Influence of welding speed on corrosion behaviour of friction stir welded AA5086 aluminium alloy

The plates of AA5086 aluminium alloy were joined together by friction stir welding at a fixed rotation speed of 1000 r/min various welding speeds ranging from 63 to 100 mm/min.Corrosion behavior of the parent alloy(PA),the heat affected zone(HAZ),and the weld nugget zone(WNZ)of the joints were studied in 3.5%(mass fraction)aerated aqueous Na Cl solution by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The corrosion susceptibility of the weldments increases when the welding speed increases to 63 and 100 mm/min.However,the value of corrosion rate in the weldments is lower than that in the PA.Additionally,the corrosion current density increases with increasing the welding speed in the HAZ and the WNZ.On the contrary,the corrosion potential in the WNZ appears more positive than in the HAZ with decreasing the welding speed.The WNZ exhibits higher resistance compared to the HAZ and the PA as the welding speed decreases.The results obtained from the EIS measurements suggest that the weld regions have higher corrosion resistance than the parent alloy.With increasing the welding speed,the distribution and extent of the corroded areas in the WNZ region are lower than those of the HAZ region.In the HAZ region,in addition to the pits in the corroded area,some cracks can be seen around the corroded areas,which confirms that intergranular corrosion is formed in this area.The alkaline localized corrosion and the pitting corrosion are the main corrosion mechanisms in the corroded areas within the weld regions.Crystallographic pits are observed within the weld regions.

Fabrication and Characterization of Poly Lactic Acid Scaffolds by Fused Deposition Modeling for Bone Tissue Engineering

Three-dimensional porous poly-lactic acid(PLA) scaffold was fabricated using fused deposition modeling(FDM) method including 30%, 50% and 70% nominal porosity. Study of phases in initial polymeric material and printed scaffolds was done by X-ray diffraction(XRD), and no significant phase difference was observed due to the manufacturing process, and the poly-lactic acid retains its crystalline properties. The results of the mechanical properties evaluation by the compression test show that the mechanical properties of the scaffold have decreased significantly with increasing the porosity of scaffold. The microstructure of scaffolds were studied by scanning electron microscope(SEM), showing that the pores had a regular arrangement and their morphology changed with porosity change. The mechanical properties of the poly-lactic acid scaffolds printed using fused deposition modeling, can be adapted to the surrounding tissue, by porosity change.

Effect of deep cryogenic treatment on the formation of nano-sized carbides and the wear behavior of D2 tool steel

The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, hardness test, pin-on-disk wear test, and the reciprocating pin-on-fiat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.

Effect of deep cryogenic treatment on the properties of 80CrMo12 5 tool steel

The effect of deep cryogenic treatment on the mechanical properties of 80CrMo 12 5 tool steel was investigated. Moreover, the effects of stabilization （holding at room temperature for some periods before deep cryogenic treatment） and tempering before deep cryogenic treatment were studied. The results show that deep cryogenic treatment can eliminate the retained austenite, making a better carbide distribu- tion and a higher carbide amount. As a result, a remarkable improvement in wear resistance of cryogenically treated specimens is observed. Moreover, the ultimate tensile strength increases, and the toughness of the sample decreases. It is also found that both stabilization and tem- pering before deep cryogenic treatment decrease the wear resistance, hardness, and carbides homogeneity compared to the deep cryogeni- cally treated samples. It is concluded that deep cryogenic treatment should be performed without any delay on samples after quenching to reach the highest wear resistance and hardness.

铜/黄铜异种搅拌摩擦焊接头在碱性溶液中腐蚀行为（英文）

本研究旨在研究0.015 mol/L硼砂溶液(pH 9.3)中铜/黄铜异种搅拌摩擦焊(FSLW)接头的点焊熔核区(NZ)的腐蚀行为。在焊接过程中,采用高热和低热两种热输入异种焊接铜/黄铜板,高热和低热输入分别为710 r/min,16 mm/min和450 r/min,25 mm/min。通过开路电位(OCP)测量、电化学阻抗光谱(EIS)和Tafel极化实验对硼酸盐缓冲溶液中试样的电化学行为进行评估。用扫描电子显微镜对试样表面形貌进行观察。结果表明,由于热输入量的减小导致的NZ腐蚀,点焊熔核区的晶粒尺寸和电阻升高的幅度降低。Tafel极化实验和电化学阻抗光谱分析结果表明,与金属铜和黄铜不同的是,在焊接过程中,NZ试样的热输入的减少改善了腐蚀行为。此外,焊接过程中热输入的增加对形成具有较高保护性能被动薄膜的条件不利。

中间层成分对GTD-111/IN-718高温合金在瞬时液相连接过程中显微组织和力学性能的影响

研究使用不同的中间层瞬时液相连接两种异种高温合金的适用性。在1100℃、不同时间下瞬时液相连接GTD-111/IN-718体系,研究BNi-2、BNi-3和BNi-9三种类型的中间层对该体系显微组织和力学性能的影响。采用场发射扫描电子显微镜和能量色散光谱技术,研究接头区域的成分变化和显微组织。结果表明,非热凝固区Ni_(3)B的形成受B含量控制,相应地,Ni_(3)Si的形貌受Si含量控制。Cr含量可能会阻碍B从中间层向母材迁移,非热凝固区内Cr B的形成主要受Cr含量的影响。硼化物如镍或铬硼化物基体的形成,使共晶化合物具有高的显微硬度。与使用BNi-3和BNi-2中间层的合金接头相比,等温凝固结束后,使用BNi-9中间层的合金接头其剪切强度更低,这可能与金属焊料成分中不含Si和BNi-9中含Cr有关。

Surface treatment of titanium dental implant with H2O2 solution

The surface treatment is important for titanium and its alloys as promising candidates for dental implantation due to their bioinert surface.Titanium surface samples were modified using H2O2 solution at different times up to 72 h to boost their bioactivity.According to the results of the field emission scanning electron microscopy test,some nanostructures are formed on the surface of treated titanium samples and increased in size by increasing the time of treatment up to 24 h.After 24 h of application,the sharpness of nanostructures decreased and the micro-cracks and discontinuity in the coating surface increased.The results of the X-ray diffraction study and Raman spectroscopy revealed that anatase(TiO2)was formed on the surface of treated titanium samples.The peak intensity of Raman spectroscopy increased with an improvement in treatment time of up to 24 h and then decreased due to the discontinuity of the coating.Full wettability and ability to form apatite were reached at 6 h of treatment.It is clear that the treatment time has a significant effect on the surface treatment of titanium using the H2O2 solution.

Evaluation the Properties of Polycaprolactone/Fluorapatite Nano-biocomposite

In this study,nano-biocomposites of polycaprolactone(PCL)as the matrix and different amounts of nanofluorapatite(nFA)(0,10,20 and 30 wt.%)as the reinforcement were prepared for possible scaffold fabrication using the fused filament fabrication(FFF)3D printer.Field Emission Scanning Electron Microscopy(FE-SEM)and Energy Dispersive Spectroscopy(EDS)showed that nFA particles were well distributed in the PCL matrix.X-ray diffraction analysis(XRD)and Fourier Transform Infrared Spectroscopy(FTIR)depicted no chemical interaction between the elements of the composite.Differential Scanning Calorimetric(DSC)analysis was then used to assess the thermal properties of the composites,suggesting that this could be due to the amorphous phase formation of the intermolecular hydrogen bonds between PCL and nFA,resulting in the suppression of PCL crystallization.The results of mechanical characterization also showed that the addition of nFA up to 20 wt.%to the PCL increased the tensile and yield strength,as well as reducing the elongation at both yield and failure points and increasing the Young modulus.The best mechanical properties were obtained for the PCL/20nFA composite.Tensile strength and Young modulus were increased by 30%and 179%,respectively;meanwhile,elongation of PCL/20nFA was decreased by 70%,as compared to the naked PCL.These changes could be attributed to the better distribution of the nFA filler in the PCL matrix.According to the obtained results,PCL/20nFA could be regarded as a good composite in terms of the mechanical properties for the regeneration of the bone tissue.

Effect of Deep Cryogenic Heat Treatment on the Wear Behavior of Carburized DIN 1.7131 Grade Steel

The effects of the deep cryogenic heat treatment on the microstructural changes,wear resistance,and hardness of carburized DIN 1.7131 grade steel were investigated.Results show that cryogenic heat treatment reduced the retained austenite and increased the carbide amount.In addition,after the cryogenic heat treatment,carbide shows a more uniform distribution,as compared to the conventionally treated ones.It was also clarified that the hardness of the cryogenically treated samples was improved,but the relative improvement decreases with the distance as the surface increases.It has been shown that the wear resistance improves due to the cryogenic heat treatment,and the predominant wear mechanism is a combination of the adhesive and tribo-chemical wear.