Advanced Materials Research Vols. 418-420

Abstract: The dynamic mechanical properties of nano-hydroxyapatite (n-HA) reinforced polyamide 66 (PA66) biocomposites were studied with reference to the effect of n-HA content, frequency and physiological saline. The intrinsic properties of the components, morphology of the system and the nature of interface between the phases determine the dynamic mechanical properties of the composite. The storage modulus (E') values of n-HA/PA66 composites were much higher than those of pure PA66, indicating that the incorporation of n-HA in PA66 matrix induced reinforcing effects obviously. And the E' values of composites increased with increasing of n-HA content. The loss modulus (E") of the composite with 30wt% n-HA was higher that those of pure PA66 and the composite with 40wt% n-HA below 55°C, however, above 55°C, the E" values enhanced with increase of n-HA content. Both frequency and physiological saline had obvious effects on the dynamic mechanical properties for n-HA/PA66 composite. E' and E" values enhanced with increase of frequency, but tanδ values decreased with increasing of frequency. After soaked in physiological saline, the E' and E" values of the composite decreased.

Abstract: The size of voids beneath rigid pavement slabs is an important factor which influences the bearing capacity of roads. GPR is an advanced method for detecting voids beneath rigid pavement slabs. Combined with drilling and sampling, equations including parameters of GPR wave amplitude, horizontal size and vertical size of voids are established for analyzing the size of voids. Then, based on the equations, the horizontal size and vertical size of voids can be calculated according to the actual GPR wave amplitude.

Abstract: Microstructures and mechanical properties of pure copper weld joints are discussed under different parameters of friction stir welding. The results reveal that it is conducive to the formation of compact joint in friction stir welding by applying high speed steel tool with high anti-bonding temperature. The friction stir welding joint with compact and defect-free microstructure could be obtained when the tool rotation rate is 1250- 1650 r/min and the tool traverse speed is 20-50 mm/min. Intensively plastic deformation occurs in the soften materials of the weld nugget zone and numerous crystal particles are broken under the influence of tool stirring. The microstructure of weld nugget zone is composed of tiny isometric crystals, which is due to the dynamic recrystallization of broken crystal particles. The structure of thermo-mechanical affected zone on both sides is asymmetric. Obvious boundary of the thermo affected zone could be seen on the advancing side, and the plastic streamline is apparent.

Abstract: Rolls in the steel industry withstand very high loads, thermal cycling leading to thermal fatigue, and severe environmental. How to improve the wear resistance and elongate the service life of rolls matters a lot in reducing the consumption of rolls. In recent years, because of its better red-hardness and wear property, high speed steel (HSS) was used to manufacture the new type composite rolls. As a surface treatment technology, laser cladding can fabricate coating to improve the wear resistance of substrate. In this paper, the substrates for laser cladding were nodular cast iron rolls, Nd:YAG solid pulsed laser and continuous wave CO₂ laser were both used to explore the feasibility of preparation HSS coatings. The Nd:YAG laser cladding results that the coated layers combined metallurgically with the substrate with a lot of microcracks. The average microhardness up to 600 HV is about 2 times as high as that of the substrate. The CO₂ laser cladding results that: fully dense and crack free clad surfaces of high speed steel with an excellent metallurgical bonding were deposited. The average microhardness up to 900 HV is about 3 times as high as that of the substrate. The high-temperature (500 °C) wear rate is 40% of nodular cast iron’s in 30 min.

Abstract: This text does on research on welding behavior of the Ni3Al alloy casting MX246A of based on laser as heat source. First process parameters have effects on crack sensitive in the study. Laser power decided to heat input and the depth of the weld, which has obvious effects on the hot crack. Crack sensitivity of welding at low speed is quite lower than it at high scanning speed; low scanning speed can reduce the sensitivity of weld cracking. Because of the laser absorption and solidification of weld metal for inheritance of the basic material, grain degree of materials makes a significant impact on crack. Crack sensitivity in the fine grain areas is quite lower than it in the coarse grain areas. It is found in the study that the main reason for the weld crack is Mo elements gathering and caused the oxidation of the partial. Welding of MX246A alloy is realized on the basis of the above research, and performance of welding joint is up to more than 75% of base material.

Abstract: Laser cladding on the titanium alloy is widely applied with the development of laser technology in the industry. However, the cracks, produced during the process, greatly confine the development of laser cladding technology. Cracks are mainly resulted from the over high thermal stress in the coatings, so it is extreme important to confine the thermal stress of cladding coatings. To investigate the influence of process parameters on the cladding coating's stress, the model of laser cladding based on Ti-6Al-4V is built in the way of finite element method (FEM) and three different scanning paths are chosen to calculate the stress of cladding layer. The results show that the spire-in scanning path is the best way to minimize the cladding coatings’ thermal stress. The numerical results provide the theoretical guidance for optimization of the laser cladding process on titanium alloys.

Abstract: Formability of ultra-high strength steels is poor causing problems in bending and stretch forming. The target of this work was to improve the formability of ultra-high strength steel sheets by controlled local laser heat treatments. Three steel grades, a bainitic-martensitic 4 mm DQ960 and two martensitic WR500 with 6 mm and 10 mm thicknesses were heated by controlled thermal cycles using a 4 kW Yb:Yag –laser, followed by self-cooling. Sheets with the thicknesses of 4 and 6 mm were treated on one side only by heating up to the austenitizing temperature. The 10 mm thick WR500 sheet was heat treated separately on the both surfaces by heating to a lower temperature range to produce a shallow tempered layers. The tensile and bendability tests as well as hardness measurements indicated that laser heat treatment can be used to highly improve the bendability locally without significant strength losses.

Abstract: Considering that in the nanometer grating deposition the substrate is usually set at the center of the laser beam, the straight edge diffraction occurs. Therefore this paper analyze the straight edge diffraction effect of base model Gaussian laser field, which based on the straight edge Fresnel diffraction effects, using the theory of scalar optical, considering the situation of the actual beam waist and straight edge diffraction side not at the same position, and obtain a general and practical light intensity expression of the base model Gaussian laser under the straight edge diffraction field, and had some model analysis and simulation of its light intensity distribution characteristics.

Abstract: The West-East gas pipeline project in Western China was as an example in the research work. Expert system platform was used as a basic tool. The typical model database systems of West-East gas pipeline project was built. On the base of collection, collation, comprehensive analysis of existing data, through a case study of a large number of landslides, the induced landslides and stability control factor were becoming clear. A landslide risk assessment criteria and evaluation index system was established. On this basis, through application of expert system method, a Expert system platform based landslide risk evaluation expert system about long-distance pipeline routes was developed.It also give a application example of this expert system.

Abstract: Effects of hot extrusion processes on grain size of ZK60 alloy tubes was researched by combining numerical simulation with experimental research. The results show that grain size varies inversely as extrusion ratio and extrusion speed, with extrusion temperature being constant. In order to get the finer and homogeneous microstructure, higher extrusion ratio, higher extrusion speed and lower billet temperature should be chosen in the equipment's rated load. Isothermal extrusion is conducive to tube forming , and the smallest grain size and the better microstructure can be obtained at temperature of 300°C when other deformation conditions are constant.