Key Engineering Materials Vols. 336-338

Abstract: SHS-gravitational process was developed to synthesize the ceramic lined steel pipe, especially for elbow, conical pipe, three-way and four-way pipe and pipe with a small diameter. In SHS-gravitational process, the molten ceramic, which separated out from the reaction products due to their density difference, solidified to form the ceramic lined layer in the steel pipe when contacted with the steel pipe wall. With an X-ray diffractometer and a scanning electron microscope, it can be found that the ceramic layer is composed of α-Al2O3 and FeAl2O4. A small amount of iron also remains in the ceramic layer. There is a thin equiaxed grain area of alumina near the steel pipe wall, and then alumina was grown in form of dentrite to the surface of ceramic layer. FeAl2O4 distributes among alumina dentrite. Although the ceramic layer was solidified from one end to another end of a pipe, the microstructure of ceramic layer was almost uniform throughout the whole length of the pipe.

Abstract: A composite coating with TiC Particle of embedded in nickel based alloy has been in-situ synthesized by induction cladding a precursor mixture of nickel based alloy powder, titanium and graphite powders. The results showed that the composite coating has good metallurgical bonding with the substrate as well as there is a good wettability between the reinforcement TiC and the coating matrix. The microstructure of the composite coating is mainly composed of γ-Ni dendrite, a small amount of M23C6, and dispersed TiC particle. The volume fraction of TiC particle increases with increasing of volume fraction of titanium and graphite. The microhardness gradually increased from the bottom to the top of the composite coating. The average microhardness of the composite coating is HV0.21200, 5 times larger than that of the 16Mn steel substrate.

Abstract: Diamond film was synthesized on Co-deficient (Co content is about 0.5%) WC-Co substrate using microwave plasma chemical vapor deposition (MPCVD) equipment without special pretreatment. SEM, XRD, Rockwell-indentation test and scratch test were used to analyze the structure and morphology of the diamond film and its adhesion to the substrate. Co content was also measured by EDAX. The results show that the film synthesized is of ideal diamond structure with perfect and uniform grains, dense and continuous surface and strong adhesion. Co content on the surface of the substrate is about 0.8% after 20h deposition, which is considered as one of the main causes to get good adhesion.

Abstract: Seal materials often lose their effectiveness due to the wear of surface under the combined effect of environment and load. In this research, a metallurgical bonding composite coating reinforced with nickel -coated tungsten carbide (Ni -WC) particles was produced on 40Cr carbon steel substrate by plasma sprayed. The bond strength of the coating/substrate interface and the tensile strength of the coating itself reached 260–330 and 100–132MPa, respectively. Effects of Ni and WC contents on the wear behavior of the coating have been systematically investigated at two different wear conditions, namely the high stress pin-on-disk abrasion and three-body abrasive wear. The results show that the higher the Ni content in the coating, the lower the hardness and wear resistance. In stress pin-on-disk abrasive wear, the mass percent of Ni in the coating having the lowest wear amount was 40%, and which was 60% in three-body abrasion. In view of the above, the WC reinforcement of the composite coating plays an important role in protecting the matrix from being worn-out, whereas in the abrasive wear, the wear mechanism is mainly controlled by the scratching and micro-cutting of the matrix followed by the pull out of WC particles due to the scratching action of abrasives. The wear resistance of the 40Cr carbon steel composite coating (Ni -WC) is better than that of the flame overlaid coating.

Abstract: A nanostructured TiO2 dominated ceramic coating was fabricated on Ti6Al4V by microarc oxidation (MAO). The coating with about 30 μm thickness is porous in the outer layer and compact in the inner layer, mainly composed of rutile and a small amount of anatase TiO2, both in nano grain structure. The hardness and elastic modulus of the compact layer in the coating are about 8.5 GPa and 87.4 GPa. The adhesion strength is about 70MPa. The friction coefficient of the polished coating sliding against GCr15 steel is as low as 0.2, which is clearly superior to that of the unpolished one. This is attributed to the low surface roughness. However, the oxidation wear mechanism occurring at the later stage of wear tests leads to a gradual increase of friction coefficient.

Abstract: Resin lenses have substituted for glass lenses to be dominant productions in eyeglasses market because of lightweight, anti-impaction and easy molding. However, the problem existed that the wear resistance of resin lenses was inferior. In order to increase the wear resistance of resin lenses, we coated DLC film on PC by the method of RF-PCVD, researched the influence of depositing power, gas concentration, time on the performance of coating, chose the optimum technological parameters. The component of coating was testified by XPS. The hardness and wear resistance were tested. The results showed that DLC films deposited on PC could improve the wear resistance of material.

Abstract: Tribological behavior of B4C-SiC self-mated pairs was studied, and pre-oxidation treatment was adopted to improve the tribological properties of B4C-SiC. At the same SiC content, self-friction coefficient of B4C-SiC decreases with the increase of sliding distance, normal load, and sliding velocity; while the increasing of SiC content leads to increase of both self-friction coefficient and ware rate, which was determined to be within the range of 0.8×10-6~5.8×10-6 mm3·N-1·m-1. Pre-oxidation treatment of the B4C-SiC resulted in the formation of B2O3/H3BO3 lubricant layers, which effectively reduced the self-friction coefficient.

Abstract: Two drums suitable for a Chase Machine were made of Al metal matrix composites containing 25vol.% SiCp with 3.5 μm and 34 μm in nominal diameter respectively. The same brake pads were measured on the Chase Machine installing each individual drum. It has been found that the brake pads had better frictional performance and wear resistance against the drum with the large-size SiCp than against the drum with the small-size ones. Friction fade took place at elevated temperatures - above 316 oC, but the original level of friction coefficient could be regained rapidly upon cooling with regard to the latter. The minor level of friction coefficient was attributable to soft Al crystal structure characteristics and thick tribofilms during the testing stages.

Abstract: Conventional two-layered structure thermal barrier coatings (TBCs) with different pre-oxide layer thicknesses were produced by EB-PVD onto Ni-based superalloy. The pre-oxide layer with different thicknesses was formed after vacuum heat treatment for 2 hours and before ceramic deposition by heating the bond coat to 1323K in air for different times. It has been found that with pre-oxide layer thickness increasing from 1μm to 3.1μm, the growth rate of thermally grown oxide (TGO) increased during thermal cycling test and the thermal cyclic lifetime of TBCs decreased from 730hs to 400hs Two failure modes were observed for TBCs with different pre-oxide layer thicknesses and different TGO layer growth rates.

Abstract: The cyclic oxidation of thermal barrier coating (TBC) specimens consisting of nickel-base superalloy, low pressure plasma sprayed Ni-24Cr-6Al-0.7Y (wt.%) bond coatings and air plasma sprayed 7.5 wt.% yttria stabilized zirconia top coatings was studied at 1050°C in air, (air + 5%H2O), O2 and (O2 + 5%H2O) respectively. The oxidation kinetics of the TBC in each test environment accords with parabolic law at the initial stage and obeys almost liner law at the final stage. The cyclic oxidation life of the TBC is 500h (1h/cyc) in O2 and (O2 + 5%H2O) and 900 h in air and (air + 5%H2O). The SEM observations indicated the oxide formed along the bond coat and top coat interface after failure at 1050°C in different environments are all consisted of Al2O3, Ni(Al,Cr)2O4, NiO and Cr2O3.