| With the development of science and technology and the rapid progress of the integrated circuit industry,the requirements for the internal thermal management capability of electronic devices are also getting higher and higher,which requires the materials used in the devices to have higher thermal conductivity and stability.As a ceramic material with high thermal conductivity,high mechanical properties and chemical corrosion resistance,Aluminum Nitride(AlN)has received extensive attention in the field of substrate materials and has broad application prospects.In this paper,Boron Nitride Nanosheets(BNNSs)with large aspect ratio and good dispersibility were obtained from hexagonal boron nitride by a liquid-assisted ultrasonic exfoliation method and incorporated into AlN matrix.BNNSs/AIN composites were prepared,which greatly improved the mechanical properties of aluminum nitride ceramics.At the same time,the micro-morphology of the composites was observed,the effect of BNNSs on the mechanical properties and thermal properties of AlN was analyzed,and the enhancement mechanism of BNNSs on the mechanical properties of AlN was explored.(1)CeO2 and Y2O3 were added to AlN to study the effect of binary composite sintering aids on hot-pressing sintered aluminum nitride ceramics.AlN ceramics with high relative density were obtained by hot pressing at 1600℃.The addition of CeO2 and Y2O3 promoted the sintering and densification of the ceramics,which was beneficial to the preparation of materials with good mechanical and thermal properties.When 2 wt%CeO2 and Y2O3 were added,respectively,the best-performing sample was obtained,with a bending strength of 371 MPa,a maximum thermal conductivity of 184.4 W·m-1·K-1.The thermal conductivity of AlN ceramics is mainly affected by density,secondary phase,grain boundary structure and impurity content.The addition of sintering aids can increase the relative density of aluminum nitride ceramics,purify the crystal lattice,and improve the internal structure of aluminum nitride,thereby increasing the thermal conductivity of aluminum nitride ceramics.(2)The BNNSs/AlN composites were obtained by uniformly dispersing BNNSs into AlN using wet-milling mixture and hot-pressing sintering.The contents of BNNSs in the samples were 0 wt%,0.5 wt%,1 wt%and 1.5 wt%,respectively.The BNNSs did not produce largescale agglomeration in the material.The addition of BNNSs has a positive effect on the mechanical properties of AIN.After adding BNNSs,the bending strength is increased from 371.0 MPa to 456.6 MPa,an increase of 23.1%,and the fracture toughness is increased from 2.65 MPa·m1/2 to 4.47 MPa·m1/2,an increase of 68.7%.The improvement of the mechanical properties of composite ceramics is mainly due to the influence of grain refinement and BNNSs.Due to the existence of BNNSs,the material needs to overcome the interlayer force of nanosheets,the breaking energy of boron nitride molecular bonds and the interaction between nanosheets and AlN grains during fracture.These forces greatly increase the flexural strength and fracture toughness of the material.(3)The industrial cordierite powder was added to the BNNSs/AIN powder,and the process exploration and performance test of the AlN-containing composite ceramic material sintered at low temperature were carried out.By adjusting the process parameters of molding,debinding and sintering during the experiment,the composite ceramic material sintered at low temperature was finally obtained by debinding at 600℃ and then sintering at 950℃ under normal pressure in nitrogen.With the increase of cordierite content,the liquid phase generated during sintering increases,which is beneficial to promote the sintering of composite materials.Finally,when the cordierite content is 50 wt%,a sample with the highest relative density of 71.2%is obtained.The conductivity is 1.5 W·m-1·K-1.After forming and sintering,BNNSs still retain the intact sheet-like morphology,and the thermal conductivity of composites is affected by the phase composition,porosity and other aspects. |
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