Abstract
Si3N4 ceramic is generally recognized as being difficult to machine due to its hardness and brittleness. It is necessary to control the normal load applied and the machined depth of the abrasive particles in order to eliminate surface/subsurface damage and defects during the grinding or polishing. In this study, scratch experiments were conducted on the polished surface of Si3N4 specimens to investigate the brittle–ductile transformation and the evolution of material removal mechanisms. In addition, the cracking behaviour of Si3N4 ceramic was characterized by indentation tests. The Vickers indentation produced cracks that exhibited good developmental integrity and geometric symmetry. The results indicate that the scratch track can be divided into three stages: the ductile regime, the brittle–ductile coexisting stage, and the brittle fracture regime. The critical loads and the corresponding penetration depths of cracking occurrence in Si3N4 were recorded. The material removal of Si3N4 ceramic was primary attributed to ductile regime removal when the load was less than 9.8 N. Microcrack initiation on the subsurface was observed when the penetration depth of the scratch tip reached 8 μm or the depth of the indentation tip reached 3.2 μm. Microcracks expanded rapidly as the load was further increased, resulting in a brittle fracture of the Si3N4 ceramic.
Highlights
Silicon nitride (Si3 N4 ) ceramics are widely used in various industrial sectors owing to their excellent physical–mechanical properties, such as their high strength, low density, high thermal shock resistance, low friction coefficient, high abrasion, and corrosion resistance
The results showed that the material removal exhibited three stages depending on the scratching depth: the ductile stage at a short depth, characterized by a smooth scratching groove, curled shavings, and tiny stick-slip lines; ductile–brittle fractures coexisted in the second stage, in which the initial radial cracks, tearing, and segmental chips appeared; brittle fractures dominated the final stage, with irregular debris and spalling occurring due to the intersection of lateral and radial cracks
To obtain the critical load and critical machined depth at which the plasticity/brittleness removal transition occurred when Si3 N4 ceramics were processed under normal temperature and pressure conditions, the microscopic strain and damage on the surface of Si3 N4 ceramic material under the action of abrasive particles were studied by scratch and indentation experiments using diamond tips
Summary
Silicon nitride (Si3 N4 ) ceramics are widely used in various industrial sectors owing to their excellent physical–mechanical properties, such as their high strength, low density, high thermal shock resistance, low friction coefficient, high abrasion, and corrosion resistance. Micromachines 2021, 12, 707 load, the feed rate to the grinder, and the size of the abrasive grains played critical roles in the material removal mechanisms in the polishing of Si3 N4 ceramic surfaces [14,15,16]. To obtain the critical load and critical machined depth at which the plasticity/brittleness removal transition occurred when Si3 N4 ceramics were processed under normal temperature and pressure conditions, the microscopic strain and damage on the surface of Si3 N4 ceramic material under the action of abrasive particles were studied by scratch and indentation experiments using diamond tips. The mechanism of microcrack propagation and brittle/ductile regime removal transitions are discussed according to the experimental results This could be used to identify different material removal stages to improve the machining and polishing of Si3 N4 ceramic components manufactured for different industrial applications
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
