Advanced Materials Research Vols. 139-141

Abstract: The contact fatigue tests were carried out using three kind of steel(45, 42CrMo, 40CrNi2Mo) which were quenched and tempered to the same medium hardness(HRC37±1). The experimental equipment is JPM-1 type contact fatigue tester. During the experiment process, the contact stress is 1600MPa and the surface roughness is 0.4 um. The crack initiation and the crack propagation direction were observed by using SEM. The contact fatigue failure mechanism was also analyzed. The experimental results were analyzed by using Weibull distribution. The experimental results show that the contact fatigue crack was initiated in the roller surface. With increasing of the cycle, the initiated crack propagates into subsurface and becomes to pitting. The pitting becomes bigger and bigger and leads to failure finally. The maximum shear stress is the main driving force for the crack propagation. The contact fatigue life increases in sequence of 45, 42CrMo, 40CrNi2Mo. The contact fatigue life has the relationship with the shearing resistant stress Тk. About the same carbon content, the value of the shearing resistant stress Тk becomes greater with increasing the alloying elements. The best material used for making heavy duty gear is 40CrNi2Mo steel.

Abstract: Micro-plastic deformation is produced on the surface of the laser cladding layer by micro-forging, and crack makes a change in cladding layer. In this paper, a finite element model with a simplified panel strain model elastic-plastic of stress and strain relationship and adaptive meshing technique was used to simulate laser cladding layer crack by using DEFORM-2D software. Laser cladding process of cracks by micro-regulation forging is simulated. Comparing to the measurement of crack width, the results show that micro-forging can make the surface of laser cladding layer the residual tensile stress to adjust compressive stress, and the micro-forging can significantly reduce or eliminate the laser cladding layer crack. Reasonable and effective regulation of high-frequency micro-forging can improve the surface quality in micro-cladding layer.

Abstract: The thermal stresses generated in ZrTiN coating deposited on HSS and tungsten carbide substrates are investigated by finite element analysis and calculated by mathematics model. FEM analysis provides detailed information about all stress components. The influence of deposition temperature, substrate materials, coating thickness and interlayers on the generation is analyzed. The thermal stress of coatings has a linear relationship with deposition temperature, and an inverse relationship with the coating thickness. The results of simulated thermal stress are in accordance with the analytical method. The highest shear stress found at the interface between the coating and substrate indicates that the interface is the critical location which is learned from the failure point of view. Results also show that the insertion of TiZr interlayer between the coating and substrate can reduce the stress components especially the shear stress. The interlayer thickness has a great effect on stress reduction.

Abstract: A modified cohesive zone interface model that has a damage factor couple with the thermal cycle and humidity aging was proposed. The damage factor not only can change the cohesive zone strength acting but also can effect on the energies of separation. The modified cohesive zone interfacial model is developed and implemented in ABAQUS, as a user element subroutine, to simulate the peeling process for the specimen bonding by anisotropic conducive adhesive film (ACF) under the thermal cycle and humidity tests. Finite element explicit code and the constitutive relation of this element has been defined by the user-defined mechanical material behaviour (VUMAT). The bulk material element selected is a 4-node bilinear plane stress quadrilateral element, and the reduced integration and hourglass control are also adopted. The numerical simulated results accorded well to the experiments to illustrate the validity of the new model.

Abstract: Pb/Ni multilayer coatings, with either Pb or Ni as the top layer, were brush plated on ANSI 304 stainless steel to improve its performance as bipolar plates in polymer electrolyte membrane fuel cells (PEMFC). Surface morphology and cross-sectional microstructure of the coatings were characterized with scanning electron microscope (SEM) and optical microscope, respectively. The corrosion resistance of brush plated coatings in a simulated PEMFC environment was investigated using both three-electrode method and immersion of 300 h. Coating surfaces after the immersion were characterized with energy dispersive X-ray spectrometer (EDS). The results show that the multilayer coatings were smooth, dense, and small in grain size with clear layered structure. In the simulated PEMFC environment, the corrosion of multilayer coatings was mainly uniform corrosion. Coatings with different top layers exhibit different corrosion behaviors. Ni layer was corroded preferentially as the anode while the Pb layer was protected.

Abstract: Magnesium alloy is one of the most useful structural materials in the future. But the research report about surface strengthening of magnesium alloy is little in home and abroad. Ultrasonic impact strengthening treatment was carried out on AZ91D magnesium alloy, the change characteristics of surface microstructure was studied using SEM. The scratch hardness and wear-resistance were tested for both ultrasonic impact treatment and un-treated specimen using HRA-150 type Rockwell hardness tester and M-2000 model wear tester. The experimental results indicate that after ultrasonic impact, the grain boundary on the surfaces of AZ91D is obviously refined. When the ultrasonic impact time are 20 min, 30 min and 50 min, the scratch hardness on the surface of AZ91D increases 7.2%, 16.96% and 28.90%, respectively. For ultrasonic impact time of 50 min, the wear-resistance of treated specimen could be increased to 39.63% and 37.56% respectively for the wear time for 2 and 5 min. With increasing the ultrasonic impact time, the wear scar on the surface is become narrow. It is an effective method to increase the scratch hardness and wear-resistance of AZ91D magnesium alloy by using ultrasonic impact strengthening treatment.

Abstract: Electrodeposited Zn-Fe alloy coating has good anti-corrosion performance and has been widely applied to protect steel materials from corrosion. In this paper, Zn-Fe alloy coatings were plated from acidic sulphate bath, and the relationship between real concentration of metallic complexes ([ZnL+] and [FeL+]) in the bath, which was calculated through solving nonlinear equations by METLAB software, and components of alloy coatings was studied. When ZnSO4•7H2O added in the bath increases from 10 g/L to 50 g/L, the ratio of ferrous complex to total complex decreases from 81.96% to 46.76%, simultaneously the iron content in Zn-Fe alloy coatings decreases from 26.82% to 6.32%. As FeSO4•7H2O and (NH4)2SO4 added in the bath increases from 40 g/L to 80 g/L respectively, the ratio of ferrous complex to total complex increases from 50.02% to 66.23% and from 58.65% to 60.37% respectively, simultaneously the iron content in coatings increases from 8.26% to 13.77% and from 9.28% to 11.92% respectively. The results show that variation of concentration of metallic complexes in the bath can lead to variation of components of coating proportionally.

Abstract: In this study, the electrical discharge machining (EDM) of sintered NdFeB magnet was investigated. The surface characteristics were studied in terms of machining parameters. Correlation between the surface roughness, hardness, recast layer and the machining parameter were analyzed. Results show that an excellent machined finish can be obtained by setting the machine parameters at low pulse energy. Low pulse energy reduces the frequency of bursts of dielectric fluid and melt expulsions.

Abstract: In this paper alumina ceramic layer on worn stainless steel work piece was gotten using ultrasonic vibration aided hot-dip aluminizing and micro arc oxidation to realize green remanufacturing. Aluminum layer was gotten on the surface of stainless steel work piece using ultrasonic vibration aided hot-dip aluminizing method. The action mechanism of the hot-dip aluminizing process and the influence of ultrasonic vibration to hot-dip aluminizing process were studied and the best process parameters were achieved. Alumina ceramic layer of high hardness and wear resistance was achieved using micro arc oxidation method. The influence of current density to the characteristic of ceramic layer was investigated. The technology described in this paper can be used for the remanufacturing of worn stainless steel work piece.

Abstract: In situ reaction synthesized TiB reinforced titanium matrix composites were fabricated using rapid non-equilibrium synthesis techniques of laser cladding. TiB/Ti composite coating was treated on Ti-6Al-4V surface using Ti and B powder mixture by laser cladding. Microstructure and dry sliding wear behavior of the in situ synthesized TiB/Ti composite coatings were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), energy-dispersive spectroscopy (EDS), hardness tester and friction and wear tester. The composite coatings consist of Ti, TiB and intermetallic compounds. The TiB reinforcement dispersed homogeneously in the composite coatings. The wear tests show that the friction coefficient and wear weight loss ratio of the coatings is lower than that of the Ti-6Al-4V alloy. The composite coating was reinforced by the in situ synthesized TiB ceramic particles. Based on the SEM observation, effects of scan speed on hardness and wear resistance of the laser cladding coatings were investigated and discussed.