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Research On Preparation And Properties Of Diamond/Al Composites With High Volume Fraction Of Diamond

Posted on:2018-03-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:C Y GuoFull Text:PDF
GTID:1311330512467721Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
High volume fraction diamond/Al composite is a new perfect electronic packaging material because of its high thermal conductivity ?TC?, adjustable coefficient of thermal expansion ?CTE? and lower density. In this dissertation, the composites were prepared by two methods of diamond metallization and matrix alloying, in order to solve the chalking and losing their properties in application. The suitable processing parameters of preparation of porous diamond preforms by compression molding and composites by pressure infiltration with aluminum alloy adding ?0?40wt.%? Si and with Ti coated diamond were respectively studied. The relationship among thermal conductivity, thermal expansion behavior, bending strength, microstructure and interfacial bonding state of diamond/Al composites were also analyzed. Theoretical model for calculating the interfacial thermal resistance of Al/diamond composites with the transitional layer at the interface was put forward and the interfacial thermal conductivity?ITC? and the properties of the composites prepared by the two methods were compared. The results showed that:The binder consisting of 60wt.% paraffin wax ?PW?,15wt.% high-density polyethylene ?HDPE?,15wt.% polypropylene ?PP? and 10wt.% stearic acid ?SA? was suitable for the preparation of porous diamond preforms by compression molding. The maximum solid loading was respectively 63% and 67vol.%by diamond powders of single size ?100?m? and mixing two different size ?100?m:40?m=3:1?. And the maximum thermal debinding temperature was 430? and the total time was 12-14 hours. The strength of the debinding diamond perform was higher than 7.7MPa and the shrinkage rate was less than 2%, which meet the requirement of pressure infiltration.In the process of preparation of composites by pressure infiltration, there were a large number of undesirable interface product AI4C3 on both{001} and {111} surfaces of diamond, and the shapes were different. However, the Ti layer could avoid the formation of AI4C3 in the diamond/Al composites with Ti coating, and Ti and Al had spreaded to each other, which could improve the relative density of composites and the relative density could reach 99.4%. In the diamond/Al composites with Al-Si alloy, Si had no selectivity and was enriched on both diamond surfaces, but only Al-12.2Si alloy could improve the relative density of the composite, the density up to 99.6%. There were uniform products SiC at the interface, and it reduced the production of Al4C3. There were no graphitization in the diamond/Al composites with Ti coating and Al-Si alloy.The TC of composites improved along with the increase of the relative density, size and volume fraction of diamond particles. The TC of diamond?100?m?/Al composites with Ti coating could reach 514.1 W·m-1·K-1. The TC of diamond?100pm?/Al composites with 12.2 wt.% Si could reach 532.2 W·m-1·K-1. The TC of diamond?100?m:40?m=3:1?/Al composites with 12.2 wt.% Si could reach 557.8 W·m-1·K-1, while the TC of diamond?40?m?/Al composites with 12.2 wt.% Si could reach 415 W·m-1·K-1. The CTE of composites was greatly influenced by the properties of the matrix and it decreased with the increase" of the volume fraction of diamond particles and the decrease of diamond size. The CTE of diamond?100?m?/Al composites with Ti coating could reach 11.1×10-6 K-1. The CTE of diamond?100?m?/Al composites with 12.2 wt.% Si could reach 9.7×10-6K-1. The CTE of diamond?100?m:40?m=3:1?/Al composites with 12.2 wt.% Si could reach 8.9×10-6K-1, while the CTE of diamond?40?m?/Al composites with 12.2 wt.% Si could reach 8.52×10-6 K-1. The bending strength ?BS? of composites was sensitive to the properties of the matrix. For the same matrix, the higher the relative density of the composites was and the smaller the size of diamond was, the higher the BS of the composites was. The BS of diamond?100?m?/Al composites with Ti coating could reach 315.7MPa. The BS of diamond?100?m?/Al composites with 12.2 wt.% Si could reach 292.4MPa, while the BS of diamond?40?m?/Al composites with 12.2 wt.% Si could reach 302.9 MPa. By experiment, the performance of the composite prepared by Al-12.2Si is better than that of the composite with Ti coating.Based on Kapitza's theory, the theoretical ITC was calculated. The ITC hc-dia-Ti-Al of the composite with Ti coating was about 1.29 ×107 W·m-2·K-1 and the interface layer was composed of diamond-TiC-Ti; The ITC hc-dia-Si-Al of the composite with Al-12.2Si was about 2.3 ×107 W·m-2·K-1 and the interface layer was composed of diamond-SiC-Si. The ITC was inversely proportional to the thickness of the interfacial transition layer and proportional to the TC of the interfacial transition layer. If the thickness of Ti coating was difficult to control in the lower range, Si was a better choice.
Keywords/Search Tags:Diamond/Al composites, Thermophysical properties, Interface thermal resistance, Pressure infiltration
PDF Full Text Request
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