Effect Of Carbon Nanotubes On The Microstructure And Mechanical Properties Of Ti(C, N)-based Cermets

This thesis is composed of five chapters. In the first chapter, the microstructure and properties of Ti(C, N)-based cermets as well as its development history were introduced. Meanwhile, the development trend of carbon nanotubes (CNTs) reinforce composites was also briefed.In chapter two, electroless plating of carbon nanotubes with Ni, experimental raw materials and preparation techniques of Ti(C, N)-based cermets were introduced briefly. In chapter three, we focused on the testing method of mechanical properties and token method of microstructure of Ti (C, N)-based cermets.In chapter four, the composition-microstructure-property relationship of Ti(C, N)-based cermets was discussed, and the effects of different carbon nanotubes content on the microstructure and mechanical properties of cermets were reviewed. The conclusion of this study can be summarized as follows:(1) The diffraction peaks of binder Ni move to the right with the increase of CNTs addition; this phenomenon is not visible until the CNTs addition reach to 2.5wt%, the diffraction peaks move to the right so visiblely that the third visible almost lap over the diffraction peaks of Ti(C, N). A part of CNTs transformed to be carbon and they reacted with Ti, W and Mo dissolved in Ni, to be rims, during the sintering stage. The radiuses of the atoms of Ti, W and Mo are all longer than Ni's, so the lattice aberration of Ni decreases with the increasing CNTs addition, and relevantly the glancing angle(θ) increases, accordingly the diffraction peaks move to the right.(2) There were classical dark core/grayish rim structure and bright core/grayish rim structure in the microstructure of cermets. The volume fraction of bright core/grayish rim increases with increasing CNTs addition, so dose the volume fraction of pore.(3) With the increase of CNTs addition, the amount of pores increases, the relative density decreases, and the extent of increasing or decreasing is a little until the CNTs addition reaches to 2.5wt%. Those are relative with the agglomerating of CNTs. The changing direction of hardness is basically accordant with that of relative density. The value of transverse rupture strength increases firstly, reaches the highest at 1.0wt%, and then decreases. The fracture toughness also increases firstly, and then decreases, and the peak value present at 2.5wt%. The reinforcing mechanism of CNTs observed is polling-out mechanism. The cermet obtains the best integrated mechanical properties at the CNTs addition of 1.0wt%.Chapter five summarized the whole thesis and gave some advices on future works.