An Experimental Investigation and Analysis of PTAW Process

Experiments are conducted to deposit SS304 L powders on SS316 plates by plasma transfer arc welding process with varying four input process parameters, namely scanning speed, powder feed rate, stand-off distance, and current. The effects of these four input process parameters on deposition geometry, dilution, and bead continuity are investigated in this study. Attempts have been made to explain the experimental results with only two compound parameters, “energy deposition per length” and “powder deposition per length” instead of four independent input process parameters. It is observed that the variation of dilution is very little when the scanning speed increases from 100 to 600 mm/min and other process parameters remain constant. When the powder feed rate increases and other parameters remain constant, initially the dilution decreases rapidly and attains a minimum value which do not change further with increase in powder feed rate. It is also observed that the dilution remains almost constant around 6–9% as the stand-off distance changes from 7 to 11 mm and other process parameters remain constant. The formation of nonuniform bead is found to be due to insufficient energy deposition per length per mass of supplied powder.     

Measurement and analysis of impact dynamics suitable for modelling pneumatic transport of metallic powder flow through a directed energy deposition nozzle

In blown powder directed energy deposition (DED) additive manufacturing powdered metal feedstock is pneumatically conveyed to the meltpool via a nozzle. DED nozzles have been the subject to a growing number of research efforts using computational fluid dynamics (CFD) with multiphase flows to study and optimize powder flow. However, many research papers published to date contain powder – nozzle impact dynamics behavior that is not realistic or not derived from experiments that resemble the powder conveyance process in the DED nozzle being studied. To provide a set of data representative of DED powder flow through a nozzle particle image velocimetry (PIV) experiments were conducted using 316L stainless steel metal powder and flat targets with varying surface roughness made of oxygen free copper, mild steel, P20 tool steel, 316L stainless steel, Inconel 718, and Ti-Al6-V4. Normal coefficients of restitution (COR) were calculated and compared to several analytical and empirical models in literature.     

A new strategy for corrosion protection of porous stainless steel using polypyrrole films

In this work, a method to improve the protection against corrosion of porous sintered stainless steel is presented. It is based on the electrodeposition of polypyrrole(PPy) layers doped with a large size counterion such as dodecylbenzenesulphonic acid(DBSA), a conducting polymer with high corrosion resistance and good biocompatibility. The efficacy of PPy coating depends on the adequate adhesion between the metal substrate and the coating layer. The protection against corrosion has been tested using 316 L stainless steel(SS) powder sintered at different conditions to evaluate the effect of the sintering atmosphere(nitrogen and vacuum) and cooling rates(furnace and water) on corrosion resistance, while wrought 316 L SS has been used as reference material. In addition, two electrochemical deposition techniques have been tested to select the most adequate. Open circuit potential evolution, anodic polarization measurements and electrochemical impedance spectra have been used to evaluate corrosion protection in phosphate buffer saline medium. It has been evidenced that a more homogeneous and stable coating was obtained in the case of porous stainless steel. The corrosion potential shifted to nobler values and the anodic polarization branch became more stable. Coated porous samples have a good passivation performance with a lower stable passive current density and a higher breakdown potential. The transfer electronic resistance and the impedance module increase more than one order of magnitude. Therefore,the porosity of sintered stainless steel is seen as an advantage for the improvement of the adherence of the PPy coatings. The best corrosion protection is found for samples sintered in nitrogen and water-cooled.     

Effect of Surface Treatment and Metallic Coating on Corrosion Behavior and Biocompatibility of Surgical 316L Stainless Steel Implant

Surface engineering technology is a suitable method for coatings on the metal surfaces or performing surface modification treatment,which can improve corrosion resistance and biocompatibility of metals.In this research,corrosion behavior of Nb coating on H 2 SO 4 and HNO 3 treated AISI stainless steel 316L (SS) was evaluated.Nb coating was carried out using physical vapor deposition process on the SS.Characterization techniques including scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) technique were used to investigate the microstructure and morphology of the coated and treated SS.Electrochemical potentiodynamic tests were performed in two types of physiological solutions and compared with the pristine SS specimens.Cyclic polarization tests were performed to evaluate resistivity against pitting.Experimental results indicate that Nb coating and surface treatment of the SS had a positive effect on improvement of corrosion behavior.The decrease in corrosion current densities was significant for coated and treated specimens.The corrosion current density was much lower than the values obtained for pristine specimens.     

In vitro study on infectious ureteral encrustation resistance of Cu-bearing stainless steel

Cu-bearing stainless steel has been found to have obvious inhibition performance against encrustation in vitro. This study was aiming to further investigate the inhibitory effect of a Cu-bearing stainless steel(316 L-Cu SS) on the infectious encrustation based on its antimicrobial activity. The encrustation in presence of bacteria, antibacterial performance, urease production and Ca and Mg precipitation were examined by scanning electron microscopy, antibacterial assay, enzyme-linked immunosorbent assay and inductively coupled plasma-mass spectrometry, respectively. It was found that 316 L-Cu SS could inhibit the formation of bacterial biofilm due to the release of Cu~(2+) ions and then decrease the urease amount splitting by bacteria, which produced a neutral environment with pH around 7. However, more encrustations coupled with bacterial biofilms on the surface of comparison stainless steel(316 L SS) with an alkaline environment were recorded. It can thus be seen that the 316 L-Cu SS highlights prominent superiority against encrustation in the presence of microorganisms.     

410L和430L泡沫钢性能的比较

以410L和430L不锈钢粉为基体,以CaCl₂为造孔剂,采用粉末冶金烧结溶解法制备出不同孔隙率的410L和430L泡沫钢并分析比较其组织和性能。结果表明：410L和430L泡沫钢的基体组织都是α-Fe;在相同的腐蚀条件下430L不锈钢的抗腐蚀性更强;在烧结过程中410L泡沫钢孔壁表面的氧化程度比430L泡沫钢严重;在准静态压缩变形过程中孔隙率为73%~83%的410L泡沫钢屈服应力为22.06~5.45 MPa,相同孔隙率的430L泡沫钢其屈服应力为56.77~10.44 MPa,430L泡沫钢的抗压强度是410L泡沫钢的2~3倍;应变量为50%时,孔隙率为73%~83%的410L泡沫钢单位体积的能量吸收值为6.12~2.90 MJ/m³。应变量为50%时,孔隙率为72%~83%的430L泡沫钢其单位体积的能量吸收值为40.35~8.25 MJ/m³。430L泡沫钢的单位体积能量吸收值约为410L泡沫钢的3~5倍。     

Application of a neural network approach to the electrophoretic deposition of PEEK-alumina composite coatings

Nano-size Al₂O₃-polyetheretherketone(PEEK) composite thick films have been prepared on stainless steel substrates from non-aqueous colloidal suspensions by electrophoretic deposition (EPD). The effects on the deposition efficiency of process parameters, such as the deposition time, the difference of potential applied and their interactions were studied using a neural network approach to develop a quantitative understanding of the system. Furthermore the use of the neural network was optimized in the number of epochs, hidden layers and artificial neurons in each hidden layer by a design of experiment (DOE) analysis, demonstrating that these two methods can work together improving the final results of the neural network approach. Afterwards, a MonteCarlo analysis based on a simulation of 100,000 virtual depositions has permitted to deeply investigate the effect of independent variables (e.g. deposition time and difference of potential applied) on the deposition yield (dependent variable).     

Graphene growth via carburization of stainless steel and application in energy storage

A modified version of the carburization process, a widely established technique used in the steel industry for case hardening of components, is used for the growth of graphene on stainless steel. Controlled growth of high-quality single- and few-layered graphene on stainless steel (SS) foils through a liquid-phase chemical vapor deposition (CVD) technique is reported. Reversible Li intercalation in these graphene-on-SS structures is demonstrated, where graphene and SS act as electrode and current collector, respectively, providing very good electrical contact. Direct growth of an active electrode material, such as graphene, on current-collector substrates makes this a feasible and efficient process for developing thin-film battery devices.     

Metal–ceramic composite layers on stainless steel through the combination of electrophoretic deposition and galvanic processes

The use of metal–ceramic composite layers is of considerable technical interest for many areas of application. The use of electrochemical processes makes it possible to realize coatings on stainless steel which combine the properties of the metals with those of ceramics in an outstanding manner. The process presented here is based on a combination of electrophoretic and electrolytic deposition. At the same time, a very high ceramic ratio is attained in comparison to electrolytic dispersion depositions. It was therefore possible to achieve both nickel–zirconium oxide as well as a copper–zirconium oxide coatings with strong adhesive bonds on stainless steel. A preliminary nickel plating or preliminary copper plating of the stainless steel substrate was first realized. A nanoscale zirconium oxide powder (Tosoh TZ-8Y) from an ethanolic suspension was then applied electrophoretically onto this layer and sintered to an open-porous layer with a porosity of 40–50%. After this, the metal was galvanically infiltrated into the pores. An annealing process was then carried out to improve the layer bonding. Solid-state physical tests reveal that a good material bonding of the composite layer onto the substrate occurred as a result of diffusion processes. Metal–ceramic composite layers can be produced through a combination of electrophoretic and electroplating technology with strongly bond on the substrate by a final heat treatment.     

Additive manufacturing of copper-stainless steel hybrid components using laser-aided directed energy deposition

Combining dissimilar materials in a single component is an effective solution to integrate diverse material properties into a single part.Copper-stainless steel hybrid components are attracting more and more attention since the high thermal conductivity of copper can greatly enhance the thermal performance of stainless steel,which benefits its applications in many industries.However,direct joining of copper and stainless steel such as SS316 L is challenging since they preserve significant dissimilarities in physical,chemical,and thermo-mechanical properties.This paper aims to fabricate well-bonded copper-SS316 L hybrid parts using a laser-aided directed energy deposition (DED) process.A nickel-based alloy Deloro 22 (D22) is introduced between copper and SS316 L to address the detrimental issues in copper-SS316 L direct joints.Using this technique,defect-free interfaces are achieved at both the D22-SS316 L and copper-D22 transition zones.Tensile testing of Cu-D22-SS316 L and D22-SS316 L hybrid parts shows the fracture occurs at pure copper and SS316 L region,respectively,indicating an excellent bonding at the interfaces.Ascending in the building direction,a transition of grain structure is observed.A significant diffusion zone is obtained at both the D22-SS316 L and the Cu-D22 interfaces.The large diffusion distance results in a smooth variation in microhardness over the dissimilar materials.The microhardness increases from SS316 L to D22 with the highest value of 240 HV and then decreases from D22 to Cu with the lowest value of 63 ± 4 HV.Testing of thermophysical properties of the Cu-D22-SS316 L system indicates there is a ～300 ％ increase in thermal diffusivity and a ～200 ％ increase in thermal conductivity when compared to pure SS316 L.The significant increase in thermal diffusivity and conductivity validates the enhanced thermal performance of SS316 L when it is joined with pure copper.     

Thermal spraying of a nitrogen alloyed austenitic steel

Stainless steel coatings provide an alternative to protect steel surfaces against corrosive attack. The 316 L stainless steel coatings have been conventionally produced by different spraying processes for such applications. Because the nitrogen alloyed stainless steels exhibit not only superior mechanical properties, but also better corrosion behaviour than conventional stainless steels, in this study the coatings of a nitrogen alloyed austenitic steel were produced using a high velocity oxy-fuel (HVOF) spraying process and an atmospheric plasma spraying (APS) process. Due to much stronger deformation strengthening, the coatings deposited by the HVOF spraying process presented a much higher microhardness than the coatings deposited by the APS process. Moreover, the coatings deposited by the HVOF spraying process were also more corrosion resistant than the coatings deposited by the APS process, because the oxidation of the powder material during HVOF spraying was much lower than that during APS. Compared with the coatings of the conventional stainless steel 316 L, the nitrogen alloyed steel coating deposited by the HVOF spraying process showed a much better corrosion performance.     

Coated WC powders by sputtered nanostructured Ni and stainless steel

The efficiency of the powder surface modification depends on their surface characteristics. Sputtering has been revealing an important skill for the coating of powders with metal and metal alloys, with important consequences on the surface properties. However, some modifications in the holder of this particulate substrate have obliged to set up some changes in a non-conventional sputtering system. The aim of the present work is to demonstrate the efficiency of the prototype developed and the influence of deposition parameters in the quality of coated powders; tungsten carbide powders and austenitic stainless steel (SS) and nickel targets have been selected. These types of materials are used in tungsten carbide parts/devices as binders to promote the technological process; as coatings they decrease the interparticle friction reducing the pressure of shape forming as well as the temperature of sintering process.     

Characteristics of Laser-Fabricated Metal Structures

Laser-aided direct fabrication technology is developed to produce three-dimensional metal alloy structures directly from the constituent elements. The shapes of the structures are designed using Computer Aided Design (CAD) tools and are fabricated as real parts by fusing powders with a laser beam. In this study, alloy structures of simple plate like geometry were produced by mixing stainless steel (SS 316) powder with either copper or aluminum powder. The thickness of the component is related to the process parameters through an energy balance equation, which is verified against experimental data. Material properties such as hardness, strength and conductivity are analyzed and optical micrographs are presented to exhibit the microstructure of the alloy. The results show improved hardness at certain locations in the alloy, higher thermal conductivity of stainless steel. However, the structures broke due to brittle failure under tensile loads.     

铁氧化菌作用下316L不锈钢点蚀电化学特性的研究

采用电化学测量、交流阻抗技术、扫描电镜观察和能谱分析等实验方法,研究了316L不锈钢在铁氧化菌(IOB)溶液中的腐蚀电化学行为,分析了炼油厂冷却水系统微生物腐蚀的特征及机制,结果表明,在含有IOB溶液中的自腐蚀电位(Ecorr)、点蚀电位(Epit)和极化电阻(Rp)均随浸泡时间的增加呈现出降-升-降的变化趋势;在含有IOB溶液中的腐蚀速率均大于在无菌溶液中;IOB的生长代谢活动及其生物膜的完整性和致密性影响了316L不锈钢表面的腐蚀过程,使不锈钢表面的钝化膜层腐蚀破坏程度增加,加速了316L不锈钢的点蚀.     

激光选区熔化成形工艺对304L不锈钢冲击韧性的影响

目的 了解激光选区熔化(SLM)成形工艺参数对304L不锈钢冲击韧性的影响,从而得到304L不锈钢的最佳成形工艺参数。方法 对激光功率300~340 W,激光扫描速度800~1 500 mm.s^?1条件下的激光选区熔化成形304L不锈钢开展冲击试验,通过表面硬度、微观组织及断口形貌观察对冲击韧性的影响规律进行分析。结果 SLM成形304L不锈钢微观组织为跨越熔池生长形成的不规则柱状晶粒,成形工艺参数对试样表面硬度影响不显著;随着激光功率的增大和激光扫描速度的降低,304L不锈钢断面致密程度提高,孔洞类缺陷尺寸减少且数量减少,冲击韧性增大,冲击功最大值为141.9 J。结论 基于冲击试验结果,在激光体能量密度为100~140 J/mm³的条件下,304L冲击韧性稳定在138 J左右,为SLM成形304L材料的最佳成形参数区间。     

选区激光熔化不锈钢全流程关键问题研究现状与进展

选区激光熔化(SLM)是制造精度最高的金属增材制造工艺,用于制造复杂几何形状的金属零件。316L不锈钢具有面心立方结构,在从熔融态冷却至室温的过程中通常不发生固态相变,基于这种特性,316L不锈钢成为SLM中应用最广泛的金属材料。与传统工艺相比,SLM工艺虽然能够生产高致密、高性能的零件,但是它无法避免孔洞、空隙等缺陷的出现,且存在力学性能差异和需要后处理加工等问题。为了解决这些问题,需揭示SLM制造工艺参数对性能的影响规律。综述了SLM-316L制备全流程前、中和后期在原始粉末、工艺参数及后处理方面的研究现状,首先讨论了粉末质量指标及制粉工艺对不锈钢制件的影响机理;其次总结了激光输入功率、扫描速度等工艺参数对制件性能影响的研究现状;最后对表面机械磨损处理、电解抛光等后处理方式及制件性能影响规律做了简要总结。阐明了通过SLM影响因素预测不锈钢成形零件力学性能的学术观点,以期为获取高质量零件、促进不锈钢材料的实际应用提供一些参考。     

不锈钢及其镀膜复合材料气相氢渗透研究

叙述了全金属超高真空气相氢渗透装置和HR－1超低碳不锈钢镀膜复合材料的研制，以及氢通过不锈钢基体及其镀膜复合材料的气相氢渗透实验．实验表明，镀膜复合材料的氢渗透率比基体材料降低二个量级以上。     

Enhancing ductility and fatigue strength of additively manufactured metallic materials by preheating the build platform

The effect of preheating the build platform (process) on the microstructure/defect structure (structure) as well as the tensile and fatigue behaviour (property) of the laser beam powder bed fused (LB‐PBF) 316L stainless steel (SS) is investigated. Preheating the build platform to 150°C (P150) affects the thermal gradient and cooling rate resulting in the reduction of the volumetric defects (i.e., gas‐entrapped pores and lack of fusion (LoF)) as compared with the condition where the build platform is non‐preheated (NP). The ductility of P150 LB‐PBF 316L SS is improved as compared with the NP counterpart, resulting from the less volumetric defects as well as the change in the crystallographic orientation of the grains in P150 condition. In addition, preheating the build platform is found to enhance the fatigue resistance of LB‐PBF 316L SS specimens. This is associated with fewer and smaller volumetric defects in P150 specimens as compared with the NP ones.     

Reactive sintering of stainless steel

Abstract

Pressed and sintered 316L type stainless steel compacts have been produced using an innovative process termed reactothermitic sintering RTS. This technique has the ability to produce full density, near net shape parts using conventional compaction and mesh belt furnace practices. It utilises chemical reactions at the surface of the stainless steel powders in which the energy balance is matched to provide transient liquid films that can be frozen at high cooling rates to consolidate the material without slumping. Small quantities of elemental aluminium and nickel powders are added before compaction that react, during sintering, both with themselves and with oxide layers present on the bulk stainless steel powder surfaces. In addition to the naturally occurring oxides present on the surface of stainless steel powders, artificial oxide layers, deposited by sol-gel and direct thermal oxidation, have been used to aid investigations into the nature of the reactions involved. The RTS technique leads to the generation of novel microstructures in the systems described that are characterised by negligible interconnected porosity. The present paper details the experimental programme undertaken to ascertain and substantiate these phenomena together with a model of how porosity is eliminated in this system.     

Direct metal deposition (DMD) of H13 tool steel on copper alloy substrate: Evaluation of mechanical properties

H13 tool steel powder was clad on copper alloy substrate both directly and using 41C stainless steel (high Ni steel) powder as a buffer layer by direct metal deposition (DMD). Cu-steel bimetallic die casting and injection molding tools are of high interest for reduction of cycle time by efficient heat extraction due to high thermal conductivity of copper. The mechanical properties of these bimetallic structures were investigated in terms of bond strength, impact energy and fracture toughness. The bond interfaces of these claddings showed porous and crack free transition regions. The bond strength was higher in the directly clad H13 tool steel compared to the H13 tool steel clad with 41C stainless steel as buffer layer. The fracture morphology in tensile test specimens showed ductile dimple fracture. Presence of necking just below the interface depicted the softening of substrate in heat affected zone (HAZ) during cladding. The Charpy impact energy is little higher in the 41C stainless steel buffered specimens compared to the directly clad H13 tool steel specimens but the fracture toughness results showed reduction of fracture toughness in the 41C stainless steel buffered specimens due to the low strength in the tensile test. However the fracture toughness value was in the ductile region for both deposits.