Peiqing La

A study of Ni3Al coating on carbon steel surface via the SHS casting route

A nickel aluminide (Ni 3 Al ) coating on a carbon steel surface was fabricated by the self-propagating high-temperature synthesis (SHS ) casting route. Coating phases were determined by using X-ray diVraction ( XRD). The microstructure of the coating and bonding interface between the substrate and the coating, and the distribution of elements adjacent to the interface, were analyzed by using electron probe microanalysis (EPMA). The microhardness of the coating was measured. The tribological properties of the coating at diVerent elevated temperatures were investigated and the worn surfaces at diVerent temperatures were analyzed by EPMA. The elemental chemical state of the worn surface was determined by using X-ray photoelectron spectroscopy ( XPS). The results show that the coating was composed of Ni 3 Al phase, and that its microstructure was dense and pure. Elements had diVused mutually at both sides of the interface and a metallurgical bonding interface was formed. The heat of the reaction coarsened the grain size of the substrate near the interface. The hardness of the coating is higher than that of the substrate. Wear loss and friction coeYcient of the coating vary with the testing temperature. The coating had a good resistance to oxidation at elevated temperature. Oxidation of the coating occurred as a result of friction at the temperature of 873 K. The mechanisms of combustion synthesis of Ni 3 Al coatings on carbon steel substrates are discussed in detail. It is pointed out that the combustion temperature and the wettability between the product of the reaction and the substrate are significant to obtain the coating.

Wear of plasma-sprayed nanostructured zirconia coatings against stainless steel under distilled-water conditions

The friction and wear properties of plasma-sprayed nanostructured and traditional zirconia coatings against stainless steel were investigated with a sliding, reciprocating and vibrating test machine under water-lubricated conditions. The counterface was a 10-mm diameter AISI316 stainless steel ball. It was found that the plasma-sprayed nanostructured zirconia coating possessed better wear resistance than traditional zirconia coating. The wear rates of the nanostructured zirconia coatings are in the range from one-fourth to four-fifths of the traditional zirconia coating under loads ranging from 20 to 50 N. The plasma-sprayed nanostructured zirconia coating also reduces wear rate of the friction pair materials. The higher wear resistance of the plasma-sprayed nanostructured zirconia coating is attributed to its enhanced cohesion, improved microhardness and homogenous microstructure. The wear mechanisms of nanostructured and traditional zirconia coatings under water-lubricated conditions are discussed.

Study of wear resistant MoSi2–SiC composites fabricated by self-propagating high temperature synthesis casting

Abstract MoSi 2 composites with 10, 15 and 20 wt.% SiC were fabricated as wear resistant materials by self-propagating high temperature synthesis (SHS) casting route. The composites were analyzed with X-ray diffraction (XRD) and scanning electron microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS). Hardness, toughness and wear rate of the composites were measured. XRD examination showed that the composites mainly consisted of MoSi 2 , SiC and Al 2 O 3 phases. Content of Al 2 O 3 was about 3 wt.% in the composites. Microstructures of the composites varied with the amount of SiC. Silicon carbide phase presented in the composites was in the term of large particles or short fibers depending on the amount of SiC presented in the composites. Cracks existed near interfaces of the large SiC particles and MoSi 2 matrix in composites with 10 and 15 wt.% SiC whereas they did not appear in composite with 20 wt.% SiC. Hardness and toughness of the composites increased with increase of SiC. Wear rate of the composites and its sensitivity to load dramatically decreased with SiC. Composite with 20 wt.% SiC had the best properties.

Tribological properties of Ni3Al-Cr7C3 composite coating under water lubrication

The tribological properties of Ni3Al-Cr7C3 composite coating under water lubrication were examined by using a ball-on-disc reciprocating tribotester. The effects of load and sliding speed on wear rate of the coating were investigated. The worn surface of the coating was analyzed using electron probe microscopy analysis (EPMA) and X-ray photoelectron spectroscopy (XPS). The results show the friction coefficient of the coating is decreased under water lubrication. The wear rate of the coating linearly increases with the load. At high sliding speed, the wear rate of the coating is dramatically increased and a large amount of the counterpart material is transferred to the coating worn surface. The low friction of the coating under water lubrication is due to the oxidizing of the worn surface in the wear. The wear mechanism of the coating is plastic deformation at low normal load and sliding speed. However, the wear mechanism transforms to microfracture and microploughing at high load with low sliding speed, and oxidation wear at high sliding speed. It is concluded that the contribution of the sliding speed to an increase in the coating wear is larger than that of the normal load.

A study of MoSi2MoS2 coatings fabricated by SHS casting route

Abstract Coatings were fabricated on a steel substrate by a self-propagating high temperature synthesis (SHS) casting route. The processing is described in detail. The phases in the coating were examined using X-ray diffraction (XRD). The microstructures of the coatings were analyzed with optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). Tribological properties and microhardness of the coatings with 6–12 wt.% MoS 2 were measured. The experimental results show that the coatings were composed of MoSi 2 and MoS 2 phases and coatings with 6–12 wt.% MoS 2 had dense microstructure. Metallurgical bonding had formed between the coatings and the substrate. Friction of the coatings with 6–12 wt.% MoS 2 is lower than its steel substrate. Microhardness and wear resistance of the coatings with 6–12 wt.% MoS 2 are higher than that of the steel substrate. Near the interface microhardness of the coating varies with the distance to the interface.