Copper Matrix Composites Fabricated via Field Assisted Sintering Technology for Thermal Management Applications

Open Access
Author:
Rape, Aaron M
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 05, 2015
Committee Members:
  • Jogender Singh, Dissertation Advisor
  • Suzanne E Mohney, Committee Member
  • Joshua Alexander Robinson, Committee Member
  • Anil Kamalakant Kulkarni, Special Member
Keywords:
  • Thermal Conductivity
  • Thermal Transport
  • Copper-diamond
  • copper-tungsten
  • composite materials
  • SPS
  • FAST
  • Thermal Simulation
Abstract:
This thesis provides significant evidence to support the hypothesis that Field Assisted Sintering Technology (FAST) can be used as an effective method to develop high performance thermal management materials. The work presented in the theis can be divided into two parts: 1) The fabrication of composite material systems 2) The characterization of the composite material systems that have been developed. The material development portion of the thesis focuses on developing copper based composite materials with the objective of improving a specific thermal property or properties. Copper-tungsten composites were developed to produce composite materials with relatively high thermal conductivity and low coefficient of thermal expansion (CTE). FAST proved to be effective in producing materials that had very high density. Copper based material systems were combined with diamond particles were then developed to reduce CTE while improving thermal conductivity compared to the best known commonly used pure metal, copper. It was discovered that a pure copper matrix was not effective to develop quality composite systems due to the poor interface that existed between the matrix and diamond particle. Several approaches were taken to improve the interface. Incorporating low melting temperature materials that would become an in-situ liquid phase showed some effectiveness in improving the interface and thermal conductivity. Unfortunately, the thermal conductivity was not able to be improved due to the lack of chemical reaction between the diamond particles and the matrix. Copper alloys containing zirconium were found to be the best solution to improving the interface. Zr migrated to the interface from the matrix during the sintering process and formed a very thin layer of carbide. Finite element analysis (FEA) was employed to provide further insight into the composite materials. The analysis revals that the thermal conductivity of the alloy matrix changes as a result of the Zr migration from the matrix to the interface. The copper alloy approach was extended to include carbon nanotubes instead of diamond particles. While the Zr migration and carbide formation was also observed, the composites did not show good thermal properties because of agglomerations of the carbon nanotubes. The result was a composite material that had low density due to porosity within the pockets of nanotubes. The porosity was also severely detrimental to the thermal conductivity of the composites.\\ Composite materials made from a combination of pure metals and thermally annealed pyrolytic graphite (TPG) were fabricated as heat spreading materials. The results were characterized using a customized apparatus designed specifically to measure the thermal spreading cabability of a material. The materials containing TPG showed a more uniform heat distribution and lower maximum temperature than their pure metal counterparts. Thermal modelling was carried out via FEA to determine the thermal interface resistance of the composite.