Tungsten/copper composite sheets prepared by a novel encapsulation rolling technique

•The W-18.5 wt% Cu composite sheet was prepared by encapsulation rolling process.•The macro-cracking on the periphery of sheets is avoided after encapsulation rolling.•The composite sheet is as thin as 0.75 mm with the relative density of 99.8%.•The thermal conductivity and CTE decreases with the rolling reduction ratio.•The composite sheet shows excellent thermal properties for heat sink applications. This study reports on a novel encapsulation rolling process for producing thin crack-free W-18.5 wt%Cu composite sheets. An increased rolling reduction ratio leads to the majority of the tungsten (W) particles being deformed and elongated along the rolling direction. Some W particles break into small particles under the large rolling force, resulting in a significant reduction in particle size. The rolling reduction ratio significantly affects the mechanical and electrical properties. It is observed that the highest values of relative density and hardness are 99.8% and 457 HV, after a total thickness reduction of 75%. The electrical conductivity, thermal conductivity and coefficient of thermal expansion (CTE) decreases significantly with the rolling reduction ratio. At the rolling reduction ratio of 75%, the W-Cu composite achieves a low CTE of 7.19 × 10−6/K but with a low thermal conductivity of 129.18 W/(mK). Furthermore, annealing at 1000 °C shows a negligible effect on the electrical and thermal conductivities of the W-Cu composite sheet when the annealing time is less than 3 h. Instead of the matrix phases, the W-Cu interfaces are deemed to play a significant role in determining the electrical and thermal conductivities. Therefore, improving the W-Cu interfacial bond is crucial to achieving high electrical and thermal conductivity while maintaining a low CTE.