particle-matrix bond strength and therefore improved composite mechanical properties in the SiC-reinforced materials compared with the Al2O3-reinforced materials. © 1990

Transient liquid-phase sintering of ceramic-reinforced Fe-based composites

The microstructural development of ceramic-reinforced iron-based composites has been studied. The composites were fabricated via powder metallurgy and liquid-phase sintering, a processing route which achieves near-net-shape with good ceramic particulate dispersion. Two matrix alloys were used, Fe-1 wt% C-1 wt% Si and Fe-2 wt% Cu; up to 30 wt% (≈36 vol%) yttria-stabilized zirconia in the form of ∼20 μm particles was added to these alloys. The microstructural evolution of these composite materials was studied by examining the densification rate and volume fraction of liquid phase as a function of time. Different particle/matrix interfaces developed in the two composites. A glassy silicon-rich layer formed in the Fe-1C-1Si-YSZ composites and a more limited crystalline layer was found in the Fe-2Cu-YSZ composites. © 1991 Chapman & Hall

Effect of plasma spray processing variations on particle melting and splat spreading of hydroxylapatite and alumina

Splats of hydroxylapatite (HA) and alumina were obtained via plasma spraying using systematically varied combinations of plasma velocity and temperature, which were achieved by altering the primary plasma gas flow rate and plasma gas composition. Particle size was also varied in the case of alumina. Splat spreading was quantified via computer- aided image analysis as a function of processing variations. A comparison of the predicted splat dimensions from a model developed by Madejski with experimental observations of HA and alumina splats was performed. The model tended to underestimate the HA splat sizes, suggesting that evaporation of smaller particles occurred under the chosen experimental conditions, and to overestimate the observed alumina splat dimensions. Based on this latter result and on the surface appearance of the substrates, incomplete melting appeared to take place in all but the smaller alumina particles. Analysis of the spreading data as a function of the processing variations indicated that the particle size as well as the plasma temperature and velocity influenced the extent of particle melting. Based on these data and other considerations, a physical model was developed that described the degree of particle melting in terms of material and processing parameters. The physical model correctly predicted the relative splat spreading behavior of HA and alumina, assuming that spreading was directly linked to the extent of particle melting