Properties And Structural Correlation For Electroless Plating Ni-W-P Alloy Deposits

Using SX2-2.5-10model of box type furnace on alloy coatings for annealingtreatment, contrast heat treatment before and after, analysis the hardness, wearresistance, corrosion resistance and other characteristics about macroscopic properties;Both using scanning electron microscopy and optical microscope on coatings, analysisthe surface, using EDS analyzer on coatings, analysis the components, using XRDtechnique, by jade software, analysis the coatings grain size, lattice strain and degree ofcrystallization; Further development the linkages between macro-and micro-structureabout alloy plating before and after heat treatment, make it clear that the mechanism ofcrystallization on macro-properties of alloy coatings.The results show that, the medium phosphorus content coatings is the mixedcrystal structure on plated state, there has certain content of Ni crystal in the coatings,the coatings surface topography is rendering cell structure, the content of Ni in coatingsis lower, the grain size and degree of crystallization is lower too, at the same time, as Wand P joined, lead the lattice distortion and larger micro-strain. Heating the coatings,with the heat temperature increased, the coatings surface becomes smooth and uniform,the degree of crystallization and the content of crystalline phase is increasing, themicroscopic strain is decreasing, when the temperature reached about400℃, the Ni3Pstart precipitation, the grain size of Ni3P is larger than Ni, when the temperature reached500℃above, the grain size of Ni is larger than Ni3P. But even if the temperature up to600℃, the coating is not fully crystallized, there still remains a number ofnon-crystalline. In the processing, the coatings hardness gradually increased with thetemperature’s increasing and reached the maximum at500℃, it is mainly because thefactor which can improves the hardness, such as the degree of crystallization, grain sizeof crystalline phase, the various factor’s relative amount, these factors competing toeach other; When the heat temperature exceeding500℃, the coatings hardness isdecreasing with the temperature increased, it is mainly due to the weakened effect thatthe coarsening size on Ni3P which strengthened Ni; The coatings wear resistancevariation is similar to hardness, the maximum wear resistance corresponds to the highestdegree of hardness, it appears at500℃; and the minimum wear resistance correspondsto the lowest degree of hardness, it appears at the plated condition; The corrosionresistance of coatings can roughly be divided into three sections, below the300℃, the corrosion resistance of coatings is increased with the temperature increased, it isdecided the coatings decreasing stress; When the temperature is300℃-500℃, thecorrosion resistance of coatings showed a declining trend, in this temperature region,the Ni3P phase increased the amount of corrosive micro-batteries, it caused the coatingvolume shrinkage and producing holes; When the temperature reached500℃above, thecorrosion resistance of coatings is increased, this mainly due to the coating ofcrystalline phases in large grain size, not only reduce the number of corrosivemicro-batteries, but also have a favorable area rates which has a large cathode and smallanode,so it improved the corrosion resistance of coating.