Mechanical,machining and corrosion properties of Al5083-carbon nanotubes composite produced by friction stir processing

In the current work, composites of Al5083 aluminum alloy and carbon nanotubes were developed by friction stir processing. Grain size reduction was observed in the composite from a starting size of 115 μm±4.6 μm to 11 μm±3.3 μm. Higher hardness, yield strength and ultimate tensile strength were measured for the composite at the cost of losing ductility compared with friction stir processed Al5083 and base alloy. This behavior can be understood by considering the influence of grain size and carbon nanotubes. Machining studies carried out by conducting drilling experiments demonstrate decreasing cutting forces for the composite compared with friction stir processed Al5083. However, compared with base alloy, composite exhibited higher cutting forces at all of the cutting parameters. Corrosion behavior of the materials assessed by electrochemical tests demonstrates the promising effect of grain refinement on enhancing the corrosion resistance of friction stir processed Al5083. However, presence of carbon nanotubes marginally decreased the corrosion resistance of composite compared with friction stir processed Al5083. From the results, it can be understood that the addition of carbon nanotubes significantly enhance the mechanical properties and machinability. However, addition of carbon nanotubes on decreasing the corrosion performance is a noteworthy observation.     

Enhancing the lifetime and corrosion resistance of gears made of carbon steel

Gears for structural machines require high fatigue strength for high performance. Generally, gears made of carbon steel easily corrode, thus, shortening their fatigue life. The aim of this paper is to improve the fatigue strength of carbon steel gears by means of heat treatment method which was nitriding composed of 95 % nitrogen gas as well as 5 % hydrogen gas, and to investigate its properties after nitriding. Therefore, in order to find the optimum nitriding temperature to increase the hardness and corrosion resistance of gears, the gas nitriding process was conducted at two different tube furnace temperatures: low (550 °C) and high (1150 °C), both for four hours. Microstructural and mechanical property evaluation of the low and high temperature nitrided low-carbon steel BS970-080A15 were studied and the results were compared to identify which gear had better performance in terms of hardness as well as corrosion resistance. The results from Vickers hardness test and weight loss analysis proved that high temperature nitrided carbon steel is harder and more corrosion resistant than the low temperature one.     

Additive manufacturing of AlSi10Mg samples using the selective laser melting technique: correlation between tensile and torsion behaviour

Additive manufacturing offers unique possibilities to produce complex components, which would not be possible or only very difficult to be realizable with conventional manufacturing processes. The potential of additive manufacturing of aluminum alloys has already been realized in prototyping, but still offers potential in the establishment of series applications. For enabling the establishment of additive manufacturing in series applications, comprehensive knowledge about the material behavior is necessary. This study examines the torsional behavior of additive manufactured AlSi10Mg samples and shows the correlation between tensile and torsional strength. Comprehensive torsion tests with strain gauges were performed and significant directional dependencies were shown. The correlation factor in the area of torsional yield strength/tensile yield strength and torsional strength/tensile strength was determined and was compared with the yield/failure conditions according to Tresca and von Mises.     

Effect of partial replacement of carbon by nitrogen on intergranular corrosion behavior of high nitrogen martensitic stainless steels

The microstructure evolution and intergranular corrosion (IGC) behavior of high nitrogen martensitic stainless steels (MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric acid tests and double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests. The results show that the partial replacement of C by N first reduces and then increases the size and content of precipitates in high nitrogen MSSs, and converts the dominant precipitates from M₂₃C₆ to M₂N, furthermore first improves and then deteriorates the IGC resistance. The high nitrogen MSS containing medium C and N contents provides good combination of mechanical properties and IGC resistance.     

Effect of heat treatment on the corrosion resistance and mechanical properties of selective laser melting Ti6Al4V alloy

The present work shows that the effect of several heat treatments on the corrosion resistance and mechanical properties of Ti6Al4V processed by selective laser melting (SLM). The microstructure of Ti6Al4V alloy produced by selective laser melting exhibited bulky prior β columnar grains, and a large amount of fine acicular martensites α′ were observed inside the prior β columnar grains. The acicular martensitic α′ were transformed to a mixture of α and β after heat treatment, and the grain size increases with the increase of heat-treated temperature. The results of 3.5 wt% NaCl solution electrochemical corrosion test showed that the heat-treated samples possess a higher corrosion resistance than the as-received sample. Among of them, the sample after heat-treated at 730 °C exhibited best corrosion resistance and excellent fracture strain. The sample heat treated at 1015 °C showed worst mechanical properties due to the formation of Widmanstätten structure.     

Investigation of the properties of nickel-boron/nano-diamond composite coatings upon pre/post heat treatment

The study has explored the physical and chemical properties of nickel-boron/nano-diamond composite coatings upon pre/post heat treatment. The nano-composite coatings were produced by electroless plating. In fact, the effects of using the nano-diamond additives (0 g l⁻¹, 0.1 g l⁻¹, 0.3 g l⁻¹, 0.5 g l⁻¹, 0.7 g l⁻¹) were investigated in pre/post heat treatment. According to the results, the micro-hardness of the nickel-boron/nano-diamond composite coating produced in the bath containing 0.5 g l⁻¹ nano-diamond additive reached to 1005 HV 0.05 upon post-heat treatment. Also, the corrosion resistance of the nickel-boron/nano-diamond composite coatings was modified by using the nano-additive or heat treatment. But, adding nano-diamond particles reduced the ductility and wear resistance of the nickel-boron coatings. We also found, modification of the properties (ductility and wear resistance) of the composite coatings was achieved by using the heat treatment.     

纳米SiO2/环氧复合钢板涂层材料机械及耐腐蚀性能

研究了纳米SiO₂添加量对环氧复合钢板涂层硬度、 T弯和应变等机械性能的影响, 并通过盐雾试验和电化学交流阻抗技术对涂层的耐腐蚀性能进行了测试。研究表明, 纳米SiO₂添加量为2.0%时, 涂层性能有较大的提高, 铅笔硬度从H提高到2H, T弯从4T改善到2T, 涂层的耐盐雾时间也由720h增加到1030h, 提高了40％以上。从电化学交流阻抗谱图得出, 添加量为2.0%的纳米SiO₂复合涂层的阻抗值最大, 高于未添加纳米SiO₂涂层的阻抗值近2个数量级。另外, 涂层的SEM照片显示, 纳米SiO₂添加量为2.0%时, 颗粒较均匀地分散, 黏接紧密, 形成较为致密的复合涂层。      

含Cu抗菌不锈钢的工艺与耐蚀性能

与普通0Cr17铁素体不锈钢和0Cr18Ni9奥氏体不锈钢相比，含铜铁素体和奥氏体抗菌不锈钢均具有良好的冷热加工性能和焊接性能．通过提高浇铸温度，抗菌不锈钢能保持良好的铸造性能．奥氏体抗菌不锈钢的抗应力腐蚀性能比0Cr18Ni9不锈钢有很大的提高，而铁素体抗菌不锈钢比0Cr17有明显的下降．与相应的普通不锈钢相比，两种类型抗菌不锈钢的耐点蚀性能均略有下降．     

离子注入Nb不锈钢双极板的耐孔蚀性能研究

为了探索离子注入Nb不锈钢双极板在模拟质子交换膜燃料电池(PEMFC)中的性能,采用极化曲线、恒电位试验和电化学阻抗谱等方法研究了离子注入铌316不锈钢在PEMFC环境中耐孔蚀性能的影响.研究表明:模拟PEMFC环境中316不锈钢和离子注入铌316不锈钢试样均发生孔蚀;Nb离子的注入提高了抗孔蚀性能,且随着介质温度的升高,孔蚀倾向加剧.孔蚀的诱发是离子注入铌316不锈钢表面水解形成Nb(OH)+4,导致钝化膜局部溶解破坏所致.模拟PEMFC环境中316不锈钢表面注入铌层膜电阻Rcoat、电荷转移电阻Rct升高,而注入铌层的电容值Ccoat、双电层电容Cct下降,表明注入铌层成为高电阻、低电容的阻挡层,对基体起到良好的保护作用.     

Effect of tempering temperature on microstructure and properties of aluminium-bearing high boron high speed steel

Heat treatment is of great significance to the performance improvement of high speed steel. Via heat treatment, the microstructure of high speed steel can be improved, thus greatly improving the material performance. The effect of tempering temperature on the microstructure of aluminium-bearing high boron high speed steel (AB-HSS) was investigated by optical microscope (OM), scanning electron microscope (SEM) and x-ray diffraction (XRD). The hardness and wear resistance of the alloy at different tempering temperatures were tested by Rockwell hardness tester, micro-hardness tester and wear tester. The experimental results indicate that the tempering microstructure of aluminium-bearing high boron high speed steel consists of α-Fe, M₂B and a few of M₂₃(C, B)₆. Tempering temperature could greatly affect the wear resistance of materials. With the increase of tempering temperature, the wear resistance of aluminium-bearing high boron high speed steel firstly increase and then decrease. The alloy tempered at 450 °C has the best wear resistance and minimum wear weight loss. This study provides a reference for the formulation of heat treatment process of aluminium-bearing high boron high speed steel.     

Improve stress corrosion cracking resistance and mechanical properties of Al‐Zn‐Mg‐Cu‐Zr alloy with heterogeneous lamellae structure produced by high pressure torsion

High pressure torsion experiment followed with heat treatment were carried out on as‐cast Al‐Zn‐Mg‐Cu‐Zr alloy at 400 °C under the pressure of 1 GPa. The microstructure, mechanical property and stress corrosion resistance properties for the as‐cast and high pressure torsion processed samples were studied. The results show that high pressure torsion processing can improve the mechanical property by the refinement of grains and grain boundary precipitates, as well as the homogeneous distribution of fine matrix precipitates. On the other side, the grain refinement, broken of coarse grain boundary precipitates and narrowed precipitates free zone caused by the high pressure torsion result in the improvement of stress corrosion cracking resistance. And due to the influence of heterogeneous lamellae structure, the sample after 0.5 high pressure torsion turn shows preferable mechanical property and stress corrosion cracking resistance than the sample after 2 high pressure torsion turns.     

Influence of the microstructure on the corrosion resistance of plasma‐nitrided austenitic stainless steel 304L and 316L

Austenitic stainless steels are widely used in medical and food industries because of their excellent corrosion resistance. However, they suffer from weak wear resistance due to their low hardness. To improve this, plasma nitriding processes have been successfully applied to austenitic stainless steels, thereby forming a thin and very hard diffusion layer, the so‐called S‐phase. In the present study, the austenitic stainless steels AISI 304L and AISI 316L with different microstructures and surface modifications were used to examine the influence of the steel microstructure on the plasma nitriding behavior and corrosion properties. In a first step, solution annealed steel plates were cold‐rolled with 38% deformation degree. Then, the samples were prepared with three kinds of mechanical surface treatments. The specimens were plasma nitrided for 360 min in a H₂–N₂ atmosphere at 420 °C. X‐ray diffraction measurements confirmed the presence of the S‐phase at the sample surface, austenite and body centered cubic (bcc)‐iron. The specimens were comprehensively characterized by means of optical microscopy, scanning electron microscopy, glow discharge optical emission spectroscopy, X‐ray diffraction, surface roughness and nano‐indentation measurements to provide the formulation of dependencies between microstructure and nitriding behavior. The corrosion behavior was examined by potentio‐dynamic polarization measurements in 0.05 M and 0.5 M sulfuric acid and by salt spray testing.     

Dendritic Microstructure Affecting Mechanical Properties and Corrosion Resistance of an Al-9 wt% Si Alloy

It has been reported that the mechanical properties and corrosion resistance of metallic alloys depend strongly on the solidification microstructural arrangement. The correlation of corrosion behavior and mechanical properties with microstructure parameters can be very useful for planning solidification conditions in order to achieve desired final properties. The aim of the present work is to investigate the influence of dendritic microstructural parameters of an Al-9 wt.% Si alloy on mechanical properties and corrosion resistance. The experimental results establish correlations between secondary dendrite arm spacings (λ₂) and ultimate tensile strength (σ_u), yield strength (σ_y), corrosion potential (E_Corr), and corrosion rate (i_Corr).