Effects of carbon nanotubes on hardness and internal stress in Ni–P coatings

Abstract

Nickel–phosphorus carbon nanotube (CNT) composite coatings were prepared via brush electroplating. The CNTs were added in amounts of 0, 0·5, 1·0 and 2·0 g L−1. Half samples of these coatings were heated at 400°C for 1 h to obtain crystalline Ni–P CNT composite coatings. The hardness and internal stress of two kinds of composite coatings were studied. The results showed that the addition of CNTs improves the microhardness of crystalline Ni–P coatings; the higher the added CNT, the greater increase in microhardness. However, the effects are completely different for amorphous coatings. Heat treatment greatly increased the microhardness of amorphous Ni–P platings, but the microhardness of Ni–P based CNT composite coatings only slightly increased. The microhardness of the crystalline Ni–P based CNT composite coatings was lower than that of the crystalline Ni–P platings and was not insensitive to the changes in the added amounts of CNTs. The addition of CNTs significantly reduced the microscopic internal pressure stress of crystalline coatings; the higher the added CNT, the lower the microscopic internal pressure stress.