Numerical simulation of resistance sintering of titanium by a porous continuum approach

This paper presents a numerical model for the simulation of resistance sintering. It involves an electro-thermo-mechanical coupling, where each model is simulated as a continuum with the influence of porosities included through the distribution of relative density, i.e. the ratio of the apparent density to that of the corresponding fully dense bulk material. For the mechanical response, this involves a plasticity model based on a porous formulation. Other material data have to be supplied as a function of relative density and temperature, as for example the electrical resistivity. The numerical modeling is compared to experimentally resistance sintered titanium with good agreement in terms of pre-compaction and developed relative density and temperature during the sintering process.

Influence of molybdenum content on the microstructure of spark plasma sintered titanium alloys

Five titanium-based alloys containing 4, 8, 12, 16, and 20 wt% molybdenum additive were fabricated by spark plasma sintering process at 1200 ˚C. The samples were scrutinized in terms of relative density, phase evolution, and microstructural development. The relative density reached 99.9% with the molybdenum addition up to 16 wt% but slightly dropped in the sample with 20 wt% additive. In the specimens with 4 wt% Mo, molybdenum solved completely in the matrix and three different phase morphologies were observed, namely continuous α-Ti, laminar α-Ti, and very thin laminar β-Ti. With increasing Mo content to 20 wt%, widespread single β-Ti appeared alongside remained Mo and α-Ti. Ductile fracture mode was dominant in the samples with low Mo contents whilst it changed to brittle in the specimens with higher content of molybdenum.

3D Biomimetic Porous Titanium (Ti6Al4V ELI) Scaffolds for Large Bone Critical Defect Reconstruction: An Experimental Study in Sheep

The main goal in the treatment of large bone defects is to guarantee a rapid loading of the affected limb. In this paper, the authors proposed a new reconstructive technique that proved to be suitable to reach this purpose through the use of a custom-made biomimetic porous titanium scaffold. An in vivo study was undertaken where a complete critical defect was experimentally created in the diaphysis of the right tibia of twelve sheep and replaced with a five-centimeter porous scaffold of electron beam melting (EBM)-sintered titanium alloy (EBM group n = 6) or a porous hydroxyapatite scaffold (CONTROL group, n = 6). After surgery, the sheep were allowed to move freely in the barns. The outcome was monitored for up to 12 months by periodical X-ray and clinical examination. All animals in the CONTROL group were euthanized for humane reasons within the first month after surgery due to the onset of plate bending due to mechanical overload. Nine months after surgery, X-ray imaging showed the complete integration of the titanium implant in the tibia diaphysis and remodeling of the periosteal callus, with a well-defined cortical bone. At 12 months, sheep were euthanized, and the tibia were harvested and subjected to histological analysis. This showed bone tissue formations with bone trabeculae bridging titanium trabeculae, evidencing an optimal tissue-metal interaction. Our results show that EBM-sintered titanium devices, if used to repair critical bone defects in a large animal model, can guarantee immediate body weight-bearing, a rapid functional recovery, and a good osseointegration. The porous hydroxyapatite scaffolds proved to be not suitable in this model of large bone defect due to their known poor mechanical properties.

Microstructural, Tribology, and Densification Studies of Spark Plasma Sintered Titanium Matrix Composites Reinforced with Silicon Carbide

Spark plasma sintered titanium matrix composites (TMCs) with varying SiC contents were fabricated at 900 o C, 150 o C/min, 30 MPa, and with 5 min of holding time, and were studied for structural, mechanical and tribology performances. The phase identification and microstructure analysis of the sintered specimens were examined using X-ray diffraction and scanning electron microscope equipped with EDS. The results indicate that influence of the varied SiC content dictate the physical properties of the sintered TMCs. The densification study showed that relative density was inversely related, while Vickers hardness value was directly proportional (238.84 Hv at 1 wt. % SiC and 361.81 Hv 6 wt. % SiC). The tribology study showed that both wear rate and coefficient of friction have inverse relationship while wear resistance has a direct trend with the composite reinforcement. Sample TiNiAl – 6 wt. % SiC, with the optimum composition had the best wear performance under the constant load of 20 N. This wear performance can be attributed to the good interfacial bond formed between the TiNiAl matrix and the SiC reinforcement in the developed composites contributed from the synergetic processing conditions of the SPS process.