Key Engineering Materials Vol. 591

Abstract: Mg-Al layered double hydroxide (LDH) was modified with sodium dodecyl sulfate (SDS) by regeneration method. The structure of modified LDH (SDS-LDH) was investigated by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The composites of SDS-LDH and polyethylene (PE) were prepared by melt blending and solution mixing method with maleated PE (PEgMA) as compatibilizer. The structure of the composites and the dispersion of SDS-LDH in the matrix were investigated by XRD and transmission electron microscopy (TEM), respectively. The results reveal that SDS was successfully intercalated into the interlayer space of LDH. SDS-LDH was hardly exfoliated in PE/PEgMA by melt blending. The nanocomposites of PE/(PEgMA/SDS-LDH) were successfully prepared by melt blending PE with SDS-LDH/PEgMA master-batch obtained by solution mixing. Homogeneous dispersion of SDS-LDH in the matrix was observed by TEM.

Abstract: In this work, a new and novel test method was developed to determine the impact bending strength of ceramic composites at ultra-high temperature from 1500-2000 °C in air. Three-point impact bending test was carried out through a SiC pressure head with a dynamic force sensor fixed on a slider and movable along a guide rail. The impact load was adjusted by different saving energy and the impact speed was lower than 0.5 m/s. The center of the sample was heated up to about 1500-2000°C by oxygen-assisted spray combustion. An impact load was put on the specimen and the impact force was recorded automatically. The impact bending strength can be calculated from the maximal load and the sample size. To check the availability and reliability for this method, several ceramics including SiC, ZrB₂/SiC and C/C fiber reinforced composite without coating, were used as the testing samples. The results indicate that this method is a good and feasible method for evaluating the mechanical properties of the ceramic composite at ultra-high temperatures.

Abstract: Mechanical properties of dental materials are increasingly studied via nanoindentation testing. Due to the excellent mechanical properties, 3-mol%-Yttria-Stabilized Tetragonal Zirconia (3Y-TZP) has become an attractive high-toughness core material for fixed dental restorations. In this paper, the mechanical properties of 3Y-TZP were studied by nanoindentation. The continuous stiffness measurement (CSM) and the single load/unload cycle test controlled by displacement and load respectively were performed with a Berkovich indenter.

Abstract: It is significant to explore the fatigue contact damage of bi-layer ceramic composites in order to improve the long-time mechanical reliability of bi-layer structured dental restorations. In this study, Hertz contact test was used to compare the fracture modes and the ability of anti-fatigue damage of zirconia and alumina bi-layer composites, to analyze the effect of loading rate and other factors on the damage mechanisms of bi-layer ceramic composites. Cyclic spherical fatigue loading was put on the bi-layer alumina and zirconia composites with different substrates. The samples were observed by high depth of field stereomicroscope and digital optical microscope after test. The results showed that the fatigue contact damage mode of zirconia bi-layer composite was the porcelain fracture from radial cracks without the damage of zirconia core. The fatigue contact damage mode of alumina bi-layer composite was the alumina core failure from radial cracks as the function of contact load. For both of zirconia and alumina bi-layer samples, the number of cycles to the sample failure as the function of same maximum contact load with high loading rate was obviously smaller than low loading rate. The mechanical properties of the substrate materials had limited effects on the number of cycles to the failure of both zirconia and alumina bi-layer samples from contact-induced radial cracks as maximum contact load with low loading rate. The ability of the zirconia bi-layer composites to resist fatigue damage was much higher than that of the alumina bi-layer composites.

Abstract: This paper presents an approach to investigate the mechanical properties and failure patterns of shape memory alloy (SMA) by experimental methods. Tests were carried out under the conditions of uniaxial tension, cycling loading and impact-tension respectively. The mechanical behaviors of NiTi SMA such as the relationship of stress-stain, super-elasticity, high damping, energy dissipation and tension-shock toughness are discussed in detail. In addition, the destroy patterns of SMA materials are analyzed for varying condition of testing. Whether ductile failure or brittle fracture is decided to do much with the testing styles and strain rate of materials. It is shown that with the large restoring deformation, higher energy dissipation factor and tension-shock toughness, so NiTi SMA structural functional materials are very suitable for vibration control in engineering.

Abstract: The present study aims to investigate the oxidation behavioue of pressuerless sintered SiC ceramic with the AlN-Y₂O₃ as sintering additives. Two main aspects are considered: The evaluation of oxidation kinetics in the temperature rang 1200°C-1400°C for short term test (30hr) and the degradation of the flexural strength after oxidation at temperature 1400°C for 100hr. The microstructure of surface oxidation layer of silicon carbide at high temperature is studied, and the effect of reactive product s on the high temperature oxidation resistance is also analyzed. The results showed that the oxidation began at temperature more than 1200°C, and the oxidation kinetics is obeyed parabolic rule. After long term oxidation, the fracture strength decreased greatly.Key words: oxidation behavior, liquid phase sintering, silicon carbide

Abstract: CrAlN coatings have been deposited on K38G alloy by Closed Filed Unbalanced Magnetron Sputter Ion Plating (CFUMSIP). The microstructure, surface and section morphology of CrAlN coatings before and after oxidation were analyzed by XRD and SEM. At the same time, the mechanical properties and oxidation resistance of CrAlN coating were also studied. The results indicate that the phases in the isometric crystal CrAlN coatings with a hardness of 3500 HV and a adhension of 20 N was the coexistence of CrN and AlN. Each element of CrAlN coatings still existed at 800 and 900°C, but it demonstrated better high-temperature oxidation resistance because of denser oxide scale at 800°C. Besides, internal oxidation occurred under the two temperatures.

Abstract: Titanium and its alloys are widely used in the fields of chemistry, aerospace, biomedicine, automobile manufacturing, ship industry, and so on, due to the properties of light weight, high strength, high thermal stability and corrosion resistance. However, the shortcomings of Titanium and its alloys are prominent as well, such as unsatisfactory corrosion resistance in reducing acid, insufficient wear resistance and serious oxidation at high temperature. Surface modification can solve the problems effectively. In this paper, the recent researches of some surface modification techniques such as plasma spraying, surface alloying, magnetron sputtering and vacuum depositing to improve the corrosion resistant of titanium and its alloys are summarized. The characteristics of structures and properties of the coatings are introduced. And the future prospect of further investigations is presented.

Abstract: CrN coatings were prepared by Closed Filed Unbalanced Magnetron Sputter Ion Plating (CFUMSIP). The microstructure and morphologies of CrN coatings before and after oxidation were analyzed by XRD and SEM. At the same time, the mechanical properties and oxidation resistance of CrN coating were also studied. The results indicate that the phase in the dense CrN coatings with a hardness of 1979 HV and a adhension of 54 N was the coexistence of Cr, Cr₂N and CrN. Besides, The CrN coatings showed good high-temperature oxidation resistance at 700°C while the coating failed at 800°C.

Abstract: Alumina ceramics film which has high hardness, wear resistance and erosion resistance can be obtained using micro arc oxidation on the surface of aluminum alloy. The process parameters have great influence on the corrosion resistance of alumina ceramics film prepared by micro arc oxidation. In this research, the alumina ceramics film was gotten using micro arc oxidation with different process parameters. The corrosion resistance of ceramics coating prepared by micro arc oxidation on the surface of aluminum alloy was investigated by putting the samples into sodium chloride solution of the concentration 3.5%.The influence regularity of process parameters such as current density, impulse frequency, duty ratio and process time on the corrosion resistance of alumina ceramics film was researched. This can provide basis for the optimization of process parameters.