Structure and mechanical properties of reaction-sintered ceramic composite materials based on titanium and hafnium diborides

The structure and mechanical characteristics of ceramic composite materials based on titanium and hafnium diborides produced by reaction sintering in the course of hot pressing have been studied. It has been shown that ultradispersed structure is responsible for high mechanical characteristics of the synthesized composites.     

Porous titanium implant materials and their potential in orthopedic surgery

In orthopedic surgery bony defects remains a challenge. In generally autologous or heterologous bony transplants can be used. Main problem is the limited amount of bone and donor site morbidity. Nowadays excellent implants and scaffolds at low costs are necessary in respect to the financial problems in our health care system and the strong financial limitations in clinical medicine. Recently a biomimetic approach, in which a porous synthetic bone substitute with properties similar to these of trabecular bone has been developed (VITOFOAM?). Aim of our study was to investigate whether cp‐Ti or Ti6Al4V or stainless steel (316L) porous metal implants achieve material properties comparable to bone. Materials and Methods Three cp‐Ti, Ti6Al4V and stainless steel (316L) porous metal specimen each with a pore size of 150 to 600 μm have been tested in respect to determine the Young’s Modulus E (GPa), Compression Strength (MPa) and Porosity (%) under axial compression. Results Young’s Modulus of the cp‐ Ti samples was in the range of 1.2 to 2.8 GPa, for Ti6Al4V 2.3 to 4.1 GPa could be achieved. Compression Strength for cp‐ Ti and Ti6Al4V ranged from 30 to 65 MPa with porosity values ranged from 71 to 80 %. Discussion The highly porous nature of VITOFOAM? combined with the good biocompatibility of cp‐ Ti or Ti6Al4V and the mechanical properties make these materials ideal bone scaffolds. Trabecular bone shows pore sizes of 300–1500 μm, Young’s Modulus of 0.2–2 GPa and Compression Strength from 5–50 MPa. Porosity of spongious bone ranges from 30 to 95 %. These values are comparable to the values achieved with VITOFOAM?. Porous titanium foam with its osteoconductive properties may therefore be an ideal and cheap alternative. Implant costs can be lowered to 50 % for implants e.g. for intercorporal interbody fusion in spinal surgery. Actually further research is done to show the possibility in spinal surgery or loading technologies with Tricalciumphosphat, Hydroxylapatit, Antibiotics or Cytostatics.     

Processing and characterization of functionally graded materials through mechanical properties and glass transition temperature

Functionally graded materials (FGMs) were prepared by construction based layering method through dispersion of carbon nanoparticles in the styrene butadiene rubber matrix. The gradation of material property i.e., ‘glass transition temperature’ was brought in the nanocomposite by varying the concentration of process oil. Glass transition temperature (T_g) of FGMs was varied from − 56 to − 80 °C along the span of 3 mm thick sheet. The gradation of oil in FGMs also changes other properties like tensile strength, elongation at break, modulus, etc. Tensile strength and modulus at 100% drops down while elongation at break continuously increases while moving from one end to other end along the sheet thickness. Thermal analysis of FGMs verifies the compositional changes as well as the change in T_g along the thickness.     

Direct metal fabrication of titanium implants with tailored materials and mechanical properties using electron beam melting technology

The design of custom or tailored implant components has been the subject of research and development for decades. However, the economic feasibility of fabricating such components has proven to be a challenge. New direct metal fabrication technologies such as Electron Beam Melting (EBM) have opened up new possibilities. This paper discusses the design and fabrication of titanium implant components having tailored mechanical properties that mimic the stiffness of bone to reduce stress shielding and bone remodeling. Finite Element Analysis was used to design the tailored structures, and results were verified using mechanical testing.     

Development of laminated composite materials based on orthorhombic aluminide/titanium alloy and their tensile mechanical properties

Abstract

Laminated composite materials consisting of an orthorhombic Ti₂AlNb based alloy and an (α+β) titanium alloy have been fabricated at a laboratory scale using a two-step process involving diffusion bonding and hot rolling. The feasibility of fabrication of two and three layered materials with high quality bonding between layers was demonstrated. Preliminary assessment of the tensile mechanical properties of the obtained composite materials showed that they were superior to those of the titanium alloy and slightly inferior to the orthorhombic alloy.     

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.     

Biological materials: Structure and mechanical properties

Most natural (or biological) materials are complex composites whose mechanical properties are often outstanding, considering the weak constituents from which they are assembled. These complex structures, which have risen from hundreds of million years of evolution, are inspiring Materials Scientists in the design of novel materials.Their defining characteristics, hierarchy, multifunctionality, and self-healing capability, are illustrated. Self-organization is also a fundamental feature of many biological materials and the manner by which the structures are assembled from the molecular level up. The basic building blocks are described, starting with the 20 amino acids and proceeding to polypeptides, polysaccharides, and polypeptides-saccharides. These, on their turn, compose the basic proteins, which are the primary constituents of ‘soft tissues’ and are also present in most biominerals. There are over 1000 proteins, and we describe only the principal ones, with emphasis on collagen, chitin, keratin, and elastin. The ‘hard’ phases are primarily strengthened by minerals, which nucleate and grow in a biomediated environment that determines the size, shape and distribution of individual crystals. The most important mineral phases are discussed: hydroxyapatite, silica, and aragonite.Using the classification of Wegst and Ashby, the principal mechanical characteristics and structures of biological ceramics, polymer composites, elastomers, and cellular materials are presented. Selected systems in each class are described with emphasis on the relationship between their structure and mechanical response. A fifth class is added to this: functional biological materials, which have a structure developed for a specific function: adhesion, optical properties, etc.An outgrowth of this effort is the search for bioinspired materials and structures. Traditional approaches focus on design methodologies of biological materials using conventional synthetic materials. The new frontiers reside in the synthesis of bioinspired materials through processes that are characteristic of biological systems; these involve nanoscale self-assembly of the components and the development of hierarchical structures. Although this approach is still in its infancy, it will eventually lead to a plethora of new materials systems as we elucidate the fundamental mechanisms of growth and the structure of biological systems.     

Electrospun titanium dioxide nanofibers containing hydroxyapatite and silver nanoparticles as future implant materials

In this study, a good combination consisting of electrospun titanium dioxide (TiO₂) nanofibers incorporated with high purity hydroxyapatite (HAp) nanoparticles (NPs) and antimicrobial silver NPs is introduced for hard tissue engineering applications. The synthesized nanofibers were characterized by various state of art techniques like; SEM, XRD, TEM, TEM EDS and XPS analyses. SEM results confirmed well oriented nanofibers and good dispersion of HAp and silver NPs, respectively. XRD results demonstrated well crystalline feature of three components used for electrospinning. Silver NPs were having a diameter in range of 5–8 nm indicated by TEM analysis. Moreover, TEM EDS analysis demonstrated the presence of each component with good dispersion over TiO₂ nanofiber. The surface analyses of nanofibers were investigated by XPS which indicated the presence of silver NPs on the surfaces of nanofibers. The obtained nanofibers were checked for antimicrobial activity by using two model organisms E. coli and S. aureus. Subsequently, antimicrobial tests have indicated that the prepared nanofibers do posses high bactericidal effect. Accordingly, these results strongly recommend the use of obtained nanofiber mats as future implant materials.     

Evaluation of channel-like porous-structured titanium in mechanical properties and osseointegration

The porous titanium with a channel-like pore structure fabricated by infiltration casting followed by selectively dissolving the precursor woven three dimensional(3 D) structure technique was comprehensively investigated by means of mechanical tests, in vitro and in vivo evaluation. Such porous structure exhibited superiority in compressive, tensile strength and osseointegration. At 40% porosity, the average compressive and tensile strength reached about 145 MPa and 85 MPa, which was superior to that of other porous titanium, e.g., Selective Laser Melting or powder sintered ones, and was comparable to that of the human cortical bone. Without any bioactive surface treatment, this porous titanium exhibited good cell adhesion, rapid cell proliferation and excellent osseointegration. Based on the study, the 0.4 mm pore size resulted in the most rapid cell proliferation and the maximal BV/TV ratio and trabecular bone number of the new bone that ingrew into the porous titanium. To balance the excellent osseointegration and adequate mechanical properties, the optimal structural parameters were 0.4 mm pore size with40% porosity. This porous titanium is very promising for orthopedic applications where compressive and tensile load-bearing is extremely important.     

Microstructure and mechanical properties of brazed titanium/steel joints

Microstructure and fracture behavior of brazed joint between commercially pure titanium and low carbon steel using silver (Ag–34Cu–2Ti) and copper (Cu–12Mn–2Ni) based alloys have been characterized to determine the effect of brazing parameters and chemical composition on the strength of brazed joints. It is found that the shear strength of brazed joints strongly depends on the lap width. Furthermore, the fracture path and the value of shear strength significantly changed with the type of filler alloy. The two filler metals showed metallurgical interaction with steel and titanium forming different kinds of intermetallic compounds such as CuTi, Cu2Ti, and FeTi with silver based filler and Ti2Cu, FeTi and TiCuFe with copper based filler.     

Microstructure and mechanical properties of a high nitrogen titanium alloy

High nitrogen titanium alloy with the chemical composition of Ti–4%Cr–0.6%N was produced by solution nitriding to nitrogen-free Ti–4%Cr alloy, and then its microstructure was controlled to have fine (α + β) dual phase structure by aging treatment to improve the ductility. As solution-nitrided specimen has a platelet hcp-martensitic structure (α′) and is characterized by hard but brittle nature that has been produced by solid solution of 0.6% of nitrogen. On the following aging treatment, fine β phase formed along the original plate boundaries, resulting in a fine (α + β) dual phase microstructure. X-ray and EELS analyses revealed that nitrogen is greatly concentrated in the tempered α′ phase. Although the hardness of as-quenched material gradually decreases during the aging treatment with increasing volume fraction of β, the hardness can be kept much higher than that of the aged Ti–4%Cr alloy without nitrogen. As a result of tensile testing, it was found that the aged Ti–4%Cr–0.6%N alloy has high tensile strength over 1 GPa with moderate ductility.     

Formation of mechanical properties of powdered materials

The assumption that the boundaries of bonds are the sources of load transmission from particle to particle describes the reasons of anisotropy of the properties of semifinished products with nonequiaxial particles and points out the directions of improvement of their properties by enhancing the quality of the boundary.Translated from Problemy Prochnosti. No. 8, pp. 64–67, August, 1990.     

A histomorphometric comparison of the muscular tissue reaction to stainless steel,pure titanium and titanium alloy implant materials

Thein vivo tissue reaction to titanium and titanium-based alloys using quantitative histomorphometry was investigated. According to the guidelines for biomaterials testing suggested by ISO, 2 mm × 6 mm cylindrical specimens of chemically pure (CP) Ti, TiO₂, electrolytically coated Ti, Ti6Al4V, TiO₂-coated Ti6Al4V, TiN physical vapour deposition-coated Ti6Al4V and Ti5Al2.5Fe were implanted in the paravertebral muscles of rats, for 1–52 weeks, 316L stainless steel being used as a control implant material. After PMMA embedding, electrochemical dissolution of the implants, microtome sectioning and Masson's trichrome staining, the tissue reaction was assayed using a semi-automatic method based on the digitization of both the encapsulating membrane contours and the different cell types located within it. All materials induced a close tissue reaction. There was no statistical difference between the tested materials regarding the time-evolution of the inflammatory cells. However, when comparing CP Ti with 316L, a significant difference was found in the fibrocyte kinetics: in the short term, fibrocyte densities were lower for 316L, while beyond 12 weeks, they exhibited higher values than CP Ti. To a lesser extent, a similar observation was made when comparing CP Ti with Ti5Al12.5Fe. No statistical difference was found in the comparison of CP Ti with Ti6Al4V. The membrane thickness was identical for all tested materials and appeared not to be time-dependent.     

Numerical simulation of entangled materials mechanical properties

A general approach to simulate the mechanical behaviour of entangled materials submitted to large deformations is described in this paper. The main part of this approach is the automatic creation of contact elements, with appropriate constitutive laws, to take into account the interactions between fibres. The construction of these elements at each increment, is based on the determination of intermediate geometries in each region where two parts of beams are sufficiently close to be likely to enter into contact. Numerical tests simulating a 90% compression of nine randomly generated samples of entangled materials are given. They allow the identification of power laws to represent the evolutions of the compressive load and of the number of contacts.     

Nanostructural metallic materials: Structures and mechanical properties

The trade-off of strength and ductility of metals has long plagued materials scientists. To resolve this issue, great efforts have been devoted over the past decades to developing a variety of technological pathways for effectively tailoring the microstructure of metallic materials. Here, we review the recent advanced nanostructure design strategies for purposely fabricating heterogeneous nanostructures in crystalline and non-crystalline metallic materials. Several representative structural approaches are introduced, including (1) hierarchical nanotwinned (HNT) structures, extreme grain refinement and dislocation architectures etc. for crystalline metals; (2) nanoglass structure for non-crystalline alloys, i.e. metallic glasses (MGs); and (3) a series of supra-nano-dual-phase (SNDP) nanostructures for composite alloys. The mechanical properties are further optimized by manipulating these nanostructures, especially coupling multiple advanced nanostructures into one material. Particularly, the newly developed SNDP nanostructures greatly enrich the nanostructure design strategies by utilizing supra-nano sized crystals and MGs, which exhibit unique size and synergistic effects. The origins of these gratifying properties are discussed in this review. Furthermore, based on a comprehensive understanding of microscopic mechanisms, a broad vision of strategies towards high strength and high ductility are proposed to promote future innovations.     

Microstructure and properties of ultrafine-grained and dispersion-strengthened titanium materials for implants

Wear-resistant titanium materials with high hardness and strength can be manufactured by introducing very fine titanium silicides and carbides into an ultrafine-grained titanium matrix. Nanocrystalline titanium particles with fine and homogeneous distributed carbon and silicon were generated by high energy ball milling of titanium with silicon powder or additions of the organic fluid hexamethyldisilane (HMDS). Spark Plasma Sintering (SPS) was chosen to compact the granules to prevent grain coarsening during sintering. Additionally, the Ti₅Si₃ and TiC _x dispersoids limited grain coarsening. After sintering, the novel materials exhibited high hardness and strength, and excellent wear resistance. The electrochemical behaviour (comparable to that of commercially pure titanium) was also tested and showed the excellent suitability as an implant material.