Bimodal and monomodal diamond particle effect on the thermal properties of diamond-particle-dispersed Al–matrix composite fabricated by SPS

• Porosity of Al–65% diamond bimodal composite was less than 99%.
• The thermal conductivity was higher than 500 W/m K at 45–70% diamond fraction.
• No reaction product was detected at the interface between diamond and Al.
• The thermal conductivity of Al/70% diamond composite was 578 W/m K.
• The CTE of Al/70% diamond bimodal composite was 6.72 × 10−6 at R.T.

Diamond-particle-dispersed aluminum (Al) matrix composites consisting of monomodal and bimodal diamond particles were fabricated in spark plasma sintering process, where the mixture of diamond, pure Al and Al–5 mass% Si alloy powders were consolidated in liquid and solid co-existent state. Microstructures and thermal properties of the composites fabricated in such a way were investigated and the monomodal and bimodal diamond particle effect was evaluated on the thermal properties of the composites. The composites can be well consolidated in a temperature range between 773 K and 878 K and scanning electron microscopy detects no reaction product at the interface between the diamond particle and the Al matrix. Relative packing density of the composite containing monomodal diamond particles decreased from 99.1% to 87.4% with increasing volume fraction of diamond between 50% and 60%, whereas that of the composite containing bimodal diamond particles was higher than 99% in a volume fraction of diamond up to 65%. The thermal conductivity of the composite containing bimodal diamond particles was higher than that of the composite containing monomodal diamond particles in a volume fraction of diamond higher than 60%. The coefficients of thermal expansion (CTEs) of the diamond-particle-dispersed Al–matrix composites fall in the upper line of Kerner model, indicating good bonding between the diamond particle and the Al matrix in the composite. The thermal conductivity of the composite containing 70 vol.% bimodal diamond particles was 578 W/m K and its CTE was 6.72 × 10−6 at R.T.