Wire-powder-arc Additive Manufacturing Of Carbide Particles Reinforced Aluminum Matrix Composites

Additive manufacturing（AM,also known as 3D printing）is a layer-by-layer fabrication technology.It is expected to achieve multiple integrated goals such as material design,structure building and performance control in one fabricating process and realize personalized manufacturing.Aluminum matrix composites（AMCs）,as a class of lightweight materials with a series of excellent properties such as high strength,low density and high corrosion resistance,play a pivotal role in the AM research.However,the preparation of AMC components by conventional AM techniques（e.g.,laser and electron beam AM）suffers from a series of constraints such as expensive equipment,special specification materials,narrow process parameter windows,difficulty in regulating multiphase components,and high manufacturing costs,which limit their industrial application.The wire-based arc AM technology not only has high deposition efficiency and low manufacturing cost,but also is easy to combine/integrate with other processes,making it suitable for industrial production of large,low-complexity structural components.Nevertheless,the research focus on the preparation of composite materials based on arc AM is still in its initial stage,and there is great research space in many aspects such as equipment,materials,process parameters,forming control,and performance regulation.Therefore,in this work,a wire-powder-arc additive manufacturing（WPA-AM）experimental platform with a multi-material delivery system was built with the goal of developing a low-cost,high-efficiency,and wide-compatible AM technology for fabricating ceramic/metal composites.Based on this platform,first,the materials and process parameters for fabricating AMCs were established through process experiments,and the feasibility of building AMC components with WPA-AM was verified.Second,four typical carbide particles（B₄C,SiC,TiC,WC/W₂C）and Al5356 were used for custom composites to verify the flexibility of the WPA-AM process for fabrication of multi-material components.Then,combining the advantages of TiC-AMC and B₄C-AMC,a combined gradient AMC structure reinforced with TiC-B₄C dual-phase ceramic was built,and the synergistic regulation of the combined gradient microstructure on mechanical properties,friction and wear behavior,and damping characteristics were investigated.Further,to improve the mechanical properties of B₄C-AMC,a method of mixing nano TiC into B₄C effectively improved the fusion of B₄C and Al matrix,and reduced the defects.Finally,the TiC-B₄C combined gradient AMC was applied to fabricate an aluminum-based automobile brake disc prototype.The main results are as follows:（1）A new technique（WPA-AM）was developed for custom additive manufacturing of carbide ceramic/aluminum alloy multi-material components.The materials and process parameters for fabricating AMCs were determined through process experiments.A viable strategy of slot weld bead arrangement+swing arc process was proposed to solve the problems caused by heat accumulation and melt pool deflection,and to improve the forming quality and inter-channel bonding in the multi-bead lapping process.We found that the swing arc could regulate the formation,microstructure and properties of the deposited layers.The functional relationship between the arc swing amplitude b and the weld bead width w was established.The mechanism of eliminating columnar crystals in the interlayer fusion zone and improving bonding performance between the lapped beats was expounded.Two kinds of wire-powder coupling devices,with side powder feeding and coaxial powder feeding,were designed to realize wire-powder co-deposition.The feasibility of manufacturing B₄C-AMC by WPA-AM with side powder feeding was verified.It was found that B₄C particles were completely retained in the AMC layer,which greatly improved the wear resistance of the AMC.The ceramic/aluminum alloy multi-material components with controllable reinforcement of four carbide particles were prepared by WPA-AM with coaxial powder feeding,which reflected the flexibility of the WPA-AM technique.（2）The commonness and individuality of four typical carbide powders on arc stability,droplet transfer,AMC microstructure and properties were summarized.The effects of four typical carbide powders on the WPA-AM process under the same parameters were investigated.B₄C and SiC had more serious interference on arc stability and droplet transfer than TiC and WC/W₂C.SiC caused side arcs and droplet explosion,which changed the metal transfer mode from meso-spray transfer to short-circuiting transfer with large droplets,resulting in the worst forming quality in SiC-AMC layers.The fusion behavior of particles/Al and the influence of floating powders on the surface of the melt pool were analyzed.The lower the powder density,the thicker the floating powder layer,and the stronger the obstruction effect.The pulse arc and periodic droplet impact could entrain the powders into the melt pool,and promote the forced fluctuation and tidal flow of the pool fluid.With the increase of carbide density,the particle capture rate and content in the deposited layers improved,and the particle sinking（delamination）become more obvious.The four group AMC layers have a natural interlayer transition,and the particles well joined with Al matrix.Only WC/W₂C had a significant reaction with Al5356 matrix and formed the compound of Al₁₈Mg₃W₂.The added ceramic particles reduced the elongation of the AMCs in various degrees.TiC-AMC layers showed the highest strength（～270 MPa）and damping performance（2～3 times that of Al5356 matrix）due to the good interface bonding,but their anti-wear ability was not prominent;B₄C-AMC layers had poor mechanical properties due to the porosity and particle aggregation defects,but they showed excellent wear resistance and damping characteristics.（3）The evolution of microstructure and properties in TiC-B4C dual-phase ceramic combined gradient AMC was revealed.A combined gradient AMC（CG-AMC）structure reinforced with TiC-B₄C dual-phase ceramic was fabricated by WPA-AM with changing the powder feeding rates layer by layer.The nonlinear functional relationship between the two particle capture rates and the powder feeding rates was established.With the increase of TiC particle content from 0 to 9.2 vol.%,the average grain diameter of Al matrix decreased from 64.3μm to 18.9μm;Then,with the decrease of TiC particles to 0while the increase of B₄C particle to 5.2 vol.%,the average Al grain size increased to 33.5μm in the CG-AMC.The mechanism of grain refinement caused by heterogeneous nucleation and grain boundary obstruction was clarified.At 400℃,the Al grain growth was inhibited by particles attributed to near-neighbor grain boundary confinement and interfacial energy reduction mechanisms.It was found that the room temperature tensile properties of all layers in CG-AMC structure were not prominen,while the high temperature properties were excellent.The high temperature tensile strength of the TiC-AMC layers showed a gradient increase with the increase of TiC content,and 9.2TiC-AMC layer exhibited the highest strength of 165.6 MPa and 70.0 MPa at 300℃and400℃,respectively,which was～1.5 and～2 times of that of Al5356.The addition of B₄C caused pores and particle aggregation,resulting in a significant decrease in the mechanical properties of the corresponding AMC layers.The essential reason of B₄C greatly improving the anti-wear performance for AMC was that it changed the wear mechanism from adhesion and ploughing wear to oxidation and delamination wear.And the excellent damping property of CG-AMC was contributed by the combined action of intrinsic damping of reinforcement,grain boundary and dislocation damping mechanisms.（4）It was found that mixing nano TiC particles into B4C powders can effectively improve the mechanical properties of B4C-AMC.A 2 vol.%nano TiC+micro B₄C cross-scale,dual-phase ceramic reinforcement was designed to build AMC,which effectively improved the bonding between B₄C and Al matrix,reduced the pore and particle aggregation defects,and increased the average tensile strength and elongation from～141MPa and～4%to～208 MPa and～13%for～5.2 vol.%B₄C-AMC,respectively.Based on the excellent mechanical,tribological and damping properties of dual-phase ceramic reinforced AMC,a manufacturing strategy of casting+WPA-AM composite technique was proposed,and a TiC-B₄C combining reinforced aluminum matrix automobile brake disc prototype was prepared.In short,the WPA-AM technique was developed to solve the problem that conventional AM technology is difficult to regulate the real-time compounding of metal wire and ceramic powders,and realize the customized fabricating of particle reinforced AMCs.We hope that it can provide some references for the development of low-cost AM technology for building metal-ceramic multi-material components.