In-situ synthesis of nanodiamonds reinforced iron-nickel matrix nanocomposites and their properties

In-situ synthesis of nanodiamonds (NDs) reinforced iron-30 wt% nickel (Fe30Ni) alloy matrix composites was achieved by spark plasma sintering (SPS) using Fe30Ni alloy powders added with carbon nanotubes (CNTs) from 0.25 to 1.0 wt%. The microstructures and properties of the composites were analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, mechanical and coefficient of thermal expansion (CTE) tests. Experimental results showed that the NDs with mean size of 20 nm were generated with some residual CNTs remaining in the Fe30Ni matrix after the SPS processing at 1050 degrees C and 80 MPa. The resultant composites are NDs/CNTs hybrid reinforced metal matrix composite. The microhardness and compressive yield strength (sigma(0.2)) of the Fe30Ni composites increased monotonically with the addition of CNT contents up to 0.75 wt%. The CTEs of the composites decreased substantially with the increase of CNT contents in temperature range of 25-150 degrees C. The Fe30Ni-0.75 wt% CNT is considered to be the optimal proportion of CNTs addition, in which the sigma(0.2) increased 23.4% and CTEs decreased 64.8%, respectively. The SPS provides a new method for the in-situ synthesis of nanodiamond reinforced metal matrix composites.