Advanced Materials Research Vols. 154-155

Abstract: Ultrasonic vibration was introduced into the molten AZ91 alloy in this paper. The effects of ultrasound power (from 0 to 900W) on the microstructure and mechanical properties of AZ91 alloy were investigated. The results show that the microstructure, hardness and mechanical properties of the AZ91 alloy have been improved with the ultrasonic treatment. In this work, the mechanical properties of the alloy reached the peak value when the ultrasound power was 600W. Also, the mechanism of ultrasonic vibration in the AZ91 alloy was discussed.

Abstract: Based on the requirements for ceramic materials of cutting tool and die and the aim of improving comprehensive mechanical properties of ceramic tool and die materials, nanocomposite ceramic tool and die materials with high mechanical properties were fabricated successfully with nanometer composite method. Friction and wear properties of the developed ZrO2/Ti(C7N3) nanocomposite ceramic tool and die materials were experimentally studied in detail. Morphologies of the worn surfaces were observed and analyzed by ESEM. Wear mechanisms of nanocomposite ceramic tool and die materials were discussed with comparison with that of single-phase ZrO2 ceramics. It indicates that wear mechanisms of ZrO2/Ti(C7N3) nanocomposite ceramic tool and die materials are mechanical cold welding, abrasive wear and adhesive wear.

Abstract: Microstructure and properties of Ni-base coatings obtained by micro-plasma arc cladding was investigated. A uniform clad coating was obtained after optimizing the cladding parameters by using NiCrBSi powder. Microstructure of the coatings observed by optical and scanning electron microscopy (SEM) indicated a homogenized microstructure. It has no evident heat-affected zone and no porosity. The phase of the coating was formed by γ-N solid solution, nickel boride Ni3B, carbide Cr21.34Fe1.66C6 and Cr2B3 type chromium boride. Although it likes the laser cladding coatings, micro-plasma coatings has its own characteristic. In addition, the average microhardness and nanohardness of coatings which were much higher than the substrate were observed, and the distribution of the microhardness was drawn.

Abstract: The Ni-based alloy was used as raw materials to fabricate the surface infiltrated layer with 1-4mm thickness on cast steel substrate through vacuum infiltrated casting technology. The microstructure indicate that the infiltrated layer included surface melting and sintering layer, metallurgical fusion layer and diffusion layer. Wear property was investigated under different temperature conditions such as room temperature, 150°C, 300°C and 450°C. The results indicated that the abrasion volume of infiltrated layer was near to third of that of substrate, and it was nearly half of the substrate. This illuminated that the infiltrated had excellent wearable property. The adherence and fatigue abrasion was the main wear mechanism under low temperature. Oxidation abrasion and adherence dominated the wearing process under elevated temperature.

Abstract: A finite element model for the given gearbox has been established based on NASTRAN, which gives the gearbox theoretical modal analysis results. The dynamic loads of the bearings resulted from kinetic analysis is acted on the gearbox housing and the housing stress distribution under the action of dynamic loads is obtained by the calculation of dynamic strength for the housing. The research results provide a valuable reference for the housing design.

Abstract: Based on the classic formula of J507 coated electrode，the welding rods were prepared by adding Fe41Co7Cr15Mo14C15B6Y2 Fe-based amorphous alloy or HO8A as welding core. The surface coating on Q235 was made by manual electric arc welding with two kinds of welding rods,while Ar2 gas is used to cool the weld layer. The microstructure and wearability of welded joint and the coating layer were investigated by the means of metallographic analysis, SEM,XRD and M-2000 wear tester.The results show that the coating layer is in the amorphous state,and the wearability of surface coating with Fe-based amorphous core welding rod is better than another.

Abstract: Cored wires and high velocity arc spraying technique (HVAS) were used to produce high Mg content Zn-Al-Mg alloy coatings on low carbon steel substrates. The microstructures, mechanical properties and electrochemical corrosion behaviors of the Zn-Al-Mg coatings were investigated comparing with Zn and Zn-Al alloy coatings. And the electrochemical corrosion mechanisms of the coatings were discussed. The coatings show a typical aspect of layered thermal sprayed material structure. Chemical analysis of the coating indicated the composition to be Zn-14.9Al-5.9Mg-3.0O (wt.%). The main phases in the coatings are Zn, Mg2Zn11, Al12Mg17 and MgAl2O4, together with a little Al2O3 and ZnO. The corrosion potential of Zn-Al and Zn-Al-Mg coatings decreased a little and then increased towards the noble potential. With addition of Mg, the corrosion products accumulated to form stable passive film can block off the pores in the Zn-Al-Mg coating, and thus may prevent attack on the underlying steel substrate. The Zn-Al-Mg coatings show higher electrochemical corrosion resistance in salt solution than Zn-Al coatings.

Abstract: A carbontirided layer was produced on 20CrMnTi steel by plasma electrolytic carbonitriding (PEC/N). Scanning electron microscopy with an energy dispersive X-ray analysis was employed to study the morphology and chemical composition of the carbonitrided layer. Hardness of the layer was measured using a microhardness tester, and the phase structure was determined by X-ray diffraction. The results show that a compact carbonitrided layer can be obtained on the surface of 20CrMnTi steel. The thickness of the layer increases with carbontriding time. When the sample was treated at 120V for 20min, the thickness is 45μm and the highest microhardness is 766HV0.05. The carbontrided layers are composed of Fe3C, Fe5C2, ε-Fe3N and α-Fe.

Abstract: By adopting technique for forming colloid to manufacture Al2O3 Ceramic Substrate, the effect of aggregation reaction which is caused by pH value, temperature for shaping, evocating agent and some other factors of slurry has been researched in the processes for shaping Substrate. The result addresses that the substrate with well-proportioned in density, contractibility and over 78MPa intensity is able to be made while the pH is about 9, the temperature is between 60 and 70°, the shaping duration is no more than 30 minutes, in glass mold, and with 120 item undersize α-Al2O3 powder. To dunk the desiccating substrate for 20 minutes, it would gain the good flexibility, moreover, it is able to be cut. After it is desiccated again, it becomes firm again, this kind of characteristic can be repeated numbers of times.

Abstract: In semi condinuous casting of technincal bronze alloys homogenuous microstructure is very important for the assurance of material properties. The improvement of the knowledge about both, thermodynamics of the ternary system Cu-Sn-P and the solidification process is of main interest for the involved industry. To describe solidification of these alloys, the ternary system Cu-Sn-P in the Cu-rich corner is experimentally investigated. DSC measurements, diffusion and annealing experiments have been performed and compared with computational thermodynamics based on the Calphad approach. The so defined thermodynamic information is coupled with solidification simulation. For this, CFD calculations are done with a two phase solidification model including mass, momentum, energy and concentration transfer and applied to semi-continuous casting of technical Bronze alloys. The predicted macrosegregation pattern is in good qualitative agreement with experimentally observed result.