Microporous Titanium through Metal Injection Moulding of Coarse Powder and Surface Modification by Plasma Oxidation

Titanium is one of the most attractive materials for biomedical applications due to having excellent biocompatibility accompanied by good corrosion resistance. One popular processing technique for Ti is Metal Injection Moulding (MIM). However, there are several issues associated with the use of this technique, such as the high cost of the fine powder used, the high level of contamination and consequent alteration to material properties, as well as the large volume shrinkage that occurs during sintering. In this study, the use of a relatively coarse Ti powder with a mean particle size of 75 μm to process Ti parts with the potential for biomedical applications by MIM will be examined, compared to a commercial Ti feedstock, and subsequently coated using Plasma Electrolytic Oxidation (PEO). The results show that samples produced with the coarse powder shrink 35% less and have a relative density 14% less with an average pore size three-times larger than that of the commercial feedstock. This helps increase the potential competitiveness of MIM in the production of biomedical parts, as it reduces cost, shrinkage and results in more intentionally-induced micropores, such as are desired for biomedical implants. PEO treatment of the samples yields a thick rough coating comprised of a mixture of rutile and anatase with interconnected microporous channels and openings resembling the mouth of a volcanic crater

Production and digital image correlation analysis of titanium foams with different pore morphologies as a bone-substitute material

Ti foams are mesoporous structured materials that are characterized by their high surface area and interconnected porosity with a huge potential for biomedical applications. In this study, we investigated the production of titanium foams with different pore morphologies as a bone-substitute material via the addition of different amounts, shapes, and sizes of the space holder. Furthermore, we also carried out strain analysis using digital image correlation (DIC) in order to analyse the strain distribution across the porous samples. In addition, the nature of the relationship between the amount of the space holder added and final amount of porosity in the foams produced was also examined. The results demonstrated that the relationship between the space holder amount and porosity in the samples follows a complex one-phase exponential decay function in an increasing form. Our findings also suggest that the shape of the space holder does not play a significant role in dictating the porosity of the foams produced in the current study. However, the space holder’s shape does have a substantial role in dictating the mechanical properties of the foams produced, where Ti foams produced using a cubic or irregular space holder were found to have a lower yield stresses than those made with the spherical space holder

Structural characterisation of porous copper sheets fabricated by lost carbonate sintering applied to tape casting

In this article, we describe experimental investigations of the structural characterisations of double-layered porous copper tapes of thickness down to 0.74 mm. The porous sheets were produced by a process combing tape casting and lost carbonate sintering (LCS) to control both the porosity and pores distribution of the sheets. By varying the values of processing parameters, double-layer (porous and dense) structured tapes with open cell structure and porosities ranging from 50.0 to 81.5% are produced. Scanning electron microscopy and actual size image analysis were employed to measure the pore size and surface porosity of the porous sample. The pore size distribution was characterised using Micro-CT scanner running Skyscan NRecon software and CTAn software. A helium pycnometer was employed to obtain the bulk porosity of the porous copper samples. Statistical analysis of these measurements was used to assess the efficiency and consistency of the space holder technique used to generate porosity, as well as to draw information about the influence that different processing routes have on the resulting mesostructure of the porous copper metal, and on its properties

Open Celled Porous Titanium

Among the porous metals, those made of titanium attract particular attention due to the interesting properties of this element. This review examines the state of research understanding and technological development of these materials, in terms of processing capability, resultant structure and properties, and the most advanced applications under development. The impact of the rise of additive manufacturing techniques on these materials is discussed, along with the likely future directions required for these materials to find practical applications on a large scale

Cyclic Voltammetry Study of PEO Processing of Porous Ti and Resulting Coatings

Ti is one of the most commonly used materials for biomedical applications. However, there are two issues associated with the use of it, namely its bio-inertness and high elastic modulus compared to the elastic modulus of the natural bone. Both of these hurdles could potentially be overcome by introducing a number of pores in the structure of the Ti implant to match the properties of the bone as well as improve the mechanical integration between the bone and implant, and subsequently coating it with a biologically active ceramic coating to promote chemical integration. Hence, in this study we investigated the usage of cyclic voltammetry in PEO treatment of porous Ti parts with different amount of porosity produced by both Metal Injection Moulding (MIM) and MIM in combination with a space holder. It was found that porous samples with higher porosity and open pores develop much thicker surface layers that penetrate through the inner structure of the samples forming a network of surface and subsurface coatings. The results are of potential benefit in producing surface engineered porous samples for biomedical applications which do not only address the stress shielding problem, but also improve the chemical integrati

Design of water debinding and dissolution stages of metal injection moulded porous Ti foam production

Foams are advanced materials with controlled meso- and micro-structure, with huge potential in a variety of applications such as in the biomedical and automotive sectors. One promising technique for the production of Ti foams is Metal Injection Moulding in combination with Space Holders (MIMSH). Most existing work in the literature on MIM-SH foams reports very long debinding and dissolution periods that can extend for more than two days. In this paper, the effect on process speed of different water debinding and dissolution techniques of MIM-SH Ti foams will be investigated. Furthermore, the temperature influence on the debinding and dissolution behaviour of a PEG based binder and KCl space holder will be examined. In addition, some debound samples will be sintered in order to verify their suitability for the production of Ti foams. The results show that a heated ultrasonic bath is the fastest and most effective technique in removing the PEG and space holder, while increasing the temperature increased the removal rate up to a certain temperature (80 °C) where a significant swelling occurred, leading to a slower removal rate. The results make it possible for a more rapid production method to be designed systematically

Open pore titanium foams via metal injection molding of metal powder with a space holder

Powder methods are highly applicable for the processing of more challenging metals and forms. Examples of materials that encompass both of these are metallic foams, which are advanced materials that consist of a network of interconnected or randomly spaced macropores separated by dense or microporous cell walls. These macropores can be either open or closed, or mix of those two, depending on the manufacturing process. One popular metal foam that has received a huge amount of interest in the last decade is Ti foam, due to it offering a unique combination of properties, such as high strength to weight ratio and high permeability combined with excellent biocompatibility. In this study the use of metal injection molding of titanium powder in combination with a space holder (to create large pore spaces) is examined for the production of open pore Ti foams for biomedical applications. Potassium chloride with two different particle shapes (spherical and cubic) was used as a space holder. It was found that feedstocks prepared with spherical KCl particles had a lower viscosity and better flowability compared to those made using cubic particles. Ti foams with a total porosity of 61.25% ± 0.29 were successfully produced. The structure of the foams produced was characterized using SEM and X-ray micro-computed tomography