Stainless Steel Alloy Research Articles

Pitting corrosion on highly alloyed stainless steels in dilute sulphuric acid containing sodium chloride

Stainless steels are widely used in industrial assets and equipment. Despite their good corrosion resistance under a wide range of operating conditions, there is the possibility of pitting corrosion in the presence of chlorides. However, very few studies have identified the safe operating conditions for various high-alloyed stainless steel grades by comparing their pitting susceptibility. In this research, the susceptibility to pitting attack of five stainless steels with austenitic and duplex microstructures was examined in dilute sulphuric acid solution with varying amounts of NaCl at the temperatures of 50, 90 and 130°C. Based on potentiodynamic polarization scans, none of the test materials underwent pitting corrosion at 50°C, but differences in susceptibility to pitting attack were clear between the test materials and NaCl concentrations at the temperature of 90°C, and further temperature increase facilitated uniform corrosion. 28-day immersion tests at 90°C confirmed the pitting susceptibility of duplex grades 1.4662 (PREN 33) and 1.4462 (PREN 35) in the presence of at least 2000 mg/L NaCl, but not the susceptibility of a corresponding austenitic grade 1.4539 (PREN 34). The grades 1.4547 (PREN 43) and 1.4410 (PREN 44) were not susceptible to pitting corrosion under any of the studied conditions. The results from materials microstructural and electrochemical characterization are presented and discussed in this paper.

Fabrication and characterization of a novel mullite-stainless steel composed hollow fibre membrane for oil/water separation

Low-cost mullite-kaolinite material has recently received more attention as an alternative to conventional ceramic materials such as alumina and silica to prepare ceramic hollow fibre membranes (CHFMs) due to its high alumina contents and silica and thermal/chemical stability. However, weak bending strength is still one of the key bottlenecks that delay their commercial applications. In this work, we successfully fabricate a novel mullite-SS HFM with enhanced bending strength using mullite-kaolinite power with different stainless steel alloy (SS) 316 L contents of 0.0, 2.5, 5.0, 7.5, 10 and 12 % (w/w) as a reinforcement material by phase inversion/sintering techniques. The SS alloy was a potential material to enhance the mechanical strength of mullite HFMs due to its excellent mechanical properties. The effects of the major fabrication parameters of SS contents, mullite contents, and fabrication parameters such as air gap distance and bore fluid flow rates were well studied and evaluated through the fabrication process. Fabricated mullite-SS HFMs were characterized by morphology, porosity, pore size/pore size distribution, and bending strength. Afterwards, they were evaluated in an oil/water separation system regarding water flux and oil rejection rate. Based on the findings, there was a gradual increase in the bending strength from 32.1 to 79.8 MPa with increased SS contents from 0 to 12 % (w/w). At 10 % (w/w) SS, the satisfactory morphology with the balance between the bending strength of 66.7 MPa and porosity of 29 % was obtained. This bending strength was significantly higher than reported for mullite-kaolinite HFMs in previous works. Moreover, At 10 % (w/w) SS, the oil–water rejection performance of 96.9% and the water permeation of 290 L/m2. h was satisfactory at the sintering temperature of 1300 °C. These findings suggest the advantage of this membrane for various water treatment applications, such as oil/water separation, due to its outstanding physical properties.

Age-hardening behaviors of the weld metals of 22% Cr and 25% Cr duplex stainless steels at 400 °C

Duplex stainless steel (DSS) alloys are attractive materials for pressure components in nuclear power plants as they offer a good combination of high strength, corrosion resistance, and weldability. However, DSS suffers from embrittlement and hardening upon exposure to temperatures of 250–500 °C. Most previous studies addressed only solution-treated materials, and limited research has been conducted on weld metals. In this study, the relationship between the nanostructural evolution and hardening of 22% Cr and 25% Cr DSS weld metals (fabricated with grade-2209 and 2594 welding materials, respectively) during aging at 400 °C was investigated. The results revealed that the degree of hardening of ferrite after aging at 400 °C for 1000 h was greater in the 22% Cr DSS weld metal than in the 25% Cr DSS weld metal. The ferrite phases of both samples underwent two different phase decomposition processes during aging, (1) phase separation (α → Fe-rich α + Cr-rich α’) and (2) solute clustering to form G-phase precursors, both of which were identified within the body-centered cubic structure of ferrite in the weld metals. Phase separation was less pronounced, whereas formation of G-phase precursors was more pronounced in the 22% Cr DSS weld metal than in the 25% Cr DSS. These results indicate that the extent of formation of G-phase precursors has a significant influence on predicting the degree of hardening of ferrite. The enhanced formation of G-phase precursors in the 22% Cr DSS weld metal was elucidated using thermodynamic simulations; the formation of the G-phase precursor was predominantly facilitated by the higher Mn fraction in the 22% Cr DSS weld metal. The findings of the present study are expected to aid the selection and/or further improvement of the compositional design of DSS welding materials, thereby increasing the long-term safety of DSS welded components in nuclear applications.

Process Parameter Optimization of 2507 Super Duplex Stainless Steel Additively Manufactured by the Laser Powder Bed Fusion Technique

Laser powder bed fusion is an attractive technology for producing high-strength stainless steel alloys. Among the stainless steels, 2507 super duplex stainless steel (2507 SDSS) is known for its excellent combination of corrosion resistance and high strength. Although there are some studies that aimed at optimizing the laser powder bed fusion (LPBF) printing parameters to print highly dense 2507 SDSS parts; However, a full optimization study is not reported yet. This study aims at optimizing the printing parameters for 2507 SDSS, namely: laser power, scan speed, and hatch distance. The response surface methodology was used in generating a detailed design of experiment to investigate the different pore formation types over a wide energy density range (22.22–428.87 J/mm3), examine the effects of each process parameter and their interactions on the resulting porosity, and identify an optimized parameter set for producing highly dense parts. Different process parameters showed different pore formation mechanisms, with lack-of-fusion, metallurgical or gas, and keyhole regimes being the most prevalent pore types identified. The lack-of-fusion pores are observed to decrease significantly with increasing the energy density at low values. However, a gradual increase in the keyhole pores was observed at higher energy densities. An optimal energy density process window from 68.24 to 126.67 J/mm3 is identified for manufacturing highly dense (≥99.6%) 2507 SDSS parts. Furthermore, an optimized printing parameter set at a laser power of 217.4 W, a scan speed of 1735.7 mm/s, and a hatch distance of 51.3 µm was identified, which was able to produce samples with 99.961% relative density. Using the optimized parameter set, the as-built 2507 SDSS sample had a ferrite phase fraction of 89.3% with a yield and ultimate tensile strength of 1115.4 ± 120.7 MPa and 1256.7 ± 181.9 MPa, respectively.

Effect of induction preheating on microstructure and mechanical properties of friction stir welded dissimilar material joints of Inconel 718 and SS316L

Using an external heat source during friction stir welding (FSW) of high melting point materials is a promising approach to enhance the material flow and reduce the axial load, improving the tool life. In this study, conventional and induction heating-assisted friction stir welding (I-FSW) in joining dissimilar Inconel 718, and stainless steel (SS316L) alloy using the WC-10%Co tool was experimentally investigated. The welding was performed at a constant rotational speed of 300 rpm with welding speeds of 70 and 140 mm/min and 300 °C preheating temperature in the assisted FSW. The results show that the application of friction stir welding resulted in highly refined grains with deformed carbide particles in the stir zone of both materials, which increased mechanical properties. An increase in temperature during the I-FSW process led to a slight increase in the size of the particles and high atomic diffusion of Cr and Mo elements at the interface of the SS316L and Inconel 718 joint, which showed enhancement of the weld strength. In addition, highly dragged SS316L material into the advancing side of the Inconel 718 was observed, which was directly influenced by the preheating temperature and welding speed. The mechanical properties of the joint with preheating significantly improved at a high welding speed (i.e., at 140 mm/min). The tensile strength of the I-FSW joint at 140 mm/min was 683 MPa which was 99.8% of the base SS316L. Dynamic recrystallization resulted in grain refinement, which raised the hardness value. The results also show that preheating reduces downward axial force, enhancing the tool life.

Structural, physical, and radiation absorption properties of a significant nuclear power plant component: A comparison between REX-734 and 316L SS austenitic stainless steels

Abstract Austenitic stainless steels (SSs) are commonly used as in-core and surrounding structural materials in today’s industrial BWR and PWR systems. Such adaptable steels have also been the primary materials studied and used in several advanced nuclear reactor technologies, such as fast breeding and magnetic fusion reactors. In this study, some critical material properties, such as structural, physical, and radiation-shielding properties of REX-734 and 316L SS, were experimentally evaluated and compared to those of a number of other alloys. In addition to homogeneous element distribution, both alloys exhibit strong crystal orientation. The REX-734 alloy has a tensile strength of 1,259 MPa, whereas the 316L SS alloy has a tensile strength of 495 MPa. Moreover, nitrogen in the REX-734 alloy formed ultra-hard nitrides with Cr, Nb, and Si and precipitated into the structure and increased the strength. According to our findings, the mass attenuation coefficient values of the 316L SS sample were slightly higher than those of the REX-734 sample at all energies. It can be concluded that the REX-734 sample, with its exceptional strength qualities and excellent radiation attenuation capabilities, may be a viable nuclear power plant material for future investigations.

Stainless steel supported NiCo2O4 active layer for oxygen evolution reaction

The energy demand from a clean, renewable and cheap source has been increasingly urgent. In this work, a simple two steps preparation method was used to obtain NiCo2O4. NiCo2O4 layer was electrodeposited and calcined on two different stainless-steel alloys AISI 304 and AISI 316 L. The samples were characterized with XRD and XPS, which confirmed the material to be NiCo2O4. In both substrates the results suggest that the catalysts obtained, have good activity for OER, with an overpotential at 10 mA cm−2 of 360 and 340 mV for SS304 and SS316L respectively. However, the OER curve of the layer on SS316L achieves higher current density of 41.7 mA cm−2 while that on SS304 is 29.7 mA cm−2 at 1.7 V vs. RHE. The Tafel slope value shows better kinetics for the layer on SS304. From the EIS studies and the Nyquist plot the RCT for SS304 is 15.07 Ω and for SS316L is 36.74 Ω. This can be explained by the higher conductivity of SS304 which promotes the fast growth of nanoflowers with bigger nanopetals during the electrodeposition. The high material density in the surface causes crinkles, as can be seen in SEM analysis. This default in catalysts' morphology leads to a discontinuity in electrons transfer through the layer and then a decrease in kinetics. Another hypothesis is the presence of Mo in SS316L, which has a synergistic effect with the other metals. In this latter case the stainless-steel composition would have a direct influence on the reaction kinetics.

Electrochemical and in vitro biological behaviors of a Ti-Mo-Fe alloy specifically designed for stent applications

There is a deep interest in developing new Ni-free Ti-based alloys to replace 316 L stainless steel and Co-Cr alloys for endovascular stent application, mainly because the release of Ni can generate toxicity and allergenicity. Interactions of Ti alloy biomaterials with bone cells and tissues have been widely investigated and reported, while interactions with vascular cells and tissues, such as endothelial cells (ECs) and smooth muscle cells (SMCs), are scarce. Therefore, this study focused on the relationship among the surface finishing features, corrosion behavior and in vitro biological performances regarding human ECs, SMCs and blood of a newly developed Ti-8Mo-2Fe (TMF) alloy, specifically designed for balloon-expandable stent applications. The alloy performances were compared to those of 316 L and pure Ti, prepared with the same surface finishing techniques, which are mechanical polishing and electropolishing. Surface properties were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) and x-ray photoelectron spectroscopy (XPS). The corrosion behavior was assessed with potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests in phosphate buffered saline (PBS) solution. No significant differences were observed regarding the corrosion rate measured with PDP analyses, which was of the order of 2 × 10−4 mm/y for all the studied materials. Moreover, similarly to pure Ti, TMF exhibited an advantage over 316 L for biomedical applications, namely remarkable resistance to pitting corrosion up to high potentials. The results evidenced a good cytocompatibility and hemocompatibility, making this group of alloy a potential candidate for cardiovascular implants. In fact, both ECs and SMCs proliferated on TMF surfaces showing a 7-day viability similar to that of pure Ti. Regarding hemocompatibility, TMF did not cause hemolysis, and blood coagulation was delayed on its surface in comparison to pure Ti. When compared to 316 L, TMF showed similar hemocompatibility.

Experimental investigation and design of slip resistant aluminium alloy–stainless​ steel connections

An experimental investigation into the structural response and slip resistance of aluminium alloy–stainless steel connections fastened by means of high-strength stainless steel swage-locking pins is presented herein. Thirty-seven friction tests on aluminium alloy–stainless steel shear connections featuring different surface treatments and material grades were carried out. Complementary material tests were also performed, while the roughness and hardness of the connected surfaces were measured. The failure modes, load–slip responses, friction coefficients and preloading behaviour of all specimens are fully reported, while the test setup, specimen dimensions, configurations of fasteners, and positions of displacement measurements, are explained. The slip factors corresponding to the different surface treatments are presented, while the key parameters affecting the preload losses of the swage-locking pins and the friction coefficients are described. Finally, the suitability of various surface treatments for aluminium alloy–stainless steel connections is evaluated, while design slip factors, as well as correction coefficients accounting for the influence of different material grades and preload levels on the response of the examined connections, are set out.

Investigation of photon interaction parameters of alloys used in orthodontic treatments for dental radiology applications

In the present study, it was aimed to examine the photon interaction parameters of some alloys used in orthodontic treatments in dental and medical radiology energies. First of all, a transmission geometry consisting of 241Am (100 mCi) radioactive source and Ultra Ge detector was established to experimentally obtain the mass attenuation coefficients (μρ, cm2/g) of Beta Titanium (BT), Copper NiTi, NiTi (Nitinol) and stainless steel (SS) alloys, which are frequently used as orthodontic wires. The experimental μρ values in the energy range of 13.9–59.54 keV with the data obtained from the spectra were compared with the theoretical results generated with the EpiXS program. The μρ values at 59.54 keV were 0.760, 0.933, 0.924 and 1.315 cm2/g for BT, NiTi, Copper NiTi and SS, respectively. Based on μρ values, HVL and Zeff values were also obtained. The HVL values for BT, NiTi, Copper NiTi and SS at 59.54 keV were calculated as 0.203, 0.135, 0.138, 0.066 cm, respectively. Then, the buildup factor values of the alloys in the energy range of 0.015–15 MeV were calculated at penetration depths of 1–15 mfp. When all the results are evaluated together, SS is more effective in absorbing photons, while BT is the alloy with the highest photon buildup among the alloys studied. Besides, it is noteworthy that the alloys cause secondary scatterings. The data obtained from this study will provide information about the photon interaction parameters of orthodontic wires in dental and medical radiology applications.

Binder Jet Additive Manufacturing Process and Material Characterization for High Temperature Heat Exchangers Used in Concentrated Solar Power Applications

The U.S. Department of Energy’s (DOE) Sunshot 2030 initiative has a goal of reducing the cost of concentrating solar power (CSP) to 5 cents per kWh for baseload power plants. One of the potential pathways to this goal includes a reduction in the cost of the supercritical CO2 (sCO2) power block to 0.9 cents per kWh. Recuperators—high and low temperatures, used in the sCO2 power cycle, contribute to >50% of the cost of the power cycle. This work studies the feasibility towards a ≥10% cost reduction for High Temperature Recuperators (HTR) used in the sCO2 power cycle. One way to address the cost reduction is by leveraging low-cost additive manufacturing, specifically, Binder Jet Additive Manufacturing (BJAM) to 3D print HTRs at scale. This study focuses on the development of a BJAM process towards 3D printing HTR cores using Stainless Steel alloy 316L (SS316L). To evaluate the suitability of the BJ process towards the HTR, high level specifications of the application are translated to materials capability requirements. Subsequently, at-temperature materials testing is conducted on as-printed and sintered additively manufactured coupons. Data from the coupons are compared against cast and wrought SS316L data obtained from the literature. Results show that the tensile properties from the BJ process compare well against cast properties. Furthermore, a baseline analysis of creep testing data is established for the BJ process, and insights are drawn from the results towards future improvements of the process.

DESIGN AND STRUCTRAL ANALYSIS OF HIP-JOINT IMPLANT

An artificial joint (prosthesis) helps reduce pain and improve function. Also called total hip arthroplasty, hip replacement surgery might be an option if hip pain interferes with daily activities and nonsurgical treatments haven't helped or are no longer effective. We review the different materials, constructions, and surfaces used in the development of femoral stems, in order to solve and avoid various problems associated with their use. Femoral stem prostheses have undergone substantial changes and design optimizations since their introduction In this project a new design of hip joint implant is introduced by using Ti6Al4V(alpha-beta Ti alloy), Cobalt Chromium(Co Cr) alloy, 316L stainless steel alloy materials. All the parts are designed in CATIA V5.18 and static structural analysis was done in ANSYS WORKBENCH. The equivalent (Von Mises) stresses are analyzed and deformation of the Hip joint for all the three materials are compared. Also, Ti6AL4V has better properties that are similar to bone compared to the rest of the bio materials that are considered during the project work. KEYWORDS: Implant, Femoral stem, Femoral head, Plastic liner, Acetabular component, Support plate, Structural analysis.

Microstructural evolution of heat-treated Cr–W–V–Mo steels: effect of core-shell carbides and secondary precipitation on their abrasion resistance

This study aims at understanding the effect of different heat treatments on the evolution of the microstructure of several Cr–W–V–Mo steels having different compositions and how this latter affects their abrasion resistance. The investigation also gives insights on the formation and effect of core-shell carbides on the abrasion resistance. The commercial highly alloyed stainless steel HCx® and six newly designed Cr–W–V–Mo steels were subjected to three heat treatments: austenitizing at 900 °C and 1100 °C and subsequent quenching, and an ageing treatment at 700 °C. The microstructural analysis demonstrated the formation of Laves phase when austenitizing at 900 °C; this phase is depleting the matrix from carbide forming elements without any improvement in the wear behavior of the alloys. However, increasing the austenitization temperature to 1100 °C favored the development of core-shell carbides that contribute to increase the abrasion resistance of the alloys. The ageing treatment promoted the precipitation of secondary carbides uniformly distributed along the matrix, and they were found to have a beneficial effect on maintaining the good abrasion resistance even after subjecting the steels to a high ageing temperature (700 °C) for long duration (10 h).

Formation of Ni–Si clusters and their relationship with dislocation loops in irradiated stainless steels

Ni–Si cluster is a major contributor to the irradiation hardening in irradiated stainless steels. The heterogeneous nucleation of Ni–Si clusters is associated with radiation-induced segregation at sinks (e.g., dislocation loops), and the possible formation of Ni–Si clusters on dislocation loops may influence the evolution process of the two types of defects. Besides, the nature of Ni–Si clusters is unclear yet, reflected by the discrepancies in the reported cluster composition. In this study, model alloys of 316L stainless steel with different Si contents were irradiated to 5 dpa at 450°C. Ni–Si clusters were analyzed by atom probe tomography and were compared with the loops observed by transmission electron microscopy. Results showed that higher Si content promoted cluster number density and size but did not change cluster composition. Discontinuous torus-shaped, continuous torus-shaped, and disk-shaped clusters were discovered. The cluster shape, size, and crystallographic orientation supported the formation of torus-shaped clusters on Frank loops and perfect loops. In large torus-shaped clusters, Si and Ni tended to concentrate in the outer and inner regions of the torus, respectively, and it may be attributed to the stress field of the interstitial-type Frank loops on which the torus-shaped clusters were formed. The constant composition of large Ni–Si clusters indicated the possible existence of a preferential Ni–Si phase. Combining the results of the 1D concentration profile and the MSM using Si atoms and Ni atoms, the Ni/Si ratio of the large clusters was between 1.6–3.0.

Surface modification of hybrid composite multilayers spin cold spraying for biomedical duplex stainless steel

The performance of biomaterials in biological systems is of critical significance for advancing biomedical implants. Duplex Stainless Steel alloys are the major biomaterials due to their significant characteristics. Many functional coatings are deposited on DSS alloy surfaces utilizing numerous surface coating techniques to improve their bioactivity and protect them from corrosion degradations. Coatings of titanium dioxide (TiO2), Hydroxyapatite (HA), and zinc oxide (ZnO) have received considerable attention in the field of surface bioactive modification of DSS alloy implants. The coating techniques play a key role in increasing the required biological characteristics of DSS alloys, such as biocompatibility, mechanical properties, and corrosion resistance. In this regard, HA-ZnO, HA-TiO2, and TiO2–ZnO from each coating group are divided into single, double, and triple layers. These coatings were prepared by cold spray and deposited on the surface of the DSS alloy, followed by a heat treatment at 250 °C. The surface morphology of coated surfaces was analyzed utilizing field emission scanning electron microscopy (FESEM), atomic force microscopic (AFM), microhardness test, corrosion test in Ringer solution, and antibacterial test. The coatings showed nano-scale surface morphology with advanced crystallization and homogeneous structures; in the corrosion characteristics utilizing potentiodynamic polarization, triple layers of HA-ZnO coatings displayed advanced nanostructures with higher hardness values (514.75HV). The antibacterial test showed the triple layers of HA-TiO2 and two layers of TiO2–ZnO sensitivity to positive bacteria.

Interface analyses and mechanical properties of stainless steel/nickel alloy induced by multi-metal laser additive manufacturing

Multi-metal laser additive manufacturing is an emerging technology to fabricate complex components with excellent comprehensive performances. In this study, stainless steel/nickel alloy multi-metal has been induced by laser direct energy deposition. The microstructural evolution, compositional segregation, and crack formation at the interface of the two metals have been investigated by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, electron backscattering diffraction, and microhardness test. The results show that the microstructure morphologies are predominated by equiaxed dendrite and columnar dendrite for stainless steel and nickel alloy, respectively. The Marangoni convection effect promotes the serious compositional segregation of stainless steel on the nickel alloy side and serious segregation of 316L SS occurs locally in near the IN 718 side of the interdiffusion region. During the cooling process, the segregated stainless steel has a lower solidification temperature than the surrounding nickel alloy. The compositional segregation and different physical properties of the two metals are the main causes for the ductility dip cracking near the interface. During tensile deformation, the multi-metal fractures on the stainless steel side, and the ultimate tensile strength and elongation of the multi-metal have achieve 524 MPa and 24.8 %, respectively.

Simulation study of the thermal insulation performance of a vacuum‐insulated tube inside an electrically heated device

AbstractTo realize stable heating of a heated cigarette while effectively controlling the outer‐wall temperature of an electric heating‐type appliance, a vacuum‐insulated tube (VIT) is currently widely used for thermal insulation against the heating element. The effects of the critical parameters of the VIT, gases at different pressures, wall thickness, and material on its thermal insulation performance, were simulated using Fluent to provide guidance on the structure and performance optimization of the EHD. When the absolute pressure of gas in the VIT was <0.5 Pa, increasing the degree of vacuum did not improve the thermal insulation performance. The thermal insulation performance of VITs made from different materials (stainless steel, copper, aluminium, brass, and titanium alloy) was closely related to the emissivity and thermal conductivity of the material. Stainless steel yielded better overall thermal insulation owing to its low thermal conductivity and emissivity. Highly emissive materials, such as brass and titanium alloy, contributed to higher heat transfers through the radiation inside the vacuum chamber and external radiation from the VIT, decreasing the thermal insulation performance of the VIT. Stainless steel VITs yielded an improved thermal insulation performance as the wall thickness decreased, but at the cost of decreased mechanical stability. For a wall thickness of 0.05–0.30 mm, stainless steel yielded the best structural stability. VITs with different wall thicknesses were made from stainless steel, copper, and aluminium, and the thermal insulation performance and structural stability of the EHD were optimized.

Microstructural evaluation in dissimilar liquid phase bonding of cast Al–Si alloy and stainless steel using pure zinc filler metal

The metallurgical joining between cast A359 aluminium alloy and AISI321 stainless steel using pure Zn as the interlayer was performed slightly above Al–Zn eutectic temperature. The liquid phase was formed by a eutectic reaction between Al and Zn and subsequently isothermally solidified by diffusion of Zn into the A359 base metal (i.e. reactive transient liquid phase bonding). The formation of a Zn-rich diffusion affected zone in A359, incorporation of Si particles into the bond zone, formation of a thin Al–Fe–Si intermetallic at the steel interface, and isothermal solidification of the liquid phase and subsequent Al–Zn eutectoid transformation govern the microstructure of the joint. The resultant bond microstructure does not deleteriously affect the heat sink function of Al base metal.

Tests on slip resistant behaviour of aluminium alloy-stainless steel faying surfaces

Aluminium alloy-stainless steel structures combine the benefits of high strength-to-weight ratios of aluminium alloys with the excellent ductility of stainless steels. In order to explore the slip resistant aluminium alloy-stainless steel connections, this paper emphasized the surface characteristics and slip resistance of various surface treatments on aluminium alloy and stainless steel plates. Six applicable treatment methods for aluminium alloy-stainless steel slip resistant faying surfaces were experimentally investigated with specifications for the key parameters explored for the treatment procedures. The feasibility of two novel surface treatment methods on aluminium alloy and stainless steel surfaces was evaluated by material tests and the inspection for coatings. The key characteristics of the treated surfaces were comprehensively tested, including the 3D scanned surface topography, measured hardness and roughness. The relationships between the material type, hardness and roughness values under various surface treatments were discussed, which suggested the specific provisions for slip resistant connections in aluminium alloy-stainless steel structures were required. Friction tests of 18 shear connections were conducted to study the friction coefficients of different materials and surface treatments. The impactions of the surface characteristics on slip resistant behaviours of the treated surfaces were analysed. The roughness of the stainless steel surfaces and the hardness of the aluminium alloy surfaces influence the friction coefficients of the examined connections. Through comparative studies, the arc spraying and supersonic cold spraying, as two novel surface treatments, are suggested for the faying surfaces of aluminium alloy-stainless steel shear connections relying on their remarkably high friction coefficients. While the grit blasting and wire brushing also presented pronounced slip resistant capacities among the four examined mechanical surface treatments.

Production and characterization of AISI 316L stainless steel matrix hybrid composites reinforced with boron carbide and carbon nanotubes

In this study, microstructure, mechanical, tribological and corrosion properties of boron carbide (B4C) and carbon nanotubes (CNT) reinforced hybrid AISI 316L stainless steel matrix nanocomposites were investigated. The AISI 316L stainless steel alloy and 316L-1B4C-1CNT (vol%), 316L-2B4C-2CNT (vol%), 316L-4B4C-4CNT (vol%) composites were fabricated by hot pressing under vacuum conditions. The fabricated samples showed minor porosities regardless of the concentration of B4C and CNT. Microstructure investigations revealed that a slight grain refinement was achieved with increasing incorporation of B4C and CNT. Furthermore, Fe3C and Cr23C6 intermetallics progressively formed along the grain boundaries in the hybrid composites. The hardness, compressive yield strength and wear resistance of 316L stainless steel exhibited continuous improvement with increasing additions of B4C and CNT. However, the hybrid composites exhibited higher susceptibility to pitting corrosion.