Steel Foam Research Articles

Stainless steel foam increases the current produced by microbial bioanodes in bioelectrochemical systems

Stainless steel is gaining increasing interest as an anodic material in bioelectrochemical systems and beginning to challenge the more conventional carbon-based materials.

Quasi-static and Dynamic Mechanical Performance of Glass Microsphere- and Cenosphere-based 316L Syntactic Foams

Syntactic foams are produced by adding hollow particles to a solid matrix material. So far, few processes exist that allow manufacturing of such materials using steel matrices. Extremely versatile in this respect are powder metallurgical processes like metal powder injection moulding (MIM), which facilitate usage of different matrix alloys in combination with micro scale fillers. Existing studies on such materials mostly concentrate on quasi-static properties, with Fe99.7 matrices combined with glass microspheres as one exception for which dynamic data has been published. The present work extends the range of matrix materials by summarizing experimental studies on 316L stainless steel foams using glass microspheres as well as cenospheres for the role of introducing porosity. Quasi-static tensile and compressive properties have been evaluated at different density levels – namely 5 and 10wt.-% of microsphere addition - and are contrasted to dynamic performance as determined by means of impact testing and Split Hopkinson Pressure Bar (SHPB) techniques. Failure mechanisms of the materials are discussed in view of the experimental results, evaluations of the foams’ structural characteristics and comparison with the aforementioned existing quasi-static and dynamic data on Fe99.7 syntactic foams. Furthermore, performance is qualitatively and quantitatively compared to other types of 316L stainless steel matrix foams, such as the so-called composite metal foams (CMF) investigated by Rabiei and Vendra (2009).

English

Metal foams are special class of porous materials with novel physical, mechanical, thermal, electrical and acoustic properties. Nowadays, 316L stainless steel (SS316L) foam is considered as one of the attractive metallic materials for biomedical applications due to its excellent mechanical properties, biocompatibility, and corrosion resistance. In this study, SS316L has been used to produce metal foams by using slurry method. The compositions of the SS316L metal powder was 40 wt% and 60 wt%, PEG (3 wt %), CMC (3 wt %) and remaining the distilled water. The polyethylene glycol (PEG) and methylcellulose (CMC) was used as a binder. The raw materials were mixed by using ball milling machine. After that, the polyurethane (PU) foams were deep into the mixture then dried in the oven for 24 hours. Then, the samples were sintered in the box furnace at 1300oC. In order to identify the characterizations of the samples, there were several tests had been conducted such as X-Ray Diffraction (XRD), Energy Diffraction X-ray (EDX), morphological analysis (Optical Microscopy and Scanning Electron Microscopy (SEM)). The suitable composition of SS316L is 60 wt% with sintering temperature is 13000C which resulted better strength of metal foam.

Trenchless Repair Technology and Application of Urban Sewer System

With the constant expansion of urban construction, the rapid development of urban underground pipeline becomes complex. Due to disrepair, improper maintenance and management and other factors, the urban sewer appears varying degrees of damage phenomenon. Therefore, the urban underground sewer repair becomes an urgent problem. This article introduces the methods of trenchless pipe rehabilitation technology and developments at home and abroad. It also elaborates the technology design points of stainless steel foam cylinder repair, combining with engineering examples.

The mechanical properties and modeling of a sintered hollow sphere steel foam

This paper characterizes mechanical properties of hollow sphere (HS) steel foam, and applies calibrated Deshpande–Fleck plasticity to mechanical simulations of steel foam components. Foamed steel, steel with internal voids, provides enhanced bending rigidity, exceptional energy dissipation, and the potential to mitigate local instability. The experimental characterization of the hollow sphere foam encompasses compressive yield stress and densification strain, compressive plastic Poisson’s ratio, compressive unloading modulus, as well as tensile elastic modulus, tensile unloading modulus, tensile yield stress, tensile fracture strain, and shear yield stress and fracture strain. Since HS steel foam is compressible under triaxial pressure, Deshpande–Fleck plasticity of compressible metals was calibrated and employed in simulations. Plastic Poisson’s ratio, measured in a uniaxial test, is an important metric of foam compressibility, and it affects the response of the foam to multi-axial loadings significantly. This work is part of a larger effort to help develop steel foam as a material with relevance to civil engineering applications.

High temperature mechanical properties of low alloy steel foams produced by powder metallurgy

Cu–Ni–Mo and Mo based steel foams having different porosity levels for high temperature applications were produced by the space holder-water leaching technique in powder metallurgy. Steel powders were mixed with binder (polyvinylalcohol) and spacer (carbamide), and compacted. Spacer in the green compacts was removed by water leaching at room temperature and porous green compacts were sintered at 1200°C for 60min in hydrogen atmosphere. The successful application of foams at higher temperatures requires a good understanding of their high temperature mechanical properties. Compression tests were carried out on steel foams with different porosities at temperatures varying from room temperature to 600°C in argon atmosphere. Effect of high temperature on compressive properties of the steel foams was investigated. It was found that the compressive strength of steel foams was greater at elevated temperatures than that at room temperature. This occurs across a range of temperatures up to 400°C. Beyond this point the compressive strength decreased as the temperature increased. The reason for the enhancement of the compressive strength of Cu–Ni–Mo and Mo based steel foams is expected to be due to the effect of the dynamic age-hardening.

Mass transport and kinetics in structured steel foam reactor with Cu-ZSM-5 catalyst for SCR of NOx with ammonia

Continued research on improving heat and mass transfer properties of structured catalysts is essential for the development of an effective catalytic system. In this paper, the transfer parameters (mass and heat) and pressure drop across reactors prepared with metal foams of different materials (FeCrAl and Al) and PPI (pores per inch) are presented. The mass transfer parameter was determined by correlation using the Chilton–Colburn analogy, and the heat transfer and pressure drop parameters were determined experimentally.Additionally the kinetic properties of a short channel reactor structure based on metallic foams and template-less synthesized ZSM-5 were determined for the selective catalytic reduction (SCR) of NO with ammonia and compared to commonly used commercial solutions – i.e. packed bed and honeycomb monolith reactor structures.

Performance of stainless steel foams produced by infiltration casting techniques

Ferritic (AISI 430) and austenitic (AISI 304) stainless steel foams were produced exploiting a process based on molten metal infiltration on ceramic model. In particular, SiC foundry filter was used as space holder and, after the solidification, it has been removed by hydrofluoric acid. The produced foams are featured by three different porosity grades (10, 20 and 30 PPI) and by constant relative density (0.60). The morphology, the mechanical properties and the corrosion resistance were studied and the results were correlated to the material, the porosity, the size and the distribution of the voids. Morphologically, the structure is arboreous open-cell foam featured by interconnected cavities. This aspect, combined with the high relative density, assures high compressive plateau stress, structural integrity and good deformability. The corrosive tests, according to the ASTM A262-Met.B and NACE TM-0284, permitted to identify possible application fields for these products.

Fracture mechanics of stainless steel foams

The fracture toughness and mode I fatigue crack growth (FCG) tests for open cell stainless steel foam with 45 pores per inch (ppi) have been carried out. In this study, the R-curve of crack propagating from a pre-crack was measured for a compact tension specimen by fracture toughness test. The fracture mechanics response was simulated by using an inverted spherical foam modeling approach. The results attained for crack extension rates were described by ΔK, using the Paris-power law approach. The compact tension porous stainless steel specimens have shown full plastic collapse along the ligaments. The microstructure of the foam had a significant influence on the fatigue crack propagation rate. It was found that stainless steel foam has higher Paris exponent than solid stainless steel and the high Paris exponent was explained by crack bridging. The simulation results showed that initiation toughness values strongly depend on failing struts, resulting in cracks that are significantly curved and kinked along their weakest path in stainless steel foam. The results from this study help in predicting and improving mechanical properties of metallic foams with open cell structure.

Mechanical properties of low alloy steel foams: Dependency on porosity and pore size

Steel foams can be used as lightweight and high-functional materials in applications such as transport vehicles, machines and structural parts due to their low cost, high strength, high heat resistance and good weldability. In this paper, low alloy steel foams (Fe–1.75Ni–1.5Cu–0.5Mo–0.6C) having porosities in the range of 47.8–70.9% with different pore sizes were produced by the space holder-water leaching technique in powder metallurgy. The structural and mechanical property variations resulting from the use of spacer particles having different amounts and sizes were investigated. Irregular carbamide particles were used as spacer. The porosity and pore size of steel foams replicated the initial amount and size of the spacer. Visual inspections were performed for the coated spacers having different sizes and amounts with steel powders after the final mixing. The amount and size of spacer determined the coatability of the mixtures. A decrease in pore size improves the strength of the steel foams by sharing the load with more and smaller pores; however, small pores having the highest porosity can impair the strength because no enough metals hold the integrity of the new pore walls. The influence of pore size on stress drop ratio of steel foams was also studied. The stress drop ratio decreased with decreasing porosity of steel foams. In addition, an increase in pore size caused a bigger stress drop ratio. However, the highest stress drop ratio was determined for small pores having the highest porosity due to the interconnection of macropores in the foam structure.

Effect of heat treatment on mechanical properties of low alloy steel foams

Effect of heat treatment on compressive properties of low alloy steel foams (Fe–1.75 Ni–1.5 Cu–0.5 Mo–0.6 C) having porosities in the range of 47.4–71.5% with irregular pore shape, produced by the space holder-water leaching technique in powder metallurgy, was investigated. Low alloy steel powders were mixed with different amounts of space holder (carbamide), and then compacted at 200MPa. Carbamide in the green compacts was removed by water leaching at room temperature. The green specimens were sintered at 1200°C for 60min in hydrogen atmosphere. Sintered compacts were heat treated by austenitizing at 850°C for 30min and then quenched at 70°C in oil and tempered at 210°C for 60min. In this porosity range, compressive yield strengths of as-sintered and heat treated specimens were 28–122MPa and 18–168MPa, respectively. The resultant Young’s moduli of the as-sintered and heat treated specimens were 0.68–3.12GPa and 0.47–3.47GPa, respectively. The heat treatment enhanced the Young’s modulus and compressive yield strength of the foams having porosities in the range of 47.4–62.3%, as a consequence of matrix strengthening. However, the compressive yield stress and Young’s modulus of the heat treated foam having 71.5% porosity were lower than that of the as-sintered foam’s, as a result of cracks in the structure. The results were discussed in light of the structural findings.

Influence of Fluoride Content of Artificial Saliva on Metal Release from 17-4 PH Stainless Steel Foam for Dental Implant Applications

Highly porous 17-4 PH stainless steel foam for implant applications was produced by space holder technique. Metal release and weight loss from 17-4 PH stainless steel foams were investigated in fluoride added artificial saliva environment by static immersion test. An inductively coupled plasma-mass spectrometer was employed to measure the concentrations of various metal ions. Effects of fluoride content of artificial saliva on metal release and weight loss from the steel foams were investigated. Effects of immersion time, pH value and process parameters on the weight loss and metal release were determined. Pore morphology, pore size and mechanical properties of the 17-4 PH stainless steel foams were also characterized.

Design of protective structures with aluminum foam panels

Design of protective structures requires multiple functions and reasonable safety criteria according to target structures. Hardening is one of the common concept to protect facilities and people. A general concept of blast pressure mitigation by metal foams was proposed. In this paper, a composite panel with aluminum foams and steel skins is introduced. Aluminum foams have low density and are attractive materials to mitigate high-speed pressure by blast loads due to high-energy absorption capabilities. A steel skin with high energy absorption capacity can be effectively used to resist penetration at front surface of the barrier and debris risk at rear surface. Mechanical properties of the aluminum foam according to different densities were obtained by material tests. Three material models for concrete, steel and aluminum foam were utilized considering strain-rate effects. Using the derived material models, explicit analyses of the composite panels were performed and their performance was evaluated. The newly developed high strength foam showed higher yield strength and better energy absorption capacity resulting in lightweight protective panels. For high blast pressure, the combination of energy absorbing steel skin and relatively dense foam or thicker foam is more effective.

Cytocompatibility and mechanical properties of novel porous 316 L stainless steel

Novel 316L stainless steel (SS) foam with 85% porosity and an open pore diameter of 70–440μm was developed for hard tissue application. The foam sheet with a 200-μm diameter had superior cell proliferation and penetration as identified through in vitro experiments. Calcification of human osteosarcoma cells in the SS foam was observed. Multi-layered foam preparation is a potential alternative technique that satisfies multi-functional requirements such as cell penetration and binding strength to the solid metal. In tensile tests, Young's modulus and the strength of the SS foam were 4.0GPa and 11.2MPa respectively, which is comparable with human cancellous bone.

Constitutive Model for the Time-Dependent Mechanical Behavior of 430 Stainless Steel and FeCrAlY Foams in Sulfur-Bearing Environments

The mechanical behavior of 430 stainless steel and pre-oxidized FeCrAlY open-cell foam materials of various densities was evaluated in compression at temperatures between 450°C and 600°C in an environment containing hydrogen sulfide and water vapor. Both materials showed negligible corrosion due to the gaseous atmosphere for up to 168 h. The monotonic stress–strain response of these materials was found to be dependent on both the strain rate and their density, and the 430 stainless steel foam materials exhibited less stress relaxation than the FeCrAlY for similar experimental conditions. Using the results from multiple hardening-relaxation and monotonic tests, an empirical constitutive equation was derived to predict the stress–strain behavior of FeCrAlY foams as a function of temperature, and strain rate. These results are discussed in the context of using these materials in a black liquor gasifier to accommodate the chemical expansion of the refractory liner resulting from its reaction with the soda in the black liquor.

Characterization of 17-4 PH stainless steel foam for biomedical applications in simulated body fluid and artificial saliva environments

Highly porous 17-4 PH stainless steel foam for biomedical applications was produced by space holder technique. Metal release and weight loss from 17–4 PH stainless steel foams was investigated in simulated body fluid and artificial saliva environments by static immersion tests. Inductively coupled plasma-mass spectrometer was employed to measure the concentrations of various metal ions released from the 17-4 PH stainless steel foams into simulated body fluids and artificial saliva. Effect of immersion time and pH value on metal release and weight loss in simulated body fluid and artificial saliva were determined. Pore morphology, pore size and mechanical properties of the 17-4 PH stainless steel foams were close to human cancellous bone.

Effect of various parameters on properties of composite steel foams under variety of loading rates

Steel–steel composite metal foams (CMF) are manufactured using steel hollow spheres (with variety of different sphere sizes, surface roughness and carbon content) embedded in a stainless steel matrix through powder metallurgy technique and are investigated experimentally under compression loading with variety of loading rates. The microstructural and mechanical properties of the material were studied using optical and scanning electron microscopy, energy dispersive spectroscopy, quasi-static, and dynamic compressive loading up to 26m/s. It is observed that the yield and plateau strength as well as the energy absorption capabilities of the composite foams are increased with increasing loading rate and by decreasing sphere sizes. Such mechanical properties improved by additional carbon content in the sphere wall at strains below 17% while the effect of density, resulted from porosity content, showed an improvement on the densification strain and plateau strengths at higher than 17% strain. The effect of spheres surface roughness and carbon content on mechanical properties of CMF seemed to be minimal compared to other parameters. As a result, the features controlling the life time and performance of composite metal foams under static and dynamic loading have been categorized into two main groups. The first group that controls the yield and plateau strength of the foam at lower strain levels includes bonding strength between the spheres and matrix which is a function of the sphere surface roughness and the gradient chemical composition between the spheres and matrix. The second group that controls the relative density, densification strain and plateau strength at higher strain levels belongs to the sphere diameter and the porosity content in both spheres and matrix. Moreover, increasing the loading rate improves the yield strength of all CMF samples.

Characterization of Steel Foams for Structural Components

Experimentally measured mechanical properties of hollow sphere steel foam are the subject of this paper. The characterization of the hollow sphere foam encompasses compressive yield stress and densification strain, compressive plastic Poisson’s ratio, and compressive unloading modulus, as well as tensile elastic modulus, tensile unloading modulus, tensile yield stress, and tensile fracture strain. Shear properties are also included. These tests provide sufficient information to allow calibration of a macroscopic, continuum constitutive model. Calibrated foam plasticity parameters are tabulated, and unique feature of foam plasticity are explained. Also, initial development of mesoscale simulations, which explicitly model voids and sintered hollow spheres, is reported. This work is part of a larger effort to help the development of steel foam as a material with relevance to civil engineering applications.

Computational evaluation of limit states of thin-walled channels made from steel foam

The objective of this paper is to explore the potential strength and serviceability implications of metallic foams, specifically steel foam, utilized as a thin-walled channel structural member. A typical advantage sought in the selection of a thin-walled member is minimal weight. However, the stability of the thin walls and the related limit states constrains the extent to which weight minimization may be utilized. As a material, steel foam (literally creating air voids in the steel microstructure) offers the potential to provide increased plate stiffness for a given weight and thus create even lighter thin-walled members and structures. In this work analytical material relationships are used to explore the structural potential for steel foam. First, the local buckling and yielding of an isolated steel foam plate is explored. Second, the local, distortional, and global buckling of a prototypical cold-formed steel channel using steel foam is examined. Finally, the strength and governing limit state of the channel as a function of relative density (i.e., the degree to which the material is foamed) is explored. The results show the key tradeoff made when foaming–stiffness per weight is increased, including stiffness related to member buckling modes; however, yield strength per weight decreases. Depending on the slenderness (in local, distortional, and global modes) of the member this tradeoff can be beneficial or detrimental.

Mechanical properties of sinter-hardened Cr–Si–Ni–Mo based steel foam

Highly porous sinter-hardenable Cr–Si–Ni–Mo based steel foam for automotive applications was produced by space holder method. Steel powders were mixed with binder (polyvinylalcohol) and space holder (carbamide), and compacted. Carbamide in the green compacts was removed by water leaching at room temperature. The green specimens were then sintered at temperatures between 1100°C and 1250°C for sintering times of 15, 30 and 45min. In addition, the steel foams were sinter-hardened to enhance mechanical properties. Sinter-hardening combines sintering and heat treatment in one step by increasing the post-sintering cooling rate. This reduces the cost of operation and makes powder metallurgy more competitive. Effects of sinter-hardening process parameters on compressive strength, Young’s modulus, hardness and energy absorption of the steel foams were investigated.