Synthesis, Mechanical Behavior, and Multi-Scale Tribological Performance of Carbon Nanoparticle Reinforced Ceramic Composites
Department of Materials Science & Engineering Seminar
3:00 PM, Monday, August 8, 2016
1065 Kemper Hall
Department of Materials Science & Engineering
Advisor: Julie Schoenung
Abstract: Carbon nanoparticles have attracted significant interest in the materials science community over the past decade because of their extraordinary mechanical and functional properties. This study investigated the effects of carbon nanoparticles on the synthesis, mechanical behavior, and tribological performance of ceramic composites. Specifically graphene nanoplatelet (GNP) reinforced Al2O3 and nanodiamond (ND) reinforced WC-Co systems were investigated. Carbon based nanoparticles such as GNPs and NDs are ideal reinforcements for ceramic composites because of their unique functional and mechanical properties. GNPs have exceptional mechanical properties such as yield strength and elastic modulus, along with superb functional properties such as thermal conductivity and electrical conductivity. NDs possess the highest hardness of any materials, very high elastic modulus, and have a very high thermal conductivity.
GNPs were demonstrated to affect the sintering of Al2O3 matrix composites by wrapping around grains, inhibiting diffusion, and thereby suppressing grain growth. High applied pressures (90 MPa) during sintering were observed to exacerbate grain growth suppression, while promoting attainment of fully dense ceramic composites. Higher applied pressures facilitated the wrapping of GNPs around grains, which promoted the onset of GNP induced grain growth suppression. Grain growth suppression compensated for the decreased hardness induced by the low strength of the GNP phase along the c-axis direction. GNPs enhanced the toughness and wear resistance of the nanocomposites by 21% and 39%, respectively, due to the intrinsic energy dissipating mechanisms such as GNP sheet kinking and sliding and GNP induced phenomena such as micro-cracking and crack bridging.
The addition of ND affected the tribological performance of thermally sprayed coatings. The presence of ND enhanced room temperature wear resistance. The high thermal conductivity of ND promoted the formation of a protective tribolayer. NDs became degraded at 300 °C, and resulted in wear resistance decreasing relative to the control WC-Co coating during 300 °C reciprocating sliding wear test. The addition of ND also affected the sintering of WC-Co-ND composites during spark plasma sintering, with the effects being highly dependent on ND content. Low contents had negligible effects, while high contents lead to high porosity. In the case of WC-Co composite reinforced with 10 vol.% ND the porosity took the form of high aspect ratio oriented laminar pores throughout the sample that are believed to enhance strain tolerance, thereby enhancing wear resistance. Significant improvements in wear resistance were observed in WC-Co samples reinforced with 10 vol.% ND at both micro and macro scales. The presence of ND, particularly at high volume fractions, enhanced the wear resistance by inhibiting decarburization and promoting the formation of a thick protective silica tribolayer during macroscale wear tests with a Si3N4 counter surface.
Biography: Andy Nieto is interested in nanocomposites, nanomaterials, nanomechanics, ceramics, sintering, and thermal spray.