Ti Compacts Research Articles

Impact of hot rolling on the evolution of microstructure and mechanical properties of sintered commercially pure Ti compacts

While titanium (Ti) alloys offer significant advantages, such as high strength and corrosion resistance, their widespread utilization in various engineering sectors is hindered by their prohibitively high cost, which is attributed to expensive equipment and complex preparation processes. The present study centered on assessing the influence of multi-pass hot rolling, a commonly available industrial process, on the microstructure and mechanical properties of sintered powder metallurgy commercially pure Ti (cp-Ti). With increasing levels of accumulated deformation, the rolled materials exhibited a refined grain size, the formation of twins, and a reduced residual porosity, resulting in a tailored microstructure that enhanced the material's balance between strength and ductility. The ultimate tensile strength reached 574.8 MPa, with an elongation at break of 28.1%. The hardness peaked at 196.4 HV.

Electrical discharge consolidation of Al and Ti powders

In this paper, electrical-discharge-consolidation (EDC technique) experiments were carried out with an equipment based on the technology developed for the stud welding technology. The main advantage of the EDC technique is its high speed, on the order of milliseconds or less, which makes it particularly interesting when a high final porosity is aimed, or when the inherent nanostructure of the powders needs to be preserved. Compacts of Ti and Al were consolidated with this technique, both directly from loose powders and from cold pressed green compacts. Two different configurations (200 V – 66 mF and 800 V − 1.1 mF) were tested. Relative density, microhardness, electrical resistivity and metallographic and SEM studies were carried out to understand the changes in powder particles caused by the electrical discharge. The use of a high capacitance in the capacitors bank, despite the use of a lower voltage, results in a better consolidation process.

Concentrated solar power used in preparation of Ti – B4C composites

Concentrated solar power was employed to sinter compacts of Ti + 15 vol% B4C powder mixture. The sintering experiments were performed under protective argon atmosphere at different temperatures and sintering time without external pressure. The sintering experiments were done in 40 kW horizontal solar furnace (SF40) at Plataforma Solar de Almeria (PSA), Spain.The in situ sintering behavior of the Ti – B4C mixture is significantly affected by exothermic reaction of titanium with B4C. In the solar furnace the ignition temperature of this reaction was found to be around 1380 °C. Therefore, the exothermic reaction of Ti + B4C makes the controlling of the solar sintering of these composites very difficult.The optimal temperature of solar sintering was found slightly below 1340 °C for 30 min. No significant reduction of porosity was observed: All samples have more or less the same final porosity value as green compacts prior sintering. The prepared composite samples are brittle. Decomposition of boron carbide led to the creation of TiB2, TiC and complex TiBxC1-x phases which were confirmed by microstructural investigations.

Microstructure, Hardness, and Wear Assessment of Spark-Plasma-Sintered Ti-xAl-1Mo Alloy

Alloys from the Ti-Al-Mo ternary system are of high importance in aerospace applications due to their excellent specific strength-to-density ratio, excellent corrosion, and creep resistance up to 600 °C. However, their sliding wear behavior has not been adequately explored. Cp-Ti and Ti-xAl-1Mo (x = 3, 5, 7) based near-alpha titanium alloys were successfully compacted by spark plasma sintering. The effect of Al addition on the densification, microhardness, and wear behavior of the developed alloys was studied. Results from the experiment showed that all compacts were almost fully densified. An increase in the value of the microhardness was recorded from 208 ± 10 to 352 ± 17 HV as the Al content increased. Al additions played an important role in the wear performance of the sintered alloy as detected from the coefficient of friction obtained with the sliding time and varying normal load. The alloyed Ti compacts had improved wear resistance. The wear rate values of alloyed compacts were 14 to 48.54 pct lower compared to the sintered Cp-Ti compacts tested as the Al content increased. The best wear resistance was observed for Ti-7Al-1Mo. Scanning electron microscopy micrographs, energy-dispersive spectroscopy, and wear debris show that the major wear mechanism detected was adhesive wear.

Beta Titanium Alloys Produced from Titanium Hydride: Effect of Alloying Elements on Titanium Hydride Decomposition

The use of titanium hydride as a raw material has been an attractive alternative for the production of titanium components produced by powder metallurgy, due to increased densification of Ti compacts, greater control of contamination and cost reduction of the raw materials. However, a significant amount of hydrogen that often remains on the samples could generate degradation of the mechanical properties. Therefore, understanding decomposition mechanisms is essential to promote the components’ long life. Several studies on titanium hydride (TiH2) decomposition have been developed; nevertheless, few studies focus on the effect of the alloying elements on the dehydrogenation process. In this work, the effects of the addition of different amounts of Fe (5 and 7 wt. %) and Nb (12, 25, and 40 wt. %) as alloying elements were evaluated in detail. Results suggest that α→β transformation of Ti occurs below 800 °C; β phase can be observed at lower temperature than the expected according to the phase diagram. It was found that β phase transformation could take place during the intermediate stage of dehydrogenation. A mechanism was proposed for the effect of allying elements on the dehydrogenation process.

Forced SHS Compaction of Ti–B Blends: Influence of Mixing Conditions and Sample Mass

We explored the influence of mixing (milling) conditions and sample mass on forced SHS compaction of equiatomic Ti–B blends. An increase in mill/ball ratio was found not only give start to mechanochemical synthesis but also affected the processes of combustion and product patterning. The mass of green compacts did not affect combustion temperature. Our results may turn interesting to those engaged in combustion synthesis of new materials.

Microstructure Characterization and Properties of Ti Carbohydride/Cu–Ti/GNP Nanocomposites Prepared by Wet Ball Milling and Subsequent Magnetic Pulsed Compaction

Wide application of hard composite materials in modern technologies stimulates a search for new compositions and more efficient and cheaper ways of their obtaining. A novel Ti carbohydride/CuTi/CuTi2/GNP (few-layer graphene or graphite nanoplatelets) composites were produced via magnetic pulsed compaction of Ti, Cu and graphite powders mechanically milled in liquid organic medium for 4 h. Phase composition and microstructure were examined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Density, microhardness, ultimate compression strength, abrasive wear resistance and sliding wear resistance of the composites were studied. The composites consisted of hexagonal and cubic titanium carbohydrides, CuTi2 and CuTi intermetallics, ~ 5 wt% of GNP and amorphous carbon. The presence of GNP and amorphous carbon resulted in higher wear resistance under conditions of dry friction against steel (1 wt%C, 1.5 wt%Cr) but lower composite density, microhardness, ultimate compression strength and abrasion wear resistance as compared with the GNP-free composites.

A Study of Laser Micromachining of PM Processed Ti Compact for Dental Implants Applications.

The paper deals with the experimental study of laser beam micromachining of the powder metallurgy processed Ti compacts applying the industrial grade fibre nanosecond laser operating at the wavelength of 1064 nm. The influence of the laser energy density on the surface roughness, surface morphology and surface elements composition was investigated and evaluated by means of surface roughness measurement, scanning electron microscopy (SEM), energy dispersive X-Ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis. The different laser treatment parameters resulted in the surfaces of very different characteristics of the newly developed biocompatible material prepared by advanced low temperature technology of hydride dehydride (HDH) titanium powder compactation. The results indicate that the laser pulse energy has remarkable effects on the machined surface characteristics which are discussed from the point of view of application in dental implantology.

Fabrication of reinforced α+β titanium alloys by infiltration of Al into porous Ti-V compacts

We present an efficient process to fabricate reinforced titanium α + β alloys. Porous Ti compacts containing vanadium were prepared by a metal injection molding process. Infiltration of molten Al and subsequent heat treatments were performed to synthesize a variety of Ti-V-Al alloys. The V-added specimens showed better mechanical properties than those of V-free Ti-Al intermetallic compounds. Microstructural observation of the fracture surface revealed that the lamellar structure in the Ti-V-Al alloys plays an important role in improving their mechanical properties by postponing the propagation of cracks. Notably, the lamellar structures in the Ti-V-Al alloys disappeared and the mechanical properties deteriorated as the Al infiltration duration time increased. Therefore, Al infiltration time is a crucial factor for successful growth of well-defined lamellar structured α + β phases in Ti-V-Al alloys.

Effect of Cenosphere Size and Volume Fraction on the Microstructure and Deformation Behavior of Ti-Cenosphere Syntactic Foam Made Through Powder Metallurgy Route

Abstract An attempt was made for making Titanium–cenosphere metal syntactic foams with varying relative densities, using different cenosphere sizes and volume fractions. Cold compaction of Ti and cenosphere powder mix was carried out at a pressure of 75 MPa, followed by sintering at 1100°C for 2 h. The sintered foam samples were characterized in terms of microstructure, primarily to observe the extent of cenosphere crushing, distribution of cenosphere, and extent of sintering. Uniform distribution of cenosphere with some extent of cenosphere crushing has been observed within the Ti matrix. XRD and EDX analysis confirms the oxidation of Ti particles to a small extent and also the entrapment of crushed cenosphere shells within the matrix, which makes the foam stronger but brittle in nature. The plateau stress, energy absorption, and modulus of these foams vary with the cenosphere size and volume fraction. Foams made with finer size cenosphere exhibits higher plateau stress and higher energy absorption for a fixed cenosphere volume fraction and at a constant foam density. Crushing of cenosphere, while compaction causes an increased density of the foam as compared to the theoretical value. As a consequence, the foam with higher cenosphere volume fraction or with coarser cenosphere size exhibited marginally higher strength and energy absorption. The variation in deformation mechanism as a function of cenosphere size and volume fraction was examined. These foams exhibited considerably higher strength and stiffness than the conventional foam and demonstrate the possibility of using them for biomedical and engineering applications.

Combustion synthesis in bi-layered (Ti−Al)/(Ni−Al) system

We investigated the peculiarities of the combustion wave propagation as well as the structure and phase formation in bi-layered metal powder compacts of (Ti−Al)/(Ni−Al), with a special emphasis on the use of infrared thermography to monitor the reaction front propagation. The location of the combustion wave front along the direction of propagation at different times was determined to calculate the front velocity. The data of SEM analysis demonstrated the welding of two layers during combustion with the formation of a transition layer with a thickness of about 200μm and a sharp diffusion barrier for Ti in the Ni-Al layer.

Application of High-pressure gas milling process to pure Titanium for harmonic structure design

In this study, a new heterogeneous microstructural design based on bimodal grain size distribution, termed as harmonic structure, is proposed for the strengthening of Pure Ti to achieve improved mechanical performance. Moreover, to ensure contamination-free high purity Ti compacts, a new high pressure gas milling process, called Jet milling, has been proposed for the controlled mechanical milling. The resulting milled powder exhibited bimodal microstructure consisting of nanosized grains in the near-surface region and micron-sized coarse grains in the centre of powder particle. The spark plasma sintering of milled powder led to the full density Ti compacts with harmonic structure. The harmonic pure Ti compacts exhibited significantly better combination of strength and toughness as compared to the homogeneously coarse-grained compacts prepared from initial powder.

ChemInform Abstract: Phase Evolution During the Reactive Sintering of Ternary Al—Ni—Ti Powder Compacts.

AbstractPhase formations by reactive sintering is studied for 0—40 at.% Al in equiatomic mixtures of Ni and Ti under pure and dry Ar (20—1200 °C).

Phase evolution during the reactive sintering of ternary Al–Ni–Ti powder compacts

The formation of various aluminides and intermetallic compounds in the Al–Ni–Ti ternary system offers great potential for a wide variety of applications. In the present work, reactions occurring during the heating of compacted ternary Al–Ni–Ti elemental powder mixtures were studied using differential scanning calorimetry (DSC). The effect of composition on the reaction behavior was studied by varying the aluminum addition (0–40 at.%) to nickel and titanium powders in equal proportions. The powder mixtures were compacted and heated in a DSC at 20 °C min−1 up to 1200 °C, using a continuous flow of pure and dry argon gas. The reaction behavior in binary Ni–Ti (1:1) powder compacts and Al–Ni–Ti samples containing 25 and 35 at.% aluminum, was studied in detail by interrupting the heating of samples at different stages of reaction. Phase evolution was followed by examining the sintered samples using X-ray diffraction technique, scanning electron microscopy and energy dispersive spectroscopy.The DSC plots showed two main exothermic peaks corresponding to reactions taking place below and above the melting point of aluminum. For all the Al–Ni–Ti samples studied, the first exothermic peak was observed in the interval 595°–625 °C, and the heat release increased with increase in the aluminum content of the samples. At 700 °C, microstructural studies showed that Al3Ni and Al3Ni2 were the major constituents and only a thin layer of Al3Ti was observed around the titanium powder particles, indicating a diffusional barrier. The second exothermic peak was observed in the interval 938°–946 °C which corresponds to the reaction between nickel and titanium. Titanium-rich and nickel-rich ternary compounds, in addition to some binary compounds have been observed after this reaction in all the ternary compositions studied. The formation of AlNi2Ti (τ4) phase together with some new ternary compounds was observed in most of the Al–Ni–Ti samples heated to 1200 °C. Among these, two phases correspond to compositions close to Al2Ni3Ti5 and Al36Ni28Ti36, whose structural characteristics and stabilities are yet to be confirmed in literature.

Factors Affecting the Compaction and Densification Behavior of Ti(C, N)-Based Cermet Powders

In this study, the effects of the major factors on compaction and densification behavior are investigated for Ti(C, N)-based cermet powders. The relative density equation for green compact of composite powders is modified to predict the green density of Ti(C, N)-based cermet powders prepared under different degrees of pressing pressures, and the theoretical values are found to be in good agreement with experimental results. It has been found that the composite powders with micron-sized particles have a better compatibility than those with nano-sized particles by analyzing the effects of the particle size and purity on the starting mono-powders. It has also been found that the volume shrinkage and porosity of the former are lower than that of the latter. In addition, it shows that high oxygen content has a negative impact on both the compatibility of composite powders and the uniformity of pore size distribution of sintered cermets. It has also been discussed in this study how the pressing parameters such as pressing pressure, pressing temperature, and dwell time influence the resulting cermets. The results indicate that a better compatibity is reached at a pressing rate of 100 mm/min or a pressing temperature of 100°C.

Improving the uniformity in mechanical properties of a sintered Ti compact using a trace amount of internal lubricant

Large sintered powder compacts are likely to be associated with variability in mechanical properties; an improvement of the uniformity of the mechanical properties of sintered powder compacts is important for powder metallurgy. In this work 0.3–1wt.% stearic acid (SA) or magnesium stearate (MgSt) was added to a 40mm diameter Ti powder compacts with height to depth (H/D) ratio of unity to give a more uniform green density. Tensile test pieces were cut from selected positions in each sintered compact to obtain the distribution of mechanical properties. Results revealed that variations in mechanical properties are due to the pore morphology with respect to size, aspect ratio and preferred orientation. A trace amount of lubricant significantly improves the uniformity in mechanical properties by optimizing the porosity distribution and minimizing the pore size and aspect ratio of pores after sintering. Such an effect was achieved by reducing the initial green density inhomogeneity and the stress induced by the mismatch of sintering shrinkage. However a relatively high 1wt.% SA addition with a large particle size created burnt-off pores in the top and bottom zones. MgSt is not recommended since it significantly increases the oxygen content. An addition of 0.6wt.% SA is the best choice due to the even pore distribution, small pore size and acceptable level of oxygen pick up.

Influence of porosity on mechanical behaviour and gas permeability of Ti compacts prepared by slip casting

Porous titanium compacts with porosity in the range of 12.3–35.3vol% were fabricated by slip casting. Slip casting is emerging to be an attractive process for fabrication of porous titanium products. The mechanical properties, fracture morphology, gas permeability, pore size analysis and pore shape factors for the porous Ti compacts were determined for different porosity levels. A decreasing porosity level resulted in less open porosity and gas permeability, reduced pore size, and an increased tensile stress and elongation. The mechanical properties of porous titanium compacts produced by slip casting were comparable with more conventional press and sintered materials at the same porosity levels. Theoretical models for tensile stress and ductility as a function of porosity were examined and incorporated into the results and differences between the theoretical models and experimental results are discussed. The pore shape factor analysis showed that tensile loading would stretch the pores in the compacts to produce more irregular pores, which were acting as linkage sites to allow the propagation of cracks. Additionally, a novel interconnected pore characterisation method using ammonium meta-tungstate solution is presented. By using backscatter scanning electron microscopy, the interconnected pores can be directly observed.

Sinter-coating method for the production of TiN-coated titanium foam for biomedical implant applications

Titanium foams for biomedical implant applications were produced by space holder technique. Novel sinter-coating method was used for the production of TiN layer on foams in order to enhance wear and corrosion resistance. In literature, Ti compacts were sintered in vacuum or argon atmosphere and then expensive and complex coating processes were carried out on sintered specimens. In this study, the titanium foams were sintered in N2 atmosphere at 1200°C. Biocompatible TiN layer was coated on foam surface by gas nitriding simultaneously during sintering. Sinter-coating combines sintering and TiN coating in one step by sintering the green specimens in N2 atmosphere. This reduces cost of operation and time. In addition, alkali treatment was used to activate surface of foams for partially induce a bioactive bone-like apatite to enhance bioactivity. Alkali treatment was performed by soaking the foams in NaOH solution and then heating at 600°C. After alkali treatment, foams were immersed into simulated body fluid to induce a bone-like apatite layer on foam surface.

Compaction of Ti–6Al–4V powder using high velocity compaction technique

High velocity compaction technique was applied to the compaction of pre-alloyed, hydride–dehydride Ti–6Al–4V powder. The powder was pressed in single stroke with a compaction speed of 7.10–8.70ms−1. When the speed was 8.70ms−1, the relative density of the compacts reaches up to 85.89% with a green density of 3.831gcm−3. The green samples were sintered at 1300°C in Ar-gas atmosphere. Scanning electron microscope (SEM) was used to examine the surface of the sintered samples. Density and mechanical properties such as Vickers micro hardness and bending strength of the powder samples were investigated. Experimental results indicated that with the increase in impact force, the density and mechanical properties of the compacts increased. The sintered compacts exhibited a maximum relative density of 99.88% with a sintered density of 4.415gcm−3, hardness of 364–483 HV and the bending strength in the range of 103–126.78MPa. The springback of the compacts decreased with increasing impact force.

Strengthening effects in precipitation and dispersion hardened powder metallurgy copper alloys

The hardening of copper and copper alloy matrix using powder metallurgy (PM) techniques and different ways for dispersoids formation, as well as analysis of their single and combined effects on the strength of obtained material at room and elevated temperatures, have been presented and discussed. Gas atomized Cu–3.8wt.%Ti and Cu–0.6wt.%Ti–2.5wt.%TiB2 (Cu–Ti–TiB2) powders and mechanically alloyed powder Cu–4wt.%TiB2 were used as starting materials. The powders were consolidated by hot isostatic pressing (HIP) and hot pressing (HP). Optical, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX), as well as transmission electron microscope (TEM) were used for microstructure characterization of the compacts. High strengthening of the Cu–Ti compacts was achieved by thermal treatment (aging) as a consequence of the development of modular structure and precipitation of metastable Cu4Ti(m). Hardening in the Cu–Ti–TiB2 compacts is due to simultaneous influence of the following factors: the development of modular structure, precipitation of metastable Cu4Ti(m), and the presence of TiB2 dispersoid nanoparticles. In case of Cu–TiB2 compacts, high starting values of hardness and hardness on the elevated temperatures result from the presence of finely distributed TiB2 particles in copper matrix obtained by mechanical alloying. Cu–Ti–TiB2 composite yields much higher hardness values compared with the binary Cu–Ti alloys, owing to primary TiB2 dispersions formed during atomization. Separation of metastable Cu4Ti precipitate and the presence of significantly finer TiB2 particles in the copper matrix are the reason for higher hardness values at peak temperatures (400–500°C) in multiple-hardened copper alloy compared to the dispersion-hardened.