Strengthening mechanism and metal/ceramic bonding interface of cold sprayed TiNp/Al5356 deposits

As the literature reported, the microhardness of particle reinforced metal matrix composite coatings fabricated by cold spraying (CS) could be significantly increased compared to pure metallic coatings by CS. However, the correlation between the strengthening mechanism of reinforcements and the microhardness increment is still not well revealed. Therefore, in this study, two strengthening mechanisms of reinforcement particles in CSTiNp/Al5356 coatings, i.e. the strain hardening effect of reinforcement particles tamping on the metal matrix and the dispersion strengthening effect of uniformly dispersed reinforcement particles, were studied, and the proportions by two strengthening effects were qualitatively characterised as a first approximation by a proposed microhardness calculation model based on the hardness data of both the as sprayed and heat treated coatings. Results show that the dispersion strengthening effect of TiN particles plays a greater role in microhardness increment than the strain hardening effect of TiN tamping on the Al5356. In addition, the bonding interface of metal/ceramic particles in TiNp/Al5356 coatings was characterised using a transmission electron microscope for revealing the bonding features at the interface. Results show that although an intimate contact (i. e. bonding) is formed at the TiNp/Al5356 interface, the bonding is relatively weak, with some cracks or pores possibly present at the interface.