Research On The Technology And Performance Of Short Fiber/Ti(C,N)-Based Cermets Composites

Ti(C,N)-based cermets are functional structure materials with excellent high temperature mechanical properties. Ti(C,N)-based cermets would be the preferred alternative products for traditional cemented carbides, and they are widely used in the mechanical machining, aerospace, geological exploration, petroleum chemical industry, auto parts and other fields. However, the shortage of the strength and toughness of the Ti(C,N)-based cermets strongly limits the wider application. Therefore, the toughness and strength improvement of Ti(C,N)-based cermets has become the focus of the domestic and foreign researches. At present, the researches of the toughness and strength improvement are mainly concentrated on optimization formulation of raw materials, refine of raw material particles and improving production technology and other methods However, the research of the fiber reinforced Ti(C,N)-based cermets has seldom reported up to now. In view of this, this study explores the feasibility and the effect of the added toughened fiber on the microstructure and mechanical properties of the Ti(C,N)-based cermets.Firstly, the effect of carbon fiber content on the microstructure and mechanical properties of the Ti(C,N)-based cermets were studied. The results showed that, with the increase of carbon fiber content, the sense of hierarchy at the fracture section was enhanced and the number of the exposing fiber gradually increased. The main micro-fracture mechanism of Ti(C,N)-based cermets were concluded as crack deflection, fiber debonding, fiber pullout, fiber fracture and fiber bridging. The density and the porosity of Ti(C,N)-based cermets decreased and increased, respectively. While the flexural strength of the cermets increased firstly and then decreased. When the carbon fiber content was 4wt%, the cermets achieved the best comprehensive mechanical properties, with the hardness of 12.25 GPa, the bending strength of 446.37 MPa which was increased by 9.3% when compared with the Ti(C,N)-based cermet without carbon fiber, indicating that the addition of appropriate amount of carbon fiber can improve the strength and toughness Ti(C,N)-based cermets.Secondly, the influence of carbon fiber surface modification, fiber coating thickness and the ball milling time of the modified fiber on microstructure and mechanical properties of the Ti(C,N)-based cermets were investigated separately. The results showed that the surface modification of carbon fibers can greatly improve the compatibility between the fiber and Ti(C,N) matrix, and thus could improve the overall performance of the cermets. Whereas, when the fiber coating was too thick, the porosity of the matrix became higher, and the defects became obvious, and finally the mechanical properties of materials decreased. On the other hand, the add fiber size became small, and thus the properties of the materials will be reduced, with the increasing ball milling time. The final conclusion was, the compatibility between the fiber and the matrix can greatly improve, and the controlled low porosity was obtained, when the thickness of the fiber was 1 μm, with ball milling time of 0.5 h.Lastly, the effect of the content of alumina fiber on the microstructure and mechanical properties of the Ti(C,N)-based cermets was studied. The results showed that, The density and porosity of the cermets changed slightly when the content of the added fiber was low. The flexural strength showed a trend of first increased and then decreased, with the further increase in the fiber content. When the amount of alumina fiber was 6wt%, the overall mechanical properties of the cermets reached the best.