Preparation And Properties Of Ti(C,N)Matrix Composites Reinforced By Silicon-containing Ceramic Phase

Ti（C,N）is an important material in the fields of ceramics and refractories.Owing to its difficulties in sintering and poor oxidation resistance,the application of Ti（C,N）materials has been limited.In this paper,Ti（C,N）matrix composites were prepared by the pressureless sintering method.By introducing reinforcing phases（such as Si₃N₄,Si C,mullite,etc.）and sintering aids（such as Y₂O₃）,the Ti（C,N）matrix composites with excellent properties were prepared at a lower cost.Meanwhile,the effects of raw material ratio,sintering temperature,holding time,and the addition of sintering aids on the phase composition,microstructure,and properties of Ti（C,N）matrix composites were investigated.Based on the above work,the following conclusions can be drawn:（1）Ti（C,N）powder,Si₃N₄powder,and Al/Si/Al₂O₃composite powders were used as raw materials to prepare Si₃N₄-Ti（C,N）andβ-Sialon-Ti（C,N）composites at1450-1600℃.The mechanical properties and oxidation resistance of Ti（C,N）matrix composites were improved by Si₃N₄andβ-Sialon,and the Ti（C,N）grains were refined by Si₃N₄andβ-Sialon.The apparent porosity and the cold modulus of rupture of Ti（C,N）matrix composites was 38.8-44.8%and 20.4-37.3 MPa,respectively.Also,the resistance corrosion of Ti（C,N）-based composites was good.（2）Si C-SiO₂-Ti（C,N）composites were prepared by in-suit carbothermal reduction nitridation method with TiO₂powder,C powder and Si powder as raw materials at1400-1600℃in nitrogen atmosphere.The bonding between grains,the mechanical properties,and oxidation resistance of the composite materials were improved by the generation of Si C and SiO₂from Si powders.However,it would reduce the corrosion resistance of the materials.When the mass ratio of TiO₂,C,Si and Y₂O₃was 81:14:5:1,the comprehensive properties of the composite after holding at 1600℃for 1 h were excellent:the relative density,the cold modulus of rupture,and the elastic modulus were99.2%,242.2 MPa and 230.3 GPa,respectively.And the oxidation resistance was good.After adding Y₂O₃,Y₂O₃reacted to generate Y₂Si₂O₇,which filled the pores and enhanced the bonding between Ti（C,N）grains.Ca O was used to replace part of TiO₂in the raw material,and a new phase Ca SiO₃was formed.The mechanical properties of the composite material did not decrease significantly,and the corrosion resistance was improved.（3）TiO₂powder,C powder and Al/Si/Al₂O₃composite powders were used as raw materials to prepare mullite-Ti（C,N）composite material with the carbothermal reduction nitridation method at 1400-1600℃in nitrogen atmosphere.The mullite-Ti（C,N）composite material contained Ti（C,N）,mullite and a small amount of SiO₂.The columnar or granular mullite played the role of deflecting cracks and refining Ti（C,N）grains.As a result,part of SiO₂transformed from crystalline to amorphous,which promoted sintering,improved the density,mechanical properties and oxidation resistance of the composite,and reduced the corrosion resistance of the composite material.When the mass ratio of TiO₂powder,C powder and Al/Si/Al₂O₃composite powders was 72.47:12.53:15.00,the comprehensive properties of the composite material after holding at 1500℃for 2 h were excellent:the relative density,cold modulus and elastic modulus were 97.9%,158.0 MPa and 138.5 GPa,respectively.After adding 4 wt%of Y₂O₃,YAG(Y₃Al₅O₁₂)was formed.YAG promoted the discharge of gas and inhibited the growth of Ti（C,N）grains,which reduced the sintering temperature of the composite material to 1450℃.The relative density and cold modulus of rupture of the composite were 98.9%and 148.3 MPa,respectively.