Determination of the Young’s modulus of porous ß-type Ti–40Nb by finite element analysis

Macroporous ß-type Ti–40Nb compacts with particularly low stiffness suitable for biomedical applications were successfully processed by a space-holder sintering method with a total porosity range of 50–60%. The microstructure of these samples as well as their phase composition and their mechanical properties were carefully analyzed. The samples comprise macropores with 100–300 μm size formed by NaCl space-holder particles and micropores of 1–3 μm size within the sintered Ti–Nb alloy. The correlation between the mesoscopic Young’s modulus and the microporosity of the alloy was analyzed by combining compression tests, microcomputer tomography (μCT), and finite element analysis (FE). The derived relationship permits to predict the macroscopic Young’s modulus of macroporous compacts for a known morphology of the macroporosity.     

Fabrication and characterization of porous Co–Cr–Mo/58S bioglass nano-composite by using NH4HCO3 as space-holder

In the present study, Co–Cr–Mo/58S porous nano-composites were successfully fabricated by the use of space-holder and powder metallurgy techniques. The cold compacted Samples were heated at 175 °C for 2 h and then was raised to 1250 °C and held for 2 h. Scanning electron microscope (SEM) and optical microscope (OM) images of porous samples showed interconnected, isolated pores and appropriate range of pore sizes. The results of compressive strength and Young's modulus were in the range of 33–566 MPa and 0.19–4.46 GPa, respectively. In particular, the compressive strength and Young's modulus at the porosity of 38.5% were found to be similar to those of bone. The SEM images, pH values and Fourier-transform infrared spectroscopy (FTIR) results showed that apatite crystallites were formed on the surface of sample with 38.5% porosity during immersion in simulated body fluid which revealed bioactivity of this sample. In vitro cytocompatibility of the sample with 38.5% porosity was evaluated and cell growth was examined. SEM images revealed that cells grew on the surface and inside the pores. The present investigation has shown that this porous nano-composite is a promising biomaterial for bone tissue engineering by virtue of its porous structure, appropriate mechanical properties, bioactivity and biocompatibility.     

Porous low modulus Ti40Nb compacts with electrodeposited hydroxyapatite coating for biomedical applications

Porous ß-type non-toxic Ti40Nb alloy was prepared by compaction of mechanically alloyed powder mixed with NaCl or Mg particles as space-holder material. The compacts with porosity of 36–80% demonstrated a very low Young's modulus of ~ 1.5–3 GPa and compression strength of ~ 10–35 MPa, which is suitable for potential implant material application. Porous samples were electrochemically covered with hydroxyapatite. The influence of the deposition time and of the electrolyte concentrations on the morphology of the hydroxyapatite coating was studied. It is demonstrated that a homogenous coating of hydroxyapatite crystals with different shape and size can be obtained on the surface of the porous samples.     

Mechanical modulation and bioactive surface modification of porous Ti–10Mo alloy for bone implants

The objective of this work was to fabricate a suitable porous Ti–10Mo alloy as the human bone replacement implants. The porous Ti–10Mo alloy was fabricated by mechanical alloying and then consolidated by powder metallurgy technique. NH₄HCO₃ powder was used as space-holder. It was indicated that the mean pore size, porosity, compressive strength, and elastic modulus of porous Ti–10Mo alloy could be tailored by the amount of NH₄HCO₃, and then could be matched with those of human bones. Furthermore, porous Ti–10Mo alloy was treated by alkali heat treatment and soaked in the 1.5 times simulated body fluid (1.5SBF). It was observed that the surface and the inside pore wall of porous Ti–10Mo alloy with 25 wt.% NH₄HCO₃ covered with the apatite layer after soaked in 1.5SBF for 28 days. These phenomena indicated that the surface modified porous Ti–10Mo alloy exhibited a high potential for bone-bonding, which was expected to be used as bone tissue implant.     

Effect of sintering atmosphere on properties of porous stainless steel for biomedical applications

This study discusses manufacturing of metallic biomaterials by means of powder metallurgy with consideration for their unquestionable advantages, i.e. opportunities of obtaining materials with controllable porosity. The paper focuses on properties of 316L stainless steel obtained using the method of powder metallurgy with respect to compacting pressure and sintering atmosphere. All the specimens were compacted at 700, 400 and 225 MPa, and sintered at 1250 °C. In order to analyze the sintering atmosphere, three different media were used: dissociated ammonia, hydrogen and vacuum. The study covered sintering density, porosity, microstructure analysis and corrosion resistance. The proposed method of powder metallurgy allowed for obtaining materials with predictable size and distribution of pores, depending on the parameters of sinter preparation (compaction force, sinter atmosphere). High corrosion resistance of the materials (sintering in the atmosphere of hydrogen and in vacuum) and high porosity in the sinters studied offer opportunities for using them for medical purposes.     

Effect of porosity and density on the mechanical and microstructural properties of sintered 316L stainless steel implant materials

In this study, the microstructure and mechanical properties of sintered AISI 316L stainless steel implant materials produced by powder metallurgy (P/M) method were investigated as a function of porosity amount. AISI 316L stainless steel powders were cold-pressed with 800 MPa pressure and sintered at 1200 °C, 1250 °C and 1300 °C for 30 min in a nitrogen atmosphere. The mechanical properties of the 316L implant samples were determined by tensile, fatigue and microhardness tests. Metallographic studies such as pore formation, and fractured surface analyses were performed by Scanning Electron Microscopy (SEM) and Light Optical Microscopy (LOM). The results of this study indicate that, irregular pore formation tendencies increase with an increase in porosity (%). Furthermore, an increase in porosity was shown to decrease the mechanical properties of sintered AISI 316L stainless steel. Sintering temperature is important parameter in decreasing the porosity of P/M materials.     

Properties of porous magnesium prepared by powder metallurgy

Porous magnesium-based materials are biodegradable and promising for use in orthopaedic applications, but their applications are hampered by their difficult fabrication. This work reports the preparation of porous magnesium materials by a powder metallurgy technique using ammonium bicarbonate as spacer particles. The porosity of the materials depended on the amount of ammonium bicarbonate and was found to have strong negative effects on flexural strength and corrosion behaviour. However, the flexural strength of materials with porosities of up to 28 vol.% was higher than the flexural strength of non-metallic biomaterials and comparable with that of natural bone.     

Microstructural and mechanical characterisation of 7075 aluminium alloy consolidated from a premixed powder by cold compaction and hot extrusion

The present work concerns the processing of 7075 Al alloy by cold compaction and hot extrusion of a premixed powder. To this end, a premixed Al–Zn–Mg–Cu powder, Alumix 431D, was uniaxially cold pressed at 600 MPa into cylindrical compacts 25 mm in diameter and 15 mm thick. Subsequently, selected green compacts were subjected to either a delubrication or presintering heat treatment. Extrusion of the powder compacts was performed at 425 °C using an extrusion ratio of 25:1. No porosity was present in the microstructures of the extruded alloys. Heat treatment prior to extrusion had a great effect on the degree of alloy development in powder compacts and, as a direct consequence, remarkably affected the extrusion process and the as-extruded microstructures and mechanical properties of the processed materials. Hot extrusion caused banded structures for the alloys consolidated from the green and delubricated powder compacts. The alloy extruded from the presintered powder compact showed a fine, recrystallized microstructure which resulted in a superior combination of mechanical properties for the consolidated material.     

Preparation,characterization and cytocompatibility of bioactive coatings on porous calcium-silicate-hydrate scaffolds

The major goal of this research was to investigate and characterize the deposition of a biomimetic apatite-like coating onto the surface of 3D porous calcium-silicate-hydrate scaffolds with suitable bioactivity for potential application in bone tissue engineering. Basically, Portland cement, water, sand and lime were mixed for preparing the slurry which was poured into molds, and fine aluminum powder was added as foaming agent resulting on the formation of porous 3D structures. After aging for 28 days, these porous inorganic scaffolds were immersed in calcium chloride supersaturated solution in PBS for 7 days at 37 °C for the biomimetic layer deposition. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier Transformed Infrared Spectroscopy (FTIR) techniques were used in order to characterize the porous scaffolds and the apatite-like biomimetic coating. The results have showed that 3D constructs were successfully produced with interconnected porosity, compressive strength and cytocompatibility appropriate for potential use as an alternative in trabecular bone repair.     

Processing and properties of porous titanium with high porosity coated by bioactive titania nanotubes

A porous titanium scaffold with a porosity of 70% and a pore size of about 200–300 μm was fabricated using the space-holder sintering process. Furthermore, the bioactive TiO₂ nanotubes with a tube size of approximately 100 nm were prepared successfully on the surface of the porous titanium by anodization and heat-treatment. The bioactivity of the scaffold was evaluated by immersing the samples into the simulated body fluid for 7 days. Results show that the porous titanium scaffold coated with anatase nanotubes has the superior ability of hydroxyapatite formation. Meanwhile, the scaffold has a high compressive strength of 36.8 MPa, which can be used as a cancellous bone substitute.     

AC magnetic properties of the soft magnetic composites based on Supermalloy nanocrystalline powder prepared by mechanical alloying

The preparation and characterization of the nanocrystalline soft magnetic composite core based on Supermalloy powder obtained via mechanical alloying route are presented. The AC magnetic properties of the compacts were determined in frequency range from 100 Hz to 100 kHz for flux densities of 0.05 and 0.1 T. Composite materials were obtained by covering the Supermalloy particles with a polymer binder, then compacted into toroidal shape and finally polymerized. It is found that an increase of the compacting pressure from 600 MPa to 800 MPa leads to an increase of the compacts permeability by more than 8%. Also, reducing the polymer content from 2 wt.% to 0.5 wt.% leads to an increase of the magnetic losses (at 100 kHz and 0.1 T) by 380%. The removal of the stresses induced during compaction has been accomplished by a heat treatment at 170 °C for 120 h. This leads to a significant increase (12%) of the relative initial permeability of the compacts.     

Effects of binder system and processing parameters on formability of porous Ti/HA composite through powder injection molding

Porous titanium-hydroxyapatite (Ti/HA) composite is a developed composite material suitable for bio-medical applications. Powder injection molding (PIM) with space holder method is used to produce porous Ti/HA with mechanical properties, similar to human bone, and pores helps to initiate tissue growth. However, the differences in physical and mechanical properties of these composites are the main challenges during debinding and sintering. Therefore, the main objective is to determine effects of binder systems and processing parameters on formability of Ti/HA composite. In PIM, a binder system is necessary to produce green and ultimately sintered part. There are two binder systems and variation of sintering temperature has been used. Results revealed that Polyethylene glycol (PEG)-based binder system is applicable with NaCl space holder and optimum sintering parameters, including temperature, heating rate, and holding time of 1300 °C, 10 °C/min, and 5 h, respectively. The fabricated porous Ti/HA exhibits average porosity, pore size distribution, compressive strength, and roughness values of 55%, 60 μm to 170 μm, 370 MPa, and 0.323 μm, respectively. FESEM results showed that the pores are interconnected. It may be an appropriate material for future bio-medical applications.     

Effect of hot rolling on the enhancement of mechanical properties of low density Cu–Cr–Nb sintered alloy

Studies have been carried out on the effect of hot rolling on the enhancement of mechanical properties of sintered low density Cu–8 at.% Cr–4 at.% Nb alloy made from gas-atomised powders by vacuum hot pressing using varying pressure and temperature. The pressure is varied from 10 to 30 MPa whereas, 800, 900 and 1000 °C are three hot-pressed temperatures. Though hot rolling of porous low density hot-pressed samples results in near theoretical density, the hot-pressed sintered material with higher initial porosity shows lower strength and ductility after rolling. Hot-pressed compacts below certain density could not be rolled and the sample has cracked during rolling. The higher density material could be easily rolled and significant improvement in mechanical properties has been noticed. This has been attributed to the conversion of porosities into microscopic cracks which could not be healed due to the presence of Cr₂Nb precipitates. Finally, structure property correlation has been established.     

One-step mechanical processing to prepare LSM/ScSZ composite particles for SOFC cathode

Novel one-step mechanical processing was proposed to prepare LSM/ScSZ composite particles from the starting raw powders of LSM (strontium doped lanthanum manganite) and ScSZ (scandium stabilized zirconia) fine powder. In this paper, the properties of composite particles made by this method and the properties of the resultant cells were evaluated. As a result, LSM/ScSZ composite particles were obtained by only 10 min mechanical processing using three kinds of raw powder materials of LSM and ScSZ fine particles without extra heat. The maximum power density of the cell made by the composite particles at 800 °C reached 320 mW/cm². It was higher than that made by commercially available LSM nanosized powder. Besides, the polarization resistance of the cathode made by the composite particles at 800 °C was 0.5 Ω cm² which was lower than that made by using commercially available LSM powder. It suggests that the proposed method is very promising for producing high quality composite particles used for SOFC cathodes by more simple and energy-saving way.     

A New Approach for Manufacturing a High Porosity Ti-6Al-4V Scaffolds for Biomedical Applications

Titanium and its alloys are currently considered as one of the most important metallic materials used in the biomedical applications, due to their excellent mechanical properties and superior biocompatibility. In the present study, a new effective method for fabricating high porosity titanium alloy scaffolds was developed. Porous Ti-6Al-4V scaffolds are successfully fabricated with porosities ranging from 30% to 70% using spaceholder and powder sintering technique. Based on its acceptable properties, spherical carbamide particles with different diameters （0.56, 0.8, and 1mm） were used as the space-holder material in the present investigation. The Ti-6Al-4V scaffolds porosity is characterized by using scanning electron microscopy. The results show that the scaffolds spherical-shaped pores are depending on the shape, size and distribution of the space-holder particles. This investigation shows that the present new manufacturing technique is promising to fabricate a controlled high porosity and high purity Ti-6Al-4V scaffolds for hard tissue replacement.     

Experimental investigations on welding behaviour of sintered and forged Fe–0.3%C–3%Mo low alloy steel

Tungsten Inert Gas (TIG) welding is considered as one of the cleanest welding methods. It is generally adopted for thinner materials with moderate weld joint strengths. Welding of sintered porous materials continues to be a challenge due to the inherent porosity of the parent metals. The present research work attempts to address some of the issues relating to the welding behaviour of sintered and forged Fe–0.3%C–3%Mo low alloy steels under TIG welding. Rectangular strips of size 70 mm × 15 mm × 5 mm, obtained by blending, compacting and sintering of elemental powders of iron, graphite and molybdenum, were upset forged – both hot and cold in order to obtain alloy steel strips of various porosities. Two identical alloy steel strips of equal density were then welded both along longitudinal and transverse directions, by TIG welding, employing filler metal of suitable composition. The welded strips were then subjected to tensile test, hardness test, microstructural and Scanning Electron Microscope (SEM) fractography studies. Cold/hot upsetting of the sintered alloy preforms has led to enhanced density. As a result of improved density, their tensile strength and hardness values were also found to be enhanced. The welded alloy exhibited higher tensile strength compared to the un-welded base metal, due to strengthening by residual stress. Similarly, the strength and hardness of the welded alloy strips were found to be enhanced with increase in density. The tensile strength of welded joint is found to be higher compared to that of the base metal due to alloy metals segregation, rapid cooling and formation of acicular ferrite at the weldment of welded joint. No porosity was observed in the weld metal or Heat Affected Zone (HAZ) of the weld joint. However, the base metal had numerous micro pores, though pore migration towards weldment has not been observed.     

Catalysis,nanostructure and macroscopic property triangle in bioactive calcium-containing ceramic systems

Calcium silicate ceramics are intended for application as long-term implant materials. In the present work, attention was paid to understand the correlations between the nanostructure (aggregate size, crystallinity, porosity) and the macroscopic properties (solubility in water and simulated body fluids, SBF; hardness) varying the chemical composition. Varying the catalyst (from a base to various acids) during the chemical synthesis was shown to significantly impact on the pore size, crystallinity and mechanical properties. The basic catalyst yields the ceramics with the highest mechanical strength. Ammonia used in 1.0 or 10.0 molar ratio results in bulk ceramics with parameters required for a biomedical application, good hardness (180–200 HV) and low solubility (1–3%) in water and in SBF. The fine porosity (~ 50 nm) and homogeneous amorphous structure induce good mechanical character.     

Stretching behaviors of entangled materials with spiral wire structure

The entangled materials with spiral wire structure have been investigated in terms of the stretching behavior, mechanical properties, and stress–strain hysteresis effect. The results indicate that these materials are much more flexible than that with non-woven wire structure. They exhibit 1.05 MPa yielding strength and 5.7 MPa Young’s modulus in average at the porosity of 60%, and 2.47 MPa yielding strength and 12.3 MPa Young’s modulus in average at the porosity of 45%. Under tensile loading the materials exhibit a unique stress–strain behavior that goes through a long strain period after yielding and follows a quick stress increase on the stress–strain curve due to the ‘unclosing’ and ‘straightening’ mechanism of the spiral wire structure. In addition, these materials exhibit obvious stress–strain hysteresis effect. Their energy dissipation values determined according to the stress–strain hysteresis loops are 28.6 mJ/cm³ at the porosity of 60% and 102.3 mJ/cm³ at the porosity of 45%, which are much larger than that of the polymer foam, implying their promising applications for the energy absorption.     

Preparation and properties of porous Ti–10Mo alloy by selective laser sintering

In this study, porous Ti–10Mo alloy was prepared from a mixture of titanium, molybdenum and epoxy resin powders by selective laser sintering preforming, debinding and sintering at 1200 °C under a pure argon atmosphere. The influence of sintering process on the porous, microstructural and mechanical properties of the porous alloy was discussed. The results indicate that the pore characteristic parameters and mechanical properties mainly depend on the holding time at 1200 °C, except that the maximum strain keeps at about 45%. The matrix microstructure is dominated by α phase with a small quantity of β phase at room temperature. As the holding time lengthens from 2 to 6 h, the average pore size and the porosity decrease from 180 to 50 μm and from 70 to 40%, respectively. Meanwhile, the Young's modulus and the compressive yield strength increase in the ranges of 10–20 GPa and 180–260 MPa, respectively. Both the porous structure and the mechanical properties of the porous Ti–10Mo alloy can be adjusted to match with those of natural bone.     

Fabrication and technological properties of nanoporous spinel/forsterite/zirconia ceramic composites

In this work, nanoporous spinel/forsterite/zirconia ceramic composites were fabricated at 1600 °C for 2 h. The influence of zirconia content (up to 10 mass%) on the technological properties, nanopores formation, phase compositions, microstructure and thermal diffusivity of nanoporous ceramic composites was investigated. Nanospinel and nanoforsterite powders were synthesized via a modified co-precipitation and sol–gel techniques, respectively. Results indicated that apparent porosity of the fired nanoporous ceramic composites is mostly in the range 14.26–56.14% with the average pores diameter 35.8 nm. Using of nanopowders (spinel and forsterite) as the staring materials were achieved high mechanical (cold crushing strength ∼ 235–164 MPa) and elastic (Young’s modulus ∼ 123.6–4.5 GPa) properties of the prepared nanoporous ceramic composites. Microstructure analysis exhibited all of the crystalline phases and pores of the nanoporous ceramic composites are in the nanosize (35–40 nm). These nanoporous ceramic composites are promising porous ceramic materials for using in advanced applications due to their excellent combination properties.