Preparation and characterization of permeability and mechanical properties of three-dimensional porous stainless steel.

Porous materials are indispensable in biomedical and chemical catalysis fields, but it is still a challenging task to fabricate them with excellent permeability and mechanical properties at the same time. Herein, a new type of three-dimensional porous stainless steel (3DPSS) was fabricated by compression moulding and vacuum sintering. The pore size distribution, air permeability, and mechanical properties of 3DPSS were studied. The results indicated that the radial air permeability reached 3.1 × 10-11 m2, which was approximately 19.7 times greater than the axial air permeability. Interestingly, the axial compressive strength was 91.3% higher than the radial compressive strength and reached 1249 MPa, which was significantly better than that of conventional porous stainless steel and porous titanium as well as porous high entropy alloys. The main characteristics of 3DPSS fracture were metallurgical bonding surface fracture, necking fracture and shear fracture of the wire mesh. This study provides an effective method for the preparation of three-dimensional porous materials, which is convenient for industrial production. It is of great significance to expand the potential application range of porous materials, in particular in fields requiring comprehensive permeability and mechanical properties.

Charpy Impact Behavior of a Novel Stainless Steel Powder Wire Mesh Composite Porous Plate.

A novel powder wire mesh composite porous plate (PWMCPP) was fabricated with 304 stainless steel powders and wire mesh as raw materials by vacuum solid-state sintering process using self-developed composite rolling mill of powder and wire mesh. The effects of different mesh volume fractions, mesh diameters, and sintering temperatures on the pore structure and Charpy impact properties of PWMCPPs were studied. The results show that PWMCPPs have different shapes and sizes of micropores. Impact toughness of PWMCPPs decreases with increasing wire mesh volume fraction, and increases first and then decreases with increasing wire mesh diameter, and increases with increasing sintering temperature. Among them, the sintering temperature has the most obvious effect on the impact toughness of PWMCPPs, when the sintering temperature increased from 1160 °C to 1360 °C, the impact toughness increased from 39.54 J/cm2 to 72.95 J/cm2, with an increased ratio of 84.5%. The tearing between layers, the fracture of the metallurgical junction, and the fracture of wire mesh are the main mechanisms of impact fractures of the novel PWMCPPs.

Preparation and Tensile Properties of Novel Porous Plates Made by Stainless Steel Wire Mesh and Powder Composites.

Porous metal materials have important mechanical properties, and there are various manufacturing methods to produce them. In this paper, a porous, thin strip was fabricated by the composite rolling of stainless steel wire mesh and stainless steel powder. Then, a porous plate of stainless steel wire mesh and powder composite (SWMPC) was prepared by folding, pressing, and vacuum sintering the thin strip, and its structural characteristics and permeability were studied. The effects of the gap of the roller, gap of the powder box, number of layers by folding, and sintering parameters on the porosity and mechanical properties were also studied. The results indicated that the permeability increased with the increasing of porosity. Sintering parameters had a great influence on the mechanical properties. The larger the roll gap, the higher the porosity and the weaker the mechanical properties. As the gap of the powder box increased, the porosity decreased and the mechanical properties improved. The number of layers had no effect on the porosity. The first three stages of tensile curves of 10 and 15 layers were deformation stages and generally coincided, the time was short at the fracture stage. However, the mechanical properties got a raise when layers was 15.

Fabrication, Structural Characterization and Uniaxial Tensile Properties of Novel Sintered Multi-Layer Wire Mesh Porous Plates.

There is an increasing interest in developing porous metals or metallic foams for functional and structural applications. The study of the physical and mechanical properties of porous metals is very important and helpful for their application. In this paper, a novel sintered multilayer wire mesh porous plate material (WMPPs) with a thickness of 0.5 mm-3 mm and a porosity of 10-35% was prepared by winding, pressing, rolling, and subsequently vacuum sintering them. The pore size and total size distribution in the as-prepared samples were investigated using the bubble point method. The uniaxial tensile behavior of the WMPPs was investigated in terms of the sintering temperature, porosity, wire diameter, and manufacturing technology. The deformation process and the failure mechanism under the tensile press was also discussed based on the appearance of the fractures (SEM figures). The results indicated that the pore size and total size distribution were closely related to the raw material used and the sintering temperature. For the WMPPs prepared by the wire mesh, the pore structures were inerratic and the vast majority of pore size was less than 10 µm. On the other hand, for the WMPPs that were prepared by wire mesh and powder, the pore structures were irregular and the pore size ranged from 0 µm-50 µm. The experimental data showed that the tensile strength of WMPPs is much higher than any other porous metals or metallic foams. Higher sintering temperatures led to coarser joints between wires and resulted in higher tensile strength. The sintering temperature decreased from 1330 °C to 1130 °C and the tensile strength decreased from 296 MPa to 164 MPa. Lower porosity means that there are more metallurgical joints and metallic frameworks resisting deformation per unit volume. Therefore, lower porosities exhibit higher tensile strength. An increase of porosity from 17.14% to 32.5% led to the decrease of the tensile strength by 90 MPa. The coarser wires led to a bigger contact area between the interconnecting wires, resulting in a stronger sintering neck that exhibited higher tensile strength. The wire diameter increased from 81 µm to 122 µm and the tensile strength increased from 296 MPa to 362 MPa. The fracture morphology showed that the wires experience necking deformation and ductile fracture.

Characterization of three-point bending properties of metal-resin interpenetrating phase composites.

Metal-resin composites provide improved combinations of mechanical properties of raw materials. A novel metal-resin interpenetrating phase composite (IPCs) has been fabricated by spontaneously infiltrating unsaturated polyester resin into porous short-fiber preforms under vacuum conditions. In this study, three-point bending experiments are performed to characterize the bending properties of the IPCs. The fractographs after bending are examined to distinguish their characteristics. The flexural strength increases almost linearly from 42 ± 4 MPa to 119 ± 5 MPa in the in-plane direction and 59 ± 4 MPa to 151 ± 8 MPa in the through-thickness direction with an increasing fiber fraction ranging from 16.78 vol% to 32.11 vol%. The structures and bending properties of the IPCs exhibit significant anisotropy. Compared with the in-plane direction, higher bending strength and flexural modulus with smaller displacement at maximum bending force are observed in the through-thickness direction. The finer fibers contribute to improving the flexural strength (from 76 ± 6 MPa to 98 ± 5 MPa for the IPCs with about 23 vol% fiber fraction from 160 µm to 90 µm fiber diameters in the in-plane directions) and modulus. The fracture of the IPC after bending presents different appearances in different directions and the anisotropy becomes less severe with decreasing fiber fraction. Resin fracture, fiber necking and fracture, and debonding are the main fracture mechanisms.

Compressibility of 304 Stainless Steel Powder Metallurgy Materials Reinforced with 304 Short Stainless Steel Fibers.

Powder metallurgy (P/M) technique is usually used for manufacturing porous metal materials. However, some P/M materials are limitedly used in engineering for their performance deficiency. A novel 304 stainless steel P/M material was produced by a solid-state sintering of 304 stainless steel powders and 304 short stainless steel fibers, which were alternately laid in layers according to mass ratio. In this paper, the compressive properties of the P/M materials were characterized by a series of uniaxial compression tests. The effects of fiber content, compaction pressure and high temperature nitriding on compressive properties were investigated. The results indicated that, without nitriding, the samples changed from cuboid to cydariform without damage in the process of compression. The compressive stress was enhanced with increasing fiber content ranging from 0 to 8 wt.%. For compaction pressure from 55 to 75 MPa, greater compaction pressure improved compressive stress. Moreover, high temperature nitriding was able to significantly improve the yield stress, but collapse failure eventually occurred.

Processing, Structural Characterization and Comparative Studies on Uniaxial Tensile Properties of a New Type of Porous Twisted Wire Material.

A self-developed rotary multi-cutter device cuts stainless steel wire ropes into segments to fabricate twisted wires. Stainless steel porous twisted wire materials (PTWMs) with a spatial composite intertexture structure are produced by the compaction and subsequent vacuum solid-phase sintering of twisted wires. The stainless steel PTWMs show two types of typical uniaxial tensile failure modes, i.e., a 45° angle fracture mode and an auxetic failure mode (the PTWMs expand along the direction perpendicular to the tension). The effects of the sintering parameters, porosities, wire diameters, and sampling direction on the tensile properties of the PTWMs are carefully investigated. By increasing the sintering temperature from 1130 °C to 1330 °C, the tensile strength of the PTWMs with 70% target porosity increased from 7.7 MPa to 28.6 MPa and the total failure goes down to 50%. When increasing the sintering time from 90 min to 150 min, the tensile strength increases from 12.4 MPa to 19.1 MPa and the total failure elongation drops to 78.6%. The tensile strength of the PTWMs increases from 28.9 MPa to 112.7 MPa with decreasing porosity from 69.5% to 46.0%, and the total failure elongation also increases from 14.8% to 40.7%. The tensile strength and the failure strain of the PTWMs with fine wires are higher than those of the PTWMs with coarse wires under the same porosity. Sampling direction has a small influence on the tensile properties of the PTWMs.

Multigrid contact detection method.

Contact detection is a general problem of many physical simulations. This work presents a O(N) multigrid method for general contact detection problems (MGCD). The multigrid idea is integrated with contact detection problems. Both the time complexity and memory consumption of the MGCD are O(N). Unlike other methods, whose efficiencies are influenced strongly by the object size distribution, the performance of MGCD is insensitive to the object size distribution. We compare the MGCD with the no binary search (NBS) method and the multilevel boxing method in three dimensions for both time complexity and memory consumption. For objects with similar size, the MGCD is as good as the NBS method, both of which outperform the multilevel boxing method regarding memory consumption. For objects with diverse size, the MGCD outperform both the NBS method and the multilevel boxing method. We use the MGCD to solve the contact detection problem for a granular simulation system based on the discrete element method. From this granular simulation, we get the density property of monosize packing and binary packing with size ratio equal to 10. The packing density for monosize particles is 0.636. For binary packing with size ratio equal to 10, when the number of small particles is 300 times as the number of big particles, the maximal packing density 0.824 is achieved.