Powder Mixtures Of Ti Research Articles

Fabrication and mechanical properties of Al2O3/TiAl in situ composites doped with Nb2O5

Al2O3/TiAl composites were successfully fabricated from powder mixtures of Ti, Al, TiO2, Cr2O3 and Nb2O5 by a hot-press-assisted exothermic dispersion method. The effect of the Cr2O3 and Nb2O5 addition on the microstructures and mechanical properties of Al2O3/TiAl composites was characterized. The results showed that the specimens are mainly composed of TiAl, Ti3Al, Al2O3, NbAl3 and Cr2Al. The Vicker-hardness and density of Al2O3/TiAl composites increase gradually with the increase of Nb2O5 content. When the Nb2O5 content was 6.54 wt %, the flexural strength and fracture toughness of the composites have a maximum values of 789.79 MPa and 9.69 MPa?m1/2, respectively. The improvement of mechanical properties is discussed in detail.

Impact response of TiB2–TiB composites

TiB2–TiB composites with a TiB2 content that varied between 100 and 36 wt% were synthesized from TiB2 and Ti powder mixtures by the Spark Plasma Sintering (SPS) technique. The residual porosity, microstructure, phase composition and static mechanical properties of the composites (bending strength, hardness and fracture toughness) were determined using standard characterization techniques. The impact response of the composites has been studied in two series of planar impact experiments. In the first, the samples were shock loaded to an ultimate compressive stress of about 25 GPa in order to determine the materials Hugoniot elastic limit (HEL). In the second series, the composites were shock loaded by a modest, 3–4 GPa, compressive pulse with the purpose to define their spall strength.The experimental results show that both the static and the dynamic properties of the composites reflect their microstructure, residual porosity and phase composition, namely, the TiB2 fraction in the composites. Even a limited Ti addition (5 wt%) in the starting mixture allows to synthesize by an SPS process at a relatively low temperature (1550 °C), composites with elevated mechanical properties, in particular high hardness (∼2400 HV). The addition of 50 wt% of Ti (36 wt% of TiB2 in the composites) yields fully dense composites with a high fracture toughness (∼9.0 MPa m0.5). The wide range of the static and dynamic properties of the TiB2–TiB composites allows their tailor-design to specific applications.

Application of Microscopy and X-ray Diffraction in Optimization of the Production of NiTi Alloy by Powder Metallurgy

This paper describes the dependence of microstructure of NiTi shape memory alloy on the conditions of nonconventional powder metallurgy processing routes - reactive sintering of compressed Ni+Ti powder mixture and mechanical alloying with consequent compaction by Spark Plasma Sintering. First method was chosen as the process enabling to yield the high-purity NiTi alloy, while the second one aimed to reach the ultrafine-grained microstructure. The microstructure and phase composition of the products are compared in this work. The positive effects of high heating rate (> 300 K.min-1) and high temperature (at least 900 °C) on the reactive sintering process were recognized. Microstructure of the product is composed by NiTi matrix with dispersed Ti2Ni particles. Similar microstructure can be also obtained by mechanical alloying for at least 120 min and consequent compaction by Spark Plasma Sintering.

The influence of iron powder size on pore formation, densification and homogenization during blended elemental sintering of Ti–2.5Fe

In this study it was determined that the addition of Fe to a Ti powder mixture results in pore formation either through the slow, solid state diffusion of Fe below the eutectic point (1085°C), or as a result of Fe rich liquid formation above 1085°C. The size of the pores scales proportionally with the size of the Fe particles used. Subsequent densification at 1200°C increased with a decrease in Fe particle size. The rate of Fe in-situ alloying and microstructural homogenization during sintering was determined using a newly developed differential scanning calorimeter (DSC) method. The rate of homogenization increased with a decrease in Fe particle size. The use of sub 10μm Fe powder resulted in improved densification compared to pure Ti and leads to complete homogenization during heating to 1200°C.

Formation mechanism of B4C–TiB2–TiC ceramic composite produced by mechanical alloying of Ti–B4C powders

In this study, the B4C–TiB2–TiC composite powder was synthesized by mechanical alloying (MA) of Ti–B4C powder mixture. For this purpose, four powder mixtures of Ti and B4C powders with different molar ratios were milled. In order to study the mechanism of Ti–B4C reaction during milling, structural changes and thermal analysis of powder particles were studied by X-ray diffractometry (XRD) and differential thermal analysis (DTA). Morphology and microstructure of powder particles during milling were studied by scanning electron microscopy (SEM). It was found that during MA, after decomposition of the outer layers of B4C particles, first, C reacted with Ti and after that, B was diffused in Ti structure and TiC and TiB2 phases were formed in gradual reaction mode. Also, the results of DTA and thermodynamic analysis confirmed the suggested mechanism for Ti–B4C reaction.

Feedstock Characterization of Elemental Nickel and Titanium Powders Mixture for Metal Injection Moulding Process

The success of metal injection moulding (MIM) process is significantly influenced by the homogeneity level of the powder-binder mixture (feedstock). This paper highlights some initial characterization of the feedstock containing elemental Ni and Ti powders mixture, (50.8 at.% Ni/ 49.2 at.% Ti) mixed with Palm stearin-based binder system. The feedstock was prepared using an internal mixer, HAAKE Rheomix at a temperature of 160°C for 2 hours. The feedstock was then characterized by Differential Scanning Calorimetry (DSC), Thermogravimetric (TGA), Scanning Electron Microscopy (SEM) and Capillary Rheometer. All the results obtained were analyzed and discussed for further injection moulding process.

Synthesis, microstructure and mechanical properties of (Ti,W)3AlC2/Al2O3 composites by in situ reactive hot pressing

(Ti,W)3AlC2/Al2O3 in-situ solid solution composites were successfully synthesized from the elemental powder mixtures of TiC, Ti, Al, and WO3 using hot-press-aided reaction synthesis. The reaction path was investigated by X-ray diffractometry (XRD), and a possible reaction mechanism was proposed to explain the formation of (Ti,W)3AlC2/Al2O3 composites in which the thermite reaction between Al and WO3 formed Al2O3 and W, and the latter together with Ti2AlC and TiC reacted to form (Ti,W)3AlC2. The synthesized composites show plate-like grains packed in layer structure typical of Ti3AlC2, and the fine Al2O3 particles formed in-situ tend to disperse on the matrix grain boundaries. Compared with the monolithic Ti3AlC2 synthesized using an identical process, the Vickers hardness, fracture toughness and flexural strength of (Ti0.96,W0.04)3AlC2/5wt%Al2O3 were enhanced by 266.7%, 24.6% and 23.4%, respectively. The mechanisms by which Al2O3 increases and solid solution strengthen the hardness, toughness and strength of the material were also discussed.

Microstructural evolution during extrusion of a Ti/Al/Al35V65 (Ti–6Al–4V) powder compact and the mechanical properties of the extruded rod

The microstructural evolution during extrusion of a powder mixture of HDH Ti, Al and Al35V65 master alloy powders with a nominal composition Ti–6Al–4V(wt%) at 1300°C and the mechanical properties of the extruded rod were studied. The results show that the amount of plastic deformation of the powder particles has a significant effect on the dissolution of the Al35V65 master alloy particles which in turn significantly influences the microstructure, mechanical properties and fracture behaviour of the extruded rod. The Al35V65 master alloy particles are completely dissolved in the material passing through the extrusion die orifice due to the large amount of powder particle deformation, while a large fraction of the Al35V65 master alloy particles are not dissolved in the undeformed regions close to the top of and in the dead zone of the as-sintered compact being extruded. The average yield strength, ultimate tensile strength and elongation to fracture of the as-extruded Ti–6Al–4V alloy rod are 1255MPa, 1300MPa and 7.1%, respectively, which are comparable to those of Ti–6Al–4V alloy produced by conventional methods. The fracture behaviour of the Ti–6Al–4V alloy during tensile testing is also examined and discussed.

NiTi Intermetallic Surface Coatings by Laser Metal Deposition for Improving Wear Properties of Ti-6Al-4V Substrates

The NiTi intermetallic possesses a number of good properties, such as high wear, oxidation, and corrosion resistance. This paper focuses on the deposition of NiTi intermetallic coatings on Ti6Al4V substrate by laser melting of Ti and Ni elemental powder mixtures. The effect of varying the Ti content in the NiTi composition on the microstructure and wear properties of the coatings was investigated. The microstructure of the NiTi intermetallic coatings were characterized by the scanning electron microscope (SEM) equipped with Energy Dispersive Spectroscope (EDS). The wear properties of the coatings were performed under accelerated dry sliding wear tests. The results obtained from the SEM/EDS analysis; show that the coatings consist of Ni and Ti elements from the feedstock, and the NiTi, NiTi2and NiTi3, intermetallic phases. Dry sliding wear analysis revealed that there is correlation between the hardness and the wear rate. The coatings displayed significant improvement in wear resistance up to 80% compared to the substrate.

Mechanical alloying of nanocrystalline intermetallic compound TiFe doped with sulfur and magnesium

A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Mg and S were added as doping components to a Fe–50%(at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacities of the nanostructured alloys based on TiFe intermetallic compound were of 0.6 and 0.7wt.% at room temperature for the alloys with S and Mg, respectively. The alloys studied demonstrated a simplified activation of hydrogenation, especially for the S-containing one.

Production of Cu-TiC Nanocomposite Using Mechanical Alloying Route

In this study, Cu-TiC nanocomposites were produced by high energy ball milling of elemental powders and in-situ formation of TiC in the copper matrix. Cu-40wt% Ti powder mixture were milled for 60 h, then graphite powder was added, subsequently milling was continued for further 10 h. Based on theoretical calculations, at this composite, the amount of TiC as reinforcement should be 60.25vol% (45.47wt%). The effect of milling time on solution progress of titanium in the copper lattice was studied by X-Ray diffraction analysis (XRD) with CuKα radiation. Considering XRD of Cu-40wt%TiC after 60 h milling data and Williamson-Hall relation, crystallite size and lattice strain of copper were determined 12nm and 1.04% respectively. To ensure the formation of titanium carbide, XRD analysis was performed after pressing at 300MPa and sintering at 900oC for an hour and heating rate of 2.5oC/min. XRD pattern was indicated the formation of TiC,CuTi3and TiO2phases in Cu matrix.

Laser in-situ synthesis of TiB2–Al composite coating for improved wear performance

The study involves in-situ synthesis of TiB2–aluminum composite coating using laser processing. The coating was synthesized by laser irradiating the pre-deposited Ti and B4C powder mixture on aluminum substrate that resulted in the formation of composite by in-situ reaction. The phase and micro-structural characterization of the coatings was conducted using X-ray diffraction and scanning electron microscopy. A multi-physics based heat transfer model was developed using COMSOL™ to predict the thermal histories during the processing and explain the related microstructure evolution. The tribological properties of the coatings were investigated using a pin on disk method. The study revealed that the samples processed with higher laser energy (30kJ/mm2) yielded superior wear resistance comparatively. The wear mechanisms are discussed by post wear microstructure analysis.

Experimental investigation of combustion of a gasless pelletized mixture of Ti + 0.5C in argon and nitrogen coflows

Combustion of a pelletized mixture of titanium and carbon black placed in a quartz tube and exposed to a flow of argon or nitrogen is studied. The gas flow (cocurrent filtration) is provided by a fixed pressure gradient at the inlet and outlet of the tube, which did not exceed 1 atm. The possible modes of combustion of pelletized mixtures related to the presence of a more complex hierarchy of scales (micro, macro, and meso) compared to that of powder mixtures (micro, macro) are analyzed. A comparison is made of the burning rates of powder and pelletized mixtures. An increase in the burning rate when using pelletized mixtures was found experimentally. It is shown that the gas coflow through the pelletized mixture of Ti + 0.5C leads to an increase in the burning rate. It is established that the propagation of the flame front of the pelletized mixture of Ti + 0.5C in flows of nitrogen and argon is controlled by different reactions. In contrast to combustion of powder mixtures of Ti + 0.5C, in combustion of pelletized mixtures of Ti + 0.5C in a nitrogen flow, only one front is observed. It is proved that radiation plays a significant role in the propagation of the combustion front in the pelletized mixture of Ti + 0.5C.

Production of nanograined intermetallics using high-pressure torsion

Formation of intermetallics is generally feasible at high temperatures when the lattice diffusion is fast enough to form the ordered phases. This study shows that nanograined intermetallics are formed at a low temperature as 573 K in Al- 25 mol% Ni, Al- 50 mol.% Ni and Al- 50 mol% Ti powder mixtures through powder consolidation using high-pressure torsion (HPT). For the three compositions, the hardness gradually increases with straining but saturates to the levels as high as 550-920 Hv. In addition to the high hardness, the TiAl material exhibits high yield strength as ~3 GPa with good ductility as ~23%, when they are examined by micropillar compression tests. X-ray diffraction analysis and high-resolution transmission electron microscopy reveal that the significant increase in hardness and strength is due to the formation of nanograined intermetallics such as Al3Ni, Al3Ni2, TiAl3, TiAl2 and TiAl with average grain sizes of 20-40 nm.

Oxidation Behavior of MAX Phase Ti2Al(1−x)SnxC Solid Solution

MAX phase Ti2Al(1−x)SnxC solid solution with x = 0, 0.32, 0.57, 0.82, and 1 was synthesized by pressureless sintering of uniaxially pressed Ti, Al, Sn, and TiC powder mixtures. Annealing in air atmosphere at 200°C–1000°C triggered a sequence of oxidation reactions which reveal a distinct influence of solid solution composition on the oxidation process. With decreasing Al/Sn ratio, the characteristic temperature of accelerated oxidation reaction of A‐element was reduced from 900°C (x = 0) to 460°C (x = 1). SnO2 was formed at temperatures significantly lower than TiO2 (rutile) and Al2O3. Substitution of A‐element in MAX phase solid solution by low‐melting elements such as Sn may offer potential for reducing oxidation‐induced crack healing temperatures.

Mechanical alloying of nanocrystalline intermetallic compound TiFe doped by aluminum and chromium

Abstract A series of nanostructured alloys based on TiFe intermetallic compound were synthesized from the metallic elements in a planetary ball mill by solid state mechanical alloying. Al and Cr were added as doping components to a Fe-50% (at.) Ti powder mixture. Phase and structure transformations during mechanical alloying and subsequent annealing as well as hydrogen interaction with the alloys prepared were studied. It was shown that reversible hydrogen sorption capacity of the nanostructural alloys based on the TiFe intermetallic compound was of 0.7 wt.% at room temperature. The alloys studied demonstrated a simplified activation of hydrogenation. A correlation between the alloys behavior in their reactions with hydrogen and structure parameters of the hydrogenated samples has been discussed.

Reactive hot pressing of Ti–B–C and Ti–C at 1200°C

Abstract Stoichiometric and non-stoichiometric powder mixtures of Ti–B4C and Ti–C with 1 wt% Ni were reactively hot pressed at 40 MPa, 1200 °C for 30 min. In both systems, the combined presence of Ni and non-stoichiometry enabled complete densification. While in Ti–C, non-stoichiometry by itself plays a significant role in promoting densification, the formation of intermediate borides in Ti–B4C powder mixtures requires the additional presence of Ni which promotes full reaction through the formation of a transient liquid as established previously in Ti–BN powder mixtures.

Synthesis and mechanical properties of (Ti, Mo)2AlC/Al2O3 composite by a reaction hot pressing method

Abstract A dense (Ti, Mo)2A1C/10 wt% Al2O3 in-situ composite was successfully fabricated from powder mixtures of Ti, Al, TiC and MoO3 by reactive hot pressing sintering, and the reaction path was investigated in detail. It was found that the production of the (Ti, Mo)2A1C/10 wt% Al2O3 was composed of a series of intermediate reactions: i.e., first reaction between Ti and Al forms Ti–Al intermetallics, and the thermite reaction between Al and MoO3 producing Al2O3 and Mo. Then the intermetallics and the residual Ti and Al transformed to TiAl equilibrium phase. Finally, the (Ti, Mo)2A1C/Al2O3 composite was formed by the reaction of TiAl TiC, and Mo. The Vickers hardness, flexural strength, compressive strength and fracture toughness of the composite were 4.75 GPa, 458 MPa, 971 MPa, and 6.03 MPa m1/2, which are improved by 25%, 69%, 48%, and 146%, respectively, compared to the single-phase Ti2AlC. The reinforcing mechanism was also discussed.

Effect of Nickel on Titanium Carbide Synthesized via Tungsten Inert Gas (TIG) Method

Numerous methods have been used to produce high purity TiC. There is no previous study has been reported on the formation using single elemental powders of Titanium (Ti) and Carbon (C) with addition Nickel (Ni) by tungsten inert gas (TIG) weld method. In this work, TiC was synthesized via TIG method by arc melting elemental powder mixture of Ti and C at ~5 second (s) and 80 ampere (A). The effect Ni contents on TiC formation was investigated. The mixed raw material was ball milled for 24 hours followed by synthesis via TIG method. The arced samples were characterized by X-ray diffraction (XRD) and Scanning electron microscope (SEM). It was revealed, that small amount of Ni additive to the metal powder allows the production of dense and tough TiC.

Role of oxygen and nitrogen in mechanical alloying mechanism of Ni–Ti powder mixtures

In this study, the critical milling behaviour of Ni–Ti powder mixtures was evaluated in relation to the effect of atmospheric gases, more specifically to oxygen and nitrogen. Within the experimental conditions used, it is shown that both gases play an important role in the alloying process and that not only oxygen gas reacts with the mechanically alloyed powders but also nitrogen. The most effective mixing occurred for the mixtures with the highest contaminant contents.