Key Engineering Materials Vols. 373-374

Abstract: In order to improve surface properties, high chromium austenitic base heat-resistant cast steel was scanned with a 5kW continuous wave CO2 laser, the specimen was aged at the temperature of 600°C~900°C. The microstructure and phase composition of the specimen were analysed with optical microscopy, electronic microscope and X-ray diffractionse. The hardness was measured. The results show that as-cast structure of high chromium cast steel is coarse and non-homogeneous, and mainly consist of austenite, ledeburite and carbides. After laser surface melting, the section is divided into the melted zone consisted of fine austenite and carbides, the heat affected zone composed of austenite and eutectic carbides, and the base meta1. The melted zone is very fine structures with dendritic crystals, only at the bottom a cellular structure is observed. A continuous carbide network is located in the austenitic grain boundaries at the heat affected zone. Carbides particles distribute dispersed out, the hardness of melted zone increases 35% than the base metal after aging. The area and the hardness of various zones are related to the laser processing parameters. The hardening depth of melted zone and heat affected zone may be up to 200μm~300μm.

Abstract: Characterization of the interaction between an argon-oxygen post-discharge and hexatriacontane (C36H74) is carried out. Optical emission spectroscopy using the atmospheric band O2 (b1Σg +, v=0
X3Σg −, v’=0) at 760 nm gives simultaneously the evolution of the O(3P) concentration above the surface and the gas temperature by simulation of the rotational spectrum of the transition. Surface reactions contribute to the heating in the sample and to a substantial increase in the gas temperature. Finally, a strong correlation between the time evolutions of the transition intensity and the sample temperature is observed, suggesting that O(3P) is the main reactive species that produces the heating and the chemical changes in the HTC.

Abstract: A multiple-needle-cathode plasma surface alloying process has been developed for improving the properties of surface hardness, wear resistance and corrosion resistance of Ti6Al4V. The process is carried out at temperatures below 800 °C and facilitates the simultaneous introduction of W, Mo,nitrogen and carbon into the surfaces of Ti6Al4V forming gradient alloying layer structure with an extremely high hardness. The process is performed at working pressure of 30Pa-80Pa with 9-needle-cathode of W80Mo20 alloy rods array and a high pure graphite plate cathode as target electrode. A maximum microhardness is 4-6 times much harder than the substrate. The results show the presence of carbide and nitride ceramics phases contribute to high microhardness and wear resistance. The multiple-needle-cathode discharge plasma treatment is an effective method for improvement of the mechanical and tribological properties of titanium-base alloys by formation of graded diffusion hard surface layers. The present paper describes this novel process and properties characteristics.

Abstract: Armos fiber (F-12 aramid fiber in paper) was provided with broad application foreground as reinforcement material for advanced composites in aviation and spaceflight field, due to its outstanding properties, such as high modulus, high strength, high temperature resistance, erosion resistance and so on. However, the exertion of property was still limited by slippery surface, low surface energy and weak interfacial adhesion performance. In this study, the effects of oxygen plasma treatment time on polar functional groups introduced onto the fiber surface, surface free energy and surface topographic images were discussed by X-ray photoelectron spectroscopy (XPS) analysis, dynamic contact angle analysis system (DCA) and atomic force microscopy (AFM), respectively. It was found that the content of oxygen element and polar functional groups on fiber surface were all increased obviously after oxygen plasma treatment. The content of oxygen element on surface for untreated F-12 aramid fiber was 11.13%, while it increased to 15.20% after oxygen plasma treatment for 10 min; The content of polar functional groups on surface for untreated F-12 aramid fiber was 28.14%, while it increased to 38.11% after oxygen plasma treatment for 10 min. The polar component (γp) of fiber surface energy increased sharply from 6.82 mN/m to 36.68 mN/m after 10 min plasma treatment, the total surface free energy was increased from 46.26 mN/m to 64.66 mN/m.The results indicated that oxygen plasma treatment had introduced a large amount of reactive functional groups onto the fiber surface, and these groups can form together as covalent bonding to improve the surface wettability and increase the surface energy of fibers. At the same time, oxygen plasma treatment was able to generate a mass of bulges and grooves on F-12 aramid fiber surface, which had an active effect on increasing the chemical bond and mechanical function between fiber and resin and enhancing the interfacial adhesion performance of composite. The fiber surface grooves had been increased with the time prolonging before 10 min while decreased after 10 min, the results maybe relate to partial organic on fiber surface melting. It had an adverse effect on the interfacial adhesion properties of composite. Therefore, the optimum plasma treatment time was between 5 min and 10 min.

Abstract: An ambient-cured organosilicone resin modified with epoxy resin was synthesized with lab-synthesized polysiloxane resin and biphenix-A epoxy resin(E-20) by copolymerization at 180~190 °C for 2~3 hours. The effect of ratios between polysiloxane resin and E-20, reaction temperatures and reaction time on heat resistance and miscibility etc were discussed in detail. The experiment results showed that the epoxy modified organosilicone resin exhibited the best solubility performance and adhesion strength when the ratio of the polysiloxane resin to E-20 was 3:7. The Fourier transform infrared spectra (FTIR) revealed that hydroxy on epoxy resin had reacted with ethyoxyl on organic silicon molecular chain, but no ring-opening reaction happened on epoxy group of E-20. The excellent high-temperature resistance painting, based on these epoxy modified organosilicone resin was prepared with flake aluminum powder as temperature resistance filler, polyamide 650 as curer and WD-50 coupling agent as curing-promoter. It was shown that the temperature resistance was superior to 600°C and the adhesion strength of the coating was up to 1 grade. Scanning electron microscope(SEM) revealed the reaction happened on -Si-O-Si- and Al under high temperature improved the coatings to resist higher temperature. The mechanism of the high-temperature anticorrosion is attributed to “ring-opening reaction” and “cross-link solidification reaction”.

Abstract: Tribological performance of new brake pair is studied at different temperatures, load and speed by variable temperature friction and wear test. The research indicates that brake pair has better frictional characteristics at variable temperature as well as heat-fade resistance performance at high temperatures. Wear rate of brake block and brake disc increases with friction temperature rising, however wear-resisting performance of brake disc is comparatively stable. Load has less influence on frictional coefficient of brake pair. Wear rate of brake disc and brake block increases with load increasing, but brake block has comparatively stable wear-resisting performance. Frictional coefficient of brake pair increases and tends to stabilize gradually along with sliding speed increasing, and speed has less influence on wear rate of brake block and brake disc. Initial heat-fading occurs in brake block material along with frictional temperature rising, secondary solidification may happen when frictional temperature reaches a certain value. When temperature rises much higher, brake block begins to soften and plastic flow intensifies, in addition thermal decomposition occurs in organic substance and wear-resisting performance becomes poorer. Build-up welding material has strong age-hardening effect and stable thermal structure, which leaves surface hardness and structure performance of brake disc unchanged at high temperatures.

Abstract: This paper reported the electrodeposition of the nickel manganese alloy coatings from a sulphate bath using sodium citrate as complexing agent. The cyclic voltammetric experiments showed that the alloy initiative codeposition potential was about –0.457 V (vs.SCE). The effect of the plating conditions on the composition and the structure of the Ni-Mn were studied by energy dispersive X-ray spectrum and X-ray diffractometer, respectively. As a result, with the increase of the cathodic current density from 10 to 40 mA·cm-2, the manganese content of the deposit increased from 4.4 at% to 10.3 at%, and then it slightly decreased. The phase structure of the coating was face centered lattice (Fm3m) Ni-Mn solid solution. The corrosive polarization experiments indicated that the deposit could work as sacrificial coating for carbon steel in 3.5 wt% sodium chloride solution.

Abstract: CrAlSiN hard coatings were fabricated on the Si substrate from metallurgical Cr0.45Al0.45Si0.10 alloy target by reactive r.f. magnetron sputtering. The oxidation resistance of CrAlSiN coatings was investigated after annealing at temperatures between 900 and 1100°C for 1 hr in air. The phase identification and microstructure of CrAlSiN coatings after heat treatment were analyzed by X-ray diffraction (XRD). The hardness of CrAlSiN coating after heat treatment at 900oC for 1hr in air is slightly decreased from 30.2GPa to 28.3±1.3GPa, which was caused by the thin oxide formation on the surface of the film. The microstructure of CrAlSiN coating after heat treatment at 1000oC from 1 hr analyzed by TEM revealed two types of layer feature, including the nanocrystalline grain embedded in the Al-riched amorphous layer and reaction interface with relative high content of Si.

Abstract: Tribological properties of silicate particles as 50CC additive were evaluated on an end-face friction and wear tester. The morphologies, element distributions and micro-mechanical properties of the worn surface were investigated by means of scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and nanoindentation tester, respectively. Results indicate that friction reduction and wear resistance properties of 50CC are improved effectively by adding silicate particles, whose main composition is Mg3[Si2O5](OH)4. The friction coefficient and surface temperature are reduced 60.6% and 35.6%. The nano-hardness of the self-repairing film is increased 30.03% compared with that of the ordinary film. It can be inferred that a high nano-hardness protective film composed of Mg, Al and O is formed on the worn surface, which has a good effect on the tribological performances.

Abstract: In China’s freshwater environment, the eutrophication phenomenon has become more and more serious in recent years. The changes of water quality may induce the variation of metal’s corrosion behavior. In this paper, carbon steel as common material of hydraulic structure was the investigated object, and its early corrosion behavior affected by microbes (algae and microbe) in eutrophic lakes was studied using immersion test, electrochemical measurements and infra-red spectrometry techniques. The experimental waters were natural eutrophic water and microbescleaned water. The former was fetched from eutrophic East Lake in Wuhan City, Hubei Province of China, and the preparation of later was making natural eutrophic water sterilized and algae removed by UV radiation. In order to present the changes of carbon steel’s corrosion behavior in natural eutrophic freshwater with and without microbes, comparative experiments were conducted in lab. Both weight loss method and electrochemical techniques showed that, the corrosion rates of carbon steel decreased in early stage for the influence of microbe existence. The analysis of infrared spectra indicated that, corrosion product on the surface of coupons taken from natural eutrophic water, mainly were δ hydroxyl ferric oxide, magnetic iron ore, γ hydroxyl ferric oxide, α hydroxyl ferric oxide and β hydroxyl ferric oxide, with relative concentration ratio of 1:0.314:1.003:0.634: 0.654. While corrosion product on the surface of carbon steel taken from the microbes-cleaned water, mainly were α hydroxyl ferric oxide and γ hydroxyl ferric oxide, with relative concentration ratio of 1:1.215.