Search

A new technology, duplex ion nitrocarburizing and sulphurizing technology (DINS), for friction reduction and anti-scuffing applications of diesel engine cylinder was studied. Duplex ion nitrocarburized-sulphurized layer was prepared on the surface of CrMoCu alloy cast iron by using the DINS process. The morphology, phase structure and tribological behaviors under sulphur contained additive lubrication were investigated. Results show that the sulphide surface layer of the duplex layer is mainly composed of close-packed hexagonal structured FeS phase and cubic structured FeS2 phase. The nitrocarburized sub-surface layer of the duplex layer is mainly composed of Fe2C and Fe3N phases. The harder nitrocarburized layer can provide effective support to the softer sulphide layer and avoid its lamellar tear. The synergistic effect between the duplex layer and the sulphur contained additive lubricant, resulted in 10% and 33.3% reduction in coefficient of friction and wear volume, respectively, compared with those of the sulphurized surface, and 25% and 50.1% reduction, respectively, compared with those of the plain surface. Bench test of diesel engine further demonstrated that the DINS process can provide the treated cylinder with superior properties in anti-scuffing and friction reduction, so that it can be used to prolong the service life of the cylinder.

Mechanical milling of Mg 1 − x Fe x B 2 with x =0–0.4 led to the formation of amorphous phase. For x =0, the hexagonal MgB 2 phase was formed after a heat treatment at 450 °C or above with critical temperature T c =38–40 K. Fe-substituted MgB 2 phase was formed after annealing at 450 °C or above when x =0.05, 0.1 and 0.2. Fe solubility in the MgB 2 phase decreased with increasing annealing temperature, while lattice parameters ( a and c ) decreased. It has been found that critical temperature T c increased with increasing annealing temperature. For Mg 0.6 Fe 0.4 B 2 powder, MgB 2 phase could not be formed after crystallization. Single solid-solution MgB 2 phase could be formed in Mg 0.95 Fe 0.05 B 2 after annealing at 450 °C. This sample exhibited paramagnetic between 30 and 290 K with a high magnetic moment of μ Fe =5.5–6.0 μ B . An anomaly (minimum in reciprocal magnetic susceptibility) was observed below 30 K, accompanied by magnetic splitting in Mossbauer spectroscopy.

A MgB 2 powder was mechanically milled for different times. X-ray diffraction indicated the formation of an intermediate phase with an unknown structure before formation of amorphous phase. The intermediate structure was superconducting below 18 K, while the amorphous phase was non-superconducting till 4.2 K. After heat treatment at 700 °C, all the mechanically milled samples formed back into the hexagonal MgB 2 structure with T c = 39 K. X-ray and Raman investigations suggested that the intermediate structure was metastable with a lattice compression, which was probably associated with the reduction in transition temperature.