Sintering Of Titanium Research Articles

Sintering of Porous Titanium Using the Spark Plasma Sintering Technique for Application as a Joint Prosthesis

Sintering of Porous Titanium Using the Spark Plasma Sintering Technique for Application as a Joint Prosthesis

Fabrication of high-performance Magnéli phase Ti4O7 ceramics by in-situ hot-pressed sintering in a single step

Magnéli phase ceramics have gained extensive attention in a variety of fields, including batteries, electrocatalysis, and wastewater treatment, due to their distinctive properties. In this study, high-performance Magnéli phase Ti4O7 ceramics were synthesized by in-situ hot-pressed sintering of titanium (Ti) and titanium dioxide (TiO2) in a single step. The effects of the sintering temperature and Ti content on the phase transformation and morphology of ceramics were investigated. Moreover, the mechanical properties and electrical conductivity of the samples were systematically characterized. Results show that the sample with the Ti/TiO2 weight ratio of 0.09 sintered at 1000 °C has impressive comprehensive properties, including a high bulk density of 4.281 g·cm−1, a mean value of flexural strength of 125.58 MPa, and an excellent conductivity of 1129 S·cm−1. Furthermore, an evolution mechanism of the in-situ sintering for Ti/TiO2 was discussed based on the experimental data, and the pattern of variation observed by samples can be reasonably explained.

Mechanism of thermal gradients in spark plasma sintering of titanium and the resultant graded microstructure: A novel strategy of incorporating master sintering curve into finite element modeling

Spark plasma sintering (SPS) is an efficient consolidation process for metals and ceramics because of its high heating rates, lower sintering temperatures and shorter holding time than other sintering processes. To understand and utilize the thermal gradients that occur in SPS, the present work developed a strategy to incorporate master sintering curve (MSC) into a thermal-electric (TE) finite element modeling (FEM) to enable continuous nodal-specific simulation of the evolution of thermal and electrical properties of the powder compact with respect to both relative density and temperature during SPS. This combined model is proposed as an alternative to the thermal-electric-mechanical fully coupled model that is more computationally expensive and difficult to parameterize experimentally. Pure Ti was selected as the material for experimental verification because of its technological importance for aerospace and defense applications. While lab-scale Ti samples were sintered for construction and validation of MSC, a scaled-up Ti sample with diameter of 70 mm was made via SPS, and its microstructure were characterized to verify the accuracy of the MSC - TE FEM combined model. Both modeling and experimental results showed that the local relative density of the pure Ti decreased as the location moved radially from center to surface. The location-specific relative densities predicted by the combined model were within ±1.5% deviation from the experimental results, which verified the ability and accuracy of the MSC-TE FEM combined model to guide experimental design and parameter selection for control and utilization of gradients in SPS to achieve graded microstructure. • SPS of pure Ti has an apparent sintering activation energy of of 156.5 kJ/mol • Master sintering curve is incorporated into FEM for improved prediction of gradients • The accuracy of MSC-FEM combined model is experimentally validated • Deviation between the experimental and simulated results are <1.5%

Numerical Simulation of Resistance Sintering of Titanium by a Porous Continuum Approach

AbstractThis 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.

Sintering High Green Density Direct Powder Rolled Titanium Strips, in Argon Atmosphere

Presently, the majority of titanium powder metallurgy components produced are sintered under high vacuum due to the associated benefits of the vacuum atmosphere. However, high-vacuum sintering is a batch process, which limits daily production. A higher daily part production is achievable via a continuous sintering process, which uses argon gas to shield the part from air contamination. To date, there has been limited work published on argon gas sintering of titanium in short durations. This study investigated the properties of thin high green density titanium strips, which were sintered at the temperatures of 1100 °C, 1200 °C and 1300 °C for a duration of 30 min, 60 min and 90 min in argon. The strips were produced by rolling of −45 µm near ASTM (American Society for Testing and Materials) grade 3 hydride–dehydride commercially pure titanium powder. The density, hardness, tensile properties and microstructure of the sintered strips were assessed. It was found that near-full densities, between 96 and 99%, are attainable after 30–90 min of sintering. The optimum sintering temperature range was found to be 1100–1200 °C, as this produced the highest elongation of 4–5.5%. Sintering at 1300 °C resulted in lower elongation due to higher contaminant pick-up.

Sintering of titanium in argon and vacuum: Pore evolution and mechanical properties

Reducing porosity can help to improve the mechanical properties of an as-sintered material. An alternative is, however, to tailor the size, distribution and morphology of the residual pores without having to further reduce porosity. This study investigates the sintering of commercially pure titanium (CP Ti) in a flowing argon (Ar) atmosphere and compares the results with sintering in a vacuum of 10−2 Pa. The CP Ti sintered in Ar at 1300 °C for 2–3 h exhibited a marginally lower density but clearly better tensile ductility than Ti sintered in vacuum. The sensitivity of tensile ductility to residual pores was analyzed. Samples sintered in Ar exhibited much lower sensitivity than those sintered in vacuum. The superior ductility arises from the beneficial effect of sintering in Ar, which resulted in a greater number of but smaller residual pores with lower pore aspect ratios and finer matrix grains due to the grain-growth inhibiting role of the residual pores. The reason is attributed to the entrapped Ar in the closed pores during sintering, which is insoluble in Ti at the sintering temperature. The ever-increasing internal pore pressure prevents further pore shrinkage after reaching a critical size. The final pore size range is predicted and compared with experimental observations. Sintering of titanium in Ar is advantageous over sintering in vacuum in terms of both pore size distribution and pore morphology within a reasonable isothermal sintering period (e.g., 3 h at 1300 °C). Therefore, it can be more attractive for non-fatigue critical applications than sintering in vacuum.

Molecular dynamics study of temperature and heating rate–dependent sintering of titanium nanoparticles and its influence on the sequent tension tests of the formed particle-chain products

Sintering of multiple single-crystal titanium (Ti) nanoparticles (NPs) during additive manufacturing by using ultrafast laser was simulated using molecular dynamics (MD). The aim was to better understand how factors such as sintering temperature and heating rate would influence the mechanical properties of the ultrafine-sized sintered products, i.e., Ti “NP-chains.” For this purpose, the effects of heating and strain rate on the tensile behavior of the final sintered products were studied in detail. Ti NP-chain precursors with weak neck connections were first created through solid-state sintering process at room temperature. They were later heated very rapidly to 800 K, 1200 K, or 1500 K with two different heating rates of 0.04 K/ps and 0.2 K/ps, and maintained at these high-temperature levels for 1 ns to mimic the fast temperature rise and short equilibration due to femtosecond/picosecond laser irradiation. The formed Ti NP-chains with different neck connection strengths were then cooled to 298 K. Those final NP-chains were subjected to uniaxial tension at three different strain rates of 0.001%/ps, 0.01%/ps, and 0.1%/ps. Our simulation results indicate a strong correlation between the tensile strength of the final NP-chain product and the heating rate during the previous short sintering process (including the ultrafast temperature rise and up to 1-ns high-temperature equilibration). A slower heating rate to a higher temperature level yields larger neck connection diameters in the final NP-chain product, resulting a higher tensile strength. Furthermore, our results demonstrate that high strain rates applied to the NP-chains with stronger neck connections result in an improvement in the tensile strength and ductility of the final products. In contrast, sintered products resulting from a lower temperature level show an elastic-brittle-damage behavior. Due to the weak neck connections and limited crystal sliding, the heating rate effect during sintering does not have a significant effect on the tensile strength.

Molten salt shielded synthesis of oxidation prone materials in air.

To prevent spontaneous oxidation during the high-temperature synthesis of non-oxide ceramics, an inert atmosphere is conventionally required1,2. This, however, results in high energy demand and high production costs. Here, we present a process for the synthesis and consolidation of oxidation-prone materials, the 'molten salt shielded synthesis/sintering' process (MS3), which uses molten salts as a reaction medium and also to protect the ceramic powders from oxidation during high-temperature processing in air. Synthesis temperatures are also reduced, and the final product is a highly pure, fine and loose powder that does not require additional milling steps. MS3 has been used for the synthesis of different ternary transition metal compounds (MAX phases, such as Ti3SiC23, Ti2AlN4, MoAlB5), binary carbides (TiC) and for the sintering of titanium. The availability of high-quality powders, combined with energy and cost savings, may remove one of the bottlenecks for the industrial application of these materials.

Properties of NiTi Shape Memory Alloy Micro-Foils Obtained by Pulsed-Current Sintering of Ni/Ti Foils

Successful one-step manufacturing of micro-foils of NiTi shape memory compound by pulsed-current sintering of nickel and titanium is reported. Sandwich-like starting configurations of Ni/Ti/Ni (ST1, ST4), Ti/Ni/Ti (ST3), and a simple Ni/Ti (ST2) one, were used. XRD and differential scanning calorimetry (DSC) measurements revealed multistep martensitic transformation, much more pronounced for ST1 than for ST2 and ST3. SEM/energy dispersive X-ray spectrometer (EDS) measurements showed the predominant NiTi phase in ST1, ST4, and other intermetallic compounds in addition to it, for ST2 and ST3. The temperature dependence of the electrical resistance for ST4 shows a peak corresponding to the R-phase and a high residual resistivity. The shape memory effect of 100% was obtained for ST1 and ST4, with the temperature range of its recovery dependent on the initial strain. The ST2 and ST3 materials revealed brittleness and a lack of plasticity due to the dominancy of the austenite phase and/or the intermetallic compound content.

Lattice Microarchitecture for Bone Tissue Engineering from Calcium Phosphate Compared to Titanium.

Additive manufacturing of bone tissue engineering scaffolds will become a key element for personalized bone tissue engineering in the near future. Several additive manufacturing processes are based on extrusion where the deposition of the filament will result in a three-dimensional lattice structure. Recently, we studied diverse lattice structures for bone tissue engineering realized by laser sintering of titanium. In this work, we used lithography-based ceramic manufacturing of lattice structures to produce scaffolds from tricalcium phosphates (TCP) and compared them in vivo to congruent titanium scaffolds manufactured with the identical computer-aided design data to look for material-based differences in bony healing. The results show that, during a 4-week period in a noncritical-size defect in a rabbit calvarium, both scaffolds with the identical microarchitecture performed equally well in terms of bony regeneration and bony bridging of the defect. A significant increase in both parameters could only be achieved when the TCP-based scaffolds were doped with bone morphogenetic protein-2. In a critical-size defect in the calvarial bone of rabbits, however, the titanium scaffold performed significantly better than the TCP-based scaffold, most likely due to its higher mechanical stability. We conclude that titanium and TCP-based scaffolds of the same microarchitecture perform equally well in terms of bone regeneration, provided the microarchitecture meets the mechanical demand at the site of implantation.

Enhanced Homogenization of Vanadium in Spark Plasma Sintering of Ti-10V-2Fe-3Al Alloy from Titanium and V-Fe-Al Master Alloy Powder Blends

Strong and ductile powder metallurgy (PM) Ti-10V-2Fe-3Al alloy has been fabricated by spark plasma sintering (SPS) of titanium and V-Fe-Al master alloy powder blends at 1100°C for 30 min under 30 MPa. The homogenization of vanadium, which dictates the realization of a uniform microstructure of the Ti-10V-2Fe-3Al alloy, was markedly accelerated by SPS. The mechanism is attributed to the intensive Joule heating effect produced by the direct current passing through the electric conducting powder blends, rather than through spark plasma discharge, because homogenization occurred mainly after near full identification had been achieved. The chemical and microstructural homogeneity ensured the achievement of excellent tensile properties of PM Ti-10V-2Fe-3Al in the as-sintered state, with tensile strength >1250 MPa and elongation >10%.

Sintering of HDH Ti powder in a solar furnace at Plataforma Solar de Almeria

The brand new technology for sintering of titanium was tested: For the first time, titanium powder was pressure less sintered under argon atmosphere at different temperatures and time, in 5 kW vertical axis solar furnace at Plataforma Solar de Almeria (PSA), Spain. The decrease of final porosity with increasing sintering temperature and time at constant heating rate is observed. The obtained results are compared with those obtained for identical green powder compacts sintered in vacuum furnace. Final porosity below 5% was achieved and shorter sintering times were observed. Radial shrinkage of samples at solar furnace is almost the same as at vacuum furnace. On the contrary axial shrinkage is 20% higher. It was proposed that this can be attributed to argon gas used during sintering and due to the different heating in solar furnace during sintering. Argon at lower temperature acts as a heat transfer medium and helps to distribute the heat more homogeneously into the powder compacts. At higher temperature it remains enclosed in the pores thereby increasing a bit final compact porosity when compared with vacuum furnace. It was further showed that the contents of O, N, H in final compacts depend predominantly on their concentration in original powder. The observed increase due to technology is 300 ppm for oxygen and 80 ppm for nitrogen. Hydrogen concentration decreased significantly. Microhardness dependence on porosity of prepared samples was also investigated and microhardness of bulk Ti prepared in solar furnace was estimated to be 282.2 ± 28.3 HV0.5.

Temperature Calculation for Laser Sintering of Titanium and Niobium Taking into Account Properties Change due to Powder Layer Shrinkage

The model of laser sintering with regard to explicit porosity evolution of powder layer has been suggested. Due to porosity reduction the shrinkage occurs, thermal - physical properties (the heat capacity, thermal conductivity coefficient) and reflection coefficient of laser irradiation change. It has been shown that additional mechanism of convective heat transfer connects with powder layer thickness evolution. It was detected that model obeys some prognostic properties and allows to reveal the area of technological parameters where homogeneous properties of sintered layer form.

Press and Sintering of Titanium

Titanium based alloys show very high strength to density ratio, and could be the choice of material for a wide range of applications. By practicing press and sintering for production of Ti components, high materials utilization can be assured, and at the same time costly machining operations can be limited. Difficulties in processing and high cost for powders have been limiting factors for progress, but recent development indicates good possibilities on cost effective use of TiH2 powder in the press and sintering segment. In this paper, influence of processing parameters and powder properties on final sintered component properties are discussed.

Phase Content of Interfaces Ti/Al3Ti in Metal-intermetallic Laminate Studied by x-ray and Synchrotron Diffraction

The present investigation focuses on the phase content of micron composite layers studied by x-ray and synchrotron diffraction. The Ti–Al3Ti composite has been produced by reaction sintering of titanium and aluminum foils under pressure. Sintering was finished when Al layer was fully consumed to form an intermetallic Al3Ti. X-ray diffraction (Bragg-Brentano geometry with a flat-plate sample) showed that composite layers basically contain only Ti and Al3Ti phases. Synchrotron diffraction allowed to reveal the presence of residuals of Al phase. Diffraction experiments were performed at the SR beamline №4 of the VEPP-3 storage ring. The frame capture mode with the use of the synchrotron beam, 0.4×0.1 mm, allowed proving the absence of Al2O3 phase particles along the Ti/Al3Ti interfaces.

Fracture toughness of Ti–Al3Ti–Al–Al3Ti laminate composites under static and cyclic loading conditions

The static and cyclic fracture toughnesses of a Ti–Al3Ti–Al–Al3Ti laminate composite material containing at most 15 vol % intermetallic compound are studied. Composite specimens are prepared by terminating reaction sintering of titanium and aluminum foils under pressure. The fracture of the titanium layers is quasi-cleavage during cyclic crack growth and is ductile during subsequent static loading.

Formation of Intermetallic Structures by Spark Plasma Sintering of Titanium and Aluminum Powders

Sintered compacts fabricated by spark plasma sintering (SPS) at 1050оС were investigated. Titanium and aluminum powders in a ratio of 25 % (at.) and 75 % (at.) respectively were chosen as starting materials. Powder mixture heating up to elevated temperatures led to a partial loss of an aluminum component and to the formation of a multiphase structure consisting of Al3Ti, Al2Ti, AlTi and AlTi3. The density of sintered powder mixtures was 3.7 g/cm3; an average microhardness value was about 470 HV.

Metal-Intermetallic Laminate Ti-Al3Ti Composites Produced by Spark Plasma Sintering of Titanium and Aluminum Foils Enclosed in Titanium Shells

Metal-intermetallic laminate composites are considered as promising materials for application in the aerospace industry. In this study, Ti-Al3Ti composites enclosed in titanium cases were produced by reactive spark plasma sintering. Sintering was carried out at 1103 K and 1323 K (830 °C and 1050 °C) for 10 minutes. In both cases, high-quality Ti-Al3Ti composites containing thin transition layers at the interfaces were obtained. Al2Ti, AlTi, and AlTi3 intermetallic phases and a solid solution of aluminum in titanium were observed in the transition layers by scanning and transmission electron microscopy. The material sintered at 1323 K (1050 °C) had higher strength in comparison with the composite obtained at 1103 K (830 °C). However, the hardness of the intermetallic component in the sample sintered at higher temperature decreased due to the grain growth. The impact toughness values of both materials were approximately identical.

Processing of Titanium and its Alloys by Microwave Energy

Microwave sintering of titanium and its alloys is a recent development in powder metallurgy of titanium. The sintering in an atmospheric pressure argon gas environment or vacuum is potentially cost effective and energy efficient compared to conventional sintering methods due to the possibility of direct microwave heating of the titanium powder via in-depth energy deposition augmented by hybrid heating in a ceramic casket. The in-depth heating permits very rapid processing (cycle times of potentially less than 10 minutes) which is intended to preserve a very fine grain structure in the final product resulting in excellent mechanical properties and the possibility of superplastic forming. We are investigating this approach using an S–Band microwave system. The process can be also used for composites, laminates, direct alloying, and functionally gradient materials. Evaluations to optimize different parameters for controlling the final density, microstructure, and properties of these materials are underway and results are discussed.

The effect of lanthanum boride on the sintering, sintered microstructure and mechanical properties of titanium and titanium alloys

An addition of ≤0.5 wt% lanthanum boride (LaB6) to powder metallurgy commercially pure Ti (CP-Ti), Ti–6Al–4V and Ti–10V–2Fe–3Al (all in wt%) resulted in improved sintered density, substantial microstructural refinement, and noticeably increased tensile elongation. The addition of LaB6 led to scavenging of both oxygen (O) and chlorine (Cl) from the titanium powder during sintering, evidenced by the formation of La2O3 and LaClxOy. The pinning effect of La2O3, LaClxOy and TiB inhibited prior-β grain growth and resulted in subsequent smaller α-laths. The formation of nearly equiaxed α-Ti phase is partially attributed to the nucleation effect of α-Ti on TiB. The improved sintered density was caused by B from LaB6 rather than La, while excessive formation of La2O3 and TiB with an addition of >0.5 wt% LaB6 resulted in a noticeable decrease in sintered density. The improved tensile elongation with an addition of ≤0.5 wt% LaB6 was mainly attributed to the scavenging of oxygen by LaB6, partially assisted by the improved sintered density. However, an addition of >0.5 wt% LaB6 led to the formation of large La2O3 aggregates and more brittle TiB whiskers and therefore decreased tensile elongation. Balanced scavenging of O is thus important. The optimal addition of LaB6 was 0.5 wt% but this may change depending on the powder size of the LaB6 to be used.