Preparation And Properties Of Two-dimensional Ti₃C₂ MXene Reinforced Titanium Matrix Composites

Titanium Matrix Composite（TMC）can significantly improve strength and service temperature by introducing reinforcing phase in titanium or titanium alloy,and has great potential for application in critical components in aerospace,weaponry,and military industries.Among them,two-dimensional nanolaminate materials are considered as ideal reinforcing phases for TMC due to their high specific strength,high specific modulus and better structural properties.However,when 2D materials/TMCs prepared by powder molding techniques（powder metallurgy and 3D printing）,structural damage of 2D materials,reaction with Ti matrix,and failure to retain 2D materials have occurred,resulting in weak strengthening effect of 2D materials and poor material properties.The root cause of the above problems is that the strengthening mechanism of 2Dmaterials in Ti matrix is not clear,and it is not possible to design and prepare 2D materials to enhance TMC through the strengthening mechanism effectively,so it is not possible to make the maximum effect of 2D materials.Currently,the main preparation methods of composite powder of 2D materials and Ti include ball milling method and liquid phase reduction method.The former mixes 2D materials with Ti powder through mechanical external force,but the strong van der Waals forces in 2D materials lead to difficulty in uniform dispersion during the ball milling process,while the external force injection tends to destroy the structural integrity of 2D materials,resulting in the increased reactivity of 2D materials and difficulty in retaining them after forming;the liquid phase reduction method is By chemically treating the 2D material,the oxidized 2D material is easily dissolved in the solution,and the oxidized 2D material is attached to the surface of Ti powder by using the liquid phase method,and finally the composite material is reduced at high temperature to obtain a kind of reduced 2D material.However,after solving the problem of uniform distribution of 2D materials in Ti powder,new problems also arise.The structure of 2D materials after oxidation and reduction is defective,which tends to reduce their mechanical properties,and finally,the sintering process also causes an increase in reactivity,which eventually leads to the inability of 2D structures to be retained in the matrix and produce new substances.At present,there is still a lack of a monolayer,uniformly coated,highly pure,and less reactive 2D material@Ti composite powder during sintering,which seriously limits the development and application of 2D material/TMC.To address this problem,this thesis proposes an innovative idea of using a more stable chemical structure of two-dimensional lamellar Ti₃C₂MXene material instead of two-dimensional lamellar graphene material,together with solid-liquid fluidized bed coating technology and gas-solid fluidized bed debinding technology to coat a single-layer,uniform and high-purity Ti₃C₂MXene on the surface of Ti powder to construct a highly stable Ti₃C₂MXene@Ti composite powder.Specifically,the accordion-like Ti₃C₂MXene was delaminated and exfoliated into Ti₃C₂MXene dispersion by DMSO intercalation technique,and the surface functional group modification of the monolayer Ti₃C₂MXene dispersion was carried out by using CTAB（Cetyl Trimethyl Ammonium Bromide）cationic modifier,which successfully changed the surface negativity of monolayer Ti₃C₂MXene to positive.Combining the characteristics of solid-liquid fluidized bed for uniform flow of liquid and the technical characteristics of gas-solid fluidized bed for uniformly blowing the powder in suspension,the preparation of monolayer,uniformly coated and surface pure Ti₃C₂MXene@Ti composite powder was achieved.Finally,the composite powder was processed and shaped by rapid sintering（SPS）technology to achieve uniform dispersion and effective retention of Ti₃C₂MXene within the Ti matrix,which in turn improves the mechanical properties as well as facilitates the study of strengthening mechanisms.By studying the regulation laws of accordion-like Ti₃C₂MXene monolayer exfoliation and uniform encapsulation,the Ti₃C₂MXene retention behavior during rapid sintering,the conformational relationship between Ti₃C₂MXene/TMC organization and properties,and the strengthening mechanism and strengthening efficiency of second-phase Ti₃C₂MXene in Ti matrix,the following innovative results were achieved.（1）The feasibility of preparing monolayer Ti₃C₂MXene dispersions from accordion-like Ti₃C₂MXene after DMSO（dimethyl sulfoxide）intercalation treatment was confirmed,and it was verified that CTAB cationic modifier could change the Ti₃C₂MXene surface functional groups and finally make the monolayer Ti₃C₂MXene surface positively charged,which was sufficient for the subsequent homogeneous coating of Ti₃C₂MXene.（2）The regulation law of coating monolayer Ti₃C₂MXene on Ti powder was explored,and the effects of the concentration of Ti₃C₂MXene dispersion and the flow rate of solid-liquid fluidized bed on the coating powder were determined.When the concentration is too high,due to the presence of large amount of Ti₃C₂MXene in the solution,a large amount of buildup can not be avoided during the drying process.When the concentration is too low,a small amount of Ti₃C₂MXene in uneven contact with a large amount of Ti powder,resulting in some Ti powder failing to be completely coated.It was further found that the best Ti₃C₂MXene@Ti composite powder was obtained by fluidization at a flow rate of 38 m L/min for 120 min at a MXene dispersion concentration of 0.5 wt.%.At the same time,the Ti₃C₂MXene surface functional groups were eliminated by de-hybridization at 750℃through the gas-solid fluidized bed to achieve the purity of the encapsulated powder.（3）The densification behavior and Ti₃C₂MXene retention behavior of Ti₃C₂MXene@Ti composite powder sintered rapidly at 900℃were investigated,and it was found that the powder had high densification（98.5%）after sintering at a content of 0.2 wt.%of Ti₃C₂MXene in the composite matrix,while Ti₃C₂MXene was retained intact and no new material was generated.The tensile yield strength of the formed samples reached 710 MPa,which is 63%higher than the tensile yield strength of pure titanium,and maintained a high plasticity（strain of 12.5%）.（4）The strengthening efficiency of Ti₃C₂MXene in titanium matrix composites was calculated and its strengthening mechanism was determined.The three Ti₃C₂MXene fracture modes contributed to the improved performance of Ti₃C₂MXene/Ti composites.By studying the strengthening mechanisms of 2D materials,it is found that thermal adaptation and solid solution strengthening occupy a small part,while Ti₃C₂MXene in Ti matrix hinders grain growth and transfers load as the main strengthening mechanisms.