Papers by Author: Juan Liu

Abstract: Two kinds of harding coatings: WC-12Co and CrC-25NiCr were made by active combustion-high velocity air flue (AC-HVAF). By the rotating disc test rig, the systematical experiments were carried to study the wear resistance and mechanisms of coatings on different test conditions: pure water cavitation and sandy water silt erosion. On the sandy water silt erosion test condition, the wear resistance of HVAF coatings is better than that of metal matrix. However, it is reverse on the other test condition. Basing on the scanning electron microscope (SEM) analysis, the surface morphology of coating surface after wear was studied. And the influence of adhesion strength, micro-hardness and porosity ratio of HVAF coating on wear resistance was researched in detail.

Abstract: Slurry pumps are used to transport the liquid fluids with solid particles in the industries. The materials of flow passage in a slurry pump are subjected to severe damage due to abrasive erosion. This paper compares the abrasive erosion for an engineering ceramics i.e. hot pressed Si3N4 ceramics and a high chrome cast iron i.e. Cr26 by laboratory test and industrial operation. The results indicate that the erosion rate of Cr26 is much larger than that of hot pressed Si3N4 ceramics under the same test conditions. That indicates that the engineering ceramics is a promising alternation of the expensive material such as Cr26 in the application of slurry pumps. It is noted that the erosion pattern such as scale ripple has the similar features for both materials, even the hardness of hot pressed Si3N4 ceramics is much higher than Cr26. Further, the scale ripple is suspected to be originated from the relatively weak grain boundary and enhanced by cavitation.

Abstract: A slurry pot tester was used to evaluate the erosion behavior of alumina (Al2O3), zirconia toughened alumina (ZTA), and silicon nitride ceramics. The eroded surface of sample was studied by scanning electronic microscope and the primary erosion wear mechanisms for ceramic materials were analyzed. On the same experimental condition, erosion wear resistance of materials follows this rule: Si3N4>ZTA>Al2O3. The key factor affecting erosive wear performance of ceramics is their microstructure. The primary erosive wear mechanisms for Al2O3, ZTA and Si3N4 ceramics are lateral crack propagation, whole grains pulled out and plastic deformation. The erosive wear performance of Si3N4 ceramic is the best in this experiment, due to their microstructure morphology with elongated grains.

Abstract: Engineering ceramics have a high application potential for wear-protection of different equipment used for electric power generating, mining and mineral industries. The ZTA (zirconia toughened alumina) and alumina (92%, 95%) have been prepared. Effects of varying the impact velocity and volume content of erodent particle and erosive time are investigated. Scanning electron microscopic examination of the eroded ceramic surfaces provides insights into the erosive wear mechanisms. The material removal processes include chipping out of lateral cracks caused by impact of the erodent particles, grain boundary cracking and grain pull out, as well as plastic deformation caused by the repeated sliding and impact of the particles.