Materials and Technologies in Engineering
Advanced Manufacturing and Materials
Materials and Technologies in Mechanical Engineering
Materials Design and Applications
Materials Engineering and Nanotechnology
XIV International Scientific and Practical Conference "New Polymer Composite Materials"
6th Asia Conference on Mechanical and Materials Engineering
Porous Metals and Metallic Foams
Material Engineering and Manufacturing
Materials and Technologies in Construction and Architecture
22nd Brazilian Conference on Materials Science and Engineering
Advanced Materials Research QiR 15
Composite Materials and Material Engineering II
Advanced Manufacturing and Materials
摘要: Surface modification using fine shot peen (FSP) comparing to and combining to hard film coating TiAlN-PVD on commonly used hardened cold work tool steel are studied in this research for their resistance to adhesive wear. Ball on disk tests were carried out to investigate the performances of those surface modification methods. In comparison to hard thin film coating, PVD-TiAlN coated tool was superior to FSP modified tool for its wear resistance. However, combining FSP and nitriding on TiAlN coated tool had higher wear resistance than that of TiAlN coating alone. Moreover various types of texture obtained from different FSP conditions were also investigated. The average roughness parameter (Ra) which is commonly used is not a good representative to determine the surface required for wear resistance enhancement for FSP. As Ra relates to the magnitude of the roughness profile only. The spacing parameters seem to be more effective. The larger the surface spacing after FSP, the higher is the wear resistance.
摘要: Dual precipitates of carbide and copper particles formed within Cu-Ti microalloyed DP (Dual Phase) steel in the present study. The precipitation behaviors of tiny precipitates, especially in the ferrite matrix, were checked precisely by several methods, such as optical microscopy, high resolution transmission electron microscopy, and hardness testing. It was found that copper particles nucleated only on the interphase precipitated TiC and were not dispersed randomly within the ferrite matrix. Therefore, the formation of dual precipitates within the ferrite grains should be considered as separated phase transformation; initially, only titanium carbides form during the austenite decomposition reaction, after which copper particles heterogeneously nucleate on these carbides. Furthermore, as compared to Cu microalloyed DP steel, the tempering behavior of martensite in the Cu-Ti microalloyed DP steel showed a tempering hardening characteristic.
摘要: Two types of steels which are different in Ni content were tested in three groups of different quenching temperatures and same tempering temperature respectively under the same conditions, and then tested the mechanical properties and observated the microstructure, comparing with the effects of different Ni content on the microstructure and properties. When 1Ni-steel is under the different quenching temperature, its tensile strength range is 1269-1290MPa and changes subtlely. The yield strength and impact energy reach the highest at 910°C, and the mircostructure is fine and uniform. With the quenching temperature increasing, the strength of 3Ni-steel decreases ,but the toughness increases comparing with both kinds of the steels, the microstructure of 3Ni-steel has much more hard phases in its tempered martensite microstructure. Its tensile strength, yield strength and toughness are higher than 1Ni-steel at the lower quenching temperature. The inclusions of 3 Ni-steel are characterized by spheroidization and refinement. In the NACE-A test, the SSC resistance of 3Ni-steel is better than that of 1Ni-steel, which indicates that the high Ni steel has better comprehensive properties.
摘要: Friction stir welding is most commonly used for joining aluminum alloy parts. After welding, residual stresses occurred in the welded joint caused by non-uniform cooling rate. Friction stir welding usually generates tensile residual stress inside the workpiece which affects the strength in addition to the fatigue life of materials. Compressive residual stress usually is beneficial and it can be introduced by mechanical surface treatment methods such as deep rolling, shot peening, laser shock peening, etc. In this research, deep rolling was used for inducing compressive residual stress on surface of friction stir welded joint. The residual stresses values were obtained from X-ray diffraction machine. Influence of three deep rolling process parameters: rolling pressure, rolling speed and rolling offset on surface residual stresses at the welded joint were investigated. Each factor had 2 levels (23 full factorial design). The statistical analysis result showed that the rolling pressure, rolling speed, rolling offset, interaction between rolling pressure and rolling speed, interaction between rolling speed and rolling offset were statistically significant factors, with the most compressive residual stress value approximately -391.6 MPa. The appropriated deep rolling process parameters on surface residual stress of AA7075-T651 aluminum alloy friction stir welded joint were 1) rolling pressure about 150 bar 2) rolling speed about 1,400 mm/min 3) rolling offset about 0.1 mm.
摘要: Metal Inert Gas (MIG) welding process is a common welding process for carbon steels. During the cooling after welding, non-uniform cooling cause tensile residual stress on the surface of welded joint and, in most cases, in Heat Affected Zone (HAZ) also. The tensile residual stress is undesirable because it affects the strength and shorten the workpiece fatigue life. In order to convert the tensile residual stresses to desirable compressive residual stresses, the mechanical surface treatment like deep rolling process was used in this research. The surface residual stresses were measured by XRD machine with the sin2ψ method. For statistical analysis of significant factors used in deep rolling process, there are three factors each factor has two levels: rolling pressure, rolling speed and number of passes. Taguchi experimental design was used in conjunction with a deep rolling process to determine factors affected the surface residual stresses and surface microhardness. The results of the research showed that the most significant factors that affect the surface residual stress and surface microhardness were the number of passes, followed by the rolling pressure and the rolling speed, respectively. The maximum compressive residual stress measured at the welded joint was -521.5 MPa. The highest measured surface microhardness was 266.2 HV at the welded joint. The appropriated factors of deep rolling process for JIS SS400 MIG welding were rolling pressure 270 MPa, rolling speed 1,500 mm/min and number of passes 3 times.
摘要: Al 7xxx alloy is a heat treatable Al alloy with superior strength. Solution treatment in precipitation hardening sequence of the alloy has an important role to dissolve second phases and bring vacancies out to form precipitates in the ageing process. Another strengthening can be done by Ti addition as grain refiner. As cast alloy by squeeze casting was homogenized at 400 °C for 4 h. Solution treatment was conducted at 220, 420, and 490 °C, followed by rapid quenching. Subsequent ageing was conducted at 130 °C for 48 h. Characterization was performed by optical microscope, SEM-EDS (Scanning Electron Microscopy – Energy Dispersive Spectroscopy), Rockwell hardness testing, XRD (X-Ray Diffraction), and STA (Simultaneous Thermal Analysis). Ti added alloy showed rounder grains, lower hardness, and more reduction in second phase volume fraction along with increasing solution treatment temperature than those in alloys without Ti addition. Otherwise, the alloy final hardness was increasing and higher after the ageing process due to higher second phase dissolution which leads to more precipitates formed.
摘要: Residual stress has a significant influence on mechanical strength of a manufactured part and is considered to be related with process parameters and grinding signals. This paper investigates the relationship between residual stress and forces in the grinding of maraging steel 3J33. Features in time and frequency domains are extracted from tangential and normal grinding forces via various signal processing techniques. A two-round selection based on the statistical criterion is proposed to choose the best features that are related to the residual stress in the surface layer. The selected features are combined linearly in order to develop an empirical regression model that is capable of predicting residual stress well. The predicted residual stress values are compared with those measured from the experiment performed under different process parameters, and the result shows a favorable agreement quantitatively.
摘要: Nonlinear Twist Extrusion (NTE) is a new severe plastic developed (SPD) method for producing grain refinement by extruding and twisting bulk materials through the channel designed for more effective straining compared with the so-called twist extrusion (TE). In this experiment pure magnesium was pressed using NTE for up to 4 passes. The pressing was conducted under two different temperatures, the first pass was conducted in 523K followed by pressing from 2 to 4 passes at 473K pressing temperature. The microstructure of the material is observed with increasing number of passes using optical microscopy (OM), laser microscope and scanning electron microscopy (SEM) electron backscattered diffraction (EBSD). Grain size decreased with increasing passes and become finer than those obtained by other SPD processing. If compared by the same equivalent plastic strain, and it suggests that NTE is a promising approach in strengthening bulk material. The grain size of the as-received material reduced from 97μm down to 3μm after 4 passes. Moreover, the hardness of material also increasing up to 41Hv for the first pass and constantly increased with the increasing number of pressing. This result shows that NTE is one of the promising methods in severe plastic deformation.
摘要: A new type of machining method called half-spread-out helix modified roll is used to carry out numerical control machining and simulation of spiral bevel gears in this paper. The transformation from traditional machine tool adjustment parameters into processing input parameters of five-axis CNC machining center was realized. The simulated gear model of this machining method is obtained, and the coordinates of its tooth surface points are compared with points coordinates of theoretical tooth surface which are generated according to the traditional machining method. From the comparison, the correctness of this numerical control machining model is verified.