Applied Mechanics and Materials Vols. 80-81

Abstract: Copper and copper alloy’s manual self-propagating high-temperature synthesis (SHS) technology was introduced in this paper. Through research of weld and analysis of manual SHS welding process, mechanism of copper and copper alloy’s manual SHS welding is expounded. This type of weld rod was only operated in terms of some welding technology, including welding method, weld technique parameter, weld operate. The chemical compositions of the weld rod was the key to the final weld quality. The powders include thermit, slagging elements and alloying addition. When the content of (CuO+Al) was 60%wt~80% in the thermit, the rod showed excellent combustion behavior and the test plates H62 were welded successfully.The slag system of CaO-Al₂O₃-SiO₂ have the lower melting point and high deformation power, which fit to meet the need of the weld slag system of copper and copper alloy’s manual SHS welding. The high melting point Al₂O₃ can be digested and absorbed in two ways, generating CuO·Al₂O₃ ceramics and reducing the melting point to float upward into slag with the help of the solvent.

Abstract: Lamellar cementite will be spheroidized in drawn pearlitic steel wire during galvanization process. To understand the evolution of the microstructure in this process, effects of isothermal time on microstructure of drawn pearlitic steel wires were investigated by using scanning electron microscope (SEM), transmission electron microscope (TEM) and DSC Technique. Experimental results showed that the lamellar cementite would transform to spheroidized cementite during the isothermal treatment. During the heating process, no endothermic or exothermic peak existed in pearlitic strand, while an obvious exothermic peak appeared in cold drawn pearlitic wire at about 380°C. It results from the spheroidization of lamellar cementite. The dislocation density was very low in pearlitic strand, but the dislocation density increased shapely after drawing. During the isothermal treatment at 450°C, the high dislocation density zone disappeared and some cementite became spheroidized. The cementite spheroidization phenomena first began at the boundary of pearlitic blocks or grains, and then in the high dislocation density zone in pearlitic blocks.

Abstract: Diamond-like carbon (DLC) films exhibit high hardness, high wear resistance and a low friction coefficient. They are extensively utilized in the mechanical, electronic and biomedical industries. Due to the gas barrier properties, it is used in the food industry also. To investigate the binding capacity of the DLC with the substrate and reduce the contamination for foods. The DLC (a-C: H) films on the glass slide and PET film were prepared successfully for different process parameters by plasma enhanced chemical vapor deposition (PECVD). In order to characterize the DLC film, the images of DLC was visualized by the atomic force microscope (AFM). The films were analyzed by Fourier transform infrared spectroscopy (RTIF). The contact angle and oxygen permeation analyzer (OTR) of the PET with and without the DLC coating were investigated experimentally. The results show that the DLC coating can improve the barriers and surface properties.

Abstract: In this paper, a new kind of Sn-Bi lead-free solder was fabricated via rapid solidification method by adding a series of microelements which can optimize the properties of Sn-Bi solder. When the solder was manufactured by Single Roller Melt Spinning Process, the faster the cooling rate is, the better the effect of restraining Bi segregation is. When the melt spinning rate was up to 1000 rpm, it had the best result. The effects of microelements on the melting characteristics, microstructure and properties of the new solder were also systemically studied. The results show that when the added content of Ag is 0.7%, Cu 0.3%, Ge 0.1%, In 0.5% and Sb 0.5%, the microstructure of the solder is fine, the extent of Bi segregation obviously decreases and the mechanical property is similar to that of Sn-37Pb solder. The melting point of the new solder is close to that of the Sn-37Pb solder. The mechanical and soldering properties are also similar to that of it.

Abstract: The pre-corrosion damage tests of LC4 aluminum alloy with the shot peening surface treatment and un-shot peening surface treatment are performed under two different time levels: 12h and 24h. Based on the observation of the corrosion morphology of aluminum alloy, the corrosion damage mechanism of shot peening aluminum alloy can be divided into three stages: intergranular corrosion occurs first, and then denudation generates, at last pitting corrosion occurs as denudation depth reaches a certain degree. For shot peening aluminum alloy, the denudation depth, mass loss and the total depth of corrosion damage are used to represent the corrosion characteristics. With the corrosion time increase, the three parameters all increase correspondingly.

Abstract: Si₃N₄-Ti(C,N) nanocomposites fabricated by vacuum hot pressing with Al₂O₃ and Y₂O₃ as additives were investigated. The results showed that the α-Si₃N₄ phase converted completely into whisker-shaped β-Si₃N₄ grains after vacuum sintering at 1700°C. Suitable addition and well dispersion of the Ti(C,N) particles can restrained the lateral growth of the β-Si₃N₄ grains, increasing aspect ratio of the β-Si₃N₄ grains and improving bending strength of the composites. Fracture toughness of the composites is higher than that of the β-Si₃N₄ ceramics, and the main toughening mechanism is crack bridging due to the higher aspect ratio of the β-Si₃N₄ grains.With the addition of 1vol% of Ti(C,N), the composite has a relative density of 99.31%, Vicker’s hardness of 15.9 GPa, bending strength of 993 MPa, and fracture toughness of 9.9 MPa·m^1/2.

Abstract: Foamed aluminum has been recently developed as one of new structure functional materials due mainly to its excellent properties such as energy absorption property. It is significant to investigate the compressive behavior and energy absorption property of foamed aluminum under the condition of static and dynamic loading. The compressive deformation behavior of foamed aluminum with open pore structure was experimentally studied and the effects of the porosity, the type of materials, the pore size and the sample size were discussed in detail by means of the orthogonal experiments. The results showed that the type of materials had the most evident influence on the compressive property of foamed aluminum among the factors investigated, and that the size effects of the experimental results were observed.

Abstract: This paper reveals a preparation method of a new type of porous metal. Because of the high cost and low quality, the actual large-scale application of porous metal is not very widespread. The new manufacturing methods proposed by paper will enhance the practical application of porous metals. The hollow part of hollow metal balls can be used as the main body of porous metal to manufacture porous metal. First, a hemispherical-thin layer metal structure was obtained by plastic processing from a metal plate. Then, this metal structure was connected appropriately according to the body-centered cubic structure to from a new type of spherical porous metal. The method is simple, high productivity, easy control and low cost.

Abstract: In this work, tungsten inert gas cladding (TIG), is utilized to in-situ synthesize the (Ti,W)C based cermet cladding layers. The microstructure and microhardness of the cladding layers were analyzed by scanning electron microscopy (SEM) and microhardness tester. The grain abrasion resistance of the cladding layers is also discussed. The grain abrasion resistance of the coating is also discussed. The results showed that excellent bonding between the coating and the AISI 1045 steel substrate was uniform, continuous and almost defect-free. (Ti,W)C cladding layers have compact microstructure and high microhardness. The grain abrasion resistance of the coating is attributed by the compact microstructure.

Abstract: Partial penetration means partial body of projectile is in target, the other out of target. Analysis model of slender nose projectile partial penetrates steel target is proposed base on cavity expansion theory (plate thickness is smaller than projectile nose length), and the variation relation of penetration depth with initial velocity is concluded when projectile partially penetrates steel target. Penetration tests are carried out on hard projectile penetrates steel target, and the predicted results of penetration depth have good agreement with experimental results.