Microstructure and properties of thermal-sprayed NiCrWRE coatings

The powders of NiCrW and NiCrWRE alloys were flame sprayed on a medium-carbon steel substrate by thermal spray welding. The micro- structure and tribological behavior of coatings were studied experimentally by means of scanning electron microscopy （SEM）, field emission gun scanning electron microscope （FEGSEM）, and wear tests. The addition of CeO2 modifies the coating morphology from a needle-like structure to a roughly cubic morphology; the refining and purifying effect of rare earth elements makes the microstmcture more compact and finer. Analysis of the worn surfaces reveals that the coatings with CeO2 addition show improved abrasive wear resistance over those without CeO2. By adding CeO2, the hardness of the coatings is significantly increased, and the wear resistance of the coatings is enhanced.

Rare earth effect on the microstructure and tribological properties of FeNiCr coatings

FeNiCr alloys with various amounts of La2O3 powders were thermally sprayed onto steel substrate.Electron probe microscopy analysis （EPMA）,X-ray photoelectron spectroscopy （XPS）,and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration were employed to investigate the properties of the sprayed coatings.The results show that rare earth can refine the microstructure effectively and make the element distribution uniform,which leads to the improvement in the properties of the coatings.Meanwhile,the wear rate of the FeNiCr alloy with 1.5% La2O3 is smaller than those of the other coatings.Interestingly,the rare earth can reduce the friction coefficient and act as a self-lubricant in the oxide debris layer formed on the worn surface in friction.The wear mechanism of the coatings is oxidation wear,and a large amount of counterpart material is transferred to the coatings.

Effect of CeO_2 on Microstructure and Bond Strength of Fe-Ni-Cr Alloy

Fe-Ni-Cr alloy powders with and without 0.4% CeO_2 were flame sprayed on the surface of 1045 carbon steel substrate. The effect of rare earth oxide CeO_2 on the interface layer and microstructure was investigated by X-ray diffraction analysis, SEM and EDS. Based on our previous work, comparison on the microstructure of a Fe-Ni-Cr alloy with and without 0.4% CeO_2 addition was made. The correlation between the microstructure and bond strength was studied. The addition of CeO_2 in Fe-Ni-Cr alloy shows promise results for providing good bonding strength as well as tribological properties. The results show that the hardness of the coatings can be improved by addition of 0.4% CeO_2, and the shape of powders is more spheroidal. The combination of three aspects, namely small, well-distributed microstructure, the well-distributed matrix and promotion of diffusion leads to the improvement in bond strength of Fe-Ni-Cr alloy with addition of 0.4% CeO_2.

Effect of some parameters of formation on surface graphite-bronze composite layer prepared by vacuum infiltration casting technique

Surface composite up to 3.0 mm in thickness with compact microstructure was fabricated successfully via vacuum infiltration casting technique on the bronze substrate under the optimum experimental conditions: the vacuum degree of -0.08 MPa, pouring temperature of 1220℃, grain size of 0.20-0.24 mm, preheating temperature of 180℃. The preform was mainly composed of graphite particles and binder NJB (self-fabricated binder). The vacuum degree, pouring temperature, preheating temperature and grain size during infiltration casting play an important role on the process of forming the surface composite. The results show that three cases are obtained in the vacuum infiltration casting technique: no infiltration, partial infiltration and full infiltration. The main reason of no infiltration is that the vacuum degree is not enough so that the force acting on the liquid metal is lower than the resistance due to the surface tension and the pouring temperature is somewhat low. Partial infiltration is because of somewhat lower vacuum degree and pouring temperature. Full desired infiltration is on account of suitable infiltration casting conditions, such as vacuum degree, pouring temperature, grain size and preheating temperature. The influencing effect of vacuum degree is most obvious for the formation of surface composite, then pouring temperature and particle size. The infiltration mechanism is discussed on the bases of the different processing conditions.