Effects of porosity on corrosion resistance of Mg alloy foam produced by powder metallurgy technology

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.

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

Fabrication and characterization of closed-cell magnesium-based composite foams

Effect of homogenizing heat treatment on the compressive properties of closed-cell Mg alloy foams

Magnesium (Mg) and some of its alloys are attracting increasing interest as promising biodegradable materials for medical applications due to their analogous mechanical properties in relation to bone tissues, functional roles in the human body, decent biocompatibility, and higher strength to weight ratio than other metallic, polymeric, and ceramic biomaterials. Porous Mg and Mg alloys can be used as bone substitutes with bone-mimicking characteristics. Since the structures of bone tissue and porous Mg materials are similar, host bone cells can grow into the pores of an Mg scaffold and form new bone tissue. Moreover, the gradual biodegradation of porous Mg and Mg alloys after implantation, followed by the absorption of Mg ions in the body, eliminates the necessity of removing the implant via a subsequent surgical procedure, which makes Mg scaffolds more favorable than other porous metallic biomaterials. Different production methods have been developed in the fabrication of porous Mg and Mg alloys, which can be classified into two categories: the melt processing method and the solid processing method, according to the state of materials that are being processed. Casting, metal–gas eutectic solidification, infiltration, and negative salt-pattern molding processes are examples of melt processing methods in which a blowing agent is introduced into the molten metal followed by stirring, or by infiltration of a bed of hollow spheres, or by the introduction of a gas or even a vacuum into Mg melt prior to solidification. Powder metallurgy with a blowing agent or space holder can be considered as a solid processing method. There are also other methods in which Mg alloy chips, strips, or fibers are used as a starting material, and a porous structure is formed through one or both of the melt and solid processing methods. Some porous Mg and Mg alloys have also been made through a combination of metallurgical and mechanical processes. The technological advancements as well as the increase in understanding of porous structures and properties cause many methods to be utilized to produce porous structures. However, some methods are not economically viable. Some methods produce a porous structure that is not suitable for implant applications due to the nonbiocompatible residues in the final product or inappropriate pore size and porosity. Therefore it is crucial to choose a production method that is suitable to produce porous Mg and Mg alloys with a controlled pore size, shape, and porosity that are compatible with medical applications. This chapter elucidates a variety of manufacturing methods for porous Mg and Mg alloys. The macro- and microstructures, mechanical and corrosion properties, and in vitro and in vivo biocompatibility of different porous Mg and its alloys are highlighted. We provide insights for a comprehensive understanding of the characteristics of porous Mg and Mg alloy produced through different methods in order to enable the fabrication of Mg scaffolds with improved mechanical and biological properties. Furthermore, the manufacturing methods for producing Mg scaffolds are technologically, scientifically, and technically advanced and economical. Future research directions in the field of porous Mg alloy biomaterials are also provided.

Production methods and characterization of porous Mg and Mg alloys for biomedical applications

Effects of specimen aspect ratio on the compressive properties of Mg alloy foam

Nucleation and growth of nanoscale precipitates and the effect on properties during secondary isothermal aging in thin-band of Cu-0.8Cr-0.1Zr alloy

Applying pre-strain can not only change the microstructure and the mechanical property of metal material but also affect sheet metal stamping ability. In this paper, taking H260 low-alloy steel and TA2 titanium alloy as experimental materials, pre-strain ranging from 0 to 0.16 was applied using the one-step and the multi-step method respectively. Microstructure observation, tensile test, bending test, and cup bulging test were conducted on the pre-strained samples. Results show that in the pre-strain loading stage, the slipping and twinning deformation occurs in the TA2 alloy sample while dislocation sliding mainly happens in H260 low-alloy. With pre-strain increasing, the product of ultimate tensile strength and elongation rate gradually decreases, and the true ultimate tensile stress and accumulating elongation change rarely. The “product of yielding strength and elongation rate” can be enhanced by applying a pre-strain of 0.04 on the condition that plasticity is still at a high level. In the pre-strain range of 0 - 0.16, a bending test with a 30.8 °-opening angle can be completed on H260 steel. The springback angle changes from negative to positive with an increase in pre-strain. The bending ability of TA2 titanium alloy is very poor, for a crack can easily occur even in the original sample. The cupping value decreases gradually with an increase in pre-strain. The cupping value of TA2 titanium alloy is higher than that of H260 low alloy steel for the constant pre-strain. A quite large difference exists between the two experimental materials. Pre-strain loading pass has no significant effect on the microstructure evolution, mechanical properties, and stamping properties.

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Zhiguo Wang

Papers

Effects of specimen aspect ratio on the compressive properties of Mg alloy foam

Nucleation and growth of nanoscale precipitates and the effect on properties during secondary isothermal aging in thin-band of Cu-0.8Cr-0.1Zr alloy

Effect of pre-strain on microstructure and stamping ability of TA2 titanium alloy and H260 low-alloy steel