Forming Laminated Titanium Matrix Composites With Interlocking Structure Based On Direct Ink Writing And Corresponding Mechanical Properties Investigation

Laminated titanium matrix composites(LTMCs)are widely used in various industries because of their superior strength-toughness balance performance,which have broad application prospects.However,conventional molding methods such as explosion welding,hot pressing,diffusion welding and accumulative roll bonding suffer from weak interfacial bonding,inability to regulate the interfacial structure and limited component complexity.In this paper,bimaterial printing of 0.8vol% BNNSs/TC4 ink and TC4 ink were carried out by direct ink writing(DIW)to build an interlayer "interlocked" interface.Dense interlayer "interlocked" laminated TC4-Ti B/TC4 composites reinforced by Ti B nanowires were obtained by combining DIW with fast hot pressed sintering(FHPS),and their mechanical properties were investigated.The main results are follows:(1)The 0.8 vol% BNNSs/TC4 composite powder was prepared by stepwise variable speed ball milling method,which can effectively disperse and evenly embed BNNSs on the surface of TC4 substrate and realize the uniform distribution of BNNSs.The first low-speed ball milling of BNNSs can effectively disperse the agglomerated BNNSs and distribute them on the surface of the stainless steel balls;the subsequent addition of TC4 powder was again subjected to the second lowspeed ball milling to ensure the uniform embedding of BNNSs on the surface of TC4.The uniformly dispersed BNNSs play a role in preventing the agglomeration of the matrix powder to a certain extent.(2)A pneumatic DIW printing device capable of satisfying multi-material printing was developed independently.The ink ratios consist of TC4 powder or BNNSs/TC4 composite powder and binder,and the solvent-volatile printing ink was prepared in the ratio of 7:3 by volume,and the method of heating-assisted stirring to thicken the printing ink was proposed and defoamed by the self-prepared centrifugal defoaming device.A multi-material printing process based on DIW was proposed to prepare the laminate titanium matrix composites reinforced with BNNSs by predesigning interlayer "interlocked" structures.The preparation protocol was developed for the preparation of DIW-style interlayer "interlocked" laminated titanium matrix composites.The effect of printing with different types and internal diameters of printing needles and the influence of printing parameters on the quality of the blanks were investigated.(3)Based on the results of the thermogravimetric analysis,the debinding temperature was investigated and the best debinding effect was found when the debinding temperature was set at50°C,180°C and 400°C.The effect of the heating rate on the quality of the debinded parts was also investigated and the results showed that the faster the heating rate,the worse the ability of the degreased parts to maintain their original shape.When the heating rate was set at 1°C/min,not only can obtain high quality debinded parts,but also can improve the debinding efficiency.The effect of holding time on the debinding effect was investigated which was found that when the holding time was set at 1 hour,well-shaped,crack-free degreased parts were successfully obtained with a16% shrinkage of the debinded parts.In addition,the effect of different buried powders on the debinded parts was investigated which was found that a small particle size TC4 powder(average particle size smaller than the particle size of TC4 powder in the blanks)was the most suitable.By placing titanium sponge at the inlet end of the tube furnace and using a mixture of argon-hydrogen(95:5 argon to hydrogen)as a protective gas with a set flow rate of 120 ml/min,the oxidation of the debinded parts could be effectively avoided.(4)The debinded parts were sintered by FHPS,the parts were gradually densified by both current and pressure,and the interlayer "interlocked" structures were successfully retained after sintering.The 0.4 vol% Ti B/TC4 composites with uniform distribution of the reinforcing phase was prepared by the same process.The tensile performance tests revealed that the interlayer "interlocked" LTMCs had an improved strength(by 9.1% to 1206 MPa)compared to the unconfigured 0.4 vol% Ti B/TC4 composites with uniform distribution of the reinforcement while preserving the high toughness.In the interlayer "interlocked" LTMCs,the composite layer and TC4 layer were separated by the interlocked interface and show different fracture morphologies.(5)The intrinsic mechanism of tensile strength and toughness improvement of the interlayer "interlocked" LTMCs was analyzed: The in-situ reaction between BNNSs and TC4 generates a three-dimensional reinforced configuration;the nailing effect of the in-situ generated Ti B nanowires refine the grains and prevent dislocation slip;the interlayer "interlocked" interface deflect the cracks significantly,prevent the crack expansion,and improve the overall material toughness,which provides a method and basis for molding complex and tough composite components.