Abstract: W/Cu functionally gradient materials (FGMs) are fabricated by a novel
process—multi-billet extrusion (MBE). Different W/Cu superfine powders made by mechanical alloying (MA) are used to improve the sinterability of W/Cu compacts. Good quality of three-layer W/Cu extrudes are obtained after confirming the extrusion parameters and the type and the content of binder during extrusion process. The green products are pressureless sintered at the temperature
range of 1100-1300 oC for 1 h. W/Cu FGMs with relatively high density and high homogeneous microstructure are attained after sintering at 1200 oC for 1 h. The mechanisms for the enhance of sinterability and improvement of density of the mechanical alloyed (MAed) W-Cu powder products have been discussed. X-ray diffraction and scanning electron microscope are used to identify and observe phase constitution and microstructure, respectively.
Abstract: Effects of the mold rotating speeds on the gradient microstructure and properties of heavy cross-sectional WCP/Fe-C composites made in a self-made centrifugal machine have been investigated with SEM, EDS etc. The results show the ring sample of WCP/Fe-C composites made in a centrifugal machine was free of any defects. And the transition layer between the working layer of WCP/Fe-C composites and matrix Fe-C alloy core was also perfect. The experimental results also show that the WCP-radius-directional distribution in the composites was a continuous component gradient one, which was changed with the various mold rotating speeds. At 1000 rpm the volume fractions of the WC particle from outer layer to inner layer were about 70 vol% to 50 vol% and, at 1400 rpm the volume fractions were about 80 vol% to 65 vol% respectively. The hardness and impact
toughness of the working layer of WCP/Fe-C composites were changed with increasing of the mold rotating speeds respectively. Finally, the mechanism of the effects of the mold rotating speeds was discussed in the paper.
Abstract: Ni/Ni-aluminide//Ti/Ti-aluminide laminate composite, considered as a functionally
gradient material, was manufactured by thin foil hot press technique. Thick intermetallic layers of NiAl and TiAl3 were formed by a self-propagating high-temperature synthesis (SHS) reaction, and thin continuous layers of Ni3Al and TiAl were formed by a solid-state diffusion. Fracture resistance with loading along the crack arrester direction is higher than crack divider direction due to the
interruption of crack growth in metal layers. The Ni3Al and NiAl intermetallic layer showed cleavage and intergranular fracture behavior, respectively, while the fracture mode of TiAl3 layer was found to be a intragranular cleavage. The debonding between metal and intermetallic layer and the pores were observed in the Ni/Ni-aluminide layers, resulting in the lower fracture resistance.
Abstract: This work deals with a novel processing method that combined extrude with laminate
molding for preparing polymeric graded material (PGM). The variations of inhomogeneous property were generated by altering the feeding speed and/or weight ratio of the components as well as changing the order or numbers of the folded layers. Three modes of polypropylene (PP)/ talcum powder (talc) flat PGM (signed with T1, T2, T3) are fabricated successfully by using this new
technique. The preparation, structure and property of the resultant PP/talc graded composite were investigated. Results indicate that the composition, morphology and properties show a gradient variation along their thickness direction of the flat PGMs.
Abstract: In the present paper, a kind of Mo-Ti system functionally graded material with a continuous change of composition was formed via particle settling method at first, and then it was desified by hot-press under 1473K-30MPa-1h. Finally, by using an axisymmetric finite element method, the fabricated thermal stresses in a disk-shaped Mo-Ti FGM were calculated. The results showed that the thermal stresses changed continuously with the smooth variation of graded composition. The residual tensile stresses in the Mo-Ti FGM with a continuously changed composition were located in the medial region of graded layer and the radial compressive stresses distributed in the Mo- and Ti-rich sides. The calculated maximum residual tensile stresses in the Mo-Ti FGM were much lower than the bending strength of Mo-Ti alloys, which demonstrated that during fabrication no damages occurred in the Mo-Ti FGM with continuously graded composition.
Abstract: Based on equivalent transformation by means of mathematically rigorous analytics, the stress analysis of heavy cross-sectional, non-homogeneous Functionally Graded Composites (FGCs) has been performed by the layering calculation model in axis-symmetrical mechanics problems. The partially calculated results of the non-homogeneous layered thick-walled metal tube are similar to the design and practice of machine forging moulds manufactured with special welding electrodes
developed by the German Capilla Company. The analysis is used complementary to the investigation of the quantitative analysis of thermo-mechanical properties, or the so-called anti-design and the optimization of the graded structure for FGCs.
Abstract: In the present paper, the relationship between characteristic wave impedance and
compositions was mainly investigated in order to find a suitable theoretical model for predicting the impedance value of Ti-Mo system composites and FGM. At first, dense Ti-Mo composites with different weight fractions of Mo were prepared. Then the transverse and longitudinal wave velocities of the samples were measured and the characteristic wave impedance values were obtained. A mixture model was adopted to estimate the characteristic wave impedance value of Ti-Mo composites. Comparisons between the estimated and experimental results demonstrated that
the suggested model was sufficiently accurate to predict the characteristic wave impedance value of Ti-Mo system composites and FGM.
Abstract: The Mo surface alloying layer was prepared on Ti6Al4V substrate using the plasma
surface alloying technique. The component, structure and hardness of the Mo surface alloying layer were investigated. The impact test was used to determine the fatigue behavior of the Mo surface modified Ti6Al4V. The results showed that the Mo surface alloying layer enhanced the surface strength of Ti6Al4V substrate. The Mo surface alloying layer has a duplex structure with diffusing and coating layers. The diffusing layer in which the component and hardness change gradually could enhance load-bearing capacity to the surface coating and ensure the durability of the coating. In the impact test, the Mo modified Ti6Al4V showed excellent fatigue behavior and the cohesive failure mode was observed.
Abstract: Fretting wear tests of bonded MoS2 coating under radial and composite fretting mode have been carried out on a new fretting rig. The maximum applied load was respectively 200N, 400N and 800N with a constant loading speed of 12mm/min. Dynamic analyses in combination with microscopic examinations through SEM and XPS have been performed. Experimental results showed that such MoS2 coating exhibited an excellent radial fretting damage resistance, and its damage strongly depended upon the applied maximum loads and inclined angle under composite fretting condition. The fretting damage mechanism of MoS2 coating also discussed under different fretting modes. The XPS analysis revealed that the oxidation of MoS2 crystal was played an important role in damage. The fretting wear of MoS2 coating was mainly represented by the mechanism of delamination and oxidation wear under composite fretting conditions.
Abstract: TiB2-Cu Interpenetrating phase composites (IPCs) were prepared by combustion synthesis of elemental titanium, boron and copper powders. The synthesized product consisted of two spatial continuous phases: TiB2 and copper. Using the experimental data, thermo-physical and mechanical parameters of the materials established the temperature and stress fields made of FEM. Thermal
shock behavior of TiB2-Cu IPCs was also investigated using a plasma torch arc heater and the results showed no cracks were found on the thermal shock surface of the TiB2-Cu IPCs. The experimental and numerical modeling results can be used to explain the actual thermal shock resistance and reveal its complex behavior under the severe condition.