冷喷涂金属化的界面金属粘合机理

Abstract

Metallization of ceramics is drawing more and more attention in industries. The mechanisms involving higtbonding strength between cold sprayed metallic coatings and ceramic substrates are not yet clear. In this studyaluminum (Al) particles and alumina (AlO,) substrates were emploved to reveal impact phenomena in coldspraying. Electron backscatter diffraction equipment (EBSD) and high-resolution transmission electron microscope (HRTEM) were used to investigate the interfacial microstructures of the Al particles and Al,0, substratesComputational fluid dynamics (CFD) and finite element analysis (FEA) were emploved to quantitatively characterize the temperatures and plastic strains at the interfaces. The bonding strength of the Al coatings and Al,0.substrates was measured and the analysis to the fracture morphologies was also conducted. The results show thatthe Al particles at the interfaces presented fine-grain and amorphous structures, and the Al,0, substrates experienced a britle rupture, The Al coatings bonded on the ceramic surfaces due to mechanical interlocking ancheteroepitaxy. The results offer more details to understand the bonding mechanisms of metallic particles ancceramic substrates.

1. Introduction

Metallization of ceramic materials has become an important issuefor their use in electronic information industries due to their excellentthermal conductivity, high-temperature insulation, and low dielectricconstant (Belyakov et al., 2012). Kosarev et al. (2018) reported theAl2O3 and AlN ceramics coated with cold-sprayed Cu coatings, whichcan withstand more than 100 thermal cycles in a temperature rangedfrom -60 to +150C. Many kinds of technologies are employed torealize the metallization of ceramic materials. For example, Moritaet al. (1991) utilized laser-sublimating and electroless plating to depositthin metallic layers on AlN substrates to repair or customize circuits.Song et al. (2019) used direct bonding to deposit AgCuTi metallic layerson SiC ceramics to bond GH99 superalloys and ceramics. It is worthnoted that the new phase TiC was observed between AgCuTi metalliclayers and SiC ceramics, which was regarded as the product of chemicalbonding. Reboun et al. (2017) employed silk-screen printing to fabri-cate thick copper films on alumina for power electronic industries. Theaverage adhesion strength of the copper film was 43 MPa. Ritter et al.(2017) investigated the high temperature co-fifired ceramic technology for ceramic sensors, in which the platinum heater and self-heated yttria stabilized zirconia disc were bonded. Brust et al. (2016) applied physical vapour deposition and chemical vapour deposition to fabricate Ti and TiN thin fifilms on Al2O3 and ZrO2, respectively, to improve the wettability of fifiller materials on ceramics.

Cold spraying is a relatively new ceramic metallization technologyin which a high-temperature and high-pressure gas obtains a high veocity through an energy transformation in a De Laval nozzle; particlesare accelerated to high velocities (300-1500 m/s) by the gas, andimpact onto a substrate and form a coating in a solid-state (Assadi et al.2016). Compared to the coatings fabricated using other metallizationprocesses, cold sprayed coatings have higher purity and lower oxidationdue to the low temperature characterization of cold spraying (Smith.2007).

Cold spraying can be used to metallize ceramics, in which aluminum(Al), titanium (Ti) and copper (Cu) coatings were used as the coatingmaterials, and alumina (Al,O,), aluminum nitride (AlN), silicon nitride(SiN4), silicon carbide (SiC), magnesium fluoride (MgF2), lead zirconate titanate (PZT) and zirconia (ZrOz) were employed as thesubstrates. Ko et al. (2016) reported the amorphization and atomicintermixing phenomena at the interface of Cu/AlN and Al/ZrO.bonding couples. The authors attributed bonding between metal andceramic to chemical adhesion. Wiistefeld et al. (2017) reported localheteroepitaxial growth phenomena in the bonding couple of Al/AlNLocal heteroepitaxy between Al and AlN was attributed to the increaseof the substrate temperature and the recrystallization or melting of Alcoatings. However, the heteroepitaxial growth was not found for otherceramics. Drehmann et al. (2018) attributed the bonding to mechanicainterlocking in several bonding couples, e.g. Al/SiC, Al/SiN4, Al/MgF2Kromer et al. (2018) pre-treated rough surfaces on SiC and AlO3ceramics using laser surface texturing before cold spraying, whichpromoted mechanical anchoring between metal and ceramic. In addi.tion, King et al. (2010) reported that mechanical adhesion took place bypenetrating aluminium into the open pores on the smooth PZT sub.strates. Another interesting issue should be noted that the bondingstrength of the metallic coatings on these ceramics did not present quitedifferent no matter whether the heteroepitaxial growth phenomenonwas reported or not. This suggests that the bonding mechanisms between metallic coatings and ceramic substrates are still not clearlyunderstood.

Therefore, in this investigation, Al particles were deposited onAl2O3 ceramics to form coatings using cold spraying. The microstructure evolution of the Al particles was characterized and simulatedduring impact. More detailed inspections to the interfaces of the coat-ings and substrates were conducted using EBSD and HRTEM. Thebonding mechanisms of the Al coatings on the AlO3 substrates werediscussed.

2. Experiment details

2.1. Feedstock and equipment

A commercial pure Al powder (Changsha Tianjiu Metal MaterialsCo. Ltd, Changsha, China) was employed as feedstock. The morphologyof the particles was characterized using a scanning electron microscope(FESEM, Ouanta FEG250, FEl, Hillsboro, USA), and the particles pre-sented a spherical shape (Fig. la). The particle size distribution of thepowder was measured using a laser granularity analyzer (S3500-special, Microtrac, Montgomeryville, USA), and the average diameter ofthe particles was 69 um (Fig. 1b). The AlO3 ceramic plates (YunyiElectronics Co. Ltd, Guangzhou, China) with a dimension of25 mm x 20mm x 1mm were used as substrates. The surface morphology of Al2O3 ceramic plate was shown in Fig. 1c. The substrateswere cleaned using alcohol in ultrasonic for ten minutes beforespraying.

A commercial cold spray equipment (Kinetics 3000, Cold GasTechnology GmbH, Ampfing, Germany) was employed. Nitrogen wasused as propelling and delivering powder gas. The pressure and tem-perature of the gas were 2.2 MPa and 300 C, respectively. The standoffdistance of the nozzle was set as 30mm. The traverse speed of the nozzle was 0.05 m/s.