Processing and properties of zirconia-CNT composites

• Main Author: Melk, Latifa
• Other Authors: Universitat Politècnica de Catalunya. Departament de Ciència dels Materials i Enginyeria Metal·lúrgica, Luleå tekniska universitet, Anglada Gomila, Marcos Juan, Antti, Marta-Lena
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universitat Politècnica de Catalunya 2016
• Subjects: Àrees temàtiques de la UPC::Enginyeria dels materials; Luleå
• Online Access: http://hdl.handle.net/2117/96356; http://hdl.handle.net/10803/396100; https://doi.org/10.5821/dissertation-2117-96356

La consulta íntegra de la tesi, inclosos els articles no comunicats públicament per drets d'autor, es pot realitzar prèvia petició a l'Arxiu de la UPC Cotutela Universitat Politècnica de Catalunya i Luleå tekniska universitet In the last decades there has been growing interest in developing ceramic materials with high fracture toughness (Klc) and strength for structural applications. In the specific case of 3 mol% yttria-doped tetragonal zirconia (3Y-TZP), KIC can be increased by promoting phase transformation from tetragonal (t) to monoclinic (m) phase in front of a propagating crack tip referred to as transformation toughening. However, the stronger the tendency for stress induced transformation, the higher the risk for prematura spontaneous t-m transformation in humid atmosphere. This phenomenon, which is referred to as ageing, hydrothermal degradation or low temperatura degradation (LTD) induces microcracking and loss of strength and limits the use of 3Y-TZP. The resistance to L TO can be increased by reducing the grain size into the nanoscale by using Spark Plasma Sintering (SPS). However, the reduction of grain size may reduce t-m phase transformation in front ofthe crack tip and therefore fracture toughness may decrease. One way to enhance KIC is the incorporation of a second phase as a toughening mechanism into zirconia matrix. In the present study, M.JltiWalled Carbon Nanotubes (l'v1VVCNTs) were used to reinforce zirconia matrix. A novel method was developed in this project in order to measure the "true" fracture toughness of small cracks of 3Y-TZP/CNT composites. The method is based on producing a very sharp notch using Ultra-short Laser Ablation (UPLA). The same method was also applied to a high toughness zirconia ceramic 12Ce-Zr02 with 300 nm grain size, which has much higher plateau fracture toughness than SPSed 3Y-TZP with 177 nm grain size. Moreover, the wear behaviour of zirconia/CNT composite was investigated by studying the effect of CNTs on the friction coefficient and the wear rate of the ...