Strengthening mechanism of sub-nano NiP and CuP phases particles on the Pb-Sn bronze alloy.

The influence of the sub-nano NiP and CuP phases on the microstructure, mechanical properties, and strengthening mechanism of Cu-20Pb-5Sn-xP (x = 0,0.05,0.1,0.3,0.5) alloy were discussed under the addition of P to obtain a new Pb-Sn bronze alloy applying for bimetallic cylinder block. The results showed that the tensile strength and hardness of the Pb-Sn bronze alloy increase with the P contents, while the elongation increased first and then decreased. The main strengthen mechanism was that sub-nano NiP and CuP phases dispersed in the matrix, hindering the movement of dislocations during deformation. Additionally, the grain refinement also contributed to the improvement of mechanical properties. The NiP phase is easier to form than the CuP phase. And it is easier to combine with the matrix and more stable. The NiP and CuP phases were studied by using different characterization techniques, such as OM, SEM, EDS, XRD, TEM and First-principles, Phase diagram calculation method. When P is added to the alloy, the NiP phase first appears in the alloy, and when the P content increases to more than 0.3 wt%, the CuP phase begins to appear. This is because the NiP phase is easier to form than the CuP phase and is more stable. Only after part of P reacts with Ni dissolved in copper to form NiP, the remaining P and Cu can form CuP.