High-temperature Wetting And Brazing Properties And Mechanisms Of Two Typical Carbide-metal Composites

Carbide/metal composites are of great research significance and have broad application prospect due to the combination of high hardness,good heat and corrosion resistances of carbide ceramics and excellent ductility and toughness of metals.For instance,the SiCp-Al composite is a suitable option for the advanced electronic packaging because of a variety of advantages including tailorable coefficient of thermal expansion?CTE?,high thermal conductivity?CT?,low weight and compatible strength.And the WC-Co cemented carbide are widely used in cutting tools,press molds and mining bits owing to the combination of WC and Co metal.In this paper,the high volume faction SiCp-Al composite and WC-8Co cemented carbide were selected as two typical carbide/metal composites and investigated by surface metallization,high-temperature wetting and brazing experiments.The related microstructures,microchemistry and phase compositions of brazing alloys,wetting interfaces and brazing joints were analyzed systematically by SEM,EDS and XRD.Moreover,the joint shear strength and fracture behavior were investigated,and the wetting and brazing mechanisms of the two composite were deeply discussed.The main conclusions or results are shown as follows:The Al-20Cu-6Si brazing alloy is mainly composed of Al₂Cu,Al₂Si and??Al?phases,and the Mg₂Si phase is produced in the Al-20Cu-6Si-?1,3,5?Mg alloy due to the interactions between the Mg and Si atoms.The liquidus temperatures of Al-20Cu-6Si?-0,1,3,5?Mg brazing alloys are534.3,531.9,529.8 and 531.4°C,respectively.Three self-made Cu based alloys mainly consist of??Cu?solid solution,while the NiAl intermetallic compound forms in the Cu-18Ni-10Al alloy.The liquidus temperatures of three Cu-Ni-Al alloys decrease from 1202 to 1186 and 1176°C with the Al concentration increasing from 2.5 wt.%to 5 wt.%and 10 wt.%.The 70%SiCp-Al composite is covered entirely with a dense and uniform cellular microstructure after electroless Ni-plating.The surface roughness of the Ni+SiC composite coatings increases from⁹7 to 419,436 and 457 nm with the SiC concentration in the bath increasing from 0 to 3,6,9 g/L.This can be explained that the increasing SiC particles can act as the nucleating agent and thus decrease the sizes of globular nodules,resulting the higher surface roughness.The as-plated coating presents a amorphous structure,and the amorphous Ni-P in the Ni-P?-SiC?coatings are completely crystallized into nickel crystal and Ni₃P when the heat-treatment temperature is increased to 400°C.The SiC additions in the Ni-P coating can contribute to decrease the difference of coefficient of thermal expansion between the coating and the SiCp-Al composite substrate to a certain extent,which is beneficial to the coating/substrate interfacial bonding.The critical load?Lc?of the Ni–P–SiC composite coating on the SiCp-Al composite reaches the maximum of 84.9 N while using the SiC concentration of 3 g/L and heat-treated at 200°C.All the contact angles of the Al-Cu-Si?-Mg?/SiCp-Al systems are over 90°at 580°C due to the presence of Al₂O₃ film,showing a non-wetting behavior.Mg element in the Al-Cu-Si?-Mg?alloys can moderately improve the wettability of the molten Al-Cu-Si?-Mg?on the SiCp-Al composite because of the interactions between the Mg and Al₂O₃ film.The contact angles of Sn,Sn-3.5Ag and Sn-3.5Ag-0.5Cu on the coated SiCp-Al composites increase with the increase of SiC concentration,and all the three Sn-based filler metals show non-wetting on the Ni-P-9SiC/SiCp-Al substrate.An interaction layer composed of Ni-Sn-P and Ni-Sn or Cu-Ni-Sn phases forms at the Sn,Sn-3.5Ag and Sn-3.5Ag-0.5Cu/Ni-P?-0,3,6?SiC coated SiCp-Al interfaces,while only Ni-Sn-P phase can be observed at the Sn,Sn-3.5Ag and Sn-3.5Cu-0.5Cu/Ni-P-9SiC coated SiCp-Al interfaces.When the Al-20Cu-6Si?-0,1,3?Mg alloys are used as filler metals to braze 70%SiCp-Al composite,some unbonded area can be detected in the brazing joints.The maximum shear strength of 75 MPa can be obtained while using Al-20Cu-6Si-5Mg as filler metal.However,an obvious interfacial layer can be observed in the two Ni-P?-3SiC?coated SiCp-Al brazed joints using the Sn-3.5Ag-0.5Cu as filler metal,and the two joint shear strength values are about 30 and 38 MPa.Pure Cu,Ag-28Cu and self-made Cu-Ni-Al alloys present good wettability on the WC-8Co cenmented carbide.For the Cu and Ag-28Cu/WC-8Co systems,no obvious reaction layer can be detected at the interfaces,while an obvious degeneration layer with continuous thin strip forms in the cemented carbide adjacent to the Cu-Ni-Al/WC-8Co interface due to the strong interactions between the Co in cemented carbide and Cu,Ni,and Al in the Cu based alloys.The Cu-19Ni-5Al/Ni-coated WC-8Co system presents fast spreading and excellent wettability with final contact angle of¹0°,and increasing the Ni coating thickness can markedly prevent the formation of degeneration layer in the cemented carbide.An Fe-Cu-Co transition layer is detected at the WC-8Co/Cu interface,while no obvious reaction layer is observed at the whole WC-8Co/Ag-28Cu/SAE1045 brazing seam.Some?+?phase enriched with Al,Co and Ni elements can be detected in the the three WC-8Co/Cu-Ni-Al/SAE1045 brazed joints.A degeneration layer forms in the WC-8Co substrate adjacent to the Cu-Ni-Al/WC-8Co interface in the three brazed joints due to the escape of Co in the WC-8Co to the inetrlayer,and the degeneration degree becomes much more serious with the increase of Al content in the Cu-based alloys.The Ni coating on the WC-8Co cemented carbide can effectively decreases the thickness of degeneration layer,which can be attributed to the decreased diffusion of Co in the cemented carbide,resulting from the consumption of the Al in the interlayer due to the strong interactions between the Al and Ni in the Ni coating.The thickness of?+?phase at the interlayer/cemented carbide interface gradually increases with the thickness of Ni coating,brazing temperature and holding time increasing,while that at the interlayer/steel interface decreases gradually and even disappears.The WC-8Co/SAE1045 joints brazed using pure Cu and Ag-28Cu alloy as filler metals are provided with average shear strength values of about 172 and 136 MPa,respectively,and both the two joint fractures occur in the interlayers.Compared with the other two brazed joints,the WC-8Co/Cu-19Ni-5Al/steel brazed joint presents higher average shear strength of over 200 MPa while brazing at the1210°C for 7.5 min,and its joint shear fracture path passes across the ductile interlayer,interlayer/cemented carbide interface and the brittle degeneration layer,showing a mixed ductile-brittle fracture.The maximum joint shear strength of³28 MPa is obtained while Ni-plating of⁷8?m thick and brazing at 1210°C×5 min.Similarly,the typical joint shear fracture path passes along the interlayer,Cu-19Ni-5Al/WC-8Co interface and degeneration layer in turn.