LU Jin-wen, GE Peng, ZHAO Yong-qing. Influence of Mo on Microstructure of Ti-Mo Alloys and Strengthening Effects[J]. Journal of Materials Engineering, 2013, 0(9): 1-5.
The effects of Mo on the microstructure and mechanical properties of a series of β forged Ti-Mo alloys at different solution treatment temperatures and time were studied with an emphasis on the relationship between β-grain size and mechanical properties. The results show that the microstructure and crystal structure of solution treated alloys are sensitive to Mo contents. Ti-1Mo and Ti-2Mo alloys are composed of equiaxed α phase. Ti-4Mo alloy is composed of acicular α' and β grain boundary. When Mo content increases to 10% (mass fraction) or higher, the retained β phase becomes the only dominant phase. The β-grain size is not only relative to solution treatment temperatures and time, but also relative to Mo contents from statistical results. It indicates that the β-grain size increases with the increasing of solution treatment temperature and decreases with the addition of Mo contents under the same solution time. The strength of the alloys increases with the decreasing of grain size, but the plasticity of the alloys changes little. The mechanism of strengthening was also analyzed.
LI Bin, CHEN Zhao-ke, XIONG Xiang. Microstructure and Mechanical Properties of C/C Composites with Gradient Distributed TaC Interlayer[J]. Journal of Materials Engineering, 2013, 0(9): 6-10.
TaC ceramic interlayer was deposited on carbon fiber in three-dimensional fine-woven punctured felt by using chemical vapor infiltration method. By controlling the flow direction of the reaction gases in the preform, C/C composites with gradient distributed TaC interlayer were obtained. Microstructure, flexural property and fracture toughness of the as-prepared composites were studied. The results show that TaC interlayer is deposited on the surface of carbon fiber and presents a gradient distribution in C/C composites. The average flexural strength and fracture toughness of the as-prepared composites are 272.6MPa and 5.0MPa·m1/2, respectively. In general, with the decreasing of the TaC content along the thickness direction (Z-axis) of the composites, the length of carbon fiber pulled out from the carbon matrix becomes shorter. In TaC-rich area, TaC content has significant influence on fracture behavior of the composites. The fracture behavior of the TaC-rich area is brittle in outer layer which has more TaC, while change to pseudo-ductile in inner layer which has less TaC.
PENG Ning-qi, TANG Guang-bo, LIU Zheng-dong. Effect of Two-stage Cooling Rate on Austenite-ferrite Phase Transformation in High Temperature Transition Region[J]. Journal of Materials Engineering, 2013, 0(9): 11-15.
Effects of different two-stage cooling rates on start temperature and microstructure of ferrite transformation were studied with metallographic microstructure, stress-temperature curves and small strains in the cooling process. The two-stage cooling rate of C-Mn steel in high-temperature transition zone of deformed austenite was controlled by Gleeble thermal mechanical simulator. The results show that ferrite transformation start temperature drops and ferrite volume fraction increases when this way of front fast cooling and subsequent slow cooling at the high temperature transformation zone of supercooled austenite, compared with the same time continuous cooling, and when rapid cooling rates of 100℃/s in the preceding stage, decline of ferrite transformation start temperature can reach 100℃ and ferrite volume fraction is nearly double. Therefore, the cooling way of front ultra fast cooling (UFC) and subsequent slow cooling is helpful to enhance amount of ferrite transformation and reduce ferrite phase transition temperature in order to refine the ferrite grain.
CHEN Yu-lai, DONG Chang-zheng, CAI Qing-wu, WAN De-cheng, LI Liang, QI Yue. Effect of Mo and Ni on Microstructure and Mechanical Properties of Carbide-free Bainite Ultra-high Strength Steels[J]. Journal of Materials Engineering, 2013, 0(9): 16-21.
Continuous cooling transformation diagrams of three steels with different composition were determined. Microstructure evolution behavior and mechanical properties of three steels that was formed by continuous cooling and rolling in the air were investigated by transmission electron microscopy and scanning electron microscope. The influences of addition of Mo/Ni on microstructure and mechanical properties of the steels were also analyzed. The results show that adding Mo/Ni can effectively delay ferrite transformation and decrease Ms temperature, which equals to promote medium-temperature bainite transformation. The microstructure of the steels evolves from F+GB+M/A to CFB(BF+AR) after adding Mo and Ni alloy.In general,the thickness of bainitic ferrite in No.2 hot-rolled plate (with Ni) is thinner than No.3 steel(with Mo) and coarse bainite can be observed in No.2 steel which leads to a deterioration in toughness.However, the thickness of bainite ferrite in No.3 steel(with Mo) varies little and the film shaped carbon-enriched remaining austenite well distributes between BF lathes.The mechanical properties tests of three steels indicate that adding Mo/Ni can remarkably improve both tensile strength and toughness,but Mo and Ni have different effects,adding Ni offers a higher strength while adding Mo is more helpful to improve toughness of high-strength steels.
WANG Dong, ZHAO Jun, LI An-hai, CUI Xiao-bin. Microstructure-level Modeling for Hardness Prediction of WC-Co Cemented Carbides[J]. Journal of Materials Engineering, 2013, 0(9): 22-26,31.
A model is proposed by taking the microstructure of the cemented carbides into consideration and combining with the finite element simulation of micro-indentation experiments, in order to predict the hardness of WC-Co cemented carbides. The "random method" is applied to construct the microstructure model, with Co volume fraction, average grain size distribution, grain centroid distribution and grain orientation angle distribution being considered. The results show that the actual microstructure characteristics of material can be reconstructed, and the hardness is greatly affected by the microstructural parameters, among which Co volume fraction and the average grain size distribution are the most significant ones. The simulation results agree well with the experimental ones, and the established model is proved to be effective to predict accurately the hardness of WC-Co cemented carbides.
YU Jian-ming, WEN Tong, YUE Yuan-wang, WU Shi-ren, LEI Fan, XIAO Bing-e. Parameters Optimization of AZ31 Magnesium Alloy Processing Map Based on BP Neural Network[J]. Journal of Materials Engineering, 2013, 0(9): 27-31.
The hot deformation experimental information of AZ31 magnesium alloy was obtained by using the Gleeble-1500 thermal simulator, and the relevant prediction models between flow stresses and strain, strain rate, temperature were established by samples training based on BP neural network, and the processing map of AZ31 was constructed by those prediction models. The results show that flow instability of AZ31 is mainly distributed in two regions including low temperature and high strain rate region and middle temperature and low strain rate region. The region of higher power dissipation factor would be regarded as an optimal processing zone when temperature and strain rate are controlled at the following level: 340-440℃ and 0.01-0.02s-1 respectively. The results of network prediction of flow stresses are in good agreement with experimental results by using the trained neural network model. The maximal relative error is 6.67%. The processing maps which are plotted in different deformation conditions demonstrate that AZ31 is sensitive to temperature and strain rate rather than strain.
WU Hui-bin, LIU Yue-ting, WANG Li-dong, LIU Li-fu. Influence of Cr Content on Microstructures and Acid Corrosion Properties of X120 Grade Pipeline Steel[J]. Journal of Materials Engineering, 2013, 0(9): 32-37,43.
Effects of Cr on microstructures and acid corrosion properties of X120 grade pipeline steel were studied with SEM and TEM and mass loss. The mechanical properties results show that the microstructures of four tested steels are all tempered martensites, and the mechanical properties are all up to X120 grade. Yield strength and tensile strength of the four tested steels are improved with the increasing of Cr content. The precipitated phases of tested steels are (Nb, Ti) (C, N). Precipitation of Cr is little, and was only discovered in the 3Cr steel through the experiment. The corrosion experiment results indicate that the corrosion scales on the four tested steels have two layers structure under the condition of CO2/H2S. The outer layer is mainly containing FeS, the inner layer FeCO3. Cr enriches in the inner layer, and the content increases with the increasing of Cr element in matrix. The Cr-rich enhances the compactness of the corrosion scales, and the scales have ion-passing-selectivity, which hinders the moving of anion to matrix, and finally the resistance to CO2/H2S corrosion increases.
ZHUANG Dong-dong, WANG Zuo-cheng, ZHANG Jian-qiang, CHEN Pei-dun, CHEN Kun, MA Zheng-wei, GU Guo-hua. Experimental Study of Recrystallization of Low Carbon Al-killed Steel Sheets with Different Rolling Reduction[J]. Journal of Materials Engineering, 2013, 0(9): 38-43.
Hardness, metallographic microstructure and texture of low carbon Al-killed steel sheets rolled at different cold-rolled reductions and annealed at different temperatures were investigated by means of Vickers hardness tester, OM and XRD. The results indicate that, with increasing cold-rolled reduction, recrystallized starting temperature and finishing temperature drop down and the recrystallized grain size decreases. However, the role of grain refinement is weakened when cold-rolled reduction rates are higher than 68%. The recrystallization has completed as soon as annealing begins at the annealing temperature of 680℃. With holding time, quantity of the cake grains increases and the cake degree of grains exacerbates. The nucleation and growth of grains is adequate by sufficient holding time in the process of recrystallization. At the higher annealing temperature, the value of favorable {111}/detrimental {100} orientation texture becomes bigger at the same cold-rolled reduction. In this condition, 720℃ is the appropriate annealing temperature to acquire the favorable deep-drawing property. The occurrence of secondary recrystallization is not conducive to mechanical properties with an annealing temperature of 760℃ and a total cold-rolled reduction of 58%.
ZENG Li, WANG Yan, LI Sha, LI Yang, JIN Xian-zhe. Microstructure Evolution of GH4700 Superalloy for 700℃ Ultra-supercritical Boilers[J]. Journal of Materials Engineering, 2013, 0(9): 44-47.
By thermal compression experiment, microstructure analysis, combined with thermodynamic and kinetic calculation methods, the microstructure evolution of GH4700 superalloy for 700℃ ultra-supercritical boilers was studied.The results show that the GH4700 superalloy is more sensitive to the deformation temperature and strain rate. As the deformation temperature decreases and the strain rate increases, the flow stress of the superalloy increases rapidly.The mode of its dynamic recrystallization nucleation is a typical strain-induced grain boundary migration nucleation.The hot deformation activation energy and grain growth activation energy are 345.0948kJ/mol and 252.05kJ/mol respectively.
ZHOU He-rong, JIE Gan-xin, MA Jian. Corrosion Behavior of Polyester Powder Coating in Simulated Sea Environment[J]. Journal of Materials Engineering, 2013, 0(9): 48-53,59.
The corrosion behavior of 6063 aluminum alloy with powder coating in 0.6mol/L NaCl(pH=7.0) solution was investigated by metallographic microscope and electrochemical impedance spectroscopy (EIS). The results show that artificial defect is covered with corrosion products after the sample of powder coating without chromic acid passivation immersed into 0.6mol/L NaCl(pH=7.0) solution for 50 days. Chromatic aberration value of powder coating increases. Corrosion behavior does not occur at the border of artificial defect of the sample. Corrosion rate of 6063 aluminum alloy without chromic acid passivation is about five times higher than that for the sample with chromic acid passivation by EIS test. Aluminum passivation film can delay the corrosion of aluminum alloy and improve the impedance of defect and perfect coating.
GE Mao-zhong, XIANG Jian-yun, ZHANG Yong-kang. Effect of Laser Shock Processing on Mechanical Properties of AZ31B Magnesium Alloy[J]. Journal of Materials Engineering, 2013, 0(9): 54-59.
In order to investigate the effect of laser shock processing(LSP) on mechanical properties of AZ31B magnesium alloy. AZ31B magnesium alloy sheets were treated by using Nd:YAG laser with a wavelength of 1054nm, a pulse width of 15ns, a pulse energy of 10J and a spot diameter of 3mm. The results show that a nanostructured surface layer can be produced on an AZ31B magnesium alloy by using the optimized laser parameters,and the surface grain size is about 20nm. Residual compressive stress induced by LSP at the surface of the specimen is up to -125MPa. The tensile strength and the yield strength are improved by 16.9% and 16.3%, respectively. Surface microhardness is improved by 91.8%. The microstructures of specimens by LSP were analyzed by TEM and SEM, and the mechanism which caused the mechanical properties improvement was discussed.
PANG You-xia, XU Yan, ZHANG Hao, TANG Yong, LIU Hou-cai. Erosion Resistance of Micro/Nano Composite Coating[J]. Journal of Materials Engineering, 2013, 0(9): 60-63.
In order to repair the flow parts of the fluid machinery under erosive wear environment, based on the basis of the erosive wear mechanism, the viscous sub-1ayer and anti-erosion coating of organic compound elastomeric coating were optimized by selecting micro/nano particles. Erosion resistance test was carried out with the coating of the specimen, as well as four different surface treatment methods by using rotary abrasion test device coated in simulated working conditions. Erosion wear results were analyzed and compared by using mass loss method and SEM. The results show that after 35h erosion wear test, the specimen mass of five different surface treatment methods in the process of erosion wear has the similar variation, the micro/nano composite coating has the best erosion resistance, basically no mass loss. The erosion resistance of matrix powder coated specimens is the worst. The coating can effectively repair the parts of the over-current and improve the flow components erosion resistance.
LI Quan, YANG Jin, JIANG Xian-quan, CHENG Ren-ju, LIU Wen-jun, ZENG Bin. Microstructure Uniformity Investigation of Hot Extruded AZ Series Alloys[J]. Journal of Materials Engineering, 2013, 0(9): 64-68.
The AZ10, AZ31, AZ61 and AZ91 magnesium alloys were deformed with extrusion simulation system on Gleeble 1500D.The characteristics of extruded microstructure were analyzed. The affecting factors on uniformity of the microstructure were investigated. The results show that the content of alloying element, homogeneous annealing, and extrusion ratio have significant effects on microstructure uniformity of extruded alloys. With homogenization before extrusion, the higher the content of alloying element is, the more nonuniform the microstructure is, and the finer the recrystallized grains are.The extruded alloys without homogenization annealing have big block due to incomplete recrystallization, surrounded by extremely fine grains. The microstructure becomes gradually uniform and the area of unrecrystallization reduces with the increase of extrusion ratio.
WANG Dong-ning, LI Jia-lu, JIAO Ya-nan. 3D Meso-geometrical Model of Plain Weave Fabric and Finite Element Modeling Under Ballistic Impact[J]. Journal of Materials Engineering, 2013, 0(9): 69-74,78.
The 3D mesoscopic geometrical model of plain weave fabric was built. A commercially available finite element analysis code (LS-DYNA) was used to model the dynamic response of fabric under the condition of ballistic impact of a rigid sphere. The geometry of the model was based on the photomicrographs of sectioned laminates, which helped us define the accurate and real yarn geometry. Yarns were modeled as orthotropic elastic and the parameter and the failure criteria were referred to the actual Kevlar fabric. Friction between the yarns and sphere was considered. The residual velocity was obtained by setting the striking velocity. The ballistic limit velocity V50 of the single fabric was calculated. Results indicate that the delicate deformation process and failure mechanism of the fabric are finely captured, and good agreements between simulation and the test data are obtained in terms of the V50 and the failure mechanism of the fabric.
FENG Li-bang, LI Hui, HAO Xiang-zhong, CHAI Chang-sheng, XUE Xiang-jun, HAO Xue-xing. Structure and Thermal Resistance of Phosphoric Acid-modified Phenol-formaldehyde Resin[J]. Journal of Materials Engineering, 2013, 0(9): 75-78.
A new phenol-formaldehyde resin was prepared by modification of phenol-formaldehyde resin with phosphoric acid. The structure and thermal resistance of the phenol-formaldehyde resin before and after modification were investigated by Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Meanwhile, the mechanical property of the modified resin was evaluated by measuring the tensile shear strength and compressive strength. Results show that new bonds of P—O—C and P＝O with higher bond energy are introduced into phenol-formaldehyde molecules after modified by phosphoric acid. As compared with the unmodified phenol-formaldehyde, the heterocyclic structure with higher thermal stability forms and the aromaticity increases in modified phenol-formaldehyde molecules. Consequently, the low decomposition at elevated temperature is resulted. As a result, the thermal resistance and mechanical properties of the phenol-formaldehyde resin are improved markedly.
JIAO Ze-hui, SONG Xi-ping, ZHANG Min, YU Hui-chen. In-situ Tensile Study for Fully Lamellar and Duplex Microstructures of High Nb Containing TiAl Alloys at Elevated Temperature[J]. Journal of Materials Engineering, 2013, 0(9): 79-83,90.
The high Nb containing TiAl alloys with fully lamellar (FL) and duplex (DP) microstructures were investigated based on the in-situ tension tests at 750℃. The results show that DP has better tensile strength of 958MPa and area reduction of 45.1%. FL has lower tensile strength and little ductility. The microcracks initiation and propagation occur on DP specimen surface. The amount of microcracks increases and the microcracks widely distribute with the increasing loading. The microcracks hardly grow after initiation. There are a small number of microcracks observed on FL specimen surface. For DP structure, the vermiculated cracks form through the coalition of small holes. For FL structure, microcracks initiate along interlamellar and colony boundaries, being perpendicular or a large angle to the loading axis. But near the fractured location, it is the translamellar propagation cracks that result in the rupture.
LIU Ya-hu, CAI Xue-yuan, ZHU Yan-chao, ZHANG Lin-jiao, YANG Jian-hong. Research Progress in SiC Nanoparticles Aggregation and Dispersion[J]. Journal of Materials Engineering, 2013, 0(9): 84-90.
The recent research progress on the aggregation and dispersion of SiC nanoparticles was presented. The formation mechanisms and types of micro/nanoparticle agglomeration along with differences between them were introduced. Based on listing processing methods of agglomeration, the influence of pH and viscosity of suspension and types of dispersing agents for SiC nanoparticles were shown. The charge states, chemical composition and surface modification of primary SiC particles were elaborated. With summarizing the isoelectric point (IEP) of SiC before and after adding dispersions, toluoyl-polyethylene imine (T-PEI) was chosen to analyze its molecular structure and working mechanism, and compared with traditional dispersant from adsorption amount, viscosity and Zeta potential. According to the forming mechanism of SiC powder aggregation and research status of its dispersion, the characteristics and microstructure of SiC nanoparticles, as well as its dispersion optimization to increase industrial production efficiency, should be developed in the future.
CHEN Jian-xun, ZHAO Xing-ke, LIU Da-yong, HUANG Ji-hua, ZOU Xu-chen. Research Development of SnAgCu System Lead-free Solders in Electronics Packing[J]. Journal of Materials Engineering, 2013, 0(9): 91-98.
The SnAgCu solder with a wide application was identified as the best substitute for the traditional SnPb solder in electronic assembly industry. However, this alloy had some weaknesses, such as low anti-oxidation ability, the formation of large, brittle intermetallic compounds at the solder and substrate interface, less creep and fatigue resistance of joints during service condition compared to the eutectic SnPb solder. The microstructures and properties of SnAgCu alloy can be significantly improved with the addition of alloying elements and nanoparticles. Therefore, the reliability of solder joints can be enhanced. It is beneficial for the development novel high-performance SnAgCu solder with element additives. Based on the development of SnAgCu system lead-free solders at home and abroad, this paper summarizes the effects of alloying elements and nano particles on the wettability, anti-oxidization, microstructures, solder joints reliability of SnAgCu system lead-free solders. The present problems in the process of the applications of SnAgCu system lead-free solders are reviewed, some proposals are put forward which may provide a guide for the study of SnAgCu system lead-free solders.
