Preparation And Properties Of Co-continuous Phases TiC_x-Cu Cermets

Cermets material with an excellent combination of mechanical properties,physical and chemical properties are desirable for a wide range of critical applications due to their high hardness and strength,high elastic modulus,corrosion and wear resistance,good electrical and thermal conductivity,which,thus,make them promising candidates used as cutting tools,high-speed bearings,heat-resistant coatings,wear-resistant parts,anti-ablative materials,etc..However,a major bottleneck in the widespread commercial use of cermets is their poor wettability between ceramic and metal phases,the low toughness,as well as the thermal mismatch in an environment of sudden rise or fall in temperature.Leveraging on these issues,this study was aimed at developing a new type of cermet with comprehensive performance and higher value in the application by exploring an effective method to improve the interfacial wettability and bonding condition,designing and tailoring the microstructure and subsequent heat treatment process of as-prepared materials.In this work,we present the first successful synthesis of co-continuous TiC_x-Cu cermets by two-step process involving the preparation of non-stoichiometric porous TiC_x(x=0.5?0.7)preforms using Ti powder and nano acetylene carbon black as the initial raw material,followed by impregnating molten Cu into the porous TiC_x under pressureless conditions.A systematic exploration of impact factors including porosity,grain size and morphology of TiC_x as well as the stoichiometric ratio of C to Ti on the microstructure and phase morphology of TiC_x-Cu were conducted.The strength,toughness,hardness,and thermal shock resistance of fabricated samples were tested.We highlighted the analysis of correlation between microstructure and practical performance.Based on the investigation aforementioned,the fracture toughness and the strength of TiC_x-Cu material could be further improved by conducting subsequent solution treatment.Remarkable outcomes are summarized as follows:(1)The structure of porous TiC_x preform was mainly dominated by the amount of foam-introducing agent,sintering temperature,holding time and initial stoichiometric ratio of C:Ti.The porosity of TiC_0.5 preforms was linear proportion to the amount of foam-introducing agent.With the increase of sintering temperature and extension of holding time,the grain of TiC_0.5 grew up through mutual annexation,leading to more compact preform with reduced porosity.When the initial stoichiometric ratio of C to Ti increased from 0.5 to 0.7,the x value of TiC_x tend to coordinate correspondingly from0.57 to 0.69.In addition,the increase of carbon content will hinder the grain growth of TiC_x and the shrinkage of the preform,resulting in the decrease of grain size and the increase of porosity.(2)Co-continuous TiC_x-Cu cermets with various metal content,different TiC_x grain morphology and changeable stoichiometry of TiC_x were prepared by pressureless infiltration.The results showed that reactive wetting behaviors between Cu and TiC_xgive rise to the strong interface.During the infiltration process,molten Cu reacted with Ti originating from TiC_x to form a new Cu₄Ti alloy phase,which will induce the metal phase to enter the inside of TiC_x grains and form the special root-like inner crystal structure.The x value in TiC_x of cermets increased in comparison with that in preforms before infiltration.Herein,the TiC_xpreforms with different x values(x=0.5,0.6,0.7)tend to be0.76 after Cu infiltration since of the deintercalation of Ti atoms out of TiC_x preform and reaction between Cu and TiC_x.(3)Co-continuous TiC_x-Cu cermets showed high strength and toughness due to their special microstructure and strong interface bonding.The flexural strength and fracture toughness of TiC_0.5-Cu cermets were determined to be 801±42 MPa and 10.9±1.1MPa·m^1/2,respectively.The flexural strength and fracture toughness of TiC_0.7-Cu cermets could be reached to 1091±59 MPa and 14.8±0.6 MPa·m^1/2,respectively.The fracture morphology of the material shows three mixed modes,ductile fracture of metal phase,transgranular fracture of ceramic grain,and metal root pulling out in the grain.The combined mechanisms of crack deflection,bridging,bifurcation and metal phase pullout during crack propagation significantly increase the fracture energy of the material,thus improving the strength and fracture toughness of the fabricate cermet material.(4)The thermal shock behavior of TiC_0.5-Cu cermets at different temperatures was tested.The results showed that the residual strength tended to reflect non-monotonically with the increase of thermal shock temperature.When the thermal shock temperature was lower than 800°C,the residual strength decreased with the increase of temperature.When quenched at 800°C,the residual strength was 535 MPa,which was 33.2%lower than that before thermal shock.When the thermal shock temperature rose to 1000°C,the residual strength increased by 6.4%to reach 852 MPa.The strength was just decrease slightly after repeated thermal shocks at 1000°C even for 20 times.This unique thermal shock resistance can be attributed to the grain refinement of metal phase caused by rapid cooling from 1000°C and the further adaptation optimization of interface phase.(5)The samples of TiC_0.5-Cu,TiC_0.6-Cu and TiC_0.7-Cu were solution heat treated.The effects of solution temperature and time on the strength and toughness of the cermets were explored.The results showed that subsequent treatment process significantly improve the fracture toughness of the material,which,meanwhile,leading to the enhancement of strength to different degrees.However,for different x values,the optimal aging temperature and time had different effects.For TiC_0.5-Cu,when soluted at 925°C for 60 min,the fracture toughness and the strength increased by 32.1%and 16.7%,reaching to 14.4±0.5 MPa·m^1/2 and 935±35 MPa,respectively.For TiC_0.6-Cu,when soluted at 925°C for 30 min,the fracture toughness and the strength increased by 15.6%and 6.2%,reaching to 16.3±0.6 MPa·m^1/2 and 963±23 MPa,respectively.For TiC_0.7-Cu,when soluted at 925°C for 10 min,the fracture toughness and the strength increased by11.5%and 4.9%,reaching to 16.6±0.8 MPa·m^1/2 and 1145±84 MPa,respectively.The excellent results were mainly caused by the grain refinement and solid solution strengthening of metal phase during heat treatment.