Preparation And Tribological Properties Of TiC_x Reinforced Fe Matrix Composites

In order to obtain a kind of wear-resistant ceramic reinforced iron-based composites,this thesis focused on enhancement of the wettability between ceramic reinforcement and Fe matrix where a Ti₃AlC₂ ceramic with an unique nanolayered structure was applied as a precursor to prepare TiC_x reinforced Fe based by using in situ reactive hot pressing techniques.For the as prepared composites,the microstructures and the mechanical properties such as flexural bending strength,compressive and tensile strength and hardness as well as the friction coefficient and wear rate as a function of normal load and reinforcement content were characterized and tested.At the same time,the friction mechanism of the composites was also analyzed.The results show that:（1）To obtain TiC_x-Fe composites with different reinforcement volume content（7.6%,15.61%,24.07%,33.47%）,Ti₃AlC₂ powders（volume content varied from 10%to 40%）and Fe powders were selected as raw materials by hot pressing at 1400℃ for 30 min under Ar atmosphere first,then decreased the temperature to 1250 °C by applying a pressure of 30 MPa for 30min.After sintering,all the TihAlC2 powders were fully decomposed into TiC_x while Al atoms diffused into Fe matrix.（2）In the three point bending tests,the Fe based composites loaded with 7.6 vol.%TiC still kept excellent plastic that the specimens were not able to be fractured.In the tensile tests,the strength could reach 419 MPa with an elongation of 6.82%while in the Fe based composites loaded with 15.6 vol.%TiC_x,the bending strength and tensile strength as well as elongation could reach 987 MPa and 518 MPa and 5.19%,respectively.From the fracture surface of tensile specimens,large amount of dimples and tear ridges were observed indicating a good explanation of higher strength and toughness.However,increasing volume fraction of the ceramic reinforcements in the Fe matrix led to an increase of brittleness.Both in the bending and compression tests,it showed a brittle fracture nature.In the Fe based loaded with 24.07 vol.%TiC_x,the three point bending strength could reach 786 MPa while the compressive strength of the composites loaded with 33.47 vol.%TiC_x could reach 1356 MPa which was ascribed to the good wettability between the ceramic reinforcement and Fe matrix.（3）The friction coefficient of the as prepared composites was in the 0.36⁰.453 range under the dry friction condition with a speed of 10 m/s.The wear rate of the Fe based composites loaded with 7.6 vol.%TiC_x varied significantly with the changing of normal loads,it ranged from 8.69×10-6 mm3/N·m to19.25×10-6 mm3/N·m.However,in the other composites,the wear rate was relatively stable with changing of the normal loads and was kept in a small value range.The friction coefficient of TiC_x-Fe and 24.07%TiC_x-Fe-based composites decreases with the increase of velocity（5 m/s～20 m/s）,and the wear rate increases with the increase of velocity.This was mainly due to the formation of an oxidation layer in the friction surface.（4）Under a lubrication friction condition with a speed of 10 m/s,the friction coefficient of the composites firstly decreased and then became relatively stable with the increasing of the normal loads.It was reduced with the increasing reinforcement content and was in the 0.095～0.17 range.The wear rate was also reduced with the increasing reinforcement content but increased with the increasing normal loads and ranged in 2.17～5.91×10-7 mm3/N.f-m.The excellent friction properties were due to the formation of the oxidation films and lubrication oil.