Microstructure characterisation of hypereutectoid aluminium bronze composite coating

Hypereutectoid aluminium bronze coating was deposited onto an E.N. 10503 steel using plasma transferred arc welding (PTA). Microstructure characterisation of the coating and a section near the steel substrate joint was carried out using SEM, EBSD, EDS in conjunction with XRD and depth-sensing nano-indentation. The constituent phases in the coating were identified as: martensitic Cu3Al ?1' phase, solid solution of Al in Cu ? phase and the intermetallic Fe3Al ?1 phase. The region near the steel substrate was characterised by high hardness, large grains and presence of Cu precipitates. No cracks were observed in this region. The coating has high hardness of 4.9GPa and Young’s modulus of 121.7GPa. This is attributed to homogeneous distribution of sub microns size Fe3Al intermetallic phase. The implications of the coating to the engineering application of sheet metal forming are discusse

The effects of substrate dilution on the microstructure and wear resistance of PTA Cu-Al-Fe aluminium bronze coatings

Cu-Al-Fe aluminium bronze alloys are good candidates for precious tools and forming dies due to their high wear resistance, good sliding properties and low tendency for adhesion to ferrous metals. Plasma transferred arc (PTA) is an effective process for deposition of such robust coatings by enhancing the bond between the bronze coating and steel substrate. However, the microstructure and wear characteristics of these coatings are strongly influenced by the diffusion of substrate elements (mostly iron) to the interface. In the present study, the effects of substrate dilution on the microstructure and wear behaviour of Cu-Al-Fe alloy deposited by PTA on medium carbon steel substrate were investigated. The results show that the deposition current controls the melting temperature and iron dilution which result in the formation of Cu3Al martensitic β1' phase in a low dilution and the ordered β1 phase in high dilution. The wear behaviour of the coating is dominated by failure of the matrix phase. Low dilution coating with martensitic phase exhibits the highest wear resistance. On high diluted Fe rich coating, pile up of dislocation on the intermetallic K phase leads to surface cracks and delamination of the coating resulting in a high wear rate