Key Engineering Materials Vols. 373-374

Abstract: The microstructure evolution and the growth behavior of intermetallic compounds (IMCs) at Sn-xZn-2Cu/Cu (x=6.5, 8.8, 10 and 12, wt%) interfaces during soldering were investigated. The results indicate that planar Cu5Zn8 layer is formed at each interface of Sn-8.8Zn-2Cu/Cu, Sn-10Zn- 2Cu/Cu and Sn-12Zn-2Cu/Cu couples for all soldering time. However, for Sn-6.5Zn-2Cu/Cu couple, it is Cu5Zn8 phase that formed at the interface within shorter soldering time (1 h and 4 h), but the interfacial reaction products become a double layer structure of Cu6Sn5 phase (near Cu substrate) and CuZn phase (near solder) for longer soldering time (25 h and 49 h). The thickness of IMC layers in all couples increases exponentially with the soldering time. It is also found that for the same soldering time, the thickness of IMC layers increases with increasing Zn content in the solder.

Abstract: Aiming at improving the impact wear-resistant performance of metals, a new sort of surfacing electrode named TKCE50 was developed in this paper. This electrode is a Fe-Mn-Cr-Mo-V alloy system and belongs to iron-base wear-resistant materials. Tests like hardness, wear loss and impact-abrasion test were performed on the samples surfaced with the electrode. The results indicated that TKCE50 had not only good welding technological properties, but also super work-hardening effect and perfect impact wear-resistance. In addition, the work-hardening and wear-resistant mechanisms for this electrode were discussed based on corresponding experimental investigation and theoretical analysis.

Abstract: In this paper, the mechanism, characteristics and categories about corrosion of offshore engineering equipments are investigated. Some of selected advanced surface engineering techniques for corrosion control are introduced. On account of particularity of oceanic environment and performance requirements for the equipments, the paper proposes corresponding anticorrosion measures for offshore engineering equipments. And as a tentative study on surface engineering management & analysis, the paper presents a scenario of anticorrosion design from the viewpoint of System Engineering, including preparation, storage and conveyance of anticorrosion materials, as well as R&D, operation, and management of anticorrosion facilities. It is expected that advanced surface engineering techniques used in anticorrosion can help offshore engineering equipments with good viabilities, perfect performances, low rate of failure, long life-time and high rate of readiness. Anticorrosion design of offshore engineering equipments is of far reaching importance not only to develop our Advanced Manufacturing Technology facing towards 21st century but also to implement sustainable development of our national economy, as well as to our national economy strength.

Abstract: Electrochemical corrosion behaviors of two common-used ship coatings——epoxy aluminum coating, chloride rubber iron red coating and their composite coatings immersed in 3.5%NaCl solution were investigated using electrochemical impedance spectroscopy combined with open circuit potential measurements and SEM micrograph analysis. Potential-time result indicates that the free corrosion potential of these three coatings with immersion time are more positive than that of metal substrate, which can serve as barrier layer to protect metal substrate from corrosion. During the course of immersion, increasingly negative shift potentials with time reveal the growth of electrochemical area of anode and corrosion takes place continuously. EIS shows that corrosive species can penetrate into coatings and reach the coating/substrate interface promptly, causing the decrease of its shielding role and the beginning of electrochemical corrosion. SEM micrographs suggest that coatings were compact and continuous compared with obviously coarse and loose after corrosion, indicating the penetration of corrosive species destroys cross linkage of coatings. Composite coatings present better protection performance, displaying the effect of “1+1>2” remarkably.

Abstract: Effects of shape and distribution of the hard phases (Fe, Cr)7C3 and Cr7C3 on wear resistance of Fe5 deposited metal obtained by plasma arc welding with electromagnetic stirring were investigated. The deposited layers were subsequently characterized by SEM observation, wear tests and hardness measurements. The hardness of the deposited layers was increased and then decreased with increasing the applied current. With the current of 3 A and the electromagnetic frequency of 10 Hz, the hardness of deposited metal reached maximum value of about HRC 68, which was increased about 19% compared with that of the deposited metal without electromagnetic stirring. The wear weight loss of the deposited metal with 3 A and 10 Hz is greatly decreased. It is confirmed that the shape and the distribution of hard phase significantly affect wear resistance of the deposited metal. The slag M7C3 is transformed into hexagon during electromagnetic stirring with 3 A and 10 Hz. And the regular distribution of hexagon M7C3 in the deposited metal resulted in the excellent wear resistance.

Abstract: Nanostructured and conventional WC-Co coatings were deposited on 1Cr18Ni9Ti stainless steel substrate using an atmospheric plasma spraying facility. The friction and wear behavior of the resulting cermet composite coatings in water environment was comparatively investigated. It was found that the nanostructured and conventional WC-Co coatings had similar friction coefficients under the same testing conditions. However, the nanostructured WC-Co coating had better wear resistance than the conventional WC-Co coating as slid against both Si3N4 ball and stainless steel ball. At the same time, the stainless steel or Si3N4 counterpart matched with the nanostructured WC-Co coating had a much smaller wear rate as well, and as compared to rubbing against the ceramic ball counterpart, the two types of coatings rubbing against the stainless steel ball registered lower friction coefficients and wear rates.

Abstract: High temperature tribological behavior of nano-Al2O3 in different base oils were tested by a SRV multifunctional test system. The results show that the nano-Al2O3 particles can obviously improve the antiwear and friction reducing properties of the base oil under high temperature and high load. The friction coefficients of the base oil with added nano-Al2O3 are reduced about 35%, and abrasion loss reduces about 60%. When temperature is 500°C and load is 500N the pure base oil has lost lubricative function, but the base oil with added nano-Al2O3 can still remain the lower friction coefficients. Tribological behavior should be similar to the “ball bearing” lubrication action of the nano-Al2O3 particles, so the movement between the two tribological pairs becomes sliding/rolling.

Abstract: Sliding experiments lubricated with hydroxyl silicate magnesium particles as additive were performed under ambient condition and different loads by using an AMSLER friction and wear tester. The surface topographies and compositions of worn surface of 45 steel rings were analyzed by SEM and EDAX. The experimental results show that the friction load had great effect on generation of the frictionally-formed protective coating. No protective coating formed on the worn steel surface under lower friction load. However, a smooth and continuous protective coating can be developed on the worn surface of the steel when the friction load is high enough. The chemical composition of the protective coating is roughly the same as the additive. The additive can be fractured, stretched and flowed along the sliding direction under high contacting stress and instantaneous flash temperature, which result in coating being formed.

Abstract: In this paper, TiN coating was deposited onto the nitrided 32Cr2MoVA by multi arc ion plating and proceeded line contact fatigue experiment to investigate the influence of hard coatings on the contact failure properties of nitriding steel. The results of experiment show that pitting is primary type of contact fatigue failure for TiN coated 32Cr2MoV and the pits on the TiN coated surface are shallower and smaller than that of the nitrided 32Cr2MoV. After TiN coating produce crisping and desquamation under higher contact fatigue loads, the exposed matrix surface begin to bear the contact load. The superficial microstructure of TiN coated 32Cr2MoV was more fine, and content of nitrides were higher than that of the nitrided, which insured the distribution of hardness gradient of subsurface was more rational than that of nitrided 32Cr2MoV. The contact fatigue strength of TiN coated 32Cr2MoV is greater about 200MPa than that of the nitrided 32Cr2MoV.

Abstract: In the present work, surface-coated Cu nanoparticles with FCC structure and an average size of 40 nm were prepared by reducing reaction and surface modification technique. The morphology and phase structure of the nano-copper were characterized by transmission electron microscope (TEM). The ball-on-disc tester and ring-on-block tester were performed to study the tribological properties of surface-coated Cu nanoparticles as oil additive. The tests were carried out under the lubrication of 50CC oil alone and oil containing surface-coated nano-copper additives. The morphologies and elementary distributions of the worn surfaces were analyzed by scanning electron microscope (SEM) and energy dispersive spectrometry (EDS), respectively. Results indicate that surface-coated nano-copper additives can significantly improve the wear resistance and load-carrying abilities of 50CC oil, as well as reduce friction coefficient. A soft copper protective film is formed on the worn surface lubricated with oil containing nano-copper additives, which separates the worn surfaces, avoids their direct contact and reduces friction and adhesive wear. Besides, the grooves and small valleys on the worn surfaces are found to be partly filled and repaired by nano-copper, as makes the worn surface repaired and smoother.