Research On The Preparation And Abrasive Wear Properties Of Ti(C, N)-based Cermets With High Nitrogen Content

Ti（C,N）-based cermets is a promising candidate for conventional WC-based hardmetalsbecause of their excellent properties and lower costs. In this paper, series of Ti（C,N）-basedcermets with high nitrogen content were produced by vacuum sintering technology. The effects ofN additions on the microstructure and mechanical properties of Ti（C,N）-based cermets have beenstudied using SEM, EDX,XRD etc.In the first part of this dissertation, the influences of N element added by TiN on the cermetshave been studied. The results were obtained as follows: the hard phase core became finergradually and distribute evenly with the increase of nitrogen addition, the rim phase becamethinner. At the same time, the cermets exhibited higher abrasive wear resistance as the N additionincrease, and the abrasive wear morphology of the cermets changed from deep grooves formed byplastic deformation to small pits caused by micro brittle fracture. When the amount of N was3.6wt.%, the cermets had the best properties with TRS of1873MPa, hardness of89.9HRA and K_ICof20.7MPa m^1/2. However, when the N addition was further increased to4.2wt.%, the TRS andabrasive wear resistance of the cermets decreased due to a lower densification, and there weresome macro cracks and large holes in the abrasive wear morphology.The influences of N element added by solid solution of Ti(C_1-x,N_x) on the cermets have beenstudied. Some conclusions were drawn as follows: the grain size and porosity of the cermets weremore sensitive to the N/C ratio. The higher the N/C ratio was, the thinner the rim phases were andthe finer the grains became. But when the N/C ratio reached5/5, the grains grewed up which wereowned to the agglomeration of the hard phase. Meanwhile, the porosity of the cermets increasedwith the increasing of N/C ratio. On this basis, Ti(C_0.6,N_0.4) was introduced as the N sources toincrease the nitrogen content up to4.2wt.%, the cermets showed the best abrasive wear resistanceand properties with the TRS of1954MPa, hardness of89.5HRA and KICof22.4MPa m^1/2, whichwere all attributed to the fine and uniform grains as well as the moderate thickness of rim phases.The effects of AlN additions on the cermets have also been studied, it was found that themicrostructure and properties can be improved furtherly with a proper AlN addition. The inner rimphases turned thinner or even disappeared and the outer rim phases also became thinnersignificantly with the increasing of AlN addition. When the amount of AlN was too high, therewould be some grey phases without a core whose structure was similar to the outer rim phases. Asthe additions of AlN in the cermets increasing, the transverse rupture strength increased in the beginning and then decreased, the hardness increased steadily, the fracture toughness increasedgenerally after a first decrease, and the abrasive wear resistance improved gradually and thenreduced slightly. When the amount of AlN addition was1wt.%, the cermets have the best abrasivewear resistance and comperehensive properties with TRS of2051MPa, hardness of90.8HRA andK_IC of20.3MPa m^1/2.Finally, the typical abrasive wear process and mechanism as well as speed, load and abrasiveparticle size of working conditions of Ti（C,N）-based cermets have been studied. It was found thatthe abrasive wear mechanism could be abrasive cutted furrows, or micro brittle fracture andceramic hard phase particles pulled out, also may be a reflection of their combined effects.Theabrasive weight loss of the cermets increased as the speed got faster, but decreased when the speedcame to4100r/min. It had positive correlation with the load as it increased gradually, but risedfastly when the load turned to90N. However it showed approximate linear reduction tendency asthe mesh of abrasive particles increased.