Advanced Materials Research Vols. 941-944

Abstract: Electrochemistry experiments such as polarization curve and alternating-current impedance are adopted to study the electrochemistry behavior of Fe-Cr-Ni alloy (Inconel 690 alloy) in the caustic solution of 50% NaOH +0.3%SiO₂+0.3%Na₂S₂O_3. The results show that Inconel 690 alloy appears two anodic passivation areas, the passivation of the alloy elements Cr and Ni mainly contributes to the lower potential passivation area and the higher potential passivation area is mainly attributed to the passivation effect of the alloy elements Fe and Ni, especially the later. When Na₂S₂O is added into the high-temperature caustic solution, it can accelerate the anodic dissolution of Inconel690 alloy, retard or impede its passivation and decrease the stability of the surface passivation film, which is mainly attributed to the effect of Na₂S₂O₃ on the anodic polarization behavior of Ni.

Abstract: Plasma nitriding is a thermochemical treatment method to make the metal surface reinforced. It can be used to significantly improve the surface hardness, abrasion resistance, fatigue strength, corrosion and erosion resistance. This paper presents a study of the influence of nitriding temperature and holding time on the nitriding effect while different nitriding process parameters are adopted on Ta-10W board samples by plasma nitriding technology. The result shows that nitriding temperature is the key parameter to the final effect of nitriding. Samples nitrided at 950 ^oC for 10h get thicker nitride layer and more nitrogen in nitride layer.

Abstract: Multibranched silicon microstructure, such as branched root-like microwires and branched coralline-like micorwires, have been rationally synthesized via a simple one-step, inexpensive, and catalyst-free fabrication technique. The multiple-branched root-like silicon microwires which obtained at 0.07% Sr addition of Al-Si alloys have lengths of several tens of micrometers and its transverse sizes range from 300 to 500 nm, while the transverse sizes of multiple-branched coralline-like silicon microwires are much smaller. The recommend of patterning process of multiple-branched silicon microwires show that selective corrosion of Sr modified Al-Si alloys is that the aluminum is wiped out while the silicon micorwires as a hidden microstructure revealed by etching.

Abstract: In order to improve the surface wear-resistance and overall shock-resistance of 65Mn steel, effects of rare earth (RE) particle size, adding amount and boronizing time subjected to quenching and medium-temperature tempering treatment were studied systematically. Optimizing basic component of low-temperature boronizing reagent and RE types, the depth of boronizing layer was selected as main evaluation parameter through the orthogonal test of RE-boronizing. Experimental results show that, cerium oxide with particle size of 20nm and content of 4% has the best effect of accelerating boronizing process on 65Mn steel at 700°C for 9 h, and the depth of boronizing layer with RE-boronizing is about 3.3 times than without adding RE; meanwhile, the heart of 65Mn steel still keeps good strength and toughness due to temper troostite microstructure. It can be concluded that the strengthening and toughening treatment of low-temperature RE-boronizing can obtain hard-surface and tough-core properties on 65Mn steel.

Abstract: The high temperature creep tests of standard specimen and double U-notched specimen of T92 steel were carried out under different stresses at 600°C and 650 °C. Then scanning electron microscopy was used to observe the fracture morphology. The results show that the notch weakens plasticity, and weakening with the notch acuity. Under multiaxial stress state, the failure mode of T92 steel gradually transfers from ductile dimple to brittle quasi-cleavage fracture. Compared with uniaxial stress state, the dimples under multiaxial stress state are smaller and shallower, within lots of carbides and second phase particles. The notch slows the connection, growth and gather of microvoids, and exhibits notch strengthening effect.

Abstract: This paper evaluates the ballistic resistance of AA5083-H116 aluminum plates against conical-nose steel projectiles impact using Arbitrary Lagrange-Euler (ALE) finite element methods. The target material was modeled with the Johnson-Cook constitutive relation using 2D axisymmetric elements with ALE rezoning. Impact vs. residual velocity curves were constructed and the ballistic limit velocity was determined. It is found that the ballistic limits increase almost linearly with increasing plate thicknesses. The numerical results have been compared to available experimental results, and good agreement was in general obtained. The study shows that the ALE formulation works well for large deformation in ballistic penetration.

Abstract: Contact stress and Pull-out stress formatted by piston and the valve seat directly affects the piston seal and friction wear performance. It is of great realistic significance to study on distribution of the contact stress and the assembly relationship between piston and valve seat. Finite element analysis methods were used to obtain the distribution of the contact stress in static and dynamic conditions. Problem of piston size selection was analyzed between different assembly interferences. Simulation results indicate that contact surface average Mises stress of valve seat was about equal to yield strength of materials with interference in 0.01mm; while in conditions of interference in 0.02mm and 0.03mm; radial deformation of valve seat was obvious. Based on analysis and considering mechanical properties of materials, unilateral interference between piston and seat would not exceed 0.01mm; when friction coefficient was defined as 0.05 and unilateral interference was set as 0.01mm, output stress would be 892.14N, which far less than hydraulic pressure arising from pull-out stress who would only be 300N. Therefore, 0.01mm unilateral interference can completely meet the use requirements.

Abstract: Based on energy balance equation, the relationship between the biggest impact contact force with the pit depth in the process of impact was derived by the relationship between impact energy and indentation depth, T700S/5228 and T300/5222, two different toughness of carbon/epoxy resin composite material, are chose. The corresponding relationship between impact energy (static pressure mark force) and indentation depth was got by the contrast analysis on the low speed impact test and the static pressure mark test, and showed the similar trend with static pressure mark test of static force and indentation depth relationship. This similar trend that obvious turning points were appeared in some indentation depth showed the effectiveness that using the quasi static method to simulate the low-velocity impact of composite laminate to a certain extent.

Abstract: The compressive strength of oil well cement would be damaged by high temperature in deep oil wells, which was caused by the obvious change of the components and microstructure of cement hydration products. The adaptability of common oil well cement for cementing under higher temperatures was confined by above reasons. Characteristics of development and change of compressive strength of Class G oil well cement were studied under different temperatures by using Static Gel Strength Analyzer and High Temperature-High Pressure curing chamber. The influence law of temperature and silica sands on compressive strength was analyzed. The results showed that the critical temperatures at which the compressive strength begun to decline were about 110°C and 150°C respectively; The compressive strength increased with curing time during the initial period and would reduced after it reached a certain value when temperature exceeded 110°C; For cement with silica sands, the compressive strength development trend was in the shape of two-stage form with increase of curing time within the range of 110~150°C, but for 160~200°C temperature range the development form was in the shape of single stage; The reasonable amounts of silica sands which would be added to cement slurry to enhance the compressive strength of hardening paste were determined to be 30%~40%.

Abstract: Method for determining the plastic properties of metallic materials was proposed based on the functional relationships between representative stress, representative strain and nominal hardness which were established with the aid of dimensional analysis and finite element simulation. The errors of 0.2% yield strength and strain hardening exponent of five engineering metals were from-17.1% to 15.4% and from -0.125 to 0.11, respectively,which satisfied the need of engineering application and verified the effectiveness of the method.