Tribological properties and corrosion resistance of nickel-based composite mold inserts containing lubricant nanoparticles for micro-injection molding

Abstract

During the micro-injection molding process, the lifetime of mold inserts is severely limited by high-pressure impact conditions and demolding friction. To investigate the tribological properties and durability of mold insert, nickel-based composite mold inserts have been fabricated by electroforming adding polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS2) and tungsten disulfide (WS2) nanoparticles, respectively. The surface morphology of pure nickel (Ni) and composite mold inserts were characterized. The Ni grain sizes of the composite mold inserts significantly decreased without changing the grain orientation and phase composition. The maximum microhardness of Ni-WS2 mold inserts was increased from 278.2 HV of pure Ni to 456.0 HV, an increase of 1.64 times, while the minimum friction coefficient against Si3N4 ball was reduced to 0.25. In addition, Ni-WS2 mold inserts exhibited excellent tribological properties, and their wear resistances were further investigated at different sliding speeds and external loads. With the increase of sliding speed and load, the self-lubricating property of the composite mold inserts would gradually disappear and the wear rate would increase significantly. The formation of a uniform and dense friction transfer film is the key to reducing the friction coefficient and wear rate. Furthermore, the corrosion resistance of the mold inserts was improved to some extent with the addition of the three nanoparticles. In dynamic electrochemical tests, the corrosion current density of Ni-PTFE mold insert was 3.083 ± 0.228 × 10−6 A/cm2 and the corrosion rate was 0.036 ± 0.003 mm/year, which showed the best corrosion resistance.

Keywords

• Tribological property
• Composite mold insert
• Lubricant nanoparticle
• Wear
• Corrosion resistance