Advanced Materials Research Vols. 89-91

Abstract: Molecular dynamics (MD) simulation with a tight-binding potential is used to studied the mechanical behaviors of nanoimprinted Cu-Ni alloys before and after annealing. The annealing process consists of three different stages. Initially, there is a gradual heating from the original temperature of 300 K to the specified annealing temperature of 823 K and then it is followed by a period of constant heating at that temperature, after which the specimen temperature is allowed to cool gradually to the original temperature. The results showed that when the punch is advancing, the punching force obtained from the simulation with a tight-binding potential is lower than with the Morse potential. The internal energy of Cu-Ni alloys decreased with increasing the temperature and the component of Cu during the annealing process. In addition, comparing the residual stress in the Cu-Ni alloys with and without annealing treatment, the stress is significantly released after annealing.

Abstract: The inside corrosion of failed automotive mufflers collected in China was investigated and the composition of the automotive exhaust gas condensate collected from HONGQI automobile was analyzed. According to the analyzed result of collected condensate’s composition, the corrosion resistance of a new designed high Cr stainless steel (B439M) bearing Nb and Ti and a low Cr T409L stainless steel were studied with a condensate corrosion test method which simulates the inside corrosion of automotive mufflers. The life of the two materials was estimated by extreme value analysis of the maximum corrosion depth obtained by the dip dry test (DDT). The life of type B439M steel was 1.6 times as long as that of type T409L steel. To clarify the corrosive process of the simulated condensate test, the electron work function (EWF) on the two stainless steels’ surface was evaluated. It was demonstrated that the surface of new designed stainless steel exhibited markedly improved resistances to corrosion during a simulated condensate test cycle and the corrosive process of simulated condensate test was evaluated and discussed.

Abstract: The main purpose of this research is to evaluate the wear resistance of titanium matrix composites (TMCs). Reinforcements, TiB and TiC, were formed by in-situ reaction between boron carbide and commercial pure titanium. The confirmation of the sound synthesis of TMCs was done by phase identification. And then, sliding wear test were carried out to verify the wear resistance of TMCs by means of the coefficient of friction, wear loss and morphology wear track. The results of wear test indicate that TMCs have superior resistance than AISI H13 tool steel at the condition of severe loads.

Abstract: The effect of four different niobium(From 0-0.1%) addition on the mechanical properties of allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steels has been investigated in this paper. The results show that (1) The 0.06%Nb steel acquired superior strength and toughness combination by applying 1250°C×60min solution treated, finish rolling at 850°C, and air cooling. The corresponding mechanical properties of the thick plate(30mm) is: σb>1050MPa, σ0.2>700MPa,δ5>17%,Akv>90J. (2) The addition of niobium refine the grain size of FGBA, and promoted the transformation of bainite structure. With the increase of niobium content, the refinement of ferrite grain and bainitic cluster is improved. (3) More refined M-A island is acquired by the small addition of niobium. According to M-A Analysis tools and transversal methods, with the rise of niobium content, the volume fraction of M-A island increase from 21% to 35%, and the average size of M-A island decrease from 1.1μm to 0.7um. (4)It is suggested that 0.02-0.06% niobium can improve the mechanical properties of the steel obviously. However, excess addition of Nb (0.1%) deteriorates the impact toughness obviously. (5)Under the synthetic roles of the microstructure refinement and precipitation strengthen, 60-160MPa yield strength improvement has been acquired in the low carbon air cooling bainitic steel by the small addition of niobium. (6)This steel is with low production cost since the alloying element Mn is cheap.

Abstract: The preparation of automotive catalysts and commercial oxidation catalysts in stationary sources use a large amount of noble metal precursors. Moreover, during their preparation high energy (gas and temperature) is necessary for treatment processes. In order to develop a higher sustainable process, the plasma-assisted catalysts synthesis could be a solution. The use of plasmas for catalysis is already well developed and plasma treatment was already used in a low pressure system to replace the thermal calcination steps of the catalysts. Fluidized bed reactors offer the possibility to lead to homogenous treatment and have the additional advantage of excellent heat transfer rates between the gas and the particles, so that it can modify the catalytic properties of the prepared materials. The aim of our work is to prepare plasma-assisted catalysts dedicated to pollution abatement in stationary or mobile sources. For stationary sources, the first prepared catalysts are palladium based catalysts, which were chosen since the main reducing agent in combine heat power is methane. In the case of mobile sources, we have worked with silver based catalysts since ethanol could be chosen as a sustainable alternative reducing agent to replace ammonia. After the preparation of the different catalysts, the low fluidized bed plasma reactor was used to modify Pd/ γ-alumina and Ag/γ-alumina catalysts. A comparison with “classical calcination” in air at 500°C was performed in order to show the advantages of plasma treatments. The first catalytic results show that plasma treated catalysts lead to higher pollutant abatement than classically prepared ones. Thus, concerning the plasma process, we have studied the role of the plasma treatment time as well as the nature of the gas treatment. The characterization of the catalysts is in course in order to understand the influence of plasma treatment parameters on catalytic results.

Abstract: The linear friction welding (LFW) behavior of Ti-6Al-4V, a commercial α + β titanium alloy, was investigated using oscillation frequencies ranging from 30-70 Hz and axial pressures from 50-110 MPa. LFW samples were examined using electron backscattered diffraction (EBSD) to relate the texture to the welding parameters and to the estimated strain and strain rate. Characterization of the welds included analysis of the microstructure of the weld and of the thermomechanically affected zones (TMAZ) in relation to the parent material.

Abstract: Advanced High Strength Steels (AHSS) are key materials in the conception of car body structures, permitting to reduce their weight while increasing their behavior in crash conditions. Nevertheless, the weldability of AHSS presents some particular aspects, in that complex failure types involving partial or full interfacial failure can be encountered more often than with conventional mild steels during destructive testing, despite high spot weld strength levels. This paper aims at characterizing the behavior of different AHSS spot welds under two quasi-static loading conditions, tensile shear and cross tension, often used in the automotive industry for the determination of their weldability. Interrupted cross tension and tensile shear tests were performed and spot welds failure was investigated with optical micrographs, SEM fractography and 3D-tomography in order to follow the three-dimensional crack paths due to the complex loading modes. A limited number of failure zones and damage mechanisms could be distinguished for all steel grades investigated. Moreover, numerical simulation of the tests was used to better understand the stress state in the weld and the influence of geometrical features such as weld size on the occurrence of the different failure types.

Abstract: During the atmospheric re-entry phase, the thermal protection of a spacecraft vehicle is submitted to air plasma. The transfer of the kinetic energy of the gases to the surface leads to an important heating of the nose cap and leading edges. The energy released from the recombination of oxygen atoms on the surface produces an additional amount of heat, increasing further the temperature. This excess of heat can damage the protection materials. This last mechanism leads to the oxidation of the surface and an accelerated ageing of the material. The oxidation produces a new surface layer of oxide such as SiO2 (Passive oxidation) and leads to the ablation of the material by the formation of CO, CO2, SiO and to the diffusion of oxygen in the bulk creating micro-cracks in the material (Active oxidation). Thus the composition of the surface and consequently the protection material properties are modified. The atmospheric re-entry conditions are created with a non equilibrium low pressure RF plasma chemical reactor. The ageing of the material and the diffusion of oxygen are studied by mass spectrometry analysis of 18O isotope for temperatures ranging from 300 – 1000 K. Silicon Carbide targets are covered with two different coatings, Chromium oxide, and Chromium oxide/ Silica. Oxygen diffusion in the material bulk for the targets was followed by Secondary Ion Mass Spectroscopy (SIMS).Mass Spectrometry shows the formation of CO and CO2 pointing out the process of ablation. This ablation is much lower in the case of polluted sample (with Chromium oxide). SIMS analyses show that Cr2O3 acts like a barrier in the oxidation of the material by limiting the diffusion of oxygen in the bulk.

Abstract: Surface defects are an inevitable characteristic of the raw material employed in the drawing of copper wires. These defects may cause problems in the processing of the material, both during the drawing down to wires and in the final manufacturing of artifacts with the produced wire. The literature reports few analyses covering the importance of these initial defects, as well as concerning their evolution or eventual healing during the drawing. The present paper presents such an analysis for a 12.7 mm diameter copper bar displaying artificial defects 1mm wide and 0.3mm deep. Low angle drawing led to the almost complete healing of the defect after three drawing passes with a 10% reduction of area each. The use of a high semi-angle die led to a completely different situation, where no such defect healing was observed.

Abstract: A multi-scale nonlinear homogenization procedure is presented for the analysis of the in-plane structural response of masonry panels characterized by a regular texture. A Cosserat continuum model is adopted at the macroscopic level, while a classical Cauchy model is employed at the microscopic scale; proper bridging conditions are stated to connect the two scales. The constitutive behaviour of bricks and mortar at the microscopic level is based on a scalar damage model, non symmetric in tension and compression. As for the regularization of the strain softening response, the standard fracture energy method is used at micro-level, while at the macro-level the inner capabilities of Cosserat continuum are exploited. A numerical example is presented and a comparison with an experimental test is performed.